Drought Deceit — Can Artificial Stress Signals Be Used as Plant Growth Retardants?

Long-distance signals moving from roots to shoots in response to drought lead to reduced vegetative growth. The hypothesis that the artificial manipulation of one of these signals, alkalization of the xylem sap, can reduce problems of excessive growth in arable crops, has been tested in oilseed rape (canola; Brassica napus L.) and barley (Hordeum vulgare L.). Experiments with detached shoots have shown that both crop species can respond to artificial alkaline xylem sap with reduced leaf expansion. Applications of alkalizing agents to intact plants, either as pH buffer sprays or as solid calcium carbonate, have successfully retarded leaf expansion. The retardation has, however, either been inconsistent (possibly through difficulty in penetrating the variable epicuticular wax layer) or of very short duration (possibly through efficient buffering of internal pH). It can be inferred from these results that the greatest commercial potential for alkalizing growth retardants may be with high-value, short-duration crops that do not have a thick layer of epicuticular wax, and using either multiple applications or persistent formulations.