Photosynthesis and respiration by the flag leaf and components of the ear during grain development in wheat

Abstract

Rates of photosynthesis and dark respiration of the ears and flag leaves of three varieties of wheat grown at 21 DC under a constant light intensity of 3200 f.c. were measured by infrared gas analysis twice weekly throughout the period of grain development. Measurements were made on both the intact ears and the separated grains and ear structures, in air and in a mixture of nitrogen plus 320 p.p.m. CO2. Dry weights of the grains, ears, and main stems were also determined. Photosynthesis by the grains was near maximal at the light intensity measured inside the glumes, and nearly balanced the loss of CO2 by dark respiration, until the grains ripened. Grain photosynthesis accounted for 33-42% of gross ear photo synthesis. Ear photosynthesis, which was much higher in awned varieties, contributed up to 76% to total grain requirements during early growth, this proportion falling to a minimum of about 26% in Sonora (awned) and 15% in Gabo (unawned) during the period of most rapid grain growth, before rising again as grain growth slowed. Over the whole period of grain development the contribution to grain requirements by ear photosynthesis was 33% in Sonora and 20% in Gabo. The rate of photosynthesis by the flag leaf blades varied apparently in response to changes in the demand for assimilates. In Sonora, requirements by the ear during the period of most rapid grain growth were equivalent to 131 and 43 mg CO2 per ear per day for growth and respiration of the grain respectively, while net photosynthesis at that time by the ear, flag leaf blade, and stem plus sheaths was 50, 126, and 42 mg CO2 per day respectively. Photosynthesis by the ear and flag leaf blade alone could meet the needs of the ear at all times, and grain growth did not appear to be limited by the supply of assimilate. © 1970 CSIRO.