EFFECTS OF SALT STRESS ON GROWTH, PHOTOSYNTHESIS AND NITROGEN-FIXATION IN CHICKPEA (CICER-ARIETINUM L.)

Plants of chick-pea (Cicer arietinum L. cv. ILC1919) inoculated with M esorhizobium ciceri strain ch-191 were grown in a controlled environme ntal chamber, and were administered salt (0, 50, 75, and 100 mM NaCl) during the vegetative period. Four harvests (4, 7, 11, and 14 d after treatment) were analysed, The aim was to ascertain whether the negativ e effect of saline stress on nitrogen fixation is due to a limitation on the photosynthate supply to the nodule or a limitation on the nodul ar metabolism which sustains nitrogenase activity. Plant growth was af fected only by the highest NaCl concentration, whereas nitrogenase act ivity was affected from 50 mM, At the first harvest, Rubisco, PEPC and MDH activities in leaves rose with salt, but fell during the followin g harvests. The increase of PEPC and MDH in nodules at the two first s amplings was clearly related to salt concentration. While 50 mM NaCl i ncreased GS and GOGAT in nodules at some harvests, 100 mM strongly inh ibited these activities at all the harvests. The accumulation of proli ne, amino acids and carbohydrates was clearly related to salt especial ly in the leaves, whereas in the nodules the protein content was boost ed by salt. Although photosynthesis declined with NaCl, the response o f nitrogen fixation to salt was more pronounced. This situation, toget her with carbohydrate accumulation, suggests that the lack of photosyn thate does not cause the inhibition of nitrogenase activity under this type of stress. The similar trend observed for the PEPC-MDH pathway a nd the ARA support the hypothesis concerning the limitation in the sup ply of energy substrate, mainly malate, to the bacteroids. The accumul ation of compatible solutes is more a consequence of damage produced b y salt stress than of a protective strategy,