Effects of Phenylmercuric Acetate on Stomatal Movement and Transpiration of Excised Retula papyrifera Marsh. Leaves.

Effects of 10(-3)m, 10(-4)m, and 10(-5)m phenylmercuric acetate (PMA) on stomatal movement and transpiration of excised Betula papyrifera leaves were investigated. Duco cement leaf prints and transpiration decline curves were used for the analysis of stomatal condition. PMA induced stomatal closure and decreased transpiration. Stomata of leaves treated with any of the 3 PMA concentrations closed earlier and at a higher relative water content than did stomata of untreated leaves. As determined from transpiration decline curves, PMA at 10(-3)m caused an increase in apparent "cuticular" transpiration. However, the increase appeared to result largely from some PMA-poisoned stomata which remained open for prolonged periods. Considerable PMA toxicity was observed, with 10(-3)m and 10(-4)m concentrations causing browning of leaves. PMA treatment caused a decrease in chlorophyll content, even at a low PMA concentration (10(-5)m) which influenced stomatal response only slightly and did not cause evident browning of leaves. The time and degree of stomatal opening varied with stomatal size. Large stomata tended to open earlier and close later than small stomata. Hence, in Betula papyrifera stomata of various size classes were considered as physiologically different populations.