The Photosynthetic Bacterium Rhodopseudomonas palustris Strain PS3 Exerts Plant Growth-Promoting Effects by Stimulating Nitrogen Uptake and Elevating Auxin Levels in Expanding Leaves

Abstract

Rhodopseudomonas palustris strain PS3, a phototrophic bacterium, was originally isolated from a paddy field located in Taipei city, Taiwan, and showed positive effects on the growth of leafy vegetables. The aim of this study was to clarify the mechanism of the beneficial effects exerted by PS3 on plants. An ineffective R. palustris strain, YSC3, isolated from a paddy field located in Yilan County, was used as the negative control for comparative analyses. We cultivated non-heading Chinese cabbage (Brassica rapa var. chinensis) in 1/2 strength Hoagland hydroponic solution, in which nitrate is the main nitrogen source. We evaluated various plant physiological responses to inoculation with different bacterial inoculants. The N use efficiency (NUE) of PS3-inoculated plants was dramatically higher than that of YSC3-inoculated plants. The nitrate uptake efficiency (NUpE) was significantly elevated in plants treated with PS3; however, no excess nitrate accumulation was observed in leaves. We also noticed that the endogenous indole-3-acetic acid (IAA) levels as well as the cell division rate in the leaves of PS3-inoculated plants were significantly higher than those in the leaves of YSC3-inoculated plants. We examined the bacterial transcription of some genes during root colonization, and found that the expression level of IAA synthesis related gene MAO was almost the same between these two strains. It suggests that the elevated endogenous IAA in the PS3-inoculated plants was not directly derived from the exogenous IAA produced by this bacterium. Taken together, we deduced that PS3 inoculation could promote plant growth by enhancing nitrate uptake and stimulating the accumulation of endogenous auxin in young expanding leaves to increase the proliferation of leaf cells during leaf development.

From Lab to Farm: Elucidating the Beneficial Roles of Photosynthetic Bacteria in Sustainable Agriculture

“…As shown, PNSB microbial inoculants could not only increase the yield and quality of edible plant biomass, but also alleviate the biotic and abiotic stress in crops and mitigate environmental stress. It has been demonstrated that the addition of PNSB by foliar spray or soil application significantly improves the growth responses of leafy crops, such as pak choi (B. chinensis L.), mustard spinach, sugar leaf, spinach and lettuce [41][42][43][44][45][46][47][48]. Similarly, the use of Rhodobacter sphaeroides NR3 enhanced the carotenoid content of spinach (14-138%) and mustard spinach (4.1-21%) [44].…”

“…Increasing NUE is critical to improve crop yield, reduce N fertilizer demand and alleviate environmental pollution. PNSB has been reported to improve the NUE of plants [41,42,45]. Elbadry and Elbanna found that inoculating rice with R. capsulatus DSM155 in the presence of N fertilizer could increase the nitrogen content in roots by 20%.…”

“…Wong and colleagues reported that the nitrate contents in the leaves of Chinese cabbage were significantly lower in plants in which the roots were inoculated with R. palustris PS3 than in plants that were not inoculated [45]. Furthermore, Hsu and colleagues demonstrated that the NUE of plants was remarkably increased in the presence of PS3 inoculation, allowing nitrate to be effectively catabolized [42].…”

“…Hsu and colleagues found that while inoculating an elite PNSB strain R. palustris PS3 in the hydroponic nutrient solution during cultivation of non-heading Chinese cabbage, not only was the yield increased, but also the nitrate content was remarkably decreased by 88% [41]. Intriguingly, although the nitrate uptake was significantly elevated in the PS3-inoculated plants, the excess nitrate was not accumulated in the tissues [42]. This is because the plants showed high N use efficiency (NUE) in the presence of R. palustris PS3 [42].…”

Structure and function of rhizosphere and root endophyte microbial communities associated with healthy and root rot diseased Panax notoginseng

“…), especially in the healthy samples from the LJ site. It is reported that a compound produced by Rhodopseudomonas can promote plant growth, and studies have shown that Rhodopseudomonas can induce resistance in plants[54]. In tobacco, Rhodopseudomonas induces tobacco mosaic resistance to protect against tobacco mosaic immunity[55].…”