Relation between senescence and stomatal opening: senescence in darkness [Seedling oat leaves]

The senescence (proteolysis and loss of chlorophyll) of isolated leaves of oat seedlings in the dark is inhibited or delayed by compounds of six different types: phenazine methosulfate, fusicoccin, α ,α′-dipyridyl, cycloheximide, spermidine, and two cytokinins. In every case but the last, these compounds in optimum concentration caused the stomata to open and remain partly or completely open throughout the 72- or 96-hr experimental period. The cytokinins caused only a partial opening, which is ascribed to their exerting two different effects. Taken together with the previous report that five different treatments that accelerated or promoted senescence in the light caused stomatal closure or occlusion, these data establish a general parallel between stomatal aperture and senescence, with strong indication that the stomatal aperture is the causal factor. A possible explanation of the relationship is proposed.