Morphological, Anatomical and Physiological Responses Related to Differential Shoot vs. Root Growth Inhibition at Low Temperature in Spring and Winter Wheat

Several morphological, anatomical and physiological changes and their relationship with differential root vs. shoot growth inhibition at low temperature (5°C) were studied in spring and winter wheat cultivars. Root:shoot ratios, expressed either as a function of root and shoot fresh weight or as a function of root and leaf areas, increased at low temperature and this increment was more pronounced in spring cultivars than in winter ones. Although winter cultivars developed relatively smaller root systems at 5°C, this characteristic was counterbalanced by a lower stomatal frequency and increased thickness of epidermal cell walls in leaves unfolded at this temperature, relative to spring cultivars. Likewise, at 5°C a decrease in the osmotic potential of shoots and roots was observed in parallel with sugar accumulation; this decrease was more marked in winter cultivars. These results indicate a differential morpho-anatomical and physiological plasticity of winter and spring cultivars during development at low temperature. The possible association between these changes and plant water economy at low temperatures is discussed.