Wheat frost injury — freezing stress and photosynthesis

Abstract

Although the lethal consequences of radiation frosts on wheat plants have been well described, effects of sublethal freezing have received little study. In this paper, studies of injury to leaves caused by freezing, and its influence on photosynthesis after thawing, are reported.

Glasshouse-grown plants of three spring wheats were frozen at several temperatures in the range 0 to –4.5°C and their reaction to freezing stress measured. Injury to leaves caused by freezing stress was found to range from no damage to death over a temperature interval of 2°. Upper leaves were more resistant than lower, and the cultivar Z501 was found to be hardier by about l¦ than either Timgalen or Gamut. Net photosynthesis by whole plants in the period after thawing was reduced to levels as low as 30° of normal rates following mild stress, recovery to normal rates occurring by the following day. Severely stressed plants failed to recover over a 3 day period.

Stomatal resistances were unaffected by low to mild freezing stress and could not explain the large reductions in photosynthesis rate following these stresses. The results have been discussed in relation to the underlying mechanisms, and to their implications for field crops.