Arbuscular Mycorrhizal Fungi (AMF) are a type of soil microorganism that can form symbiotic relationships with most higher plants and are widely distributed. They can promote plant nutrient absorption and the accumulation of secondary metabolites, thereby alleviating the toxic effects of heavy metals. This study analyzed the effects of AMF (Diversispora versiformis, D.v.) on the growth, chlorophyll synthesis, photosynthesis, reactive oxygen metabolism, antioxidant capacity, plant hormones, and root exudation of organic acids of tomato (Solanum lycopersicum L.) under cadmium (Cd) stress. This analysis aimed to elucidate how AMF enhances the Cd-tolerance of tomato. The results indicated that AMF inoculation rate of tomato seedlings ranged from 26.75% to 38.23%, and the AMF significantly promoted tomato growth. Cd significantly reduced the total plant weight, leaf number, plant height, , root fresh weight, above-ground fresh weight, and total root length by 34.17%, 9.62%, 28.94%, 21.31%, 34.09%, and 28.17%, respectively. However, AMF inoculation dramatically lowered the Cd level from 19.32 mg/kg to 11.54 mg/kg in tomato root, and effectively reduced the negative effect of Cd toxicity on seedlings’ growth. Cd stress also significantly reduced the chlorophyll fluorescence parameters, chlorophyll contents, and photosynthetic intensity parameters in seedlings’ leaves, while AMF treatment significantly increased these indicators. Under Cd stress, AMF observably increased the activities of SOD, POD, and CAT (increased by 16.13%, 12.16%, and 30.04%), reduced reactive oxygen species’ levels (H2O2 and superoxide anion decreased by 33.33% and 32.77%), and also reduced the content of osmotic adjustment substances (proline, malondialdehyde, soluble protein, and soluble sugar content decreased by 38.92%, 31.19%, 27.59%, and 49.27%) in the seedlings’ root. Under Cd condition, AMF also observably increased the auxin level (57.24%), significantly reduced the abscisic acid level (18.19%), but had no significant effect on trans-zeatin riboside and gibberellin content in the seedlings’ root. AMF can also regulate the content of respiratory metabolic products in the root under Cd condition. Cd stress markedly reduced the content of malic acid and succinic acid by 17.28% and 25.44%, respectively. However, after inoculation with AMF, these indicators only decreased by 2.47% and 2.63%. In summary, Cd stress inhibited the growth of tomato, while AMF could increase the chlorophyll fluorescence parameters and chlorophyll contents in tomato leaves and enhance photosynthesis to promote its growth. Under Cd stress, AMF could increase tomato root antioxidant capacity to reduce ROS level, thereby alleviating the toxic induced by ROS and maintaining reactive oxygen metabolism , enhancing plant's stress resistance. AMF enhances the osmotic regulation capacity and maintains the stability of cell membranes by reducing osmotic regulatory substances levels in the root system. It also enhances the Cd-tolerance of tomatoes through regulating the content of root hormones and aerobic respiration metabolites, among other pathways. Therefore, inoculating plants with AMF is a prospective strategy for heightening their adaptive capacity to Cd pollution soils.
Zhang et al. (Mon,) studied this question.
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