Effect of supraoptimal root temperature on the growth, root respiration and sugar content of cucumber plants

The effects of high root temperature on plant growth, leaf elemental composition, root respiration and sugar content in cucumber plants (Cucumis sativus L. cultivar ‘Sharp I’) were studied. Root dry weight, leaf area and leaf concentrations of most nutrient elements were all reduced as the root temperature was raised to 35°C, and to 38°C in particular. High root temperature markedly enhanced intact root respiration. This increase of root respiration was due to the stimulation of the alternative respiration. On the other hand, the cytochrome respiration deteriorated at high root temperatures. However, ATP content was not much different between the roots grown at 25° and 38°C. With the rise of root temperature, root sugars, particularly raffinose, greatly increased, while root pectin content decreased. High root temperature also adversely affected the levels of malic and fumaric acids in the roots. It is suggested that disturbance of carbohydrate metabolism in the root is a primary factor responsible for the growth inhibition and dysfunctions of cucumber roots grown at supraoptimal root temperatures.