Arbuscular Mycorrhizal Fungi and Endophytic Fungi Activate Leaf Antioxidant Defense System of Lane Late Navel Orange

Abstract

Arbuscular mycorrhizal (AM) fungi and endophytic fungi collectively symbiose well with plants and, thus, stimulate plant growth; however, it is not clear whether field inoculation of the fungi enhances the resistance potential of plants, particularly in citrus. In the present study, we inoculated AM fungi (Acaulospora scrobiculata, Diversispora spurca, and D. versiformis) and endophytic fungi (Piriformospora indica) on an eight-year-old lane late navel orange (Citrus sinensis (L.) Osb) trees grafted on Poncirus trifoliata in a field, and we analyzed the response of the leaf antioxidant defense system. Approximately 2 years after inoculation, the root fungal colonization rate and soil hyphal length significantly increased. Fungal inoculation significantly increased the activity of leaf antioxidant enzymes, such as superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase, and the content of non-enzymatic antioxidants, such as reduced ascorbic acid and reduced glutathione. As a result, fungi-inoculated plants maintained lower concentrations of hydrogen peroxide and superoxide anion radicals and lower levels of membrane lipid peroxidation (according to malondialdehyde level) in leaves than uninoculated plants. Among them, inoculation of D. spurca and A. scrobiculata showed relatively higher effects in enhancing the antioxidant defense system than the other fungi. Furthermore, inoculation of D. spurca induced expressions of CsFe-SOD, CsMn-SOD, CsPOD, CsCAT1, and CsPRR7; inoculation of A. scrobiculata and D. versiformis induced expressions of CsCAT1; CsCAT1 and CsPOD were also induced by inoculation of P. indica. All four inoculations almost upregulated expressions of CsFAD6. AM fungi had superior effects than endophytic fungi (e.g., P. indica). According to our findings, inoculation with beneficial fungi, specifically mycorrhizal fungus D. spurca, activated the antioxidant defense system of field citrus trees, thus, having potentially superior resistance in inoculated plants.

Endophytic fungus Serendipita indica accelerates ascorbate-glutathione cycle of white clover in response to water stress

“…A mechanism diagram regarding changes in ascorbate-glutathione cycle in roots of white clover inoculated with Serendipita indica (Si) under water stress (WS). ↑, the parameter was significantly increased by Si; ↓, the parameter was significantly decreased by Si; ROS, reactive oxygen species; O 2 (Li et al, 2022b).…”

“…In addition to alterations in antioxidant enzyme activities, gene expressions of antioxidant enzymes are also modulated by S. indica . For example, S. indica induced CsPOD and CsCAT1 expressions in leaves of Lane Late navel orange, together with an inhibition of CsCu/Zn-SOD expressions ( Li et al, 2022b ). The colonization of S. indica downregulated expressions of genes encoding enzymes for ascorbate synthesis in Arabidopsis thaliana ( Vadassery et al, 2009 ).…”

“…The content of hydrogen peroxide (H 2 O 2 ) in roots was determined by the method described by Velikova et al (2000) , in which 2 ml of the reaction contained 0.5 ml supernatant, 0.5 ml of 10 mmol/L potassium phosphate buffer (pH 7.0), and 1 ml of 1 mol/L KI solution. The content of superoxide anion radical (O 2 •− ) in roots was determined according to the method described by Li et al (2022b) . The concentration of malondialdehyde (MDA) was determined by Sudhakar et al (2001) .…”

“…POD activity was determined by guaiacol method ( Wu, 2018 ), in which 5 ml of the reaction consisted of 2.9 ml of 0.05 mol/L phosphate buffer, 1 ml of 2% H 2 O 2 , 1 ml of 0.05 mol/L guaiacol, and 0.1 ml supernatant. Activity of APX in roots was assayed according to the procedure outlined by Li et al (2022b) , where a reaction solution with a total volume of 2.1 ml consisted of 0.1 ml 0.06% H 2 O 2 , 1.7 ml of 50 mmol/L potassium phosphate buffer containing 0.1 mmol/L EDTA-Na 2 , 0.1 ml of 6 mmol/L ASC, and 0.1 ml supernatant. Activity of GR in roots was determined as per the method of Fatemeh et al (2020) , in which 1.0 ml of the reaction mixture contained 50 mmol/L potassium phosphate buffer (pH 7.5), supernatant, 1 mmol/L GSSG, 0.75 mmol/L [5,5′-dithiobis-(2-nitrobenzoic acid)], and 0.1 mmol/L NADPH.…”

“…Serendipita indica also increased CAT and GR activities but reduced GSH content of rice under WS, along with no change in superoxide dismutase (SOD) and APX activities and reduced ASC content (Tsai et al, 2020). In a study performed by Li et al (2022b), inoculation of S. indica in the field did not induce expression levels of CsFe-SOD and CsMn-SOD in leaves of Lane Late navel orange, but stimulated CsPOD and CsCAT1 expression levels, along with an inhibited expression of CsCu/Zn-SOD. In rice, APX and ASC were not induced by S. indica under WS (Tsai et al, 2020), suggesting that the mechanism underlying the effect of S. indica on the host ascorbate-glutathione cycle is still complex.…”