| Research Abstract |
In various serious environmental stresses, we investigated mechanism of response and adaptation of the horticultural plant resources to ultraviolet-B radiation and salt stresses.
1. By changing the various irradiation conditions such as exposure time, strength, and wavdength regions of UV-B, what kind of failure was generant to the plant by the UV-B irradiation, the physiological and ecological responses of five vegetable plant species to UV stress were investigated.
When UV-B, which reaches the surface, was divided into shorter wavelength and longer wavelength regions than 300 nm, UV of 300nm or less was not related to increase and decrease of visible light, and it showed the almost fixed quantity.
For cabbage, spinach, tomato, eggplant, and radish, UV-B was irradiated in the dark period, or light period, and the results was compared with the control. High-intense UV-B in the dark period made the surface of tested vegetable leaves into the bronze, and the leaf margin curled inside, and c
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ontracted. Visible light showed the effect that eases the damage by the UV-B irradiation. Tomato had the most UV-B sensitivity 280〜290nm of UV-B gave very intensive negative effects to the vegetables tested. Leaves that UV-B was irradiated had lacked the flexibility, and also decreased on the water content. The effect on the growth was strongly observed in younger leaves.
2. Physiological response (growth, absorption of ions and water physiology) and photosynthesis in the vegetative growth stage of Aster tripolium L.Which was able to grow under the hyper saline environment, were investigated in order to clarify the salt tolerance mechanism.
The growth lowered by water stress, and NaCl stress (300mM), and it decreased more in water stress than NaCl stress. Absorption of Na^+ and Cl^+ ino the leaves was higher in the NaCl stress than water stress, and the Na+/K+ ratio was also higher Water potential of the leaves in control, water stress, and NaCl stress lowered in order. Turgor pressure was almost same in control and NaCl stress, and lowered in water stress.
Under the atmosphere CO_2 condition (350 ppm) the rates of stomatal limiting of photosynthesis in control, water stress, and salt stress were 33%, 52% and 44% of control respectively Without the stomatal limiting the light saturation photosynthetic rate was decreased in the water stress, but not in the NaCl stress. The photosynthetic rate was decreased because of limiting the supply of CO_2 through the partial closure of the stoma under NaCl stress. Light and dark reaction systems of photosynthesis, however, were protected in NaCl stress. In the meantime, the photosynthetic rate in water stress was lowered by closure of the stoma and decrease in the ability of the dark reaction system. Less
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