ENVIRONMENTAL CONTROL FOR PLANT GROWTH IN PLANT FACTORY OPERATION AND GREENHOUSE MANAGEMENT FROM PHYSIOLOGICAL VIEWPOINT

Abstract

The enlarging plant tissue displayed significant water potential disequilibria between the water source and the enlarging cells. This disequilibria formed a water potential field (i.e., potential field of chemical potential of water) in the enlarging tissue, which is called a growth-induced water potential field. Theoretically, the growth-induced water potential field can be expressed by an equation derived from a combination of Fick's law and the conservation of mass, and can be used to determine the direction of water flow in the expanding tissues. Experimentally, cell water potentials of cells in the zone of elongation were measured with combinations of a cell pressure probe and a nanoliter osmometer. Both measured and theoretically predicted water potentials coincided well, showing that the growth-induced water potential field existed in the elongating tissue. The average magnitude of the growth-induced water potential field was estimated from the water potential difference between the water source and the expanding cells by using psychrometry. Prior to growth recovery by acclimation to environmental stress by plants, the growth-induced water potential recovered. Thus, we found that if the growth-induced water potential was measured, both growth recovery and inhibition could be predicted. Because changes in water status in plants occur prior to changes in cell expansion, if the system for water status measurements is established in plant factories and greenhouses, it may be possible to regulate crop growth more effectively.