Spezifische Störung von Entwicklung und Enzymbildung der Plastiden höherer Pflanzen durch hohe Wachstumstemperaturen

Abstract

1. At elevated growth temperatures between 32° and 34 °C synthetic processes of rye seedling plastids like formation of chlorophyll and photosynthetic enzymes (carboxydismutase) are nearly completely prevented, whereas formation of protein, of non-photosynthetic enzymes, and total leaf growth are little or not affected. 2. In the dark, carboxydismutase, which may be taken as representative of plastid behavior, fails to appear at 32°C, whereas it is normally synthesized at 22°C. Plastids of etiolated seedlings remain small at 32°C. Early formation of prolamellary bodies is normal but further differentiation of plastids cannot proceed as usual. They lack larger thylakoids, and ribosomes cannot be detected. But many osmiophilic globuli are accumulated, and characteristic tubulus like structures, which are not found at 22°C, appear in great number. 3. In light the ability of the seedlings to form chlorophyll sharply declines above 28°C. Between 32° and 34°C the leaves still reach full development but are rather chlorotic. Carboxydismutase remains extremly low in far-red as well as in red or blue light. 4. Carboxydismutase activity, which is already present, is not destroyed by high temperature, neither is the synthesis of this enzyme directly inhibited, if it is already proceeding. Maximum sensibility to the effect of high temperature is found in the youngest stages before the formation of photosynthetic enzymes has started. 5. Application of kinetin — alone or in combination with an auxin — does not restore formation of carboxydismutase at 32°C to normal rates of synthesis as observed at 22°C. 6. When seedlings are grown in 32°C between 24 and 96 hours of germination and then put back to 22°C the formation of carboxydismutase is not started again in the dark. But when they are kept in light after having been returned to 22°C a new increase of the enzyme as well as of chlorophyll is initiated. 7. The mode of action of high temperature is discussed. In many respects it corresponds to the well-known heat-bleaching effect of the unicellular alga Euglena.