«Peristomatal Transpiration» and Stomatal Movement: A Controversial View: V. Rubidium-86 in the Epidermal Transpiration Stream

Abstract

Summary 86Rb was introduced into the transpiration stream of detached leaves and rooted seedlings of several plant species and traced by microautoradiography. When the pores stayed open during the feeding 86Rb was found in the guard cells. When a dark period of 4 hours followed feeding in the light, 86Rb ions did not return to the subsidiary cells although the stomata had closed. Rubidium transport to the guard cells was reduced when the pores were closed. Then, accumulation occurred in the subsidiary cells while at the site of the guard cells grain density of the film was generally low. Using a gelatine layer, with which the leaf surfaces remained coated throughout the feeding period, small quantities of 86Rb were picked up from the external surfaces of the leaves. This was considered sufficient evidence of 86Rb excretion from the guard cells. Major conclusions are: 1. Ions accumulate by the action of peristomatal transpiration. 2. Ion fluxes are -secondary- processes in all cases of stomatal reaction. 3. The role of peristomatal transpiration is a sensory and triggering one. Peristomatal transpiration is the process by which plants sense environmental conditions. It is not a mechanism for closing stomata.