The effects of root treatments on growth of the primary leaves of Phaseolus vulgaris L.: biophysical analysis

summary Plants of Phaseolus vulgaris L. were grown at 22.5 °C and transferred to nutrient solution held at that temperature or at 10 °C; other plants were subjected to a pruning treatment that removed all lateral roots and part of the main root. Both root treatments resulted in a substantial reduction in growth of the primary leaves but did not affect leaf water potential or its components, n and P, except briefly for the root‐cooled plants. Treatments did not increase the wall yield threshold, Y, of leaf tissue which was always lower than in control plants; consequently the effective turgor for growth, P–Y, was greater in treated plants. Both treatments reduced wall extensibility, measured by a modified Instron technique and from the relationship between growth of leaf pieces and their turgor, and it is suggested that this is responsible for the reduction in leaf growth.