Ineffectiveness of cytokinin-induced chlorophyll retention in hypostomatous leaf discs

Kinetin retarded the decrease in chlorophyll content in leaf discs from 5 species of plants with amphistomatous leaves, where the upper surface was exposed to air, but not in Rumex acetosera. When leaf discs were floated so that the lower surface was exposed, the effect of kinetin was less evident. Kinetin also stimulated transpiration in leaf discs from Nicotiana tabacum (amphistomatous), but not in leaf discs from Paederia chinensis (hypostomatous). Nor kinetin did retard chlorophyll breakdown in this species when leaf discs were floated so that the stomatal surface was in contact with the solution. The ineffectiveness of cytokinins in chlorophyll retention in leaf discs from hypostomatous leaves was not due to reduced uptake of benzylaminopurine-14C. Chlorophyll retention was severely inhibited by coating the leaf surface with vaseline either in the presence or absence of kinetin. Leaf discs floated on a solution exposed to CO2-less air retained more chlorophyll than those in normal air. There is thus a close relationship between stomatal opening (as measured by stimulation of transpiration) and chlorophyll retention, as influenced by cytokinins. It is suggested that cytokinin-induced chlorophyll retention and odier effects on leaf tissues could be mediated through its effects on stomatal opening.