The F685/F730 chlorophyll fluorescence ratio as indicator of chilling stress in plants

The response of chlorophyll fluorescence to chilling temperatures was evaluated by two different experiments. In the first, the F685/F730 and the F-v/F-m chlorophyll fluorescence ratios were measured in Phaseolus vulgaris L., cv. Mondragone plants under chilling stress at 4 degrees C and moderate light (100 mu mol m(-2) s(-1)) up to 72 hours. F-v/F-m decreased linearly with chilling time indicating a photoinhibitory effect (no change was observed in the dark under the same conditions). F685/F730 underwent a rapid exponential decay followed by a linear slow decline. In a second experiment, the F685/F730 ratio, the total chlorophyll fluorescence, F685 + F730, and the leaf temperature were monitored on a single leaf in a climate chamber as the temperature was decreased from 20 to 4 degrees C. The experiment was run simultaneously on the chilling-sensitive Phaseolus vulgaris and on the chilling-tolerant Pisum sativum L. (cv. Shuttle) plants. For both species two phases related to the leaf temperature can be distinguished: the first 4-hour period during which the leaf temperature decreased from 24 to 4 degrees C, and a second period during which the leaf temperature slightly oscillated around 4 degrees C. The behaviour of F685/F730 for the bean was quite different from that of the pea plant. During the first phase, it decreased markedly for the chilling-sensitive bean while a slight increase was observed for the chilling-resistant pea. In the following period, the F685/F730 values for the pea remained constant while those for the bean were found still to decrease. On the basis of our results, the use of the chlorophyll fluorescence ratio as indicator of plant chilling sensitivity can be envisaged.