Effects and Molecular Mechanism of Mycorrhiza on the Growth, Nutrient Absorption, Quality of Fresh Leaves, and Antioxidant System of Tea Seedlings Suffering from Salt Stress.

We studied changes in plant growth, nutrient absorption, quality of fresh leaves, and the antioxidant enzyme systems of leaves treated with AMF (Glomus etunicatum) in tea (tea cultivar "Xinyang 10") seedlings exposed to 0 and 100 mmol/L sodium chloride (NaCl). The AMF colonization in the tea roots decreased observably by 50.1% after a 5-week soil NaCl (100 mmol/L) treatment. The growth, leaf nutrient levels, and leaf quality parameter contents significantly declined by 18–39% in the 100 mmol/L NaCl treatments. In contrast, these variables exhibited observably higher responses in the mycorrhizal seedlings than in the nonmycorrhizal seedlings. Furthermore, AMF improved the leaves' total amino acid concentrations dramatically, accompanied by the upregulation of the genes of the amino acid synthetic enzymes, such as glutamate dehydrogenase (CsGDH), glutamate synthase (CsGOGAT), and glutamine synthetase (CsGS), while 100 mmol/L NaCl seedlings represented a negative performance. In addition, the 100 mmol/L NaCl treatments dramatically downregulated the expression level of the tea caffeine synthase 1 gene (CsTCS1), the ascorbate peroxidase gene (CsAPX), and the 3-hydroxy-3-methylglutaryl coenzyme gene (CsHMGR) in the leaves, while the AMF seedlings represented positive performances. These results suggest that AMF may play an active role in fresh leaf quality via the partial upregulation of the relevant genes' expression. In contrast, salt stress represented the opposite result in tea. The seedlings inoculated with AMF showed significantly increased antioxidant enzyme activities, by 13.3–19.6%, including peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD), over the non-AMF inoculated tea seedlings. Still, they did not affect glutathione reductase (GR), irrespective of the NaCl condition. Further studies indicated that AMF observably upregulated the genes' expressions (i.e., CsCAT and CsSOD) in both the 0 and 100 mmol/L NaCl seedlings. Meanwhile, the 100 mmol/L NaCl seedlings represented markedly lower antioxidant enzyme activities (i.e., SOD, CAT, and POD) and gene expressions (i.e., CsSOD and CsCAT) than the non-NaCl seedlings, irrespective of AMF inoculation. These results imply that AMF has a positive role in strengthening salt tolerance and on the quality of fresh tea leaves. [ABSTRACT FROM AUTHOR]