作物の気孔運動と水分生理に関する研究 : 第1報 気孔開度自記計の改良とその利用効果

抄録

In order to study photosynthesis, respiration and water metabolism of the crop, it is necessary to know the behaviour of stomata which are the major gateway for transpiration and gas exchange. The available methods of stomatal aperture measurement are divided into three groups, that is, (1) microscopic technique; (2) infiltration method; and (3) porometler method, each of which has its own advantages and shortcomings. Among these methods, porometer which can measure continuously variable stomatal resistance is more suitable for the metabolic study of the crop than other methods which measure the actual size of stomatal aperture. It was indicated by Heath and Williams, however, that in the porometer method the stomata inside the permanently attached cup open much more widely than the stomata outside the cup. This wide opening of stomata inside the cup might be caused by CO₂ deficiency due to photosynthesis in the mesophyll within the cup. And they pointed out that such a type of recording porometer is unfit for use because of the danger of misleading the experilmental results. The present paper gives a description of a newly devised recording porometer with an attachable cup which enables continuous recording. The results of some tests by this instrument are also presented. 1. The new recording porometer is composed of clear plastic cup (0.44 cm²), mercury manometer with three electrodes, electric valve which closes silicone tube, membrane air pump and event recoder (figs.1 & 2). 2. The cup was cemented absolutely airtight with the birdlime on the lower epidermis of the leaf of the tobacco plant. No injury was detected in the leaf tissue for a long period, though leaf blade had a great number of hairs and did not show any toughness. 3. The air pressure in the porometer is constantly kept average 15mm mercury higher than the atmospheric pressure. Consequently, the air included in the porometer escapes away to the atmosphere through the stomata inside the cup (fig. 1). The mercury within manometer gradually falls to the previously decided state (P₁) according to the exhausting of the air, and then the electric valve is open and mercury is restored up to the former state (P₂) by the fresh air from the membrane air pump. The movement of the electric valve is automatically repeated by the direction of mercury, and each stroke of mercury accompanied with electric valve (M₁) is continuously recorded on the event recorder (fig. 3). 4. Stomatal viscous flow conductance in the tobacco leaf was indicated 25∼45 cc/min in the daytime which was obtained by the new recording porometer (fig. 4). This rate of viscous air flow in the porometer was 8∼15 times as much as that of the air including sufficient CO₂ for the photosynthesis of the mesophyll inside the cup. 5. A highly significant correlation (r=0.924, significant at 0.1% level) was obtained between porometer conductances inside the cup and infiltration scores outside the cup (fig. 5). 6. The facts mentioned above (4, 5) show that no CO₂ deficiency occurred in the attachable cup of the new recording porometer, and that similar stomatal movement was detected at the both sides of the cup. Accordingly, it can be said that the defect of porometer of old type, such as indicated by Heath and Wrilliams, has been completely removed. 7. The relation between porometer conductance (x) and the mean of stomatal aperture width (y) in the lower epidermis of the tobacco leaf was given by the equation of logarithm function :y=2.258+3.066 log x. A highly significant index of correlation (r_c=0.926, significant at 0.1% level) was obtained between conductances and stomatal apertures. Consequently, it will be able to estimate the stomatal apertures in the leaf by the porometer conductances (fig. 7). 8. [the rest omitted]