Leaves and nodules (bacteroids and cytosol) of alfalfa (Medicago sativa L. cv Aragon) plants inoculated with Rhizobium meliloti strain 102F51 have been analyzed for the presence of the enzymes superoxide dismutase (SOD, EC 1.15.1.1), catalase (EC 1.11.1.6), and peroxidase (EC 1.11.1.7). All three fractions investigated (leaves, bacteroids, and nodular cytosol) show Cu,Zn-SOD activity. Besides, the bacteroids and cytosol of nodules possess CN(-)-insensitive SOD activities. Studies of SOD inactivation with H(2)O(2) indicate that, very likely, a Mn-SOD is present in the bacteroids, and suggest that the cytosol contain both Mn-SOD and Fe-SOD. Bacteroids show high catalase activity but lack peroxidase. By contrast, the nodule cytosol exhibits an elevated peroxidase activity as compared with the foliar tissue; this activity was completely inhibited by 50 to 100 micromolar KCN. The significantly lower contents of H(2)O(2) and malondialdehyde (a product of lipid peroxidation) in nodules with respect to those in leaves reveal that the above-mentioned bacteroid and cytosol enzymes act in an efficient and combined manner to preserve integrity of nodule cell membranes and to keep leghemoglobin active.

An understanding of the mechanisms that determine plant response to reduced water availability is essential to improve water-use efficiency (WUE) of stone fruit crops. The physiological, biochemical and molecular drought responses of four Prunus rootstocks (GF 677, Cadaman, ROOTPAC 20 and ROOTPAC^® R) budded with ‘Catherina’ peach cultivar were studied. Trees were grown in 15-l containers and subjected to a progressive water stress for 26 days, monitoring soil moisture content by time domain reflectometry. Photosynthetic and gas exchange parameters were determined. Root and leaf soluble sugars and proline content were also measured. At the end of the experiment, stressed plants showed lower net photosynthesis rate, stomatal conductance and transpiration rate, and higher intrinsic leaf WUE (A_N/g_s). Soluble sugars and proline concentration changes were observed, in both root and leaf tissues, especially in an advanced state of stress. The accumulation of proline in roots and leaves with drought stress was related to the decrease in osmotic potential and increase in WUE, whereas the accumulation of sorbitol in leaves, raffinose in roots and proline in both tissues was related only to the increase in the WUE. Owing to the putative role of raffinose and proline as antioxidants and their low concentration, they could be ameliorating deleterious effects of drought-induced oxidative stress by protecting membranes and enzymes rather than acting as active osmolytes. Higher expression of P5SC gene in roots was also consistent with proline accumulation in the tolerant genotype GF 677. These results indicate that accumulation of sorbitol, raffinose and proline in different tissues and/or the increase in P5SC expression could be used as markers of drought tolerance in peach cultivars grafted on Prunus rootstocks.

The expansion of the world’s population requires the development of high production agriculture. For this purpose, it is essential to identify target points conditioning crop responsiveness to predicted [CO₂]. The aim of this study was to determine the relevance of ear sink strength in leaf protein and metabolomic profiles and its implications in photosynthetic activity and yield of durum wheat plants exposed to elevated [CO₂]. For this purpose, a genotype with high harvest index (HI) (Triticum durum var. Sula) and another with low HI (Triticum durum var. Blanqueta) were exposed to elevated [CO₂] (700 µmol mol^–1 versus 400 µmol mol^–1 CO₂) in CO₂ greenhouses. The obtained data highlighted that elevated [CO₂] only increased plant growth in the genotype with the largest HI; Sula. Gas exchange analyses revealed that although exposure to 700 µmol mol^–1 depleted Rubisco content, Sula was capable of increasing the light-saturated rate of CO₂ assimilation (A_sat) whereas, in Blanqueta, the carbohydrate imbalance induced the down-regulation of A_sat. The specific depletion of Rubisco in both genotypes under elevated [CO₂], together with the enhancement of other proteins in the Calvin cycle, revealed that there was a redistribution of N from Rubisco towards RuBP regeneration. Moreover, the down-regulation of N, NO₃^–, amino acid, and organic acid content, together with the depletion of proteins involved in amino acid synthesis that was detected in Blanqueta grown at 700 µmol mol^–1 CO₂, revealed that inhibition of N assimilation was involved in the carbohydrate imbalance and consequently with the down-regulation of photosynthesis and growth in these plants.