Piromyou Pongdet, Greetatorn Teerana, Teamtisong Kamonluck, Tittabutr Panlada, Boonkerd Nantakorn, Teaumroong Neung
School of Biotechnology, Institute of Agricultural Technology, Suranaree, University of Technology, Nakhon Ratchasima, Thailand.
The Center for Scientific and Technological Equipment, Suranaree University of Technology, Nakhon Ratchasima, Thailand.
Appl Environ Microbiol. 2017 Oct 31;83(22). doi: 10.1128/AEM.01488-17. Print 2017 Nov 15.
encompasses a variety of bacteria that can live in symbiotic and endophytic associations with leguminous and nonleguminous plants, such as rice. Therefore, it can be expected that rice endophytic bradyrhizobia can be applied in the rice-legume crop rotation system. Some endophytic bradyrhizobial strains were isolated from rice ( L.) tissues. The rice biomass could be enhanced when supplementing bradyrhizobial strain inoculation with KNO, NHNO, or urea, especially in sp. strain SUTN9-2. In contrast, the strains which suppressed rice growth were photosynthetic bradyrhizobia and were found to produce nitric oxide (NO) in the rice root. The expression of genes involved in NO production was conducted using a quantitative reverse transcription-PCR (qRT-PCR) technique. The gene expression level in sp. strain SUT-PR48 with nitrate was higher than that of the gene. In contrast, the inoculation of SUTN9-2 resulted in a lower expression of the gene than that of the gene. These results suggest that SUT-PR48 may accumulate NO more than SUTN9-2 does. Furthermore, the expression of SUTN9-2 was induced in treatment without nitrogen supplementation in an endophytic association with rice. The indole-3-acetic acid (IAA) and 1-amino-cyclopropane-1-carboxylic acid (ACC) deaminase produced by SUTN9-2 were also detected. Enumeration of rice endophytic bradyrhizobia from rice tissues revealed that SUTN9-2 persisted in rice tissues until rice-harvesting season. The mung bean () can be nodulated after rice stubbles were decomposed. Therefore, it is possible that rice stubbles can be used as an inoculum in the rice-legume crop rotation system under both low- and high-organic-matter soil conditions. This study shows that some rice endophytic bradyrhizobia could produce IAA and ACC deaminase and have a nitrogen fixation ability during symbiosis inside rice tissues. These characteristics may play an important role in rice growth promotion by endophytic bradyrhizobia. However, the NO-producing strains should be of concern due to a possible deleterious effect of NO on rice growth. In addition, this study reports the application of endophytic bradyrhizobia in rice stubbles, and the rice stubbles were used directly as an inoculum for a leguminous plant (mung bean). The degradation of rice stubbles leads to an increased number of SUTN9-2 in the soil and may result in increased mung bean nodulation. Therefore, the persistence of endophytic bradyrhizobia in rice tissues can be developed to use rice stubbles as an inoculum for mung bean in a rice-legume crop rotation system.
涵盖了多种能够与豆科植物和非豆科植物（如水稻）形成共生和内生关系的细菌。因此，可以预期水稻内生慢生根瘤菌可应用于水稻-豆类作物轮作系统。从水稻组织中分离出了一些内生慢生根瘤菌菌株。当用硝酸钾、硝酸铵或尿素补充慢生根瘤菌菌株接种时，尤其是在[具体菌种]菌株SUTN9-2中，水稻生物量可以得到提高。相比之下，抑制水稻生长的菌株是光合慢生根瘤菌，并且发现它们在水稻根部产生一氧化氮（NO）。使用定量逆转录-PCR（qRT-PCR）技术进行了与NO产生相关基因的表达研究。在有硝酸盐存在的情况下，[具体菌种]菌株SUT-PR48中的[基因名称]基因表达水平高于[另一个基因名称]基因。相反，接种SUTN9-2导致[基因名称]基因的表达低于[另一个基因名称]基因。这些结果表明，SUT-PR48可能比SUTN9-2积累更多的NO。此外，在与水稻的内生共生关系中，在不补充氮的处理中诱导了SUTN9-2的[基因名称]表达。还检测到了SUTN9-2产生的吲哚-3-乙酸（IAA）和1-氨基环丙烷-1-羧酸（ACC）脱氨酶。对水稻组织中的水稻内生慢生根瘤菌进行计数发现，SUTN9-2在水稻组织中一直持续到水稻收获季节。水稻茬分解后绿豆可以结瘤。因此，在低有机质和高有机质土壤条件下，水稻茬有可能在水稻-豆类作物轮作系统中用作接种物。这项研究表明，一些水稻内生慢生根瘤菌在水稻组织内共生期间可以产生IAA和ACC脱氨酶并具有固氮能力。这些特性可能在内生慢生根瘤菌促进水稻生长中发挥重要作用。然而，由于NO可能对水稻生长产生有害影响，产生NO的菌株应受到关注。此外，本研究报道了内生慢生根瘤菌在水稻茬中的应用，并且将水稻茬直接用作豆科植物（绿豆）的接种物。水稻茬的降解导致土壤中SUTN9-2数量增加，并可能导致绿豆结瘤增加。因此，可以利用内生慢生根瘤菌在水稻组织中的持久性，将水稻茬用作水稻-豆类作物轮作系统中绿豆的接种物。
