Real-time plant water potential assessment based on electrical signalling in higher plants

摘要

Real - time plant water potential assessment is postulated as an efficient tool for irrigation scheduling and automated irrigation system operation in precision agriculture. We have developed an Ag/AgCI micro-electrode enabling the continuous measurement of plant electric potential differences between roots, shoots and leaves, in response to changes in micro - environmental conditions related to light, temperature and soil water availability. Electric action (EAP) and variation (EVP) potentials havebeen detected in several plant organs; most EAP ranged -50 to -250 mV, and lasted from a few miliseconds up to 1 minute, with a very short lag time after the stimuli is imposed. In most cases, AP were followed by long term (1 to 10 hours) distinct EVP. Our results indicate that there is a clear, fast and accurate electrical signalling mechanism within the plant, which is positively correlated to the intensity and duration of micro -environmental stimuli modifying plant water potential. In several fruittrees, placed in a Faraday cage in an environmentally-controlled greenhouse, changes in EP between the base of the stem and leaf petiole (DELTA V_(L-S)) observed in response to short-and long-term drought, have been associated with a decrease in stomataconductance (gs), indicating that stomata closure might be associated with an extra-cellular electrical signal, that travels through the phloem at a speed of 2.4 cm min"1. In our experiments, the onset of irrigation (watering) has been associated with changes in EP in avocado, blueberry, lemon and olive. Even greater changes in DELTA V_(L-S) have been detected in response to drought as compared to watering; these drought-induced electrical signals were also related to changes in gs. Applications of thissignalling mechanism as an early detector of plant water stress are discussed and many questions with regard to the role of electrical signals in eliciting physiological responses in fruit tree species are proposed.