Abstract
Pot cultured wheat plants, cv. Asakaze-komugi, were grown under sufficient soil water till ripening period. They were then grouped into two soil moisture treatments, 75% (control) and 40% (water stressed) of field capacity, respectively. Photosynthesis and transpiration of various plant parts i.e. ear, top internode, leaf sheath of flag leaf, leaf blades of two or three uppermost leaves were measured using a small chamber and the effects of water stress on these physiological processes were examined. The results obtained are summarized as follows : 1. Photosynthesis and transpiration of each plant part were strongly depressed by the water deficit treatment. The extent of depression in photosynthesis and transpiration was largest immediately after the start of the water deflcit treatment. However, as the water deficit condition was prolonged, the effect diminished (Figs. 1-3). 2. The extent of depression in photosynthesis by water deficit was larger in the leaf blades than in the ear, leaf sheath and the stem. Comparing leaf blades at different positions, depression was larger in the lower leaf blades than in the upper ones. Thus, it was concluded that photosynthetic sensitivity to water deficit varied among plant parts (Figs. 4-7). 3. The sensitivity of plant parts to water deficit in photosynthesis was closely correlated with that of transpiration. This suggested that the photosynthesis sensitivity of a certain plant part to water deflcit is related to the sensitivity of the stomatal behavior of that part.
