Enironmental and physiological studies for optimization of transport systems in plants.

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Plant production depends on dynamics of transport systems in plants and their environments, where substances contributing plant production (e.g. water, photoassimilates, carbon dioxide, oxygen and nutrients) are exchanged and distributed among plant organs and their environments. This study deals with analyses of environmental effects on the transport systems concerned with root physiological functions, expansive growth of plant organs (i.e. leaf, fruit and tuber), translocation of photoassimilates and sink-source relationship in the whole plant of a leaf vegetable (lettuce), fruit vegetables (tomato and cucumber) and a root crop (sweetpotato). Hydroponic systems were newly developed for accurate control of dissolved 0_2 concentration and for solution-air culture of sweetpotato. Furthermore, plant responses were measured by the newly developed methods, i.e., 1) laser sensor systems for on-line and non-contact measurements of growth rates in fruit, stem and tuber, 2) a chamber system for on-line measurements of water balance, respiration and sap flux in an intact tomato fruit and 3) a method for evaluating translocational flux of photoassimilates through a tomato pedicel. Mechanisms of effects of root environment (i.e. dissolved 0_2 concentration and water condition) and shoot environment (i.e. light, temperature and humidity) were revealed on the basis of dynamics of the transport systems concerned. These methods and information-established for the intact whole plant can be considered to contribute to logic of environment control for optimizing dynamics of the transport systems in plants and their environment.