Photosynthetic activity of vegetable plants and its horticultural significance

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  • そ菜の光合成特性とその栽培的意義 (第3報)
  • 低炭酸ガス濃度下でのトマト苗の生理機能
  • テイタンサンガス ノウド カ デ ノ トマト ナエ ノ セイリ キノウ
  • III. Physiological responses of young tomato plant to very low carbon dioxide concentrations

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Abstract

This study was undertaken to elucidate the photosynthetic activity, carbohydrate metabolism, translocation of assimilates and mineral nutrient uptake in young tomato plants at very low carbon dioxide concentrations.<br>Radioisotopes of 14CO2, H332PO4 and 86RbCl were used as tracers under controlled conditions. Photosynthetic rates were also measured with gas exchange method by means of assimilation chambers and an infrared gas analyser.<br>Photosynthetic rate of tomato leaf was linearly proportional to the CO2 concentration within the range from 70 to 300ppm CO2 at three light intensities of 0.07, 0.16 and 0.53 cal•cm-2•min-1. In an atmosphere containing 80ppm CO2, total activity of 14C fixed into the plants dropped to 35 per cent of the normal, and at the same time significant decrease was observed in the translocation of 14C-assimilates from the leaves to the roots.<br>Fairly good amount of 14C-compounds, fixed in the evening and remained in the leaf till next morning, was translocated into the roots under normal photosynthetic conditions. In a CO2-deficient atmosphere, however, a downward translocation of 14C-compounds was slightly restricted and respiratory losses of 14C-compounds were considerably increased in the leaf.<br>Tomato plants placed in an atmosphere containing 60ppm CO2 for 2 hours had lower level of carbohydrates in the leaf and root.<br>A remarkable increase in 32P uptake was found at very low CO2 concentration in the tomato plants which had been illuminated for 6 hours before 32P-treatment. In contrast, the CO2 depletion caused marked decrease in the 32P uptake for the unlighted plants.<br>The uptake of 86Rb was considerably restricted at low CO2 concentration both in the lighted and unlighted plants. The absorption and accumulation of rubidium were highly dependent on the photosynthetic activity in the tomato plants.<br>From these results, the relationship between the translocation of assimilates and the uptake of mineral nutrients was discussed from physiological point of view.

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