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 Ch ile was evaluated by measuring the size and number of trichomes; the densit y of the stomata, the dimensions of the occlusive cells and stomatal pore i n adaxial and abaxial leaf surfaces were measured in tangential sections. T he lenght, diameter and volume of cells of spongy and palisade parenchyma t issue were evaluated in transverse and tangential sections with the purpose of estimating the surface of the cell walls exposed to the gaseous interch ange (A(mes)A). The results showed an increase in the number of trichomes a proximately 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 explai ned by the smaller cell size in plants under water stress. In addition, str essed 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.