Effect of soil moisture stress on absorption & translocation of phosphorus applied to leaves of sunflower

Abstract

Plants subjected to moisture stress undergo physiological adjustments which result in a reduction or cessation of growth. The effect which moisture stress may have on the movement of substances from leaves to regions of growth or storage, needs further clarification. In addition, the influence of moisture stress on cuticle permeability must be considered in problems dealing with the effectiveness of substances applied to leaves. Weintraub et al. (10) showed that leaves of wilting bean plants absorb less 2,4-dichlorophenoxyacetic acid (2,4-D) than do plants with adequate soil moisture. The effect of moisture stress on the subsequent translocation of 2,4-D was not measured. Pallas (5) found no effect of moisture stress on absorption of 2,4-D by bean leaves. The effect of moisture stress on translocation of the herbicide was estimated by assaying radioactivity in two 1-cm sections of the epicotyl. As the soil approached the permanent wilting percentage translocation of 2,4-D decreased to approximately half that found near field capacity. It is not clear, however, whether moisture stress caused a decreased transport of 2,4-D or altered the distribution of the translocated herbicide. Koontz and Biddulph (3) measured the effects of various factors on absorption and translocation of phosphorus applied to bean leaves. Results obtained by Dybing and Currier (2) indicate that phosphate penetrated the cuticle of Zebrina more rapidly than other chemicals tested. However, stomatal penetration of surfactant-free aqueous solutions was not clearly demonstrated. Biddulph (1) showed that movement of phosphorus from a treated bean leaf occurred in the phloem. From analyses of squash phloem exudate by Tolbert and Wiebe (9) it has been demonstrated that inorganic phosphate was the principal translocated form. We undertook the present work to measure the effect of soil moisture stress on the absorption of phosphorus by a mature leaf, the transport of phosphorus from the treated leaf, and the distribution of phosphorus to other plant parts. Of particular interest was the effect of moisture stress on the rate of accumulation of phosphorus in the more rapidly growing regions.