Chilling Injury in Cucumber Leaves

When cucumber plants are chilled at 5 ?C and 85 per cent, r.h.the leaves wilt rapidly and lose water. Chlorophyll is lostin the light, but not in the dark. If chilled leaves are placedin water, electrolytes leak out rapidly, the amount dependingon the duration of chilling. There are marked reductions inthe rates of respiration and photosynthesis; Q₁₀ for respirationis 5.0 between 15 and 5 ?C. Phospholipid levels decline, butmore slowly than the rate of water loss. Leaves recover theirinitial fresh weight, rate of electrolyte leakage, and respirationand photosynthesis rates if the plants are returned to warmconditions within 1 to 2 d. When leaves are chilled at 100 per cent r.h. they do not losewater or phospholipids; electrolyte leakage is little more thanin controls, but respiration and photosynthesis are reducedas at 85 per cent r.h. It is envisaged that the leaf cell membranes suffer a physicalchange at 5 ?C which reduces the rates of respiration and photosynthesis,but allows the passage of water and electrolytes out of thecells; the water evaporates away but electrolytes become concentratedin the walls and can be leached out of the leaf. As water islost from the leaf symptoms of dehydration appear. Phospholipidloss may be associated with enzyme action following the lossof compart-mentation.