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Long-distance communications in giant characean internodal cells involve cytoplasmic streaming as an effective means for transportation of regulatory substances. The local illumination of Chara corallina Klein ex C.L. Willdenow internodal cells with an intense 30 s pulse of white light caused a transient increase of modulated chlorophyll fluorescence in cell regions positioned downstream the cytoplasmic flow after a delay whose duration increased with the axial distance from the light source. No changes in fluorescence were observed in cell regions residing upstream of the light spot. The transient increase in actual fluorescence F0 in cell areas exposed to constant dim illumination at large distances from the brightly lit area indicates the transmission of photosynthetically active metabolite between chloroplasts separated by 1–5mm distances. The shapes of fluorescence transients were sensitive to retardation of cytoplasmic streaming by cytochalasin D and to variations in cyclosis velocity during gradual recovery of streaming after an instant arrest of cyclosis by elicitation of the action potential. Furthermore, the analysed fluorescence transients were skewed on the ascending or descending fronts depending on the position of light-modulated cytoplasmic package at the moment of streaming cessation with respect to the point of measurements. The observations are simulated in qualitative terms with a simplified streaming–diffusion model. [ABSTRACT FROM AUTHOR]

Many plant species or cultivars form variegated leaves in which blades are made of green and white sectors. On the one hand, there is little photosynthetic CO2 assimilation in white tissue simply because of the lack of functional chloroplasts and thus, leaf white tissue is heterotrophic and fed by photosynthates exported by leaf green tissue. On the other hand, it has been previously shown that the white tissue is enriched in nitrogenous compounds such as amino acids and polyamines, which can, in turn, be remobilised upon nitrogen deficiency. However, the origin of organic nitrogen in leaf white tissue, including the possible requirement for N-reduction in leaf green tissue before export to white tissue, has not been examined. Here, we took advantage of isotopic methods to investigate the source of nitrogen in the white tissue. A survey of natural isotope abundance (δ15N) and elemental composition (%N) in various variegated species shows no visible difference between white and green tissues, suggesting a common N source. However, there is a tendency for N-rich white tissue to be naturally 15N-enriched whereas in the model species Pelargonium × hortorum, white sectors are naturally 15N-depleted, indicating that changes in metabolic composition and/or N-partitioning may occur. Isotopic labelling with 15N-nitrate on illuminated leaf discs clearly shows that the white tissue assimilates little nitrogen and thus relies on nitrate reduction and metabolism in the green tissue. The N-sink represented by the white tissue is considerable, accounting for nearly 50% of total assimilated nitrate. [ABSTRACT FROM AUTHOR]

Many short-term experiments have been conducted under increasing CO[sub 2] but results have been varied and have not yet led to a conclusive quantitative understanding of the CO[sub 2] response of plant growth. This may have been partly due to a lack of explicit consideration of the positive feedback inherent in plant growth during periods of exponential growth. This feedback can increase an initial physiological enhancement of relative growth rate (RGR) into a much larger biomass enhancement. To overcome this problem, we re-analysed existing experimental data from 78 publications. We calculated the RGRs of C[sub 3] plants and their relative enhancement under elevated CO[sub 2] and derived response indices that were independent of the duration of experiments and the RGR at normal atmospheric CO[sub 2]. The RGR of unstressed plants increased by 14 ± 2% under doubled CO[sub 2], with observed RGR enhancement linearly correlated with calculated photosynthetic enhancements (based on the Farquhar-von Caemmerer-Berry photosynthesis model), but at only half their numeric values. Calculated RGR enhancements did not change significantly for temperatures from 12 to 40°C, but were reduced under nutrient limitation, and were increased under water stress or low irradiance. We concluded that short-term experiments can offer simple and cost-effective insights into plant CO[sub 2] responses, provided they are analysed by calculating relative changes in RGR during the strictly exponential initial growth phase. [ABSTRACT FROM AUTHOR]

Drought is one of the most important abiotic stresses constraining crop productivity worldwide. The objective of the present study was to investigate the differences in drought tolerance at leaf and stomatal level of black gram (genotypes: T9, KU 301, PU 19, USJD 113) and green gram (genotypes: Pratap, SG 21-5, SGC 16, TMB 37). Drought was applied for fifteen consecutive days at flowering stage (35 days after sowing). Mid-day leaf water potential (Ψ[sub L]), leaf area, photosynthesis rate (P[sub N]), leaf chlorophyll, stomatal conductance (gs) and seed yield of drought- treated plants were calculated relative to those of well watered plants. Stomatal characteristics were observed in terms of stomatal frequency (SF) and stomatal aperture size (SA). Among the studied genotypes, T9 (black gram) and Pratap (green gram) proved their better tolerance capacity to drought by maintaining higher leaf area, Ψ[sub L], P[sub N], leaf chlorophyll, g[sub s] and SA which contributed to better seed yield. Between the two crops, green gram appeared to be affected to a greater extent, as it experienced higher reduction in yield than black gram. A highly significant positive correlation (level 0.01) of seed yield was obtained with leaf area, Ψ[sub L], P[sub N], leaf chlorophyll, g[sub s] and SA, whereas SF was found to be poorly correlated with seed yield. [ABSTRACT FROM AUTHOR]

Organs of C3 plants differ in their C isotopic signature (δ13C). In general, leaves are 13C-depleted relative to other organs. To investigate the development of spatial δ13C patterns, we induced different C allocation strategies by reducing light and nutrient availability for 12 months in the Mediterranean shrub Halimium halimifolium L. We measured morphological and physiological traits and the spatial δ13C variation among seven tissue classes during the experiment. A reduction of light (Low-L treatment) increased aboveground C allocation, plant height and specific leaf area. Reduced nutrient availability (Low-N treatment) enhanced C allocation into fine roots and reduced the spatial δ13C variation. In contrast, control and Low-L plants with high C allocation in new leaves showed a high δ13C variation within the plant (up to 2.5‰). The spatial δ13C variation was significantly correlated with the proportion of second-generation leaves from whole-plant biomass (r2 = 0.46). According to our results, isotope fractionation in dark respiration can influence the C isotope composition of plant tissues but cannot explain the entire spatial pattern seen. Our study indicates a foliar depletion in 13C during leaf development combined with export of relatively 13C-enriched C by mature source leaves as an important reason for the observed spatial δ13C pattern. [ABSTRACT FROM AUTHOR]

The rate of shoot growth (vigour) in grapevines tends to decrease as the number of shoots per plant increases. Because the underlying causes of this relationship remain unclear, they were studied by variable pruning of field-grown, deficit-irrigated Merlot grapevines (Vitis vinifera L.). Shoot number ranged from 11 to 124 per vine and was inversely correlated with shoot growth rate, leaf appearance rate, axillary bud outgrowth, internode length, leaf size, shoot leaf area, carbon partitioned to the fruit (C[sub fruit]) per shoot, average daily maximum photosynthesis (A[sub max]), stomatal conductance (g[sub max]), and leaf-specific hydraulic conductance (K[sub l]). Shoot number was positively correlated with canopy leaf area, whole-vine C[sub fruit], whole-plant hydraulic conductance (K[sub v]), and canopy conductance (K[sub c]). Higher shoot vigour was associated with higher A[sub max], g[sub max], predawn leaf water potential (Ψ[sub pd]), shoot hydraulic conductance (K[sub s]), K[sub l], and K[sub v]. Vigorous shoots supported both more vegetative growth and more reproductive growth; thus fruit growth did not compete with shoot growth for photosynthates. These results indicate that the hydraulic capacity of grapevines adapts to varying shoot numbers to support leaf physiology, growth, and carbon partitioning, but adaptation may belimited, putting upper bounds on the growth of individual shoots and fruit. [ABSTRACT FROM AUTHOR]

Plant functional traits are closely associated with plant habitats. In this study, we investigated the interspecific variations in stem and leaf hydraulics, xylem and leaf anatomy, gas-exchange rates and leaf pressure-volume relationships among three Syzygium tree species in early, mid- and late successional tropical forests. The objective was to understand the response and adaptation of congeneric species, in terms of branch and leaf functional traits, to different environments. A consistent pattern of decline with succession was evident in leaf and sapwood specific hydraulic conductivity (k[sub s]), maximum leaf hydraulic conductance (K[sub leaf]), and photosynthetic rates for the three Syzygium species. Variations of k[sub s] and K[sub leaf] were correlated with changes in vessel anatomy (i.e. vessel density and diameter) and leaf flux-related structure (i.e. stomatal pore index and vein density) respectively. However, specific leaf area and leaf to sapwood area ratio did not significantly differ among the three species. In addition, the mid-successional species had the lowest values of leaf water potential at full turgor and turgor loss point and 50% loss of K[sub leaf], but the greatest value of xylem water potential at 50% loss of k[sub s]. Our results demonstrate that leaf and branch traits associated with photosynthesis and/or hydraulic conductance, rather than those associated with drought tolerance, are the key factors underlying the response and adaptation of the three Syzygium tree species along the tropical forest succession. [ABSTRACT FROM AUTHOR]

European mistletoe (Viscum album L.) is a hemiparasitic plant with perennial leaves and photosynthetic stems easily discernible according to their age. These properties make V. album the perfect species to (i) compare the mechanisms of seasonal acclimation of photosynthetic stems with those of leaves, and (ii) evaluate the influence of ageing in the efficiency of photosynthetic tissues. To achieve these general objectives, photosynthetic pigments, maximal photochemical efficiency of PSII (Fv/Fm), recovery kinetics and key thylakoidal proteins were analysed during winter and spring in leaves and at different age stems. During winter, some woody species are able to maintain photosynthetic activity, but at lower rates than during spring. In the case of V. album, photosynthetic relevance of green stems appears equal to leaves in terms of total area. Besides, mistletoe stems are able to maintain higher Fv/Fm and lower level of antioxidants than leaves, especially during winter season. The recovery from winter photoinhibition is also faster in stems than in leaves. Thylakoidal protein composition (mainly high levels of D1) also supports the idea of stems as main photosynthetic organs in V. album during winter. Further, in winter, the level of photoinhibition of V. album stems decreased concomitantly with ageing. This work highlights the importance of stem photosynthesis in plant carbon balance and demonstrates that ageing does not necessarily imply a loss of vitality in stems. European mistletoe (Viscum album) is an evergreen hemiparasitic plant characterised by a continuous photosynthetic surface composed of leaves and stems. We have taken advantage of these traits and used this species as a perfect model plant to study the interactive effect of age and winter on photosynthetic regulation. Winter, as in other temperate evergreens, induces a downregulation of photosynthesis, which in stems is compensated by an ageing-dependent stimulatory effect. Overall, this case study supports the theory of negative senescence. [ABSTRACT FROM AUTHOR]

Diatoms dominate nearly half of current oceanic productivity, so their responses to ocean acidification are of general concern regarding future oceanic carbon sequestration. Community, mesocosm and laboratory studies show a range of diatom growth and photophysiological responses to increasing pCO2. Nearly 20 studies on effects of elevated pCO2 on diatoms have shown stimulations, no effects or inhibitions of growth rates. These differential responses could result from differences in experimental setups, cell densities, levels of light and temperature, but also from taxon-specific physiology. Generally, ocean acidification treatments of lowered pH with elevated CO2 stimulate diatom growth under low to moderate levels of light, but lead to growth inhibition when combined with excess light. Additionally, diatom cell sizes and their covarying metabolic rates can influence responses to increasing pCO2 and decreasing pH, although cell size effects are confounded with taxonomic specificities in cell structures and metabolism. Here we summarise known diatom growth and photophysiological responses to increasing pCO2 and decreasing pH, and discuss some reasons for the diverse responses observed across studies. [ABSTRACT FROM AUTHOR]

Xylem-tapping mistletoes are known to have generally higher transpiration rate (T[sub r]), lower CO[sub 2] assimilation rate (A) and therefore lower water-use efficiency (WUE) than their hosts. There are long-standing contradictions in water relations and nitrogen use in photosynthesis. Gas exchange, chlorophyll fluorescence and nutrition components were investigated in a special mistletoe-host pair, Viscum ovalifolium-Sonneratia caseolaris, as the host was a mangrove growing in a saline environment. Our results show that both plants had high foliar N content, therefore it was consistent with the N-parasitism hypothesis, although the mistletoe had a lower T[sub r] than its mangrove host. It was suggested that the mistletoe reduces its T[sub r] under salt stress with N sufficient conditions. The mistletoe had a fundamental limitation of photosynthesis, and was photoinhibited with regard to high salinity, but it developed more photoprotection to thermal radiation. Additionally, both stomatal conductance (g[sub s]) and mesophyll conductance (g[sub m]) limitations on photosynthesis dominated in the mistletoe under salt stress even though it had a high foliar N content similar to the host. [ABSTRACT FROM AUTHOR]

Nax1 and Nax2 are two genetic loci that control the removal of Na[sup +] from the xylem and thereby help to exclude Na[sup +] from leaves of plants in saline soil. They originate in the wheat ancestral relative Triticum monococcum L. and are not present in modern durum or bread wheat. The Nax1 and Nax2 loci carry TmHKT1; 4-A2 and TmHKT1; 5-A, respectively, which are the candidate genes for these functions. This paper describes the development of near-isogenic breeding lines suitable for assessing the impact of the Nax loci and their performance in controlled environment and fields of varying salinity. In young plants grown in 150 mM NaCl, Nax1 reduced the leaf Na[sup +] concentration by 3-fold, Nax2 by 2-fold and both Nax1 and Nax2 together by 4-fold. In 250 mM NaCl, Nax1 promoted leaf longevity and greater photosynthesis and stomatal conductance. In the uppermost leaf, the Na[sup +]-excluding effect of the Nax loci was much stronger. In the field, Na[sup +] in the flag leaf was reduced 100-fold by Nax1 and 4-fold by Nax2; however, Nax1 lines yielded 5-10% less than recurrent parent (cv. Tamaroi) in saline soil. In contrast, Nax2 lines had no yield penalty and at high salinity they yielded close to 25% more than Tamaroi, indicating this material is suitable for breeding commercial durum wheat with improved yield on saline soils. Soil salinity is a major limitation on the growth and yield of all crop species, but especially of durum wheat, which lacks the ability to reduce sodium uptake into its leaves. This study describes the development of durum wheat breeding lines containing salt tolerance loci Nax1 and Nax2 and their performance in controlled environment and in fields of varying salinity. Results showed that enhanced sodium exclusion capability associated with Nax2 resulted in improved grain yields of up to 25% in soils with high salinity. [ABSTRACT FROM AUTHOR]

A mechanistic model of carbon partitioning, based on the Münch hypothesis of phloem transport and implemented with PIAF-Münch modelling platform (Lacointe and Minchin 2008), was tested for an architecture more complex than any tested previously. Using 11C to label photosynthate, responses in transport of photosynthate within a heavily pruned dwarf bean plant (Phaseolus vulgaris L.) to changes in source and sink activities were compared with model predictions. The observed treatment responses were successfully predicted. However, the observations could not be completely explained if the modelled stem contained only one phloem pathway: tracer from a labelled leaf was always detected in both shoot apex and root, whichever of the two leaves was labelled. This shows that bidirectional flow occurred within the stem, with solute moving simultaneously in both directions. Nevertheless, a model architecture with very little more complexity could incorporate such bidirectional flow. We concluded that the model could explaintheobservations,and that the PIAF-Münch model platform can be expected to describe partitioning in even more complex architectures. [ABSTRACT FROM AUTHOR]

This review deals with grapevine responses to water stress by examining perturbations to physiological and molecular processes at the root, shoot, leaf and berry levels. Long-distance signalling among organs is also considered. Isohydric or anisohydric Vitisgenotypes are described in relation to their response to drought, which is linked to stomatal behaviour. Stomatal regulation of grapevine under abscisic acid and hydraulic control (the latter being linked to embolism formation and recovery in water pathways upstream the stomata) is reviewed and linked to impairments of photosynthetic assimilation. We define three stages of photosynthesis regulation in grapevines that are subjected to progressive water stress on the basis of the main causes of assimilation decline. Early and late contributions of aquaporins, which play a fundamental role in water stress control, are discussed. Metabolic mechanisms of dehydration tolerance are rewieved, and variation linked to differences in transcript abundance of genes involved in osmoregulation, photosynthesis, photorespiration, detoxification of free radicals and coping with photoinhibition. Results of these defence strategies accumulated in berries are reviewed, together with perturbations of their molecular pathways. Features observed in different organs show that grapevine fits well as a complex model plant for molecular and physiological studies on plant drought avoidance/tolerance. [ABSTRACT FROM AUTHOR]

Bienertia sinuspersiciAkhani represents one form of C4photosynthesis that occurs without Kranz anatomy in family Chenopodiaceae. Analysis of transcript profiles and proteomics were made to gain information on this single-cell C4photosynthetic mechanism. Chlorenchyma cells were isolated and purified from mature leaves. From these cells, a cDNA library was made from which sequences were obtained on 2385 clones using conventional methods. To obtain a protein profile, the multi dimensional protein identification technique was used, resulting in identification of 322 unique proteins in chlorenchyma cells. After analysing datasets from the EST library and proteomics, genes and proteins were classified into 23 and 17 categories according to types of biological processes, respectively. These include photosynthesis and photorespiration, other biosynthetic and metabolic processes, cell wall modification, defence response, DNA repair, electron transport, other cellular and developmental processes, protein folding, protein targeting, protein modification, proteolysis, redox and ion homeostasis, response to biotic and abiotic stresses, RNA modification, transcription, translation, transport and unknowns. Sequence and phylogenetic analyses were made of C4cycle enzymes to characterise the relationship between homologues found in Bienertiawith public gene sequences from other chenopods and representative C3and C4species from other families. Identified photosynthetic genes and proteins are discussed with respect to the proposed function of an NAD-ME type C4cycle in this single-cell C4system. [ABSTRACT FROM AUTHOR]

C4 photosynthesis has evolved many times in 18 different families of land plants with great variation in leaf anatomy, ranging from various forms of Kranz anatomy to C4 photosynthesis occurring within a single type of photosynthetic cell. There has been little research on photosynthetic typing in the family Cleomaceae, in which only one C4 species has been identified, Cleome gynandra L. There is recent interest in selecting and developing a C4 species from the family Cleomaceae as a model C4 system, since it is the most closely related to Arabidopsis, a C3 model system (Brown et al. 2005). From screening more than 230 samples of Cleomaceae species, based on a measure of the carbon isotope composition (?13C) in leaves, we have identified two additional C4 species, C. angustifolia Forssk. (Africa) and C. oxalidea F.Muell. (Australia). Several other species have ?13C values around ?17? to ?19?, suggesting they are C4-like or intermediate species. Eight species of Cleome were selected for physiological, anatomical and biochemical analyses. These included C. gynandra, a NAD?malic enzyme (NAD?ME) type C4 species, C. paradoxa R.Br., a C3?C4 intermediate species, and 6 others which were characterised as C3 species. Cleome gynandra has C4 features based on low CO2 compensation point (?), C4 type ?13C values, Kranz-type leaf anatomy and bundle sheath (BS) ultrastructure, presence of C4 pathway enzymes, and selective immunolocalisation of Rubisco and phosphoenolpyruvate carboxylase. Cleome paradoxa was identified as a C3?C4 intermediate based on its intermediate ? (27.5?molmol?1), ultrastructural features and selective localisation of glycine decarboxylase of the photorespiratory pathway in mitochondria of BS cells. The other six species are C3 plants based on ?, ?13C values, non-Kranz leaf anatomy, and levels of C4 pathway enzymes (very low or absent) typical of C3 plants. The results indicate that this is an interesting family for studying the genetic basis for C4 photosynthesis and its evolution from C3 species. [ABSTRACT FROM AUTHOR]

Leaves and cotyledons of the terrestrial C4 plants, Bienertia cycloptera Bunge ex Boiss. and Suaeda aralocaspica (Bunge) Freitag & Schtze (Chenopodiaceae), accomplish C4 photosynthesis within individual chlorenchyma cells: each species having a unique means of intracellular spatial partitioning of biochemistry and organelles. In this study the chlorenchyma tissue in flowers and stems of these species was investigated. Flowers have an outer whorl of green tepals with a layer of chlorenchyma cells, which are located on the abaxial side, exposed to the atmosphere. Anatomical, immunocytochemical, western blots and starch analyses show that the chlorenchyma cells in tepals are specialised for performance of single-cell C4 photosynthesis like that in leaves. In the tepals of B. cycloptera, chlorenchyma cells have a distinctive central cytoplasmic compartment, with chloroplasts which contain Rubisco, separated by cytoplasmic channels from a peripheral chloroplast-containing compartment, with phosphoenolpyruvate carboxylase (PEPC) distributed throughout the cytoplasm. In the tepals of S. aralocaspica, chlorenchyma cells have chloroplasts polarised towards opposite ends of the cells. Rubisco is found in chloroplasts towards the proximal end of the cell and PEPC is found throughout the cytoplasm. Also, green stems of B. cycloptera have a single layer of the specialised C4 type chlorenchyma cells beneath the epidermis, and in stems of S. aralocaspica, chlorenchyma cells are scattered throughout the cortical tissue with chloroplasts around their periphery, typical of C3 type chlorenchyma. During reproductive development, green flowers become very conspicuous, and their photosynthesis is suggested to be important in completion of the life cycle of these single-cell C4 functioning species. [ABSTRACT FROM AUTHOR]