Rapid shoot-to-root signalling regulates root hydraulic conductance via aquaporins.

摘要

We investigated how root hydraulic conductance (normalized to root dry weight, L_o) is regulated by the shoot. Shoot topping (about 30% reduction in leaf area) reduced L_o of grapevine (Vitis vinifera L.), soybean (Glycine max L.) and maize (Zea mays L.) by 50 to 60%. More detailed investigations with soybean and grapevine showed that the reduction in L_o was not correlated with the reduction in leaf area, and shading or cutting single leaves had a similar effect. Percentage reduction in L_o was largest when initial L_o was high in soybean. Inhibition of L_o by weak acid (low pH) was smaller after shoot damage or leaf shading. The half time of reduction in L_o was approximately 5 min after total shoot decapitation. These characteristics indicate involvement of aquaporins. We excluded phloem-borne signals and auxin-mediated signals. Xylem-mediated hydraulic signals are possible since turgor rapidly decreased within root cortex cells after shoot topping. There was a significant reduction in the expression of several aquaporins in the plasma membrane intrinsic protein (PIP) family of both grapevine and soybean. In soybean, there was a five- to 10-fold reduction in GmPIP1;6 expression over 0.5-1h which was sustained over the period of reduced L_o.