POLYPHENOL OXIDASE ACTIVITIES IN EMBRYO AND ENDOSPERM OF WHEAT SEEDS DURING GERMINATION UNDER BORON STRESS

摘要

Polyphenol oxidases (PPOs) are active during germination of seeds in which the activites may be effected by environmental factors. This study was conducted to determine the effect of boron (B), an important nutrient in phenolic metabolism, on PPOs in embryo and endosperm fractions of two wheat varieties during germination. Seeds were subjected to various concentration of B for 24 h. The germination percentage of both wheat cultivars was not affected by boron concentrations up to 50 mM, and decreased by 100 mM and 150 mM. The lower boron concentrations (0, 0.1 and 50 mM) increased PPOs activity at the beginning of germination up to 6- 9 h whereas its excess levels (100 and 150 mM) decreased PPOs in embryo and endosperm during germination of both cultivars. Dopa and caffeic acid oxidasing PPOs had more activity in embryo and endosperm of drought resistant genotype Kirac-66 in all treatments as compared with those in susceptible Sultan-95. The PPO activities in both embryo and endosperm tissues of Kirac-66 seeds showed a similar occurrence, but the activities in embryos of Sultan-95 seeds were higher than endosperm. The findings suggest that wheat seeds having high PPO activity during germination in both embryo and endosperm fractions may tolerate B stress better than the seeds exhibiting low PPO activity.