Effect of temperature on ascorbate peroxidase activity and flowering of Arabidopsis thaliana ecotypes under different light conditions

Four Arabidopsis thaliana ecotypes were grown at 14degreesC and 22degreesC under two light conditions (300 muE m(-2) s(-1) or 150 muE m(-2) s(-1)) and the effect of temperature on their growth and flowering time was studied. Flowering occurred within 31 days (experimental period) at 22degreesC, whereas a decrease in growth temperature resulted in a delay in flowering (63 days) under both light conditions. At 14degreesC, membrane-bound APX (tAPX) activity decreased and total chlorophyll (Chl) content increased with growth under both light conditions. However, at 22degreesC, the tAPX activity increased and total Chl content decreased with growth under both light conditions. These results suggest that at 22degreesC oxidative stress was high under both light conditions and consequently Chl content decreased under stressful conditions or vice versa for all the four A. thaliana ecotypes studied. Under both the temperature and light conditions, soluble APX activity showed an irregular pattern of growth. The increase in tAPX activity, with growth only at 22degreesC but not at 14degreesC, suggests increased H2O2 formation in flowering plants at 22degreesC for all the four A. thaliana ecotypes studied. Before flowering, the tAPX activity showed a significantly negative correlation with flowering time. Higher oxidative stress in the lower-latitude ecotypes might induce earlier flowering than the higher-latitude ecotypes. From these results, we propose a hypothesis that H2O2 is one of the possible factors in flower induction.