Changes in chlorophyll, ribulose bisphosphate carboxylase-oxygenase, glycine betaine content, photosynthesis and transpiration in Amaranthus tricolorleaves during salt stress

We examined changes in leaf growth and chemical composition, including chlo rophyll content, ribulose bisphosphate carboxylase-oxygenase (RuBisCO), and glycine betaine (GB) in relation to photosynthesis and transpiration respo nses to salt stress in Amaranthus tricolor leaves. To induce salt stress, p lants were transferred to a growth medium containing 300 mM NaCl for 7 d fo llowed by 7 d of relief from salinity. A decrease in leaf enlargement began 3 d after salt stress, and leaves subsequently showed the same degree of r egrowth as controls after relief in non-salt medium. Chlorophyll content ex pressed on a leaf-area basis increased under conditions of salinity due to a reduction in leaf tissue water content. The decrease in chlorophyll conte nt continued throughout the 7 d of relief from salinity. The RuBisCO and so luble protein contents when expressed on a leaf dry-weight basis decreased in response to salinity, and then gradually increased during the relief per iod. GB content increased slightly up to 3 d of salt stress, and showed typ ical accumulation during salt stress. FB content decreased sharply immediat ely after plants were transferred to nonstress medium, but remained at a hi gher level throughout the relief period. A decrease in photosynthetic activ ity and transpiration rate preceded any changes in leaf area, RuBisCO or GB content. During relief from salinity, photosynthesis and transpiration rat es gradually recovered to control levels with restoration of stomatal condu ctance. The above findings suggest that the increase in CB content is impor tant in adaptation to salt stress in Amaranthus plants, although photosynth esis and transpiration responses occurred immediately after salt-stress.