Abscisic acid, ethylene and gibberellic acid act at different developmental stages to instruct the adaptation of young leaves to stress

Abstract

Drought stress represents a particularly great environmental challenge for plants. A decreased water availability can severely limit growth, and this jeopardizes the organism’s primary goal – to survive and sustain growth long enough to ensure the plentiful production of viable seeds within the favourable growth season. It is therefore vital for a growing plant to sense oncoming drought as early as possible, and to respond to it rapidly and appropriately in all organs. A typical, fast energy-saving response is the arrest of growth in young organs, which is likely mediated by root-derived signals. A recent publication indicates that three plant hormones (abscisic acid, ethylene and gibberellic acid) mediate the adaptation of leaf growth in response to drought, and that they act at different developmental stages. Abscisic acid mainly acts in mature cells, while ethylene and gibberellic acid function in expanding and dividing leaf cells. This provides the plant with a means to differentially control the developmental zones of a growing leaf, and to integrate environmental signals differently in sink and source tissues. Here we discuss the biological implications of this discovery in the context of long-distance xylem and phloem transport.

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Figures and Tables

Figure 1 Upon drought perception in the soil, the roots use the transpiration stream of the xylem to send out various (hormonal) signals to the shoot. These signals invoke physiological and molecular responses in both mature and young leaves, and—as revealed by the work of Skirycz et al.13—different hormones act at different developmental stages: ABA in mature leaf cells, and ethylene and GA in expanding and dividing leaf cells. In mature leaves this also prompts the release of secondary signals into the phloem sap, which are transported to sink tissues. In young leaves these phloem-borne signals likely contribute to the dynamic modulation of growth in response to the stress condition.

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