The distribution pattern of transpiration rate, water saturation deficit, stomata number and size, photosynthetic and respiration rate in the area of the tobacco leaf blade

Abstract

The previously found (Slavík, 1959) distribution pattern of osmotic pressure of cell sap in the area of the leaf blade of dicotyledonous type which is independent of the water balance and unchanged even with zero diffusion pressure deficit, was complemented by further data concerning the physiological heterogeneity of the adult leaf blade ofNicotiana sanderae hort. in relation to water relations and CO2 exchange. The transpiration rate from the intact leaf surface was found to be about 50 to 70 per cent lower in the apical part of the blade than in the basal part. The natural permanent water saturation deficit was found to be about 10 per cent lower in the apical part. The stomata density in tobacco as well as in sugar beet leaves were on an average 40 per cent lower in the apical part, their size being here 30 per cent higher. The relative index of the area of the stomata pores (density × square of the pore length) did not differ significantly in the two places. The photosynthetic rate (per area) in fully water saturated leaves was found to be 17 per cent lower in the apical part of the blade, the chlorophyll content (per unit area) being greater in the thicker apical part. Respiration rate measured manometrically as QO2 was significantly lower in the apical part, both when calculated according to area and to dry weight (12 per cent). Similar but much lower differences were found between the edge and the central part of the leaf blade. This physiological heterogeneity and polarity of the leaf blade originating in the ontogenesis of its extension growth is causally based on the different relative hydration levels. Thus the study of various physiological processes in different parts of the leaf blade is suitable for the investigation of their relationship to different hydration levels.