Sun smart plants : leaf to leaf signaling in response to high light stress

Abstract

At high intensities the sun has the potential to cause extensive photo-oxidative damage to plants. From dawn till sunset plants are subjected to varying light intensities across their leaves due to the angle of the sun and shade from clouds, leaves, neighbouring plants and various obstacles. Leaves under high light stress are able to communicate to the rest of the plant to acclimate against the potential threat of oxidative damage caused by the sun's rays: a system known as high light systemic acquired acclimation (HL SAA). This study explores the specific nature of HL SAA, synergistic interactions with other environmental stresses, and the long term adaptation and acclimation response to HL SAA. This necessitated the development of novel experimental systems to investigate the initiation, perception and response to HL SAA. The systems were used to investigate the HL SAA response by monitoring the induction of mRNA in distal leaves not exposed to the HL stress. Acclimation to HL is induced within minutes and the response is proportionally dependent on the quality and quantity of light. Specialized HL SAA treatments in conjunction with variations in temperature and humidity reveal HL SAA is influenced by fluctuations in humidity levels; however small changes in temperature did not affect HL SAA. Localization of hydrogen peroxide (H{u2082}O{u2082}), following HL treatments, and chemical infiltration designed to mimic HL SAA using H{u2082}O{u2082} and singlet oxygen ({u00B9}O{u2082}), show that reactive oxygen species lack the ability to induce strong HL SAA-like responses. H{u2082}O{u2082} elicited responses which were analogous to mechanical stress responses, whereas {u00B9}O{u2082} induced greater induction of HL SAA reporter gene, ZAT10, indicating its potential role in HL SAA. HL SAA induced changes in auxin accumulation and auxin-responsive genes. Long term acclimation studies also confirmed the ability of mature leaves to influence the development and acclimation of emerging and young leaves to HL stress. Show more