Effects of Rhodopseudomonas palustris PS3 on nitrogen and carbon metabolism in the Brassica rapa L. ssp. chinensis

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.