Understanding and exploiting plant hormone biology to enhance crop production under water scarcity

Abstract

There is much interest in the concept of sustainable intensification of agriculture as one of the actions that can contribute to a reduction in food insecurity for the future. However, drought can significantly limit plant productivity through an impact on a variety of processes which contribute to carbon gain, to the development of the canopy, and the establishment and filling of reproductive structures. If we are to minimize these restrictions to growth and yielding, it is important to understand the mechanistic basis of these responses. For more sustainable use of water in crop production, it is also important to understand the biology behind resource use efficiency by crops. We highlight here the importance of the influence of both hydraulic and chemical signaling on the regulation of functioning, growth, and development of plants under stress and suggest that by processing and responding to these signals, plants are able to regulate growth and development relative to the availability of water and other resources. We propose that via enhancement or suppression of different 'root signal' cascades we can intervene to sustain plant yielding under drought. We review the identity of signals limiting leaf conductance, leaf growth, and harvest index and consider prospects for manipulation of signaling, with special reference to the impact of changes in sap pH, modified fluxes of abscisic acid (ABA) and of the ethylene precursor ACC. While there are many genetic opportunities to modify stress signaling cascades to increase crop yield, crop improvement cannot immediately combat changes in the climate and increases in food demand that are happening now. It is therefore important that we use novel crop management techniques to impact some of the same biology. Such manipulations may be a cost-effective way to sustain yielding and increase water use efficiency in dryland agriculture.