Studies on the variability of stomatal density in soybean cultivars. II. Influence of restrictions of soil moisture and light intensity on stomatal density.

Abstract

The influences of soil moisture and light intensity on stomatal density (number of stomata per unit of surface area of epidermis, SD) in soybean cultivars were examined by water stress- and light shading-tests. The influences were also investigated by dividing SD into the two components, (1) the power of stomatal differentiation (Ratio of stomatal number to epidermal cell number, PS), and (2) the epidermal cell size (surface area of a epidermal cell, EC). The relationship among SD, PS and EC is shown in the equation (1). In the experiment A, soil moisture was restricted at a level of 35% of dried soil weight while the soil moisture in the control was always kept 50% to 60%. In the experiment B, light intensity was restricted by shading at a 45% level (Lux) to the control. Each plant was grown in a natural-light phytotron. Observations of stomata were made on the 5th and the 3rd leaflet in the experiment A and B, respectively. In general, the epidermis of adaxial leaf side decreased in SD and that of abaxial leaf side increased in SD with the restriction of soil moisture (Table 1, Table 2). The reverse change regarding SD between the adaxial and abaxial leaf sides was remarkably observed. Dividing SD into the components, the adaxial PS sharply decreased with the restriction of soil moisture, and this caused the decreasing effect on adaxial SD. While, the abaxial PS was kept almost constant (Table 1, Fig 1). Generally, EC decreased with the restriction and this caused the increasing effect on adaxial and abaxial SD, especially in two cultivars, Tokachi Hadaka and Ichigoo Wase. As these totalized results, it was found in the adaxial leaf side that SD decreased with the restriction. On the other hand, the epidermis of both leaf sides decreased in PS and increased in EC with the restriction of light intensity. These changes of the two components caused the decreasing effect on adaxial and abaxial SD (Table 4, Table 5, Fig. 2). Some cultivars showed the special response to water stress or light shading, and PS or EC of these cultivars changed remarkably under the condition of the restriction (Fig. 1, Fig. 2). As the results, the varietal differences of SD, PS and EC were disturbed by these environmental conditions (Table 3, Table 6).