Stress Tolerance and Stress-Induced Injury in Crop Plants Measured by Chlorophyll Fluorescence In Vivo

Abstract

The proposition is examined that measurements of chlorophyll fluorescence in vivo can be used to monitor cellular injury caused by environmental stresses rapidly and nondestructively and to determine the relative stress tolerances of different species. Stress responses of leaf tissue were measured by FR, the maximal rate of the induced rise in chlorophyll fluorescence. The time taken for FR to decrease by 50% in leaves at 0.degree. C was used as a measure of chilling tolerance. This value was 4.3 h for chilling-sensitive cucumber. In contrast, FR decreased very slowly in cucumber [Cucumis sativus] leaves at 10.degree. C or in chilling-tolerant cabbage leaves at 0.degree. C. Long-term changes in FR of barley, wheat and rye [Hordeum vulgare, Triticum aestivum, Secale cereale, respectively] leaves kept at 0.degree. C were different in frost-hardened and unhardened material and in the latter appeared to be correlated to plant frost tolerance. To simulate damage caused by a thick ice cover, wheat leaves were placed at 0.degree. C under N2. ''Kharkov'' wheat, a variety tolerant of ice encapsulation, showed a slower decrease in FR than ''Gatcher'', a spring wheat. Relative heat tolerance was also indicated by the decrease in FR in heated leaves while changes in vivo resulting from photoinhibition, UV radiation and photobleaching can also be measured.