Abstract
The effect of root temperature on phospholipid concentration and its fatty acid composition in the roots was studied with cucumber (Cucumis sativus L., cvs. Kurume-ochiai H and Suyo) and figleaf gourd (Cucurbita ficifolia Bouché) which have contrasting tolerance to low root temperature.
Phospholipid concentration in roots increased at 14°C and more so at 12°C in figleaf gourd, which is highly tolerant of low root temperature compared to cucumber. In both cultivars of cucumber, however, the concentration increased only at 12°C. The increase in phospholipid concentration in figleaf gourd roots was assumed to be due to the net increase of phospholipid synthesis within roots, but that in cucumber roots seemed to be a result of root growth inhibition. Composition of phospholipids was relatively unaffected by root temperature in all crops; phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were the main phospholipid species in the roots of all three crops.
The degree of fatty acid unsaturation of total phospholipids increased steadily in figleaf gourd as the root temperature was lowered from 25 to 12°C. By contrast, in‘Suyo’, which is the most intolerant of low root temperature among the three crops used, degree of fatty acid unsaturation was highest at 17°C and tended to decrease toward the lowest root temperature. In‘Kurume-ochiai H’it was almost unaffected by root temperature. With reduction in root temperature, fatty acid unsaturation of PE increased with little changes in that of PC in figleaf gourd. Conversely, in both cultivars of cucumber fatty acid unsaturation of PE varied little, and instead, that of PC decreased at 12°C, more greatly in‘Suyo’.
From these results it is suggested that the response of roots to low root temperature in phospholipid synthesis and its fatty acid unsaturation is related to different tolerance of these crops to low root temperature.
