Metabolism of Oat Leaves during Senescence: VII. The Interaction of Carbon Dioxide and Other Atmospheric Gases with Light in Controlling Chlorophyll Loss and Senescence

In air largely freed from CO2, senescence of isolated oat (Avena sativa cv Victory) seedling leaves is no longer prevented by white light; instead, the leaves lose both chlorophyll and protein as rapidly as in the dark. Senescence in light is also accelerated in pure O2, but it is greatly delayed in N2; 100% N2 preserves both protein and chlorophyll in light and in darkness. In light in air, most of the compounds tested that had previously been found to delay or inhibit senescence in darkness actually promote the loss of chlorophyll, but they do not promote proteolysis. Under these conditions, proteolysis can therefore be separated from chlorophyll loss. But in light minus CO2, where chlorophyll loss is rapid in controls, two of these same reagents prevent the chlorophyll loss. Unlike the many reagents whose action in light is thus the opposite of that in darkness, abscisic acid, which promotes chlorophyll loss in the dark, also promotes it in light with or without CO2. Kinetin, which prevents chlorophyll loss in the dark, also prevents it in light minus CO2. In general, therefore, the responses to light minus CO2 are similar to the responses to darkness, and (with the exception of abscisic acid and kinetin) opposite to the response to light in air.