Effect of indol-3-yl acetic acid on photosynthetic characteristics of wheat flag leaf during grain filling

Area and fresh and dry masses of flag leaf show two phases of development d uring grain filling in Triticum aestivum. The initial large increase in lea f size is mainly due to water intake. Contents of chlorophylls and caroteno ids, reducing sugars, and sucrose, Hill reaction rate, and photosynthetic a ctivity increased during leaf growth, but a noticeable decline in these par ameters followed throughout leaf senescence. The maximum accumulation of po lysaccharides and proteins occurred at the beginning of grain set, but a co ntinuous decline in their absolute values was manifested during grain filli ng. Grain priming with indol-3-yl acetic acid (IAA) at 25 mg kg(-1) stimula ted the flag leaf growth, namely its fresh and dry masses and its area. Fur thermore, the stimulatory effect was mainly due to the increase in the pigm ent formation that in turn increased the photosynthetic activity of flag le af during grain filling. On the other hand, the highest dose of IAA (50 mg kg(-1)) attenuated the growth and physiological activity of flag leaf throu gh its inhibitory action on leaf fresh and dry masses, leaf area, pigments, saccharides and protein formation, as well as its effect on (CO2)-C-14 ass imilation.