Photodynamic injury to heated leaves.

The leaves of Tradescantia fluminensis VELL, were kept in light and darkness after short-term heating (5 min and 10 min) at different temperatures. In light temperature causing injury was 10° lower than in darkness. A considerable destruction of chlorophyll occurred when the heated leaves were kept in light. If the light intensity was 4,000 lux or even lower the damage to cells was not accompanied by bleaching of chlorophyll. Light produced no effect on unheated leaves. In variegated white-green leaves of Chlorophytum elatum R. BR. light injured only green parts of leaf blades. The minimal light intensity which brought about injury of Tradescantia leaves in experimental conditions was 1,000 lux. Light of the same intensity accelerated death of heated isolated leaves of Cucumis sativus L.Light damage to Tradescantia leaves occurred when the action of light was accompanied by that of high temperature.In an atmosphere of nitrogen the injurious effect of light sharply decreased.It is suggested that the injury of heated leaves in light is caused by photooxydation which is sensitized by chlorophyll and occurs at the expense of photochemical energy which is not used in photosynthesis. Photosynthesis itself is repressed by heating.