Effects of Low Temperatures on Barley Chloroplast Membranes

Abstract

We investigated the effects of cold treatment (3 weeks at 2°C) on the photosynthetic apparatus of winter barley and maize. The ratio of the maximum (P level) to the minimum (0 level] chlorophyll fluorescence induction signal (Kautsky phenomenon], measured in vivo at 25°C, was not modified during cold adaptation of barley. On the other hand, this P/0 ratio, which is a good indicator of the activity of PSII, decreased rapidly in cold treated maize seedlings. In both species, the slow fluorescence quenching (from P to T] was not suppressed by the low temperature treatment. However, a noticeable modification of the slow fluorescence transients (P-S-M-T) was observed in cold adapted barley leaves. The M peak was strongly reduced after 3 weeks at 2°C. In non-hardened barley plants, the slow fluorescence changes were markedly inhibited at 2°C. At this temperature, chlorophyll fluorescence was blocked at P level. During cold acclimation of barley seedlings, a progressive restoration of those slow changes was observed at 2°C. This observation indicates that cold hardening of barley induces adaptation of the photophysiological activity to low temperatures. This chloroplast membrane adaptation was examined at the protein level. Electrophoretic analysis showed that cold had no influence on the chlorophyll-protein complexes of barley thylakoids. Likewise, one and twodimensional polyacrylamide gel electrophoresis of chloroplastic membrane proteins showed no marked difference between plants grown at 25°C or hardened 3 weeks at 2°C. These results suggest that cold adaptation of barley thylakoids occurs mainly at the lipid level.

Michel HAVAUX is “Aspirant F.N.R.S.”