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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background: Phosphorus (P) is often a limiting mineral nutrient for plant growth. Many soils worldwide are deficient in soluble inorganic phosphate (Pi), the form of P most readily absorbed and utilized by plants. A network of elaborate developmental and biochemical adaptations has evolved in plants to enhance Pi acquisition and avoid starvation. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

Abstract: 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 1cm in the highly resistant B. napus ZY006 to at least 9cm 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. [Copyright &y& Elsevier]