Effect of water stress on the leaf anatomy of six cultivars of the common bean Phaseolus vulgaris

The effect of water deficit on the leaf anatomy of six varieties of beans (Phaseolus vulgaris L.) commonly grown in the Central- Southern region of Chile was evaluated by measuring the size and number of trichomes; the density of the stomata, the dimensions of the occlusive cells and stomatal pore in adaxial and abaxial leaf surfaces were measured in tangential sections. The lenght, diameter and volume of cells of spongy and palisade parenchyma tissue were evaluated in transverse and tangential sections with the purpose of estimating the surface of the cell walls exposed to the gaseous interchange (A(mes)A). The results showed an increase in the number of trichomes aproximately 35% by unit of surface, a decrease in cell volume in 26% and an increase in the density of stomata of 25 to 150 in adaxial surface and 167 to 216 stomata by mm(2) in the abaxial surface. The latter could be explained by the smaller cell size in plants under water stress. In addition, stressed plants showed an increased thickness of the mesophyll from 207 to 282 mu m, and consequently, an increased specific leaf weight. The changes in the cells dimensions resulted in important changes in the relation of areas (A(mes)/A). It is concluded that the cultivars analyzed showed anatomical plasticity under water stress.