THE FAST FLUORESCENCE KINETICS: A SENSITIVE TOOL FOR EARLY DETECTION OF WATER STRESS IN SUGARCANE

WATER STRESS IS a major constraint for sugarcane production in many regions of the world, including Australia. Sensitive and non-destructive early measurement of the crop response to water stress would be of great value for producers, advisors, and researchers. Chlorophyll-a (Chla) fluorescence is well established as a tool for measurement of photosynthetic efficiency. Changes in the kinetics of Chla fluorescence can provide valuable insight into the structure and function of the photosynthetic apparatus and chloroplast membrane integrity. The parameter Fv/Fm is often used to describe the effect of stress on the quantum yield of photosystem two (PSII). In this study the polyphasic OJIP fluorescence transient was used to evaluate the response of the sugarcane photosynthetic electron transport system. Chlorophyll fluorescence was measured on three leaves in the canopy of KQ228A over a five-day water stress period, and the response analysed using the OJIP-test. The results show that several of the parameters that can be derived from the OJIP test are more sensitive and a better reflection of water stress than the Fv/Fm ratio. Evidently PSII is much more sensitive to water stress than photosystem one (PSI). In late stages of stress there are signs of a loss in membrane integrity and a disruption of water splitting in PSII.