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Leaf phosphorus (P) comprises four major fractions: inorganic phosphate (P

Soil-borne plant-pathogenic Phytopythium spp. can cause root rot and damping off on important plant species, resulting in serious economic loss. A survey in October 2021 identified soil-borne diseases occurring on Macadamia integrifolia in Yunnan Province, China. Microbes were isolated from necrotic roots of 23 trees with root rot symptoms by growing on cornmeal-based oomycete-selective 3P (Haas 1964) and P5APR (Jeffers and Martin, 1986) media at 24ºC in the dark for 7 days. Of the 56 single-hyphal isolates obtained, 18 were morphologically similar to Phytopythium vexans (van der Plaats-Niterink 1981; de Cock et al. 2015). Isolates LC04 and LC051 were selected for molecular analyses. The internal transcribed spacer (ITS) region and the cytochrome c oxidase subunit II (CoxII) gene were PCR-amplified using universal primers ITS1/ITS4 (White et al. 1990) and oomycete-specific primers Cox2-F/Cox2-RC4 (Choi et al. 2015), respectively. The PCR products were sequenced with the amplification primers and sequences were lodged in Genbank (Accession no. OM346742, OM415989 for ITS, OM453644, OM453643 for CoxII for isolates LC04 and LC051, respectively). The top BLAST hit in the Genbank nr database for all four sequences was Phytopythium vexans (>99% identity). A maximum-likelihood phylogenetic tree was constructed with analogous concatenated ITS and CoxII sequences from either type or voucher specimens of 13 Phytopythium species in the same phylogenetic clade as P. vexans (Table 1; Bala et. al 2010). Isolates LC04 and LC051 grouped most closely to P. vexans, with LC051 basal and sister to LC04 and P. vexans voucher specimen CBS119.80 with 100% support (Fig. 1). Millet seed inoculated with agar pieces colonized by P. vexans LC04 and LC51 was used to fulfill Koch’s postulates (Li et al. 2015) in a completely randomized experimental design. Four 6-month-old M. integrifolia var. Keaau (660) seedlings were transplanted into pasteurized commercial potting mix containing 0.5% (w/w) inoculum. Plants were grown in free draining pots and watered once a day. At 14 days post-inoculation, roots were discolored compared to control plants inoculated with millet seed mixed with agar plugs lacking P. vexans (Fig. 2). By 30 days post-inoculation, infected roots were discolored with obvious decay and reduction in root system size. Control plants were symptomless. P. vexans was successfully re-isolated from two lesioned roots from each plant. The infection experiment was done twice, demonstrating that P. vexans LC04 and LC51 caused root disease on M. integrifolia. P. vexans causes root rot, damping-off, crown rot, stem rot or patch canker on economically important trees in many parts of the world, including seven plant species in China (Farr and Rossman 2022). This is the first report of pathogenic P. vexans on M. integrifolia in China. Reports of pathogenic P. vexans on multiple hosts in several parts of the world suggest it should be considered a quarantine risk and included in risk mitigation or pest management plans that include other species of Phytopythium, or species of Pythium or Phytophthora, to which P. vexans has many similarities (de Cock et al. 2015).

Background Unveiling the diversity of plant strategies to acquire and use phosphorus (P) is crucial to understand factors promoting their coexistence in hyperdiverse P-impoverished communities within fire-prone landscapes such as in cerrado (South America), fynbos (South Africa) and kwongan (Australia). Scope We explore the diversity of P-acquisition strategies, highlighting one that has received little attention: acquisition of P following fires that temporarily enrich soil with P. This strategy is expressed by fire ephemerals as well as fast-resprouting perennial shrubs. A plant’s leaf manganese concentration ([Mn]) provides significant clues on P-acquisition strategies. High leaf [Mn] indicates carboxylate-releasing P-acquisition strategies, but other exudates may play the same role as carboxylates in P acquisition. Intermediate leaf [Mn] suggests facilitation of P acquisition by P-mobilising neighbours, through release of carboxylates or functionally similar compounds. Very low leaf [Mn] indicates that carboxylates play no immediate role in P acquisition. Release of phosphatases also represents a P-mining strategy, mobilising organic P. Some species may express multiple strategies, depending on time since germination or since fire, or on position in the landscape. In severely P-impoverished landscapes, photosynthetic P-use efficiency converges among species. Efficient species exhibit rapid rates of photosynthesis at low leaf P concentrations. A high P-remobilisation efficiency from senescing organs is another way to use P efficiently, as is extended longevity of plant organs. Conclusions Many P-acquisition strategies coexist in P-impoverished landscapes, but P-use strategies tend to converge. Common strategies of which we know little are those expressed by ephemeral or perennial species that are the first to respond after a fire. We surmise that carboxylate-releasing P-mobilising strategies are far more widespread than envisaged so far, and likely expressed by species that accumulate metals, exemplified by Mn, metalloids, such as selenium, fluorine, in the form of fluoroacetate, or silicon. Some carboxylate-releasing strategies are likely important to consider when restoring sites in biodiverse regions as well as in cropping systems on P-impoverished or strongly P-sorbing soils, because some species may only be able to establish themselves next to neighbours that mobilise P.

Background and aims In extremely low-phosphorus (P) environments, most Proteaceae exude carboxylates from cluster roots. These carboxylates mobilise inorganic P which leads to a relatively high leaf manganese concentration ([Mn]). However, we found that Adenanthos cygnorum (Proteaceae) in a low-P habitat did not invariably have a high leaf [Mn] in south-western Australia. We aimed to explore how A. cygnorum acquires P in severely P-impoverished habitats. Methods We determined soil P concentrations and leaf [Mn] of A. cygnorum growing within 1 m and more than 10 m away from other large Proteaceae. We also grew plants in a glasshouse to determine its root carboxylate exudation and rhizosheath phosphatase activity. Results Adenanthos cygnorum did not produce functional cluster roots. It depended on carboxylates released by a P-mobilising neighbour, Banksia attenuata (Proteaceae), to acquire P when growing in severely P-impoverished soil (− 1 dry soil). In slightly less P-impoverished soil (> 11 mg P kg− 1 dry soil), phosphatases released by A. cygnorum hydrolysed sufficient organic P that was relatively mobile. Conclusion The reliance on facilitation of P acquisition in A cygnorum depended strongly on location. We demonstrated the exudation of phosphatases, which mobilise inorganic P; this P was adequate for growth when there was sufficient organic P in soil. Facilitation of P acquisition by B. attenuata allowed A. cygnorum to extend its range into severely P-impoverished habitats where it cannot exist without facilitation. This knowledge provides a better understanding of the diversity of P-acquisition strategies in severely P-impoverished environments.

Desiccation-tolerant (DT) plants can withstand dehydration to less than 0.1 g H2O g−1 dry weight. The mechanism for whole-plant recovery from severe dehydration is still not clear, especially for woody DT plants. In the present study, we evaluated the desiccation tolerance and mechanism of recovery for a potentially new woody resurrection plant Paraboea rufescens (Gesneriaceae). We monitored the leaf water status, leaf gas exchange, chlorophyll fluorescence and root pressure of potted P. rufescens during dehydration and rehydration, and we investigated the water content and chlorophyll fluorescence of P. rufescens leaves in the field during the dry season. After re-watering from a severely dehydrated state, leaf maximum quantum yield of photosystem II of P. rufescens quickly recovered to well-watered levels. Leaf water status and leaf hydraulic conductance quickly recovered to well-watered levels after re-watering, while leaf gas exchange traits also trended to recovery, but at a slower rate. The maximum root pressure in rehydrated P. rufescens was more than twice in well-watered plants. Our study identified P. rufescens as a new DT woody plant. The whole-plant recovery of P. rufescens from extreme dehydration is potentially associated with an increase of root pressure after rehydration. These findings provide insights into the mechanisms of recovery of DT plants from dehydration.

The macadamia industry is developing rapidly in China. A brown leaf spot disease was noted in six

Plant species richness increases with declining soil phosphorus (P) availability, especially for Proteaceae in old infertile landscapes. This difference in richness might be attributed to faster diversification in lineages adapted to P-impoverished soils, i.e. species that possess specialised P-acquisition strategies, and have lower leaf P concentration ([P]) and higher seed [P]. Alternatively, a longer time for species accumulation might contribute to high species richness in low-P environments due to the geological stability of the landscapes in which they evolved. We assessed differences in diversification of Proteaceae in P-impoverished vs. nutrient-rich environments and whether these were linked to adaptations to P-impoverished soils. We explored mature leaf and seed [P] and investigated how these traits changed over the evolutionary history of the family, and within two species-rich genera (Banksia, Hakea). Faster diversification was correlated with lower leaf and higher seed [P] for species-rich genera across the Proteaceae. For Banksia and Hakea, diversification rates peaked at relatively low leaf [P], but not at the lowest leaf [P]. Ancestral state reconstructions indicated that low leaf [P] is a trait that was likely present in the early evolution of the Proteaceae, with recent transitions to higher leaf [P] across several species-poor rainforest genera. Diversification of Proteaceae correlated strongly with P-related traits. In an evolutionary context, functional cluster roots, low leaf [P] and high seed [P] were likely key innovations allowing diversification. Selection for low leaf [P] early in the evolutionary history of Proteaceae pre-adapted ancestors of this family to diversify into oligotrophic environments. We discuss how our findings are likely relevant for understanding diversification dynamics of other plant families that occur in P-impoverished environments.

Desiccation-tolerant (DT) plants can withstand dehydration to less than 0.1 g H

Schrenkiella parvula, a leading extremophyte model in Brassicaceae, can grow and complete its life cycle under multiple environmental stresses, including high salinity. While foundational genomic resources have been created for S. parvula, a comprehensive physiological or structural characterization of its salt stress responses is absent. We aimed to identify the influential traits that lead to stress-resilient growth of this species. We examined salt-induced changes in the physiology and anatomy of S. parvula throughout its lifecycle across multiple tissues. We found that S. parvula maintains or even exhibits enhanced growth during various developmental stages at salt stress levels known to inhibit growth in Arabidopsis and most crops. The resilient growth of S. parvula was associated with key traits that synergistically allow continued primary root growth, expansion of xylem vessels across the root-shoot continuum, and a high capacity to maintain tissue water levels by developing larger and thicker leaves while facilitating continued photosynthesis during salt stress. These traits at the vegetative phase were followed by a successful transition to the reproductive phase via early flowering, development of larger siliques, and production of viable seeds during salt stress. Additionally, the success of self-fertilization during early flowering stages was dependent on salt-induced filament elongation in flowers that aborted in the absence of salt. Our results suggest that the maintenance of leaf water status and enhancement of selfing in early flowers to ensure reproductive success, are among the most influential traits that contribute to the extremophyte lifestyle of S. parvula in its natural habitat.One sentence summarySchrenkiella parvula salt-resilient growth is facilitated by uncompromised primary root growth, expansion of xylem vessels, maintenance of leaf water status and photosynthesis, and early flowering.

Leptospermum polygalifolium Salisb. can accumulate high concentrations of dihydroxyacetone (DHA), precursor of the antimicrobial compound methylglyoxal found in honey obtained from floral nectar of Leptospermum spp. Floral nectar dynamics over flower lifespan depends on internal and external factors that invariably impact nectar quality. Current models to estimate nectar quality in Leptospermum spp. overlook time of day, daily (24 h), and long-term dynamics of nectar exudation and accumulation over flower lifespan. To explain the dynamics of nectar quality over flower lifespan, accumulated nectar from flowers of different ages was collected from two L. polygalifolium clones, and then re-collected 24 h later from the same flowers. High-Performance Liquid Chromatography was used to quantify DHA amount and total equivalents of glucose + fructose (Tsugar) per flower in the nectar. DHA and Tsugar amount per flower differed with flower age and between clones. In accumulated nectar, the amount of DHA and Tsugar per flower rose to a broad peak post-anthesis before decreasing. Immediately after peaking DHA declined more quickly than Tsugar in accumulated nectar due to a greater decrease in the exudation of DHA than for Tsugar. The DHA : Tsugar ratios in accumulated nectar and in nectar exuded over the next 24 h were similar and decreased with flower age, indicating that exudation and reabsorption occurred concomitantly across flower development. Hence there is a balance between exudation and reabsorption. A quantitative model suggested that flowers have the potential to exude more DHA and Tsugar than actually accumulated.

Pseudomonas pseudoalcaligenes KB-10 can enhance salinity tolerance in coriander plants. We report a draft genome sequence of P. pseudoalcaligenes KB-10, comprising a 5,241,174-bp circular chromosome containing 4,921 genes, with a GC content of 62.97%.

Phosphorus (P) fertilisers, made from rock phosphate, are used to attain high crop yields. However, rock phosphate is a finite resource and excessive P fertilisers pollute our environment, stressing the need for more P-efficient crops. Some Proteaceae have evolved in extremely P-impoverished environments. One of their adaptations is to curtail the abundance of ribosomal RNA, and thus protein, and tightly control the acquisition and assimilation of nitrogen (N) and sulfur. This differs fundamentally from plants that evolved in environments where N limits plant productivity, but is likely common in many species that evolved in P-impoverished landscapes. Here, we scrutinise the relevance of these responses towards developing P-efficient crops, focusing on plant species where 'P is in the driver's seat'.

Gladiolus is in demand worldwide as a cut-flower or landscaping plant, because of its superior commercial and ornamental value. Application of plant-based biostimulants has gained interest in the horticulture industry as an innovative and promising approach to ensure enhanced and sustainable yields along with better product quality. The influence of pre-plant corm soaks supplemented to 5% (v/v) with an aqueous extract from Moringa oleifera leaves (MLE) either alone or in combination with 50 mg/L salicylic acid (SA) or 50 mg/L gibberellic acid (GA) on the vegetative, physiological, and ornamental characteristics of potted gladiolus (Gladiolus grandiflorus) was investigated. In general, the treatment order for greatest horticultural value for all the parameters examined was: MLE + SA + GA &gt, MLE + GA or SA individually &gt, MLE alone &gt, water-only control. Compared to other treatments, corms soaked in MLE + SA + GA had the earliest sprout time (3.7 days earlier than control), shortest production time (11 days earlier than control), tallest plant (159.5 cm), greatest number of leaves per plant (8.85 leaves), greatest maximum leaf area (66 cm2), highest SPAD reading (112) and photosynthetic activity (6.7 mmol m&minus, 2 s&minus, 1), longest spike length (91 cm), greatest number of florets per spike (20 florets), longest vase life (14.8 days), greatest N (1.53%), P (0.28%), and K (0.64%) concentrations, and largest corm diameter (4.68 cm) and mass (22.25 g). The highest total protein and proline concentrations were observed with the combined application of MLE + GA + SA. Our findings suggested that MLE either alone or in combination with other plant growth regulators not only increased the yield and quality of cut spikes, but also prolonged the vase life of cut gladiolus.

Background Eucalyptus is the main plantation wood species, mostly grown in aluminized acid soils. To understand the response of Eucalyptus clones to aluminum (Al) toxicity, the Al-tolerant Eucalyptus grandis × E. urophylla clone GL-9 (designated “G9”) and the Al-sensitive E. urophylla clone GL-4 (designated “W4”) were employed to investigate the production and secretion of citrate and malate by roots. Results Eucalyptus seedlings in hydroponics were exposed to the presence or absence of 4.4 mM Al at pH 4.0 for 24 h. The protein synthesis inhibitor cycloheximide (CHM) and anion channel blocker phenylglyoxal (PG) were applied to explore possible pathways involved in organic acid secretion. The secretion of malate and citrate was earlier and greater in G9 than in W4, corresponding to less Al accumulation in G9. The concentration of Al in G9 roots peaked after 1 h and decreased afterwards, corresponding with a rapid induction of malate secretion. A time-lag of about 6 h in citrate efflux in G9 was followed by robust secretion to support continuous Al-detoxification. Malate secretion alone may alleviate Al toxicity because the peaks of Al accumulation and malate secretion were simultaneous in W4, which did not secrete appreciable citrate. Enhanced activities of citrate synthase (CS) and phosphoenolpyruvate carboxylase (PEPC), and reduced activities of isocitrate dehydrogenase (IDH), aconitase (ACO) and malic enzyme (ME) were closely associated with the greater secretion of citrate in G9. PG effectively inhibited citrate and malate secretion in both Eucalyptus clones. CHM also inhibited malate and citrate secretion in G9, and citrate secretion in W4, but notably did not affect malate secretion in W4. Conclusions G9 immediately secrete malate from roots, which had an initial effect on Al-detoxification, followed by time-delayed citrate secretion. Pre-existing anion channel protein first contributed to malate secretion, while synthesis of carrier protein appeared to be needed for citrate excretion. The changes of organic acid concentrations in response to Al can be achieved by enhanced CS and PEPC activities, but was supported by changes in the activities of other enzymes involved in organic acid metabolism. The above information may help to further explore genes related to Al-tolerance in Eucalyptus.

Using orchid mycorrhizal fungi to facilitate orchid recovery projects is considered to be an effective method for orchid conservation. In this study, we used ex situ seed baiting to isolate fungi to assist seed germination in Paphiopedilum spicerianum, a critically endangered orchid with only a single population found in south China. Two fungal species, GYBQ01 and GYBQ02, were successfully obtained and identified as belonging to Tulasnellaceae. Both fungi were capable of promoting seed germination up to the seedling stage, as the percentage of seedlings in GYBQ01 and GYBQ02 treatments reached 34.9 ± 2.7% and 50.8 ± 3.5%, respectively, at 120 days after incubation. Both fungi also showed a strong host-specific relationship with P. spicerianum. Using these fungi, we developed fungi-seed bags to be used as propagules for assisted colonization of P. spicerianum. This approach had many advantages in practice, e.g., low-cost mass production, long term storage, convenient transportation, controllable seedling quantity and density, ease of use in the field, and environmently-friendly biodegradable paper bags. This is the first time that this approach has been applied to assisted colonization of an endangered orchid, and has universal application to other orchids. Our results have potential to provide a complete solution for orchid reintroduction, as well as assisted colonization, based on symbiotic seed germination.

We compared the use of phosphorus (P) and nitrogen (N) in slow-growing Banksia attenuata (Proteaceae), which resprouts after fire and naturally occurs on deep sand, with faster-growing opportunistic B. sessilis, which is killed by fire and occurs on shallow sand over laterite or limestone. We carried out pot experiments with plants on substrates with different P availability. We measured foliar nutrient concentrations, and P allocated to major biochemical fractions. The two species had similar foliar total P concentrations, but distinct patterns of P allocation to P-containing fractions. The foliar total N concentration of B. sessilis was greater than that of B. attenuata on all substrates. The foliar total P and N concentrations in both species decreased with decreasing P availability. The relative growth rate of both species was positively correlated with both foliar nucleic acid P and total N concentrations, but there was no correlation with other P and N fractions. Faster-growing B. sessilis allocated more P to nucleic acids than B. attenuata did, but other fractions were similar. We conclude that the nutrient-allocation patterns in faster-growing opportunistic B. sessilis and slower-growing B. attenuata revealed different strategies in response to soil P availability, which matched their contrasting growth strategy.

Background Candida auris has emerged as a serious threat to human health. Of particular concern are the resistance profiles of many clinical isolates, with some being resistant to multiple classes of antifungals. Objectives Measure susceptibilities of C. auris isolates, in planktonic and biofilm forms, to ceragenins (CSAs). Determine the effectiveness of selected ceragenins in gel and cream formulations in eradicating fungal infections in tissue explants. Materials and methods A collection of 100 C. auris isolates available at CDC was screened for susceptibility to a lead ceragenin. A smaller collection was used to characterize antifungal activities of other ceragenins against organisms in planktonic and biofilm forms. Effects of ceragenins on fungal cells and biofilms were observed via microscopy. An ex vivo model of mucosal fungal infection was used to evaluate formulated forms of lead ceragenins. Results Lead ceragenins displayed activities comparable to those of known antifungal agents against C. auris isolates with MICs of 0.5-8 mg/L and minimum fungicidal concentrations (MFCs) of 2-64 mg/L. No cross-resistance with other antifungals was observed. Fungal cell morphology was altered in response to ceragenin treatment. Ceragenins exhibited activity against sessile organisms in biofilms. Gel and cream formulations including 2% CSA-44 or CSA-131 resulted in reductions of over 4 logs against established fungal infections in ex vivo mucosal tissues. Conclusions Ceragenins demonstrated activity against C. auris, suggesting that these compounds warrant further study to determine whether they can be used for topical applications to skin and mucosal tissues for treatment of infections with C. auris and other fungi.

Tropical forests play important roles in global carbon cycling. Tree-ring analysis can provide important information for understanding long-term trends in carbon-fixation capacity under climate change. However, tree-ring studies in tropical regions are limited. We carried out a tree-ring analysis to investigate the dendrochronological potential of the tropical forest tree Choerospondias axillaris (Anacardiaceae) in east-central Thailand. Our study focused on growth-climate relationships and long-term growth trends. A chronology was constructed covering the period from 1932 to 2019. The tree-ring width index of C.axillaris was positively correlated with precipitation in June, July, and October. Furthermore, growth of C.axillaris was positively correlated with the Standardized Precipitation-Evapotranspiration Index (SPEI) from July to October, indicating that growth of C.axillaris is mainly limited by moisture availability in the late monsoon season. Moving correlation analysis further revealed the consistency and temporal stability of the relationship of tree growth with monsoon season precipitation and SPEI during the period under study. There was a significant increasing trend in long-term growth from 1932 to 2002 (slope = 0.017, p < 0.001); however, long-term growth decreased from 2003 to 2019 (slope = −0.014, p < 0.001). Our study provides important insight into the growth-climate correlations of a broad-leaved tree species in a dry evergreen forest in tropical Asia.

Alpinia zerumbet is an important medicinal and ornamental plant species. Drought stress is a major concern for sustainable horticulture crop production under changing climate scenarios. Trehalose (Tre) and 5-aminolevulinic acid (ALA) are osmoprotectants that play important roles in mitigating plant stresses. In this study, the effects of foliar application of 25 mM Tre or 10 mg L−1 ALA on biochemical and physiological parameters of A. zerumbet seedlings and their growth were evaluated under well-watered and drought-stressed (65% of field capacity) conditions. Drought caused reductions in physiological parameters and plant growth. These decreases were accompanied by increases in leaf free proline and glycine betaine concentrations and peroxidase activities. Foliar application of Tre or ALA remediated physiological and biochemical parameters and plant growth. Overall, foliar application of ALA or Tre proved to be beneficial for mitigating drought stress in A. zerumbet.

Trehalose (Tre) and salicylic acid (SA) are increasingly used to mitigate drought stress in crop plants. In this study, a pot experiment was performed to study the influence of Tre and SA applied individually or in combination on the growth, photosynthesis, and antioxidant responses of sweet basil (Ocimum basilicum L.) exposed to drought stress. Basil plants were watered to 60% or 100% field capacity with or without treatment with 30 mM Tre and/or 1 mM SA. Drought negatively affected growth, physiological parameters, and antioxidant responses. Application of Tre and/or SA resulted in growth recovery, increased photosynthesis, and reduced oxidative stress. Application of Tre mitigated the detrimental effects of drought more than SA. Furthermore, co-application of Tre and SA largely eliminated the negative impact of drought by reducing oxidative stress through increased activities of antioxidant enzymes superoxide dismutase, peroxidase, and catalase, as well as the accumulation of the protective osmolytes proline and glycine betaine. Combined Tre and SA application improved water use efficiency and reduced the amount of malondialdehyde in drought-stressed plants. Our results suggested that combined application of Tre and SA may trigger defense mechanisms of sweet basil to better mitigate oxidative stress induced by drought stress, thereby improving plant growth.

Nitrogen (N) is often the nutrient limiting the decomposability of shoots from macrophytes in wetlands. We aimed to determine the effects of increasing soil N availability on the decomposition of shoots during the standing-dead phase. We measured the quality of senesced leaves from graminoids and their subsequent aerial decay under different N addition treatments (Control, 0 kg N ha−1 yr.−1; N60, 60 kg N ha−1 yr.−1; N120, 120 kg N ha−1 yr.−1; N240, 240 kg N ha−1 yr.−1) in a temperate marsh. Nitrogen addition increased N concentrations in senesced leaves and often increased phosphorus (P) concentrations. The exponential decay constants (k) of leaves from the N120 and N240 treatments were higher than the control treatment during aerial decay. Nitrogen amounts (in percentage terms) remaining in decaying leaves always significantly decreased after N addition, but the effects on P amounts varied with N addition rates. The nutrient amounts remaining in leaves during the standing-dead phase had negative relationships with the initial nutrient concentrations. Soil N availability exerts remarkable effects on the decay process of standing litters by altering the initial quality, and thus the biogeochemical cycling in temperate wetlands.

Hakea prostrata R.Br. (Proteaceae) shows a ‘delayed greening’ strategy of leaf development characterised by reddish young leaves that become green as they mature. This trait may contribute to efficient use of phosphorus (P) during leaf development by first investing P in the development of leaf structure followed by maturation of the photosynthetic machinery. In this study, we investigated the properties of delayed greening in a highly P-efficient species to enhance our understanding of the ecological significance of this trait as a nutrient-saving and photoprotective strategy. In glasshouse-grown plants, we assessed foliar pigments, fatty acids and nutrient composition across five leaf developmental stages. Young leaves had higher concentrations of anthocyanin, P, nitrogen (N), copper (Cu), xanthophyll-cycle pigments and saturated fatty acids than mature leaves. As leaves developed, the concentration of anthocyanins decreased, whereas that of chlorophyll and the double bond index of fatty acids increased. In mature leaves, ~60% of the fatty acids was α-linolenic acid (C18:3 n-3). Mature leaves also had higher concentrations of aluminium (Al), calcium (Ca) and manganese (Mn) than young leaves. We conclude that delayed greening in H. prostrata is a strategy that saves P as well as N and Cu through sequential allocation of these resources, first to cell production and structural development, and then to supplement chloroplast development. This strategy also protects young leaves against photodamage and oxidative stress during leaf expansion under high-light conditions.

A pot experiment was conducted to evaluate how nitrogen (N) availability influences cadmium (Cd) absorption, translocation and stress tolerance in roots of Populus euramericana. Seedling growth was sensitive to N deficiency, but it was unaltered by Cd exposure. Cadmium absorption by roots was promoted by N deficiency, resulting in a higher root Cd concentration compared to the N-sufficient condition. Fine-root length was tightly correlated (R2 = 0.73) with Cd concentration in roots, indicating that vigorous fine-root proliferation under N deficiency contributed to active absorption and accumulation of Cd in roots. Despite accumulation in roots, Cd translocation from roots to shoots was less active under N deficiency compared to N sufficiency. This was related to elevated glutathione reductase (GR) activity and glutathione (GSH) levels in roots after N application, which may not only promote antioxidant defence, but also facilitate the formation of GSH-Cd complexes that are uploaded into root cylinders. Nitrogen application also promoted antioxidant defense in roots via increased production of phytohormones and the level of enzymatic and non-enzymatic antioxidants. Transcript levels for genes responsible for antioxidant defense, Cd detoxification and Cd uploading were increased in roots by N application. The N-stimulated Cd tolerance, detoxification and uploading in roots are factors likely to promote Cd translocation from roots to shoots, which may enhance the biological capacity of this poplar species for phytoremediation of Cd pollution.

Black spot is a major disease of field pea (Pisum sativum L.) production across southern Australia. Known causal agents in Australia include one or more of Mycosphaerella pinodes (Berk. & Bloxam) Vestergr., Phoma medicaginis var. pinodella (L.K. Jones), Ascochyta pisi Lib., or P. koolunga (Davidson, Hartley, Priest, Krysinska-Kaczmarek, Herdina, McKay & Scott) (2), but other pathogens may also be associated with black spot symptoms. Black spot generally occurs on most plants and in most pea fields in Western Australia (W.A.), and during earlier winter/spring surveys of blackspot pathogens, some isolates were tentatively allocated to P. medicaginis var. pinodella despite different cultural characteristics on potato dextrose agar (PDA). Recently, single-spore isolations of a single culture each from an infested pea crop at Medina, Moora, and Mt. Barker in W.A. were made onto PDA. A PCR-based assay with TW81 and AB28 primers was used to amplify from the ITS-5.8S rDNA region. Purified DNA products were sequenced for the three isolates and then BLASTn was used to compare sequences with those in GenBank. Our sequences (GenBank Accession Nos. JN37743, JN377439, and JN377438) had 100% nucleotide identity with P. exigua Desm. var. exigua accessions (GI13385450, GI169894028, and GI189163921), an earlier synonym of what is now known as Boeremia exigua var. exigua ([Desm.] Aveskamp, Gruyter & Verkley) (1). Davidson et al. (2) used the same primers to identify P. koolunga, but none of our isolates were P. koolunga. A suspension of 107 conidia ml–1 of each representative isolate was inoculated onto foliage of 15-day-old field pea cv. Dundale plants and maintained at >90% relative humidity for 72 h postinoculation. Control plants inoculated with just water remained symptomless. Brown lesions were evident by 8 to 10 days postinoculation and mostly 1 to 3 mm in diameter. B. exigua var. exigua was readily reisolated from infected leaves. Isolates have been lodged in the W.A. Culture Collection Herbarium maintained at the Department of Agriculture and Food W.A. (Accession Nos. WAC13500, WAC13502, and WAC13501 from Medina, Moora, and Mt. Barker, respectively). Outside Australia, its synonym P. exigua var. exigua is a known pathogen of field pea (4), other legumes including common bean (Phaseolus vulgaris L.) (4) and soybean (Glycine max [L.] Merr.) (3), and is known to produce phytotoxic cytochalasins. In eastern Australia, P. exigua var. exigua has been reported on common bean (1930s and 1950s), phasey bean (Macroptilium lathyroides [L.] Urb.) and siratro (M. atropurpureum (DC.) Urb.) (1950s and 1960s), mung bean (Vigna radiata [L.] Wilczek.) (1960s), ramie (Boehmeria nivea [L.] Gaudich.) (1939), potato (Solanum tuberosum L.) (1980s), and pyrethrum (Tanacetum cinerariifolium [Trevir.] Schultz Bip.) (2004 and 2007) (Australian Plant Pest Database). To our knowledge, this the first report of B. exigua var. exigua on field pea in Australia, and because of its potential to be a significant pathogen on field pea, warrants further evaluation. References: (1) M. M. Aveskamp et al. Stud. Mycol. 65:1, 2010. (2) J. A. Davidson et al. Mycologia 101:120, 2009. (3) L. Irinyi et al. Mycol. Res. 113:249, 2009. (4) J. Marcinkowska. Biul. Inst. Hod. Aklim. Rosl. 190:169, 1994.

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is a serious disease of many cruciferous crops and frequently poses a threat to the sustainable and profitable production of these crops worldwide. Differences in seedling resistance to S. sclerotiorum across 46 diverse cruciferous genotypes from 12 different species were assessed by comparing the extent of pathogenesis on inoculated cotyledons under controlled conditions. Selections of Brassica carinata, B. incana, B. juncea, B. napus, and B. napus introgressed with B. carinata, B. nigra, B. oleracea, B. rapa var. rosularis, B. rapa var. chinensis, B. tournefortii, Raphanus raphanistrum, R. sativus, and Sinapis arvensis were tested. The average size of lesions on cotyledons 48 h post inoculation varied from 0.8 to 7.3 mm. The three most resistant genotypes with the smallest lesions were all from B. oleracea (viz., B. oleracea var. italica ‘Prophet’ and B. oleracea var. capitata ‘Burton’ and ‘Beverly Hills’). Representatives of R. raphanistrum, S. arvensis, B. juncea, and B. carinata were the most susceptible to S. sclerotiorum, with the largest lesions. To our knowledge, this is the first report of high levels of resistance to S. sclerotiorum in B. oleracea at the cotyledon stage and also the first report of the host cotyledon reactions against S. sclerotiorum for all tested species except B. napus and B. juncea. The mean lesion size for B. napus introgressed with B. carinata was 5.6 mm, which is midway between the lesion size for the two parent species B. napus (5.1 mm) and B. carinata (5.8 mm). Separate genetic control for cotyledon versus mature plant resistance was demonstrated by the lack of correlation between lesion size from S. sclerotiorum on the cotyledon with the severity of disease initiated by stem inoculation or natural processes in a previous field test. On the most resistant genotypes, B. oleracea var. italica Prophet and var. capitata Burton, growth of S. sclerotiorum on the cotyledon surface prior to penetration was severely impeded, production of appressoria inhibited, and both cytoplasm shrinkage and protoplast extrusion in S. sclerotiorum hyphae prevalent. This is the first report of such resistant mechanisms in B. oleracea. Genotypes with cotyledon resistance identified in this study will be of great value not only in furthering our understanding of resistance mechanisms across different cruciferous species but also could be exploited for developing commercial crucifer cultivars with high-level resistance against S. sclerotiorum.

Plants respond to soil phosphorus (P) availability by adjusting leaf P among inorganic P (Pi) and organic P fractions (nucleic acids, phospholipids, small metabolites and a residual fraction). We tested whether phylogenetically divergent plants in a biodiversity hotspot similarly adjust leaf P allocation in response to P limitation by sampling along a 2 Myr chronosequence in southwestern Australia where nitrogen (N) limitation transitions to P limitation with increasing soil age. Total P and N, and P allocated to five chemical fractions were determined for photosynthetic organs from Melaleuca systena (Myrtaceae), Acacia rostellifera (Fabaceae) and Hakea prostrata (Proteaceae). Soil characteristics were also determined. Acacia rostellifera maintained phyllode total P and N concentrations at c. 0.5 and 16 mg g-1 DW, respectively, with a constant P-allocation pattern along the chronosequence. H. prostrata leaves allocated less P to Pi, phospholipids and nucleic acids with increasing soil age, while leaf N concentration was constant. M. systena had the greatest variation in allocating leaf P, whereas leaf N concentration decreased 20% along the chronosequence. Variation in P-allocation patterns was only partially conserved among species along the chronosequence. Such variation could have an impact on species distribution and contribute to species richness in P-limited environments.

Kelps and fucoids are dominant habitat-forming seaweeds along temperate rocky coastlines. Here, we tested the physiological performance of a dominant kelp (Ecklonia radiata) and two fucoids (Scytothalia dorycarpa and Sargassum fallax), distributed along the southwest coast of Australia. Photosynthesis and respiration were measured against increments in temperature for seaweeds collected along a latitudinal gradient in ocean temperature from Kalbarri (warm) to Hamelin Bay (cool). We found a similar decrease in photosynthetic activity from cooler to warmer latitudes in all three species. Seaweeds collected from warmer locations had significantly lower chlorophyll a concentration compared to cooler locations which could explain the lower levels of photosynthetic activity at warmer latitudes. The Q10 values for photosynthesis and respiration tended to decrease from cooler to warmer locations. For all species, the optimum temperature for net photosynthesis remained similar across the locations. However, within locations, the optimum temperature for S. fallax (25.2°C) was significantly higher than E. radiata (24.0°C) and S. dorycarpa (23.6°C). The reduction rates of net photosynthesis observed after optimum temperature showed the greatest variation among the species within and across locations. A thermal performance breadth analysis revealed a broader performance range for S. fallax (21.5–28.4°C) followed by E. radiata (21.2–26.5°C) and S. dorycarpa (21.4–25.8°C). These results highlight the differences in temperature sensitivity among the three species which help explain their current distributional patterns and have potential implications for future responses to future ocean warming.

Tropical sandalwood (Santalum album) produces one of the world's most highly prized fragrances, which is extracted from mature heartwood. However, in some places such as southern India, natural populations of this slow-growing tree are threatened by over-exploitation. Sandalwood oil contains four major and fragrance-defining sesquiterpenols: (Z)-α-santalol, (Z)-β-santalol, (Z)-epi-β-santalol and (Z)-α-exo-bergamotol. The first committed step in their biosynthesis is catalyzed by a multi-product santalene/bergamotene synthase. Sandalwood cytochromes P450 of the CYP76F sub-family were recently shown to hydroxylate santalenes and bergamotene; however, these enzymes produced mostly (E)-santalols and (E)-α-exo-bergamotol. We hypothesized that different santalene/bergamotene hydroxylases evolved in S. album to stereo-selectively produce (E)- or (Z)-sesquiterpenols, and that genes encoding (Z)-specific P450s contribute to sandalwood oil formation if co-expressed in the heartwood with upstream genes of sesquiterpene biosynthesis. This hypothesis was validated by the discovery of a heartwood-specific transcriptome signature for sesquiterpenoid biosynthesis, including highly expressed SaCYP736A167 transcripts. We characterized SaCYP736A167 as a multi-substrate P450, which stereo-selectively produces (Z)-α-santalol, (Z)-β-santalol, (Z)-epi-β-santalol and (Z)-α-exo-bergamotol, matching authentic sandalwood oil. This work completes the discovery of the biosynthetic enzymes of key components of sandalwood fragrance, and highlights the evolutionary diversification of stereo-selective P450s in sesquiterpenoid biosynthesis. Bioengineering of microbial systems using SaCYP736A167, combined with santalene/bergamotene synthase, has potential for development of alternative industrial production systems for sandalwood oil fragrances.

Many plant species adapted to P-impoverished soils, including jarrah (Eucalyptus marginata), develop toxicity symptoms when exposed to high doses of phosphate (Pi) and its analogs such as phosphite (Phi) and arsenate (AsV). The present study was undertaken to investigate the effects of fungal symbionts Scutellospora calospora, Scleroderma sp., and Austroboletus occidentalis on the response of jarrah to highly toxic pulses (1.5 mmol kg(-1) soil) of Pi, Phi, and AsV. S. calospora formed an arbuscular mycorrhizal (AM) symbiosis while both Scleroderma sp. and A. occidentalis established a non-colonizing symbiosis with jarrah plants. All these interactions significantly improved jarrah growth and Pi uptake under P-limiting conditions. The AM fungal colonization naturally declines in AM-eucalypt symbioses after 2-3 months; however, in the present study, the high Pi pulse inhibited the decline of AM fungal colonization in jarrah. Four weeks after exposure to the Pi pulse, plants inoculated with S. calospora had significantly lower toxicity symptoms compared to non-mycorrhizal (NM) plants, and all fungal treatments induced tolerance against Phi toxicity in jarrah. However, no tolerance was observed for AsV-treated plants even though all inoculated plants had significantly lower shoot As concentrations than the NM plants. The transcript profile of five jarrah high-affinity phosphate transporter (PHT1 family) genes in roots was not altered in response to any of the fungal species tested. Interestingly, plants exposed to high Pi supplies for 1 day did not have reduced transcript levels for any of the five PHT1 genes in roots, and transcript abundance of four PHT1 genes actually increased. It is therefore suggested that jarrah, and perhaps other P-sensitive perennial species, respond positively to Pi available in the soil solution through increasing rather than decreasing the expression of selected PHT1 genes. Furthermore, Scleroderma sp. can be considered as a fungus with dual functional capacity capable of forming both ectomycorrhizal and non-colonizing associations, where both pathways are always accompanied by evident growth and nutritional benefits.

Orchid conservation requires a case by case, functional ecosystem approach. In this context, understanding orchid reproductive strategy would be beneficial to orchid conservation. In this study, we investigated the floral biology and pollination ecology of Paphiopedilum spicerianum, a critically endangered orchid in China. P. spicerianum is self-compatible, but dependent upon insects for pollination. Two hoverflies, Allobaccha nubilipennis and Episyrphus balteatus, were observed and confirmed as pollinators of P. spicerianum. E. balteatus was the main pollinator of P. spicerianum, having the higher visitation frequency during our observations over three years. P. spicerianum exploited E. balteatus by food deception, and shared the pollinator with co-flowering Polygonum pubescens (Polygonaceae), a nectar rewarding species. Although the population of P. spicerianum was very small and the habitat was highly fragmented, P. spicerianum achieved a stable reproductive success measured as natural fruit set (mean 25.7% pooled over three seasons). Co-flowering P. pubescens plants may play an important role in attracting pollinators and maintaining a stable reproductive success for P. spicerianum. These results demonstrate the interrelationships of plants, pollinators and food sources that need to be understood when developing conservation plans for endangered orchids.

Litter mixing effects during decomposition remain inconclusive for boreal peatlands, and such effects may vary with climate warming and associated shifts in vegetation composition. Here, litters were collected from four common species (deciduous shrub Betula fruticosa, evergreen shrub Ledum palustre, graminoid Eriophorum vaginatum, and moss Sphagnum divinum) in a boreal peatland of northeast China, resulting in 15 species combinations with species richness ranging from one to four. We determined litter mixing effects on carbon (C) mineralization rate and mass loss under aerobic conditions at 10 °C and 20 °C in a 315-d incubation experiment, and assessed the differences in litter mass loss for the individual species within monocultures and mixtures. Non-additive effects on C mineralization and mass loss were prevalent during decomposition of litter mixtures. Moreover, the sensitivity of C mineralization and mass loss to rising incubation temperature (Q10) was found to be non-additive in five and three out of 11 mixtures, respectively. Notably, mass loss of other litters in the mixtures was generally promoted by B. fruticosa, but inhibited by S. divinum in two- and three-species litter mixtures. Furthermore, B. fruticosa increased and S. divinum decreased Q10 values for mass loss of other litters in four out of seven cases. These findings suggest that the shifts in plant community composition will not only influence community-level litter decomposition through altered litter mixing effects during decomposition, but also modulate the response of litter decomposition to rising temperature in boreal peatlands.

In boreal peatlands, litter decomposition plays an important role in modulating ecosystem carbon (C) cycling and nutrient turnover. However, how climate warming and plant functional group interact to affect litter decomposition is still unclear in these ecosystems. Here, we collected fresh litters of six plant functional groups (nitrogen (N)-fixing species, deciduous tree, deciduous shrub, evergreen shrub, graminoid, and Sphagnum moss) from a boreal peatland located in northeast China. A laboratory incubation experiment was used to determine the effect of temperature (10 °C vs. 20 °C) on microbial respiration and mass loss during decomposition. Among the six functional groups, the litters of N-fixing species and deciduous shrub, followed by deciduous tree, generally had the greatest mass losses and microbial respiration rates, whereas the Sphagnum moss decomposed with the slowest rate at both incubation temperatures. Increasing incubation temperature from 10 °C to 20 °C, microbial respiration rate and mass loss increased slightly for Sphagnum moss litters (25% and 19%, respectively), but increased dramatically for vascular plant litters (84–135% and 49–85%, respectively). For litters from vascular plants, both decomposition rate and temperature sensitivity showed a tight linear correlation with the initial C:N and C:phosphorus ratios. Considering that climate warming will cause increased dominance of woody plant species coupled with decreased cover by Sphagnum mosses, this study provides clear evidence that climate warming and the associated changes to vegetation community composition can synergistically accelerate plant litter decomposition in boreal peatlands.

Highlight Phosphate transporters AtPHT1;8 and AtPHT1;9, but not AtPHT1;1, discriminate between phosphite and phosphate. Phosphate-starvation-responsive transcript profiles show altered kinetics with phosphite, hence allowing further dissection of phosphorus signalling networks., Phosphite is a less oxidized form of phosphorus than phosphate. Phosphite is considered to be taken up by the plant through phosphate transporters. It can mimic phosphate to some extent, but it is not metabolized into organophosphates. Phosphite could therefore interfere with phosphorus signalling networks. Typical physiological and transcriptional responses to low phosphate availability were investigated and the short-term kinetics of their reversion by phosphite, compared with phosphate, were determined in both roots and shoots of Arabidopsis thaliana. Phosphite treatment resulted in a strong growth arrest. It mimicked phosphate in causing a reduction in leaf anthocyanins and in the expression of a subset of the phosphate-starvation-responsive genes. However, the kinetics of the response were slower than for phosphate, which may be due to discrimination against phosphite by phosphate transporters PHT1;8 and PHT1;9 causing delayed shoot accumulation of phosphite. Transcripts encoding PHT1;7, lipid-remodelling enzymes such as SQD2, and phosphocholine-producing NMT3 were highly responsive to phosphite, suggesting their regulation by a direct phosphate-sensing network. Genes encoding components associated with the ‘PHO regulon’ in plants, such as At4, IPS1, and PHO1;H1, generally responded more slowly to phosphite than to phosphate, except for SPX1 in roots and MIR399d in shoots. Two uncharacterized phosphate-responsive E3 ligase genes, PUB35 and C3HC4, were also highly phosphite responsive. These results show that phosphite is a valuable tool to identify network components directly responsive to phosphate.

Summary Hakea prostrata (Proteaceae) has evolved in extremely phosphorus (P)-impoverished habitats. Unlike species that evolved in P-richer environments, it tightly controls its nitrogen (N) acquisition, matching its low protein concentration, and thus limiting its P requirement for ribosomal RNA (rRNA). Protein is a major sink for sulfur (S), but the link between low protein concentrations and S metabolism in H. prostrata is unknown, although this is pivotal for understanding this species’ supreme adaptation to P-impoverished soils. Plants were grown at different sulfate supplies for 5 wk and used for nutrient and metabolite analyses. Total S content in H. prostrata was unchanged with increasing S supply, in sharp contrast with species that typically evolved in environments where P is not a major limiting nutrient. Unlike H. prostrata, other plants typically store excess available sulfate in vacuoles. Like other species, S-starved H. prostrata accumulated arginine, lysine and O-acetylserine, indicating S deficiency. Hakea prostrata tightly controls its S acquisition to match its low protein concentration and low demand for rRNA, and thus P, the largest organic P pool in leaves. We conclude that the tight control of S acquisition, like that of N, helps H. prostrata to survive in P-impoverished environments.

Source at https://doi.org/10.3390/toxins9070202. Staphylococcus aureus (S. aureus) produces many different exotoxins including the gamma-toxins, HlgAB and HlgCB. Gamma-toxins form pores in both leukocyte and erythrocyte membranes, resulting in cell lysis. The genes encoding gamma-toxins are present in most strains of S. aureus, and are commonly expressed in clinical isolates recovered from menstrual Toxic Shock Syndrome (mTSS) patients. This study set out to investigate the cytotoxic and proinflammatory effects of gamma-toxins on vaginal epithelial surfaces. We found that both HlgAB and HlgCB were cytotoxic to cultured human vaginal epithelial cells (HVECs) and induced cytokine production at sub-cytotoxic doses. Cytokine production induced by gamma-toxin treatment of HVECs was found to involve epidermal growth factor receptor (EGFR) signaling and mediated by shedding of EGFR ligands from the cell surface. The gamma-toxin subunits displayed differential binding to HVECs (HlgA 93%, HlgB 97% and HlgC 28%) with both components (HlgAB or HlgCB) required for maximum detectable binding and significant stimulation of cytokine production. In studies using full thickness ex vivo porcine vaginal mucosa, HlgAB or HlgCB stimulated a dose-dependent cytokine response, which was reduced significantly by inhibition of EGFR signaling. The effects of gamma-toxins on porcine vaginal tissue and cultured HVECs were validated using ex vivo human ectocervical tissue. Collectively, these studies have identified the EGFR-signaling pathway as a key component in gamma-toxin-induced proinflammatory changes at epithelial surfaces and highlight a potential therapeutic target to diminish toxigenic effects of S. aureus infections.

Background Urinary tract infections (UTIs) are common bacterial infections in adults, and catheter-associated UTIs are the most common nosocomial infection. The rise of multidrug-resistant organisms and an increased focus on antibiotic stewardship has influenced the development of novel treatments against such infections, and there is growing interest in the use of probiotics for antimicrobial therapy. We used an ex vivo human bladder tissue (HBT) model to evaluate the antimicrobial efficacy and biocompatibility of lactobacillus-based developmental formulations (created and supplied by ICET, Inc.) for preventative treatment against common UTI pathogens. Methods To assess antimicrobial efficacy, lactobacillus-based formulations (live and attenuated) were spiked with five prevalent UTI organisms (5 × 103 CFU/mL). Ex vivo HBT explants were treated with 300 μL of spiked formulation for 6 and 24 h at 37°C, then processed and plated on selective agars. Biocompatibility studies assessed ex vivo HBT tissue viability and inflammatory response (IL-8) to lactobacillus-containing formulations with MTT assay and ELISA at 2 h post-treatment. Results At 6 h, live lactobacillus-containing formulations (29–124, 29-124C) were bacteriostatic (90.00–99.89% log CFU/mL reduction) against Escherichia coli and Klebsiella pneumoniae and bactericidal (≥99.90% log CFU/mL reduction) against Candida albicans, Enterococcus faecalis, and Proteus mirabilis. By 24 h, live formulations were bactericidal against all five organisms tested. Attenuated formulation 29–125 achieved bacteriostatic efficacy against E. coli, K. pneumoniae, and P. mirabilis and bactericidal efficacy against C. albicans and E. faecalis at 24 h. Biocompatibility assessments following 2 h exposure to lactobacillus-based formulations revealed exposed explants were fully viable, with no significant changes in IL-8 production compared with PBS-treated controls. Conclusion This study suggests lactobacillus-based formulations are effective and safe options for UTI prevention. While this static ex vivo human bladder mucosalmodel does not fully replicate the dynamic and diluting conditions that occur in vivo, we anticipate that our findings will be confirmed by future in vivo studies. Disclosures All authors: No reported disclosures.

Karst and non-karst forests occur in the same region in south-west China, but the soil water and mineral nutrients availability are different between the forests. Our hypothesis was that the leaves of karst trees would be better adapted to dry, nutrient-poor conditions than those of trees in a nearby non-karst forest. We compared the gas exchange, anatomical characteristics and mineral nutrient concentrations in leaves from 21 tree species in a tropical karst forest and 19 species in a nearby non-karst forest in south-west China. We found that the leaves of karst trees had higher P concentrations, photosynthetic capacity and water use efficiency, and greater adaxial and abaxial epidermis thickness than leaves of non-karst forest trees. Evergreen and deciduous trees differed more significantly in leaf functional traits in the karst forest than in the non-karst forest. The leaf palisade:spongy mesophyll thickness ratio was positively correlated with stomatal conductance and negatively correlated with photosynthetic water use efficiency in the karst forest but not in the non-karst forest. Our findings indicate that karst forest trees are more conservative in water use, whereas soil P deficiency could be a major limiting factor for the growth of non-karst forest trees.

Current management of Sclerotinia rot (Sclerotinia sclerotiorum) relies heavily upon cultural and chemical control options that provide, at best, only partial, sometimes sporadic control and can be cost prohibitive. Effective host resistance to S. sclerotiorum is urgently needed if Sclerotinia rot is to be successfully managed across diverse oilseed, forage and vegetable crucifer crops worldwide. Differences in resistance across 127 diverse cruciferous genotypes to S. sclerotiorum in one experiment, and a set of 55 Brassica napus lines carrying one or more B. carinata B genome introgressions in a second experiment, were assessed by field-inoculation of stems and natural ascospore infection. Reactions on B. fruticulosa, B. oxyrrhina, B. parachinensis, B. tournefortii, Camelina sativa, Carrichtera annua, Diplotaxis tenuifolia, Eruca vesicaria, Hirschfeldia incana, Raphanus raphanistrum, Raphanus sativus, Rapistrum rugosum, Sinapis arvensis and Sisymbrium irio to this pathogen are reported for the first time. Among these, and across other species previously explored, including B. carinata, B. napus, B. juncea, B. rapa, B. cretica, B. incana, B. insularis, B. nigra, and B. montana, responses ranged from highly resistant (stem lesion length 2 mm) to highly susceptible (155 mm). Against a highly virulent and prevailing pathogen pathotype, R. raphanistrum RRA 41, B. napus Mystic, B. carinata BRA 926/78, B. carinata 054113, R. sativus Krasnodar. Market B, B. carinata PI 193459 and R. raphanistrum WARR 20 all showed very high-level resistance, with stem lesion length 67 mm). There appeared to be separate genetic control for stem vs. leaf resistance, crucial to the understanding needed in developing resistant cultivars across different cruciferous crop types. While this study highlighted individual genotypes that offer great potential for improving resistance to Sclerotinia rot in commercial cruciferous crops, it also demonstrated that assessment of the overall value of a species is only possible when a significant number of genotypes within the species are tested. Overall, while genotypes with high-level stem or leaf resistance identified are of particularly significant value for developing new disease-resistant cultivars of oilseed, forage and vegetable crucifers, even genotypes with moderate levels of resistance, if deployed commercially, offer prospects of improving current integrated disease management strategies compared with current reliance upon cultural and/or chemical controls utilized in conjunction with cultivars lacking any effective resistance. As resistance was identified for the first time across many of these diverse cruciferous species, it is likely that some resistances identified constitute new sources and/or types of host resistance not previously identified.

• Most terrestrial plants form mutually beneficial symbioses with specific soil-borne fungi known as mycorrhiza. In a typical mycorrhizal association, fungal hyphae colonize plant roots, explore the soil beyond the rhizosphere and provide host plants with nutrients that might be chemically or physically inaccessible to root systems. • Here, we combined nutritional, radioisotopic ((33)P) and genetic approaches to describe a plant growth promoting symbiosis between the basidiomycete fungus Austroboletus occidentalis and jarrah (Eucalyptus marginata), which has quite different characteristics. • We show that the fungal partner does not colonize plant roots; hyphae are localized to the rhizosphere soil and vicinity and consequently do not transfer nutrients located beyond the rhizosphere. Transcript profiling of two high-affinity phosphate (Pi) transporter genes (EmPHT1;1 and EmPHT1;2) and hyphal-mediated (33)Pi uptake suggest that the Pi uptake shifts from an epidermal to a hyphal pathway in ectomycorrhizal plants (Scleroderma sp.), similar to arbuscular mycorrhizal symbioses, whereas A. occidentalis benefits its host indirectly. The enhanced rhizosphere carboxylates are linked to growth and nutritional benefits in the novel symbiosis. • This work is a starting point for detailed mechanistic studies on other basidiomycete-woody plant relationships, where a continuum between heterotrophic rhizosphere fungi and plant beneficial symbioses is likely to exist.

Mitochondrial lipoamide dehydrogenase is essential for the activity of four mitochondrial enzyme complexes central to oxidative metabolism. The reduction in protein amount and enzyme activity caused by disruption of mitochondrial LIPOAMIDE DEHYDROGENASE2 enhanced the arsenic sensitivity of Arabidopsis thaliana. Both arsenate and arsenite inhibited root elongation, decreased seedling size and increased anthocyanin production more profoundly in knockout mutants than in wild-type seedlings. Arsenate also stimulated lateral root formation in the mutants. The activity of lipoamide dehydrogenase in isolated mitochondria was sensitive to arsenite, but not arsenate, indicating that arsenite could be the mediator of the observed phenotypes. Steady-state metabolite abundances were only mildly affected by mutation of mitochondrial LIPOAMIDE DEHYDROGENASE2. In contrast, arsenate induced the remodelling of metabolite pools associated with oxidative metabolism in wild-type seedlings, an effect that was enhanced in the mutant, especially around the enzyme complexes containing mitochondrial lipoamide dehydrogenase. These results indicate that mitochondrial lipoamide dehydrogenase is an important protein for determining the sensitivity of oxidative metabolism to arsenate in Arabidopsis.

Recent studies have identified genotypic variation in phosphorus (P) efficiency, but rarely have the underlying mechanisms been described at the molecular level. We demonstrate that the highly P-efficient wheat (Triticum aestivum L.) cultivar Chinese 80-55 maintains higher inorganic phosphate (Pi) concentrations in all organs upon Pi withdrawal in combination with higher Pi acquisition in the presence of Pi when compared with the less-efficient cultivar Machete. These findings correlated with differential organ-specific expression of Pi transporters TaPHT1;2, TaPHT1;5, TaPHT1;8, TaPHT2;1 and H+-ATPase TaHa1. Observed transcript level differences between the cultivars suggest that higher de novo phospholipid biosynthetic activities in Pi-limited elongating basal leaf sections are another crucial adaptation in Chinese 80-55 for sustaining growth upon Pi withdrawal. These activities may be supported through enhanced breakdown of starch in Chinese 80-55 stems as suggested by higher TaGPho1 transcript levels. Chinese 80-55 fine roots on the other hand show strong suppression of transcripts involved in glycolysis, transcriptional regulation and ribosomal activities. Our work reveals major differences in the way the two contrasting cultivars allocate Pi and organic P compounds between source and sink tissues and in the acclimation of their metabolism to changes in Pi availability.

Plant adaptations associated with a high efficiency of phosphorus (P) acquisition can be used to increase productivity and sustainability in a world with a growing population and decreasing rock phosphate reserves. White lupin (Lupinus albus) produces cluster roots that release carboxylates to efficiently mobilize P from P-sorbing soils. It has been hypothesized that an increase in the activity of the alternative oxidase (AOX) would allow for the mitochondrial oxidation of NAD(P)H produced during citrate synthesis in cluster roots at a developmental stage when there is a low demand for ATP. We used the oxygen-isotope fractionation technique to study the in vivo respiratory activities of the cytochrome oxidase pathway (COP) and the alternative oxidase pathway (AOP) in different root sections of white lupins grown hydroponically with and without P. In parallel, AOX protein levels and internal carboxylate concentrations were determined in cluster and non-cluster roots. Higher in vivo AOP activity was measured in cluster roots when malate and citrate concentrations were also high, thus confirming our hypothesis. AOX protein levels were not always correlated with in vivo AOP activity, suggesting post-translational regulation of AOX.

Proteaceae in southwestern Australia have evolved on some of the most phosphorus-impoverished soils in the world. They exhibit a range of traits that allow them to both acquire and utilize phosphorus highly efficiently. This is in stark contrast with many model plants such as Arabidopsis thaliana and crop species, which evolved on soils where nitrogen is the major limiting nutrient. When exposed to low phosphorus availability, these plants typically exhibit phosphorus-starvation responses, whereas Proteaceae do not. This Review explores the traits that account for the very high efficiency of acquisition and use of phosphorus in Proteaceae, and explores which of these traits are promising for improving the phosphorus efficiency of crop plants.

Limitation of grain crop productivity by phosphorus (P) is widespread and will probably increase in the future. Enhanced P efficiency can be achieved by improved uptake of phosphate from soil (P-acquisition efficiency) and by improved productivity per unit P taken up (P-use efficiency). This review focuses on improved P-use efficiency, which can be achieved by plants that have overall lower P concentrations, and by optimal distribution and redistribution of P in the plant allowing maximum growth and biomass allocation to harvestable plant parts. Significant decreases in plant P pools may be possible, for example, through reductions of superfluous ribosomal RNA and replacement of phospholipids by sulfolipids and galactolipids. Improvements in P distribution within the plant may be possible by increased remobilization from tissues that no longer need it (e.g. senescing leaves) and reduced partitioning of P to developing grains. Such changes would prolong and enhance the productive use of P in photosynthesis and have nutritional and environmental benefits. Research considering physiological, metabolic, molecular biological, genetic and phylogenetic aspects of P-use efficiency is urgently needed to allow significant progress to be made in our understanding of this complex trait.

Background and aims Strawberry (Fragaria x ananassa) is a high-value crop worldwide. Fusarium oxysporum f. sp. fragariae causes rapid wilting and death of strawberry plants and severe economic losses worldwide. To date, no studies have been conducted to determine colonisation of either susceptible or resistant strawberry plants by F. oxysporum f. sp. fragariae, or whether plant colonisation by F. oxysporum f. sp. fragariae differs between susceptible and resistant cultivars.

Sclerotinia stem rot caused by the fungus Sclerotinia sclerotiorum is one of the most damaging and difficult-to-manage diseases of oilseed rape (Brassica napus) and mustard (B. juncea). Identifying oilseed Brassica genotypes with effective resistance offers the best long-term prospect for improved management of the disease. Despite some significant interactions between oilseed Brassica genotypes and S. sclerotiorum isolates reported in earlier studies, mostly a single pathogen isolate has been used to identify resistant genotypes. This paper reports the results of studies involving 53 isolates of S. sclerotiorum from the northern and southern agricultural regions of Western Australia where Sclerotinia stem rot is a serious disease of oilseed rape. Colony characteristics of isolates on potato dextrose agar were determined, and two field virulence (i.e., levels of disease severity) studies conducted. The first field study included 14 Brassica genotypes against three S. sclerotinia isolates and the second had eight Brassica genotypes against 50 S. sclerotinia isolates. Only colony diameter of isolates growing on potato dextrose agar was correlated with stem lesion length in the field. In both field experiments, there were significant effects of isolates and host genotypes, as well as a significant interaction between isolates and genotypes in relation to stem lesion length. In the first field experiment, mean stem lesion length ranged from 1 cm in the highly resistant B. napus ZY006 to at least 9 cm for susceptible genotypes Brassica juncea #2 and B. juncea Montara. The latter genotype was the most susceptible with a mean stem lesion length of 11.1. Expression of high-level resistance in B. napus ZY006 was largely independent of S. sclerotiorum isolate. In contrast, responses in B. napus genotypes, Zhongyou 821, 06-6-3792, RT108 and Charlton were much more isolate-dependent. In the first field experiment, with a greater number of host genotypes than S. sclerotiorum isolates, a higher variance ratio occurred for isolates (VR = 158.4) than for host genotypes (VR = 10.7). In the second field experiment, with a larger number of S. sclerotinia isolates than hosts, host genotypes had a higher variance ratio (VR = 458.9) compared to the isolates (VR = 71.2). Increasing the number of isolates greatly improved the capacity to differentiate levels of resistance among test genotypes. In this experiment, some genotypes showed more consistent resistant reactions (e.g., B. napus Mystic and B. juncea Xinyou 9) across different isolates and these are ideal targets for commercial exploitation of this resistance in oilseed Brassica breeding programs. From this experiment, a standardized set of three B. napus and three B. juncea genotypes were shown to be suitable for use as universal differentials to characterize pathotypes of S. sclerotiorum using octal nomenclature. Eight distinct pathotypes of S. sclerotiorum were delineated and characterized and these six host differential genotypes can now be utilized to identify and monitor the incidence and distribution of current and future pathotypes of S. sclerotiorum. Further, by providing a reliable means to characterize pathotypes of S. sclerotiorum, for the first time not only allows identification of resistance(s) against the predominant pathotype(s) of S. sclerotiorum prevailing in a particular region, but also now allows oilseed rape breeding programs to combine host resistances against several specific pathotypes of S. sclerotiorum into future cultivars.

Australia harbors some of the most nutrient-impoverished soils on Earth. Southwestern Australian soils are especially phosphorus (P) impoverished, due to the age of this ancient landscape and it being unaffected by major geological disturbance for millions of years ([Hopper, 2009][1]; [Lambers et al