Interactions between hormone and redox signalling pathways in the control of growth and cross tolerance to stress

The ability of plants to respond to a wide range of environmental stresses is highly flexible and finely balanced through the interaction of hormonal plant growth regulators and the redox signalling hub, which integrates information from the environment and cellular metabolism/physiology. Plant hormones produce reactive oxygen species (ROS) as second messengers in signalling cascades that convey information concerning changes in hormone concentrations and/or sensitivity to mediate a whole range of adaptive responses. Cellular redox buffering capacity that is determined largely by the abundance of ascorbate has a profound influence on the threshold at which hormone signalling is triggered and on the interactions between different hormones. Other antioxidants such as glutathione, glutaredoxins and thioredoxins are also central redox regulators of hormone signalling pathways. The complex network of cross-communication between oxidants and antioxidants in the redox signalling hub and the different hormone signalling pathways maximises productivity under stress-free situations and regulates plant growth, development, reproduction, programmed cell death and survival upon exposure to stress. This interactive network confers enormous regulatory potential because it allows plants to adapt to changing and often challenging conditions, while preventing boom or bust scenarios with regard to resources, ensuring that energy is produced and utilised in a safe and efficient manner.