The effects of chilling stress on the chlorophyll fluorescence of leaves

The effects of temperature lowering on the steady state chlorophyll fluorescence of leaves was investigated. Leaves from chill-sensitive species responded to a greater degree than did leaves from chill-resistant species. Arrhenius plots of fluorescence change vs temperature yielded a straight line with no breaks that would have indicated a membrane lipid phase change. We measured the fluorescence changes at high and low excitation intensitites and monitored fluorescence at 690 and 735 nm. The low temperature induced fluorescence increase and the ratio of 690 to 735 nm fluorescence were generally greater at lower light intensities. Treatment with DCMU reduced the effects of temperature on fluorescence. However, the effect of low intensity pulsing light on the fluorescence yield of DCMU-treated leaves proved to be temperature dependent. At a low pulse rate (2 msec pulse, 5 pps) a logarithmic increase in fluorescence as a function of temperature was noted. Chill-sensitive species proved to be more responsive than chill-resistant species. Slight differences between hardened and unhardened material were noted. While the causal factors for the differential sensitivity of species to temperature lowering were not investigated, fluorescence monitoring has proved to be a convenient and accurate method for investigating chill-sensitivity in leaves.