Ineffectiveness of cytokinin-induced chlorophyll retention in hypostomatous leaf discs

Kinetin retarded the decrease in chlorophyll content in leafdiscs from 5 species of plants with amphistomatous leaves, wherethe 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 stimulatedtranspiration in leaf discs from Nicotiana tabacum (amphistomatous),but not in leaf discs from Paederia chinensis (hypostomatous).Nor kinetin did retard chlorophyll breakdown in this specieswhen leaf discs were floated so that the stomatal surface wasin contact with the solution. The ineffectiveness of cytokininsin chlorophyll retention in leaf discs from hypostomatous leaveswas not due to reduced uptake of benzylaminopurine-¹⁴C. Chlorophyll retention was severely inhibited by coating theleaf surface with vaseline either in the presence or absenceof kinetin. Leaf discs floated on a solution exposed to CO₂-lessair retained more chlorophyll than those in normal air. Thereis thus a close relationship between stomatal opening (as measuredby stimulation of transpiration) and chlorophyll retention,as influenced by cytokinins. It is suggested that cytokinin-induced chlorophyll retentionand odier effects on leaf tissues could be mediated throughits effects on stomatal opening. (Received January 22, 1976; )