There is increasing pressure on irrigators to improve crop water use efficiency via deficit irrigation (DI). Individual plant water use depends on the transpiring (leaf) area and the transpiration rate of that area (determined by stomatal conductance). Much research has emphasised the role of chemical signals, rather than plant water status, in regulating leaf growth and stomatal conductance. While agronomic manipulations of signalling may decrease crop water use, can this be reconciled with maintaining crop yield? On first inspection, the linear relationship between water use and crop yield (Passioura, 1977) suggests otherwise. However, it may be possible to partially decouple irrigation (water application) from crop yield, as soil-drying induced stimulation of root growth may allow crops to access supplies of water deeper in the soil profile. Since yield increases linearly with leaf area, and signalling limits leaf expansion of crops exposed to drying soil, manipulation of the production of, or sensitivity to, such signals may sustain yield under DI. Prospects for manipulating signals involved in leaf growth regulation are considered, with special reference to the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). ACC signalling can be altered by deploying genotypes with altered ACC status, and by using rhizosphere bacteria containing the enzyme ACC deaminase. We evaluated the physiological responses of pea to one such bacterium (Variovorax paradoxus 5C-2). Under DI, plants grown with the bacterium showed increased seed yield (25-41%), seed number and seed nitrogen accumulation compared to uninoculated plants.