The Effect of Different Root Temperatures on Dry Matter and Carbohydrate Changes in Rooted Leaves of Phaseolus Spp.

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Abstract
Weekly estimates of dry matter in rooted dwarf-bean leaves (Phaseolus vulgaris) and rooted runner-bean leaves (Phaseolus multiflorus) were made with roots held at 13°, 17°, 21°, or 25° C. Most dry matter accumulated in the lamina of both species at the coldest root temperature. Roots of runner bean grew more than dwarf bean at all temperatures compared, especially at 13° and 17° C and the greater net assimilation rate, i.e. dry matter increase per dm1 per week, of runner-bean leaves at cold temperatures, is attributed to faster root growth. Shading lessened accumulation in the lamina, especially at cold root temperatures, because a greater proportion of assimilate was transferred to roots. Rates of root growth are mainly influenced by temperature, and no effect could be detected of carbohydrate accumulation in the lamina at cold temperatures on root growth after the roots were kept warmer. Water content of the lamina per unit area increased as dry matter increased. For any particular dry-matter content, the water content was greater with roots at 20° than at 13°, i.e. the leaves were more succulent with warmer roots. When roots first formed on the petioles the lamina lost sugar and subsequently regained it, faster when roots were cold. When transferred from warm to cold root temperature, sugars accumulated in the lamina. Starch changed more than sugars in response to changing root temperatures. Starch in the lamina progressively declined when roots were warm, but increased when they were cold. The starch content of the lamina was rapidly influenced by root temperature. Sugars and starch together account for less than half of the dry-matter increase in the lamina. The unidentified fraction is little influenced by changes of root temperature; it may be largely structural because the palisade cells continued to grow after the leaves were excised, although the lamina was fully expanded before the leaves were rooted. Palisade cells were larger with roots at 20° than at 13° C.

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