Physiological, metabolic, and stomatal adjustments in response to salt stress in Jatropha curcas.

Salinity is a major issue affecting photosynthesis and crop production worldwide. High salinity induces both osmotic and ionic stress in plant tissues as a result of complex interactions among morphological, physiological, and biochemical processes. Salinity, in turn, can provoke inactivation of some enzymes in the Calvin-Benson cycle and therefore affect the fine adjustment of electron transport in photosystem I and carbon related reactions. Here, we used three contrasting Jatropha curcas genotypes namely CNPAE183 (considered tolerant to salinity), CNPAE218 (sensible), and JCAL171 (intermediate) to understand salinity responses. By performing a long-term (12 months) experiment in land conditions, we investigated distinct mechanisms used by J. curcas to cope with threatening salinity effects by analyzing gas exchange, mineral nutrition and metabolic responses. First, our results highlighted the plasticity of stomatal development and density in J. curcas under salt stress. It also demonstrated that the CNPAE183 presented higher salt-tolerance whereas CNPAE218 displayed a more sensitive salt-tolerance response. Our results also revealed that both tolerance and sensitivity to salinity were connected with an extensive metabolite reprogramming in the Calvin-Benson cycle and Tricarboxylic Acid cycle intermediates with significant changes in amino acids and organic acids. Collectively, these results indicate that the CNPAE183 and CNPAE218 genotypes demonstrated certain characteristics of salt-tolerant-like and salt-sensitive-like genotypes, respectively. Overall, our results highlight the significance of metabolites associated with salt responses and further provide a useful selection criterion in during screening for salt tolerance in J. curcas in breeding programmes.

Photosynthesis and photoprotection in coffee leaves is affected by nitrogen and light availabilities in winter conditions.

Coffee is native to shady environments but often grows better and produces higher yields without shade, though at the expense of high fertilization inputs, particularly nitrogen (N). Potted plants were grown under full sunlight and shade (50%) conditions and were fertilized with nutrient solutions containing either 0 or 23 mM N. Measurements were made in southeastern Brazil during winter conditions, when relatively low night temperatures and high diurnal insolation are common. Overall, the net carbon assimilation rate was quite low, which was associated with diffusive, rather than biochemical, constraints. N deficiency led to decreases in the concentrations of chlorophylls (Chl) and total carotenoids as well as in the Chl/N ratio. These conditions also led to qualitative changes in the carotenoid composition, e.g., increased antheraxanthin (A) and zeaxanthin (Z) pools on a Chl basis, particularly at high light, which was linked to increased thermal dissipation of absorbed light. The variable-to-maximum fluorescence ratio at predawn decreased with increasing A+Z pools and decreased linearly with decreasing N. We showed that this ratio was inadequate for assessing photoinhibition under N limitation. Expressed per unit mass, the activities of superoxide dismutase and glutathione reductase were not altered with the treatments. In contrast, ascorbate peroxidase activity was lower in low N plants, particularly under shade, whereas catalase activity was lower in shaded plants than in sun-grown plants, regardless of the N level. Glutamine synthetase activity was greater in sun-grown plants than in shaded individuals at a given N level and decreased with decreasing N application. Our results suggest that the photoprotective and antioxidant capacity per amount of photons absorbed was up-regulated by a low N supply; nevertheless, this capacity, regardless of the light conditions, was not enough to prevent oxidative damage, as judged from the increases in the H(2)O(2) and malondialdehyde concentrations and electrolyte leakage. We demonstrated that N fertilization could adequately protect the coffee plants against photodamage independently of the anticipated positive effects of N on the photosynthetic capacity.

Drought tolerance is associated with rooting depth and stomatal control of water use in clones of Coffea canephora.

BACKGROUND AND AIMS: Drought is a major environmental constraint affecting growth and production of Coffea canephora. Selection of C. canephora clones has been largely empirical as little is known about how clones respond physiologically to drought. Using clones previously shown to differ in drought tolerance, this study aimed to identify the extent of variation of water use and the mechanisms responsible, particularly those associated morphological traits. * METHODS: Clones (14 and 120, drought-tolerant; 46 and 109A, drought-sensitive, based on their abilities to yield under drought) were grown in 120-L pots until they were 12-months old, when an irrigation and a drought treatment were applied; plants were droughted until the pressure potential (psi(x)) before dawn (pre-dawn) reached -3.0 MPa. Throughout the drought period, psi(x) and stomatal conductance (g(s)) were measured. At the end of the experiment, carbon isotope ratio and parameters from pressure-volume curves were estimated. Morphological traits were also assessed. * KEY RESULTS AND CONCLUSIONS: With irrigation, plant hydraulic conductance (K(L)), midday psi(x) and total biomass were all greater in clones 109A and 120 than in the other clones. Root mass to leaf area ratio was larger in clone 109A than in the others, whereas rooting depth was greater in drought-tolerant than in drought-sensitive clones. Predawn psi(x) of -3.0 MPa was reached fastest by 109A, followed progressively by clones 46, 120 and 14. Decreases in g(s) with declining psi(x), or increasing evaporative demand, were similar for clones 14, 46, and 120, but lower in 109A. Carbon isotope ratio increased under drought; however, it was lower in 109A than in other clones. For all clones, psi(x), g(s) and K(L) recovered rapidly following re-watering. Differences in root depth, K(L) and stomatal control of water use, but not osmotic or elastic adjustments, largely explained the differences in relative tolerance to drought stress of clones 14 and 120 compared with clones 46 and 109A.