Development of Frost Tolerance in Winter Wheat as Modulated by Differential Root and Shoot Temperature

Abstract

Winter wheat plants (Triticum aestivum L. cv. Urban), grown in nutrient solution, were exposed to differential shoot/root temperatures (i.e., 4/4, 4/20, 20/4 and 20/20°C) for six weeks. Leaves grown at 4°C showed an increase in frost tolerance from -4°C down to -11°C, irrespective of root temperature. In 4/20°C plants, high root temperature decreased the rate of hardening of the leaves, but did not influence the final level of frost tolerance. In roots grown at 4°C frost tolerance increased from -3°C down to -4°C, independently of shoot temperature. An accumulation of soluble sugars in the leaves was only observed when both shoot and root were grown at 4°C and was not correlated with final frost tolerance achieved. However, the rate of hardening was correlated with the soluble sugar concentration. An increase in root soluble sugar concentration was exclusively observed in roots exposed to a temperature of 4°C, irrespective of shoot temperature. Proline concentration only increased in plant parts exposed to a temperature of 4°C. The present results indicate that the importance of root temperature in low-temperature hardening of winter wheat is limited, even though exposure to differential root and shoot temperatures brought about pronounced changes in growth, soluble sugar concentration, insoluble sugar concentration and proline concentration in roots and leaves.

Key words

Frost tolerance - osmotic potential - roots - root: shoot ratio - sugar accumulation - Triticum aestivum