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Abstract: Barley seedlings were grown in pots in controlled environment chambers and progressive drought treatments were imposed 11d after sowing. Soil water content decreased from 92 to 10% following 14d without watering. Increases of biomass in shoots and roots slowed after 4 and 9d of water stress, respectively. Thirty barley root metabolites were monitored in this study and 85% were significantly altered by drought. Sucrose, raffinose, glucose, fructose, maltose, malate, asparagine and proline increased and myo-inositol, glycerate, alanine, serine, glycine and glutamate decreased during drought. Primary metabolism was likely involved in various crucial processes during water stress including, osmotic adjustment, nitrogen sequestration and ammonia detoxification. Rates of photosynthesis and stomatal conductance recovered in 2d and shoot growth commenced the 3rd day after rehydration. Root growth also exhibited a lag after rehydration but this was attributed to high nutrient concentrations during water stress. Malate and proline recovered within 1d but serine was only partially reversed 6d after rehydration. Malate, aspartate and raffinose decreased below well-watered, control levels following rehydration. Variation in the magnitude and time necessary for individual compounds to fully recover after rehydration suggested the complexity of metabolic processes initiated by re-watering. [Copyright &y& Elsevier]

Abstract: Responses of soluble amino acids and organic acids to either ambient (36Pa) or elevated (100Pa) CO2 treatments were determined using barley primary leaves (Hordeum vulgare L. cv. Brant). Total soluble amino acids were increased 33% by CO2 enrichment 9 days after sowing (DAS), but a decrease relative to the ambient CO2 treatment was observed with increasing leaf age. Marked declines of glutamine and asparagine were observed under CO2 enrichment, both diurnally and with advancing leaf age. Consequently, total soluble amino acids were 59% lower in the elevated compared to the ambient CO2 treatment 17 DAS. It was likely that chlorosis in response to CO2 enrichment negatively impacted soluble amino acid levels in older barley primary leaves. In contrast to the ambient CO2 treatment, glutamine and most other soluble amino acids decreased as much as 60% during the latter half of a 12h photoperiod in primary leaves of 13-day-old seedlings grown under enhanced CO2. Malate was decreased about 9 percent by CO2 enrichment and citrate and succinate were increased by similar amounts when measured 9 and 13 DAS. Malate accumulation was also decreased about 20% by CO2 enrichment on a diurnal basis. The onset of CO2-dependent leaf yellowing had much less of an effect on organic acids than on soluble amino acids. This above results emphasized the sensitivity of N metabolism to CO2 enrichment in barley. Increased levels of citrate and succinate in response to CO2 enrichment suggested that the tricarboxylic acid cycle was upregulated in barley by CO2 enrichment. In summary, organic and amino acid levels in barley primary leaves were dynamic and were altered by age, diurnally and in response to CO2 enrichment. [Copyright &y& Elsevier]

Experiments were performed using naturally sunlit Soil–Plant–Atmosphere Research chambers that provided ambient or twice ambient CO 2 . Potato plants were grown in pots that were water sufficient (W), water insufficient for 12–18 days during both vegetative and tuber development stages (VR), or water insufficient solely during tuber development (R). In the ambient CO 2 treatment, a total of 17 and 20 out of 31 tuber metabolites differed when comparing the W to the R and VR treatments, respectively. Hexoses, raffinose, mannitol, branched chain amino acids, phenylalanine and proline increased, although most organic acids remained unchanged or decreased in response to drought. Osmolytes, including glucose, branched chain amino acids and proline, remained elevated following 2 weeks of rehydration in both the ambient and elevated CO 2 treatments, whereas fructose, raffinose, mannitol and some organic acids reverted to control levels. Failure of desiccated plant tissues to mobilize specific osmolytes after rehydration was unexpected and was likely because tubers function as terminal sinks. Tuber metabolite responses to single or double drought treatments were similar under the same CO 2 levels but important differences were noted when CO 2 level was varied. We also found that metabolite changes to water insufficiency and/or CO 2 enrichment were very distinct between sink and source tissues, and total metabolite changes to stress were generally greater in leaflets than tubers. [ABSTRACT FROM AUTHOR]

Abstract: Global atmospheric carbon dioxide concentrations (C a) are rising. As a consequence, recent climate models have projected that global surface air temperature may increase 1.4–5.8°C with the doubling of C a by the end of the century. Because, changes in C a and temperature are likely to occur concomitantly, it is important to evaluate how the temperature dependence of key physiological processes are affected by rising C a in major crop plants including maize (Zea mays L.), a globally important grain crop with C4 photosynthetic pathway. We investigated the temperature responses of photosynthesis, growth, and development of maize plants grown at five temperature regimes ranging from 19/13 to 38.5/32.5°C under current (370μmolmol−1) and doubled (750μmolmol−1) C a throughout the vegetative stages using sunlit controlled environmental chambers in order to test if the temperature dependence of these processes was altered by elevated C a. Leaf and canopy photosynthetic rates, C4 enzyme activities, leaf appearance rates, above ground biomass accumulation and leaf area were measured. We then applied temperature response functions (e.g., Arrhenius and Beta distribution models) to fit the measured data in order to provide parameter estimates of the temperature dependence for modeling photosynthesis and development at current and elevated C a in maize. Biomass, leaf area, leaf appearance rate, and photosynthesis measured at growth C a was not changed in response to CO2 enrichment. Carboxylation efficiency and the activities of C4 enzymes were reduced with CO2 enrichment indicating possible photosynthetic acclimation of the C4 cycle. All measured parameters responded to growth temperatures. Leaf appearance rate and leaf photosynthesis showed curvilinear response with optimal temperatures near 32 and 34°C, respectively. Total above ground biomass and leaf area were negatively correlated with growth temperature. The dependence of leaf appearance rate, biomass, leaf area, leaf and canopy photosynthesis, and C4 enzyme activities on growth temperatures was comparable between current and elevated C a. The results of this study suggest that the temperature effects on growth, development, and photosynthesis may remain unchanged in elevated C a compared with current C a in maize. [Copyright &y& Elsevier]

To evaluate the combined effect of temperature and CO 2 on photosynthetic processes, leaf metabolites and growth, soybean was grown under a controlled environment at low (22/18 °C, LT), optimum (28/24 °C, OT) and high (36/32 °C HT) temperatures under ambient (400 μmol mol −1 ; aCO 2 ) or elevated (800 μmol mol −1 ; eCO 2 ) CO 2 concentrations during the reproductive stage. In general, the rate of photosynthesis ( A ), stomatal ( g s ) and mesophyll ( g m ) conductance, quantum yield of photosystem II, rates of maximum carboxylation ( V Cmax ), and electron transport ( J ) increased with temperature across CO 2 levels. However, compared with OT, the percentage increases in these parameters at HT were lower than the observed decline at LT. The photosynthetic limitation at LT and OT was primarily caused by photo-biochemical processes (49–58%, L b ) followed by stomatal (27–32%, L s ) and mesophyll (15–19%, L m ) limitations. However, at HT, it was primarily caused by L s (41%) followed by L b (33%) and L m (26%). The dominance of L b at LT and OT was associated with the accumulation of non-structural carbohydrates (e.g., starch) and several organic acids, whereas this accumulation did not occur at HT, indicating increased metabolic activities. Compared with OT, biomass and seed yield declined more at HT than at LT. The eCO 2 treatment compensated for the temperature-stress effects on biomass but only partially compensated for the effects on seed yield, especially at HT. Photosynthetic downregulation at eCO 2 was possibly due to the accumulation of non-structural carbohydrates and the decrease in g s and A std (standard A measured at 400 μmol mol −1 sub-stomatal CO 2 concentration), as well as the lack of CO 2 effect on g m , V Cmax , and J , and photosynthetic limitation. Thus, the photosynthetic limitation was temperature-dependent and was primarily influenced by the alteration in photo-biochemical processes and metabolic activities. Despite the inconsistent response of photosynthesis (or biomass accumulation) and seed yield, eCO 2 tended to fully or partially compensate for the adverse effect of the respective LT and HT stresses under well-watered and sufficient nutrient conditions. [ABSTRACT FROM AUTHOR]

Abstract: Drought can negatively impact pod production despite the fact that cacao production usually occurs in tropical areas having high rainfall. Polyamines (PAs) have been associated with the response of plants to drought in addition to their roles in responses to many other stresses. The constitutive and drought inducible expression patterns of genes encoding enzymes involved in PA biosynthesis were determined: an ornithine decarboxylase (TcODC), an arginine decarboxylase (TcADC), an S-adenosylmethionine decarboxylase (TcSAMDC), a spermidine synthase (TcSPDS), and a spermine synthase (TcSPMS). Expression analysis using quantitative real-time reverse transcription-PCR (QPCR) results showed that the PA biosynthesis genes were expressed in all plant tissues examined. Constitutive expression of PA biosynthesis genes was generally highest in mature leaves and open flowers. Expression of TcODC, TcADC, and TcSAMDC was induced with the onset of drought and correlated with changes in stomatal conductance, photosynthesis, photosystem II efficiency, leaf water potential and altered emission of blue-green fluorescence from cacao leaves. Induction of TcSAMDC in leaves was most closely correlated with changes in water potential. The earliest measured responses to drought were enhanced expression of TcADC and TcSAMDC in roots along with decreases in stomatal conductance, photosynthesis, and photosystem II efficiency. Elevated levels of putrescine, spermidine, and spermine were detected in cacao leaves 13days after the onset of drought. Expression of all five PA associated transcripts was enhanced (1.5–3-fold) in response to treatment with abscisic acid. TcODC and TcADC, were also responsive to mechanical wounding, infection by Phytophthora megakarya (a causal agent of black pod disease in cacao), the necrosis- and ethylene-inducing protein (Nep1) of Fusarium oxysporum, and flower abscission. TcSAMDC expression was responsive to all stresses except flower abscission. TcODC, although constitutively expressed at much lower levels than TcADC, TcSAMDC, TcSPDS, and TcSPMS, was highly inducible by the fungal protein Nep1 (135-fold) and the cacao pathogen Phytophthora megakarya (671-fold). The full length cDNA for ODC was cloned and characterized. Among the genes studied, TcODC, TcADC, and TcSAMDC were most sensitive to induction by drought in addition to other abiotic and biotic stresses. TcODC, TcADC, and TcSAMDC may share signal transduction pathways and/or the stress induced signal induction pathways may converge at these three genes leading to similar although not identical patterns of expression. It is possible altering PA levels in cacao will result in enhanced tolerance to multiple stresses including drought and disease as has been demonstrated in other crops. [Copyright &y& Elsevier]