role of ear photosynthesis and transpiration in sink size determination in barley

in order to investigate the contribution of ear photosynthesis and cytokinin in determining grain sink size, a pot study was conducted during january to june 2005 in cereal glasshouse of faculty of agriculture of karaj, iran. experiment was conducted in a complete randomized design with a factorial arrangement of two factors, three replications and four pots in each plot. factors included cultivar in four levels and treatments in three levels. cultivars were: m80-7, hull-less, reihan and walfajr. treatments were control, removal of ear photosynthesis and removal of ear photosynthesis plus reducing ear transpiration. all treatments were made immediately after ear emergence. results indicated that ear and 1000- grain weights were reduced by removal of ear photosynthesis in m80-7 and hill-less and by reducing of ear transpiration in reihan and walfajr. positive correlation between ear and 1000-grain weight suggested that treatments affected sink size via reduction in mean grain weight. also, treatments increased protein concentration but had no effect on ear protein content. since there was a negative correlation between 1000-grain weight and grain protein concentration, it was concluded that increased grain protein concentration was a consequence of decreased starch accumulation in grains. on the other hand, reduced ear transpiration did not induce any changes in stem mass; therefore stem remobilization did not compensate for reduction in final grain yield. it seems that ear photosynthesis and transpiration have significant role in determining sink size by providing photoassimilates and regulating cytokinin flux to developing kernels.