Studies on the Stomatal Movement of Tobacco Leaves : The behavior of stomata in the upper and lower surfaces of intact tobcco leaves in relation to transpiration and photosynthesis

Abstract

Transpiration and photosynthesis in the upper and lower surfaces of fully expanded intact tobacco leaves (var. Bright Yellow) were examined in reference to the beavior and density of stomata under controlled, turning light environment. In addition, the stomatal responses in both surfaces to varying intensity were investigated. A method of measuring continuously the transpiration rates from the upper and lower surfaces of intact leaf was described. The results were as follows ; 1. The stomatal opening in the upper and lower surfaces by the alternation of light and dark were markedly different. On the upper surface, the stomata opened a little. Both the opening and closing responses of stomata to light were more sensitive on the lower side than on the upper one. 2. The time course changes of transpiration from both surfaces following the onset or close of illumination were nearly similar to those shown by the stomtatal responses. CO₂ exchange, however, increased or decreased more rapidly as compared with the transpirational process. 3. It was observed that larger parts of transpiration and CO₂ exchange were conducted on the lower surface, and that the rate of transpiration as well as that of CO₂ exchange in both surfaces didn't corresponed to the difference of stomatal densities. Therefore, it may be quite all right to consider that their rates in both surfaces were remarkably affected by the stomatal aperture. From the observation on the relation of transpiration to stomatal aperture, it was elucidated in the lower side that transpiration rapidly rised in the range of 2.5-3.5 μ of stomatal aperture. 4. A large difference between the upper and lower leaf surfaces was recognized in the stomatal response to varying light intensity. The active stomatal opening followed by the increased light intensity was observed in the lower side. In the upper side, on the other hand, the stomatal aperture didn't increase under the condition of light intensity more than 10, 000 lx.