Temperature Dependence of Chlorophyll Fluorescence Parameters of Pea Seedlings

Abstract

Summary The thermosensitivity of the photosynthetic apparatus of 12 day-old seedlings of Pisum sativum cv. Ran was investigated within the temperature range 2–50°C at intervals of 2°C. The parameters of prompt chlorophyll fluorescence were used as a criteria of photosynthetic capacity, measured after 5 min temperature treatment (simultaneously with dark adaptation) at the respective temperature. It was established that in the temperature interval 2–42°C the ground fluorescence (Fo) did not change significantly, but above 42°C it increased dramatically. This gave us reason to suppose that temperatures higher than 44°C induced irreversible injuring of pea thylakoid membranes. The variable fluorescence (Fv) remained unchanged from 2°C to 20°C, after 22°C started to decrease first monotonously, then sharply and at 50°C it comprised only 6 % of its initial level. It was also shown that in the temperature range 2–30°C the ratio Fv/Fm, considered as a measure of PS2 activity, did not change significantly, but began to decrease at higher temperatures. After 42°C its level strongly decreased and at 50°C it was only about 10 % of the initial value of Fv/Fm. Similar changes were found for the Fv/Fo ratio. It is concluded that the physiological state and capacity of PS2 for electron transport do not changes significantly in a wide temperature range.