Light utilization in photosynthesis after cold acclimation of plants representing two different seasonal growth strategies

Abstract

Seedlings of Lodgepole pine (Pinus contorta L.) and winter wheat (Triticum aestivum L.) were cold acclimated under controlled conditions. Both temperate conifers and winter cereals have the ability to acquire high freezing tolerance during cold acclimation, and they are characterized by maintaining their green foliages during autumn and winter. Pine responds to cold acclimation by partial inhibition of photosynthesis with a low daily carbon gain, while winter wheat maintains a high activity of photosynthesis and a high daily carbon gain during cold acclimation. These different responses of photosynthesis to cold acclimation are correlated with pine reducing its need for assimilates when entering dormancy associated with termination of primary growth, while winter wheat maintains a high need for assimilates as it continues to grow and develop throughout cold acclimation. These different responses are accompanied by pine reducing its needle content of chlorophyll and developing a high and sustained ability for non-photochemical dissipation of absorbed light as heat during cold acclimation, while winter wheat show no such response. The increased capacity for non-photochemical dissipation of absorbed light energy in pine, as photosynthesis becomes inhibited by a limited sink capacity, and eventually by freezing temperatures, is viewed as an important strategy for avoiding photo-oxidative damage of the needle foliage during autumn and winter. In winter cereals, on the other hand, with its highly efficient photosynthesis at chilling temperatures through the autumn, the prevailing high yield of photochemistry can efficiently dissipate absorbed light, and no sustained non-photochemical dissipation of absorbed light is required.