Die Ökophysiologische Bedeutung, Der Zeitgeber Licht Und Temperatur Für Pigmentierung Und Entwicklung Von Chenopodium rubrum L. Keimlingen im Hinblick Auf Tages Und Jahreszeitliche Anpassung

Abstract

Under natural environmental conditions plants are subjected of light and temperature. The effects of these environmental pigment accumulation (chlorophylls, carotenoids, betacyanin) and hypocotyl elongation were investigated. Changes in chloroplast ultrastructure were studied electron microscopically. Chenopodium rubrum L. seedlings were studied under both constant and rhvthmic conditions. Light: dark cycles produced different responses in the kinetics of the accumulation of the various pigments and in hypocotyl growth. The same was true of temperature cycles. These changes under rhvthmic conditions differed from those produced by constant light and temperature. The temperature optima of chlorophyll and betacyanin was also influenced by the photoperiod. It is suggested that the blue light photoreceptor is involved in the adaptation of C. rubrum to natural environment conditions, particularly to temperature. The role of betacyenin is possibly that of a light shield at wavelength above 500 nm; it may also serve as a protection against high temperature. Both light and temperature are synchronizers for plant development. In the natural environment, the photoperiodic and thermoperiodic cycles are not in phase; a steady phase shift takes place throughout the year. Experimentally a successive phase shift between light and temperature cycles induced drastic changes in the appearance and piqmentation of C. rubrum seedlings. In the most artifical case, viz. high temperatures during darkness and low temperatures during light, the chloroplast compartment was principally affected. Grana formation could not be observed. Virtually no chlorophyll could be measured and the carotenoid content was strongly reduced. This chlorosis may be described as chronopathological, and is presumably coupled to a reduced sensitivity towards blue light. Pigmentation changes due to seasonal phase shifts and changes in temperature optima caused by the changing photoperiod would seem to play a role in the seasonal adaptation of the plant to its natural environment. .