Rhodopseudomonas palustris PS3光合菌對於小白菜氮與碳代謝之影響

Abstract

Rhodopseudomonas palustris NTUIOB-PS3為分離自台灣水田土壤的光合菌株，不僅能促進各種作物生長，亦能有效降低植體內硝酸鹽的累積。本研究之目的為探討PS3光合菌促進宿主植物生長的機制。藉由分析植物的氮素吸收效率、同化酵素活性、氮素轉運蛋白之基因表現、二氧化碳固定效率等，闡明根圈微生物對於植物生理活性之影響。將PS3光合菌接種至水耕栽培系統，促使丸葉山東小白菜的地上部與根部鮮重顯著高於未接種的控制組。因PS3處理組之根部硝酸鹽轉運蛋白基因BjNRT1.1的轉錄活性與植體內的總氮含量皆比控制組來得高，推測PS3菌株可以提昇植物吸收氮素的效能。進一步計算其氮素吸收效率 (nitrogen uptake efficiency, NupE)，發現比控制組增加約40%。此外，接種PS3的植株其生長初期的光合作用效率較高，葉面積增加了約25 %，總碳含量也提昇了70%以上。綜合上述結果推測PS3 光合菌藉由植微交互作用提昇了宿主植物的氮與碳的代謝效率，因而增加生物質量的累積。

Rhodopseudomonas palustris NTUIOB-PS3, a phototrophic purple non-sulfur bacterium, was originally isolated from paddy field in Taiwan. It can not only improve plant growth, but also reduce the nitrate accumulation in plants. The aim of this study was to investigate the mechanism of its plant growth promotion effect. We would like to elucidate the effects of rhizosphere bacteria on plant physiology through evaluating the nitrogen uptake efficiency, activity of nitrogen assimilation associative enzymes, gene expression of nitrate transporters, and CO2 assimilation rate of plants. When hydroponic solution was supplemented with the PS3 inoculant, plant growth (fresh weight of shoots and roots) of Chinese cabbage was greater than that without inoculation (control group). Since the gene expression of the nitrate transporter BjNRT1.1 in the roots and total amounts of N in the plants were dramatically elevated, we deduced that PS3 could stimulate the N uptake efficiency (NupE) of plants. The N uptake efficiency was around 40% increase in comparison with that in the control group. On the other hand, the plants inoculated with PS3 showed higher photosynthetic rate in the early stage of plants, then the leave sizes and total C amounts in shoot were increased nearly 25 % and 70%, respectively. Taken together, we deduced that PS3 improves both N and C metabolic efficiencies of plants through plant-microbe interaction, as a result of higher biomass accumulation.