Micci April, Zhang Qiuwei, Chang Xiaoqian, Kingsley Kathryn, Park Linsey, Chiaranunt Peerapol, Strickland Raquele, Velazquez Fernando, Lindert Sean, Elmore Matthew, Vines Philip L, Crane Sharron, Irizarry Ivelisse, Kowalski Kurt P, Johnston-Monje David, White James F
Department of Plant Biology, Rutgers University, New Brunswick, NJ 08901, USA.
Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, NJ 08901, USA.
Biology (Basel). 2022 Jun 7;11(6):876. doi: 10.3390/biology11060876.
We used light and confocal microscopy to visualize bacteria in leaf and bract cells of more than 30 species in 18 families of seed plants. Through histochemical analysis, we detected hormones (including ethylene and nitric oxide), superoxide, and nitrogenous chemicals (including nitric oxide and nitrate) around bacteria within plant cells. Bacteria were observed in epidermal cells, various filamentous and glandular trichomes, and other non-photosynthetic cells. Most notably, bacteria showing nitrate formation based on histochemical staining were present in glandular trichomes of some dicots (e.g., and ). Glandular trichome chemistry is hypothesized to function to scavenge oxygen around bacteria and reduce oxidative damage to intracellular bacterial cells. Experiments to assess the differential absorption of isotopic nitrogen into plants suggest the assimilation of nitrogen into actively growing tissues of plants, where bacteria are most active and carbohydrates are more available. The leaf and bract cell endosymbiosis types outlined in this paper have not been previously reported and may be important in facilitating plant growth, development, oxidative stress resistance, and nutrient absorption into plants. It is unknown whether leaf and bract cell endosymbioses are significant in increasing the nitrogen content of plants. From the experiments that we conducted, it is impossible to know whether plant trichomes evolved specifically as organs for nitrogen fixation or if, instead, trichomes are structures in which bacteria easily colonize and where some casual nitrogen transfer may occur between bacteria and plant cells. It is likely that the endosymbioses seen in leaves and bracts are less efficient than those of root nodules of legumes in similar plants. However, the presence of endosymbioses that yield nitrate in plants could confer a reduced need for soil nitrogen and constitute increased nitrogen-use efficiency, even if the actual amount of nitrogen transferred to plant cells is small. More research is needed to evaluate the importance of nitrogen transfer within leaf and bract cells of plants.
我们使用光学显微镜和共聚焦显微镜观察了种子植物18个科30多种植物叶片和苞片细胞中的细菌。通过组织化学分析，我们检测了植物细胞内细菌周围的激素（包括乙烯和一氧化氮）、超氧化物和含氮化学物质（包括一氧化氮和硝酸盐）。在表皮细胞、各种丝状和腺毛以及其他非光合细胞中观察到了细菌。最值得注意的是，在一些双子叶植物（如 和 ）的腺毛中发现了基于组织化学染色显示有硝酸盐形成的细菌。据推测，腺毛化学作用的功能是清除细菌周围的氧气并减少对细胞内细菌细胞的氧化损伤。评估同位素氮向植物中差异吸收的实验表明，氮被同化到植物活跃生长的组织中，而细菌在这些组织中最为活跃且碳水化合物更为丰富。本文概述的叶片和苞片细胞内共生类型此前未见报道，可能对促进植物生长、发育、抗氧化应激以及植物对养分的吸收具有重要意义。尚不清楚叶片和苞片细胞内共生在增加植物氮含量方面是否显著。从我们进行的实验中，无法得知植物毛状体是否专门进化为固氮器官，或者相反，毛状体是否是细菌易于定殖的结构，以及细菌与植物细胞之间是否可能发生一些偶然的氮转移。叶片和苞片内共生现象的效率可能低于类似植物中豆科植物根瘤的内共生现象。然而，植物中产生硝酸盐的内共生现象的存在可能会减少对土壤氮的需求，并提高氮利用效率，即使转移到植物细胞中的实际氮量很少。需要更多研究来评估植物叶片和苞片细胞内氮转移的重要性。
