Plasticity of Soybean Stomatal Responses to Arsenic and Cadmium at the Whole Plant Level

摘要

Heavy metals perturbate water balance in plants and hence impact stomatal aperture. After longer exposure, stomatal development also is affected, and stomatal density and size can change. Two soybean (Glycine max) varieties were experimentally selected for contrasting tolerance to arsenic and cadmium. For these cultivars, natural variability in leaf epidermal cell parameters was detected. Pot plants at first assimilating leaf stage were exposed for 10 days to 5 mg kg(-1) soil As3+ and 50 mg kg(-1) soil Cd2+ (respectively). Metals accumulated primarily in roots and exerted relatively low impact on biomass. Despite this, we observed diverse adjustments of stomata and pavement cells. In cv. Bolyi 44 the stomatal size decreased upon stress treatment, possibly to avoid further water loss. In contrast, the other cultivar Cordoba uses larger stomata that might be advantageous in gaining further resources. The observed responses varied depending on leaf type. In addition, dorsoventral stomatal responses in width, yet undescribed under metal stress, were observed. Our data show that leaf epidermal cell adjustments are flexible components of plant defense even at low metal doses, and possibly help to compromise the structural and functional needs of plant (tissue) under metal stress.