Effect of drought on chlorophyll content and antioxidant enzyme activities in leaves of three wheat cultivars varying in productivity

Seedlings of three wheat varieties (Triticum aestivum L.)-highly productive cv. Ballada, moderately productive cv. Belchanka, and low productive cv. Beltskaya-were exposed to progressive soil drought (cessation of watering for 3, 5, and 7 days) and then analyzed for chlorophyll content and activities of ferredoxin-NADP(+) oxidoreductase (FNR) and antioxidant enzymes, namely, glutathione reductase (GR) and ascorbate peroxidase (AscP). In addition, the proline content, and the extent of lipid peroxidation were examined. In the first period of water limitation, the water loss from leaves was slight for all wheat cultivars, which is characteristic of drought-resistant varieties. After 7-day drought the leaf water content decreased by 5.2-6.8%. The total chlorophyll content expressed per unit dry weight increased insignificantly during the first two periods of drought but decreased by 13-15% later on. This decrease was not accompanied by changes in chlorophyll a/b ratio. The plant dehydration did not induce significant changes in FNR activity. Activities of GR and AscP in leaves of wheat cultivars Ballada and Belchanka increased on the 3rd and 5th days of drought. Owing to the coordinated increase in GR and AscP activities, the lipid peroxidation rate remained at nearly the control level observed in water-sufficient plants. When the dehydration period was prolonged to 7 days, activities of GR and AscP in wheat cultivars reduced in parallel with the increase in malonic dialdehyde (MDA) content, indicating that the antioxidant enzyme defense system was weakened and lipid peroxidation enhanced. Unlike Ballada and Belchanka, the wheat cv. Beltskaya did not exhibit the increase in GR and AscP activities during progressive soil drought. The increase in MDA content by 16% in this cultivar was only observed after a 7-day drought period. The proline content in leaves of all wheat cultivars increased substantially during drought treatment. Thus, in wheat cultivars examined, different responses of the defense systems were mobilized to implement plant protection against water stress. The activities of antioxidant enzyme defense system depended on wheat cultivar, duration of drought, and the stage of leaf development.