Changes in the Temperature Response of Hill-Reaction Activity of Chilling-Sensitive and Chilling-Resistant Plants after Hardening

Abstract

The temperature response of Hill-reaction was measured in chloroplasts isolated from mung bean (very chill-sensitive), two tomato cultivars (less chill-sensitive) and pea (chill-resistant). Computer analysis of the plots of log rate against reciprocal of absolute temperature indicated that in each case, they were composed of three straight lines, meeting at characteristic break temperatures. Neither the activation energies (Ea's¹), calculated from the slopes of the lines, nor the break temperatures correlated with chilling sensitivity. Treatment of the two tomato cultivars at 12 °C and either low humidity (effective in reducing sensitivity) or high humidity (relatively ineffective) both caused lowered Ea values and increased unsaturation in the chloroplast membrane phospholipids. However, this evidence does not, in general, support the idea of any relationship between chloroplast membrane fluidity and chilling injury.