Vegetable Physiology Laboratory, Department of Horticulture, University of Tabriz, Tabriz, Iran.
Leibniz Institute for Vegetable and Ornamental Crops, Theodor-Echtermeyer-Weg 1, 14979, Großbeeren, Germany.
Mycorrhiza. 2018 Jan;28(1):59-70. doi: 10.1007/s00572-017-0799-3. Epub 2017 Sep 26.
Mycorrhizal symbiosis is known to be the most prevalent form of fungal symbiosis with plants. Although some studies focus on the importance of mycorrhizal symbiosis for enhanced flavonoids in the host plants, a comprehensive understanding of the relationship still is lacking. Therefore, we studied the effects of mycorrhizal inoculation of onions (Allium cepa L.) regarding flavonol concentration and the genes involved in flavonol biosynthesis when different forms of nitrogen were supplied. We hypothesized that mycorrhizal inoculation can act as a biotic stress and might lead to an increase in flavonols and expression of related genes. The three main quercetin compounds [quercetin-3,4'-di-O-β-D-glucoside (QDG), quercetin-4'-O-β-D-glucoside (QMG), and isorhamnetin-4'-O-β-D-glucoside (IMG)] of onion bulbs were identified and analyzed after inoculating with increasing amounts of mycorrhizal inocula at two time points and supplying either predominantly NO or NH nitrogen. We also quantified plant dry mass, nutrient element uptake, chalcone synthase (CHS), flavonol synthase (FLS), and phenyl alanine lyase (PAL) gene expression as key enzymes for flavonol biosynthesis. Inoculation with arbuscular mycorrhizal fungi (highest amount) and colonization at late development stages (bulb growth) increased QDG and QMG concentrations if plants were additionally supplied with predominantly NH. No differences were observed in the IMG content. RNA accumulation of CHS, FLS, and PAL was affected by the stage of the mycorrhizal symbiosis and the nitrogen form. Accumulation of flavonols was not correlated, however, with either the percentage of myorrhization or the abundance of transcripts of flavonoid biosynthesis genes. We found that in plants at late developmental stages, RNA accumulation as a reflection of a current physiological situation does not necessarily correspond with the content of metabolites that accumulate over a long period. Our findings suggest that nitrogen form can be an important factor determining mycorrhizal development and that both nitrogen form and mycorrhizas interact to influence flavonol biosynthesis.
共生真菌与植物的共生关系是最为普遍的真菌共生形式。虽然有些研究集中于共生真菌对宿主植物中类黄酮含量增加的重要性，但对这种关系的全面理解仍然缺乏。因此，我们研究了在不同氮源形式下，洋葱（Allium cepa L.）接种共生真菌对类黄酮醇浓度和类黄酮醇生物合成相关基因的影响。我们假设共生真菌接种可以作为一种生物胁迫，可能导致类黄酮醇的增加和相关基因的表达。在接种了不同数量的共生真菌并在两个时间点提供主要是 NO 或 NH 氮源后，我们鉴定和分析了洋葱鳞茎中的三种主要槲皮素化合物[槲皮素-3,4'-二-O-β-D-葡萄糖苷（QDG）、槲皮素-4'-O-β-D-葡萄糖苷（QMG）和异鼠李素-4'-O-β-D-葡萄糖苷（IMG）]。我们还量化了植物干质量、养分元素吸收、查尔酮合酶（CHS）、类黄酮醇合酶（FLS）和苯丙氨酸解氨酶（PAL）基因表达，作为类黄酮醇生物合成的关键酶。在接种丛枝菌根真菌（接种量最高）和在鳞茎生长的后期发育阶段（鳞茎生长）进行定植时，如果植物额外提供主要是 NH 氮源，则会增加 QDG 和 QMG 浓度。在 IMG 含量方面没有观察到差异。CHS、FLS 和 PAL 的 RNA 积累受共生真菌阶段和氮源形式的影响。然而，类黄酮醇的积累与菌根化的百分比或类黄酮生物合成基因转录本的丰度没有相关性。我们发现，在发育后期的植物中，作为当前生理状况反映的 RNA 积累不一定与长期积累的代谢物含量相对应。我们的研究结果表明，氮源形式可能是决定菌根发育的重要因素，氮源形式和菌根相互作用影响类黄酮醇的生物合成。
