探討光合菌Rhodopseudomonas palustris PS3促進作物生長之生理與分子機制

Elucidating the physiological and molecular mechanisms of plant growth-promoting effects exerted by Rhodopseudomonas palustris PS3

許書華(Shu-Hua Hsu)

指導教授 ： 盧虎生

共同指導教授 ： 劉啟德(Chi-Te Liu)

國立臺灣大學/生物資源暨農學院/農藝學研究所/博士(2021年)

https://doi.org/10.6342/NTU202100980

摘要

沼澤紅假單胞菌 (Rhodopseudomonas palustris) PS3菌株是一株由台灣水稻田土壤所篩選出的光合細菌，具有促進作物生長的功效。本研究從各種面向來評估PS3菌株作為植物生物刺激素的潛力。論文的第一部份探討PS3促進十字花科非結球葉菜生長的機制。該研究使用一株未具有促進植物生長功效的光合菌YSC3菌株作為對照，比較接種兩株菌的植物生理性狀。研究結果發現，雖然兩株菌都可促進根系發育，但只有PS3菌株可以提升根部的硝酸鹽轉運蛋白活性，進而提高植物的氮利用效率。接種PS3植株的葉片中之吲哚乙酸含量與細胞分裂活性都顯著提升，並觀察到年輕展開葉的葉片明顯變大，因而推測植株的光合作用總量會比較高。此外分析著生在根上的菌株基因表現，發現IAA生合成相關基因MAO在兩株菌中皆屬負調控且表現量相似，因而推測葉片中含有較高量的吲哚乙酸應非直接來自PS3所分泌的IAA，可能是PS3菌株與宿主植物之間的交互作用所致。綜合上述結果推測， PS3菌株促進植物生長的功效應是透過提升根部對氮源的吸收效率以及誘導葉片累積吲哚乙酸，進而提升葉部細胞分裂速率。
論文的第二部分是探討PS3菌株以及一株土壤益生菌Oryzomicrobium terrae TPP412對於水稻生長發育的影響。盆栽試驗所栽種的水稻品種為台梗九號，實驗結果發現將TPP412添加至含有半量化肥的滅菌土壤中可增加水稻產量; 而PS3則需添加在未滅菌土壤，即含有原生土壤微生物的條件下才能呈現生長促進功效。在田間試驗所栽種的水稻品種為台南11號，實驗結果證實在半量化肥條件下PS3具有更為顯著的產量提升效果。根據水稻產量構成要素分析結果，推測PS3菌株是藉由促進水稻穎花發育使得最終穀粒產量提升。
本研究證明了PS3光合菌潛力菌株具有促進單子葉以及雙子葉植物生長的功效，因其具有促進細胞分裂活性，推測該菌株具有成為植物生物刺激素的潛力。PS3 菌株藉由影響宿主的生理發育來促進植物生長的現象讓我們能對益生菌調控植物生長機制有更近一步的認識，也有助於有益微生物在環境永續農業上的實務應用。

關鍵字

蕓薹屬葉菜作物 ； 水稻生產 ； 生長激素 ； 氮素利用效率 ； 促進植物生長根圈有益微生物

並列摘要

Rhodopseudomonas palustris strain PS3 is a phototrophic bacterium, which was originally isolated from a paddy field. It is a plant growth promoting rhizobacterium (PGPR), able to enhance growth and yield of several crops. A comprehensive investigation to evaluate the potential of PS3 as a biostimulant for crop production was conducted in this dissertation. In the first part, we elucidated the underlying mechanisms of plant-growth promotion of PS3 through comparison of the plant and bacterial responses following the inoculation with the effective (PS3) and the ineffective (YSC3) strains in non-head cabbage (Brassica rapa var. chinensis). Although both strains could promote root development, only PS3 strain could increase the activity of nitrate transporter in roots, thereby increasing the nitrogen use efficiency of plants. This study further demonstrated that the endogenous indole-3-acetic acid (IAA) level as well as the cell division rate in the young expanding leaves were significantly increased in the PS3-inoculated plant. Furthermore, in the gene expression analysis of root-colonized R. palustris strains, the IAA biosynthesis-related gene MAO was negatively regulated in both strains and showed similar expression levels. Therefore, it suggests that the relatively high amount of IAA accumulated in the leaves was not come directly from the exogenous IAA secreted by PS3, and was caused by the interaction between PS3 and the host plant. Taken together, it is proposed that the beneficial effect of PS3 for promoting plant growth was via enhancing the nitrogen transport efficiency of the roots and elevating endogenous auxin levels in the developing leaf, thereby increasing the cell division rate in the leaves.
In the second part, the effects of PS3 and another beneficial bacterium Oryzomicrobium terrae TPP412 on the growth and yield of rice (Oryza sativa) were evaluated. Japonica rice variety “Taikeng 9 (TK 9)” was grown in the pot experiment. The grain yield was promoted while TPP412 was inoculated in the sterilized soil containing half-rate of chemical fertilizer. In contrast, PS3 only showed such beneficial effect in the unsterilized soil, suggesting the existence of indigenous soil microbes was critical to its PGP traits. In the paddy field trial, Japonica rice variety “Tainan 11 (TN11)” was grown. The experimental results verified that PS3 exerted a more significant yield improvement effect under half-rate of chemical fertilizer input. According to the analysis of rice yield components, it is proposed that PS3 could promote the rice production in field by improving the activity of spikelet development.
This study proved that the beneficial effects of PS3 in plant growth for both monocot and dicot plants under different crop production systems. Since PS3 shows the effects on activating cell proliferation in plant, indicating this strain is an elite biostimulant for improving crop production. The findings denoted in this study provide further insight in use of PGPR in plant growth enhancement regarding the physiological and developmental response of the plant partner. This will aid the selection and practical application of beneficial microorganisms in environmentally sustainable agriculture.

並列關鍵字

Brassica leafy vegetable ； rice production ； indole-3-acetic acid ； nitrogen use efficiency ； plant growth promoting rhizobacteria (PGPR)

參考文獻

Adesemoye, A.O., Torbert, H.A., and Kloepper, J.W. (2009). Plant growth-promoting rhizobacteria allow reduced application rates of chemical fertilizers. Microb. Ecol. 58(4), 921-929. doi: 10.1007/s00248-009-9531-y.

Aeron, A., Khare, E., Jha, C.K., Meena, V.S., Aziz, S.M.A., Islam, M.T., et al. (2020). Revisiting the plant growth-promoting rhizobacteria: lessons from the past and objectives for the future. Arch. Microbiol. 202(4), 665-676. doi: 10.1007/s00203-019-01779-w.

Ahemad, M., and Kibret, M. (2014). Mechanisms and applications of plant growth promoting rhizobacteria: Current perspective. Journal of King Saud University - Science 26(1), 1-20. doi: https://doi.org/10.1016/j.jksus.2013.05.001.

Aini, N., Yamika, W.S.D., and Ulum, B. (2019). Effect of nutrient concentration, PGPR and AMF on plant growth, yield, and nutrient uptake of hydroponic lettuce. Int J Agric Biol 21(1), 175-183. doi: 10.17957/Ijab/15.0879.

Ali, B., Sabri, A.N., Ljung, K., and Hasnain, S. (2009). Auxin production by plant associated bacteria: impact on endogenous IAA content and growth of Triticum aestivum L. Lett. Appl. Microbiol. 48(5), 542-547. doi: 10.1111/j.1472-765X.2009.02565.x.