EFFECT OF LOW-TEMPERATURE ON PROTEIN-CONTENT AND CELL ULTRASTRUCTURE IN CUCUMBER AND TOMATO PLANTS

Tomato (Lycopersicon esculentum Mill.) and cucumber (Cucumis sativus L .) plants were grown for 45 and 32 days, respectively, at a temperatur e of 23 degrees C during the day and 18 degrees C at night. Chilling w as performed at 6 degrees C during the last five days of growth. The e ffects of chilling on the level and composition of proteins and on the ultrastructure of leaf parenchyma cells were examined. Chilling kille d cucumber plants, but tomato plants remained alive. Morphometry did n ot show any significant ultrastructural changes in cucumber cells or c hloroplasts. Chilled tomato plants had smaller cells with a reduced vo lume of cytoplasm and smaller chloroplasts containing fewer starch gra ins and grana; the grana were smaller and contained fewer thylakoids. Electrophoretic analysis showed that chilling neither induced any new proteins nor increased the total level of soluble protein in either sp ecies. However, the content of ribulose-1,5-bisphosphate carboxylase/o xygenase decreased in the chilled tomato plants. A possible role of ce ll structural changes in plant adaptation to chilling temperatures is discussed.