In order to explore the effect and mechanism of trehalose (Tre) on the growth and cold resistance of gardenia jasminoides Ellis under low-temperature stress, 15 mmol/L of Tre was used on gardenia seedlings under different degrees of low-temperature stress. The results show that −3 °C (low-temperature stress) significantly inhibited the growth of gardenia, while Tre at 15 mmol/L restored the plant height, number of leaves, total plant weight, and fresh weight of above ground and underground parts to 88.10%, 81.05%, 98%, 87.61% and 96.68% at 20 °C (normal temperature conditions). The total length of the root, number of lateral roots, total root surface area and root volume recovered to 88.48%, 74.08%, 104.03% and 83.77% under normal temperature at 20 °C. The chlorophyll content, chlorophyll fluorescence parameters and photosynthetic intensity parameters in the leaves of gardenia jasminoides were significantly decreased under low-temperature stress at −3 °C, while the contents of chlorophyll a, chlorophyll b and total chlorophyll were significantly increased under 15 mmol/L Tre treatment. Meanwhile, chlorophyll fluorescence parameters (φPSII, Fv′/Fm′ and qP increased by 18.60%, 73.17% and 81.82%, respectively) and photosynthetic intensity parameters (Pn, Gs, Ci and Tr increased by 33.33%, 70.86%, 14.83% and 116.50%, respectively) were also increased. At −3 °C, Tre treatment significantly increased the activities of SOD, POD and CAT in roots, and reduced the content of reactive oxygen species (H₂O₂ and superoxide anion). At the same time, the contents of root osmotic regulatory substances (proline and malondialdehyde) were decreased by 15.16% and 12.65%, respectively. At −3 °C, Tre significantly increased the root auxin content and significantly decreased the trans-zeanoside content, but had no significant effects on gibberellin and abscisic acid. Tre can also regulate the content of root respiratory metabolites under low-temperature stress, increase the malic acid content by 96.77% under −3 °C, and decrease the succinic acid content by 56.34%. In conclusion, Tre reduces the content of ROS and its damage by improving the antioxidant capacity in roots and enhances the osmoregulation and stability of cell membranes by reducing the content of osmoregulation substances, hormones and aerobic respiratory metabolites in the root, thus enhancing the cold resistance of gardenia.

Gardenia jasminoides Ellis is an evergreen plant of the genus Gardenia in the Rubiaceae Juss. trehalose (Tre), as a stress metabolite of plants adapted to environmental stress, can enhance the stress resistance of plants and ensure the normal growth and development of crops. In order to explore the effect and mechanism of trehalose on the growth and cold resistance of gardenia seedlings under low temperature stress, this study treated the seedlings with trehalose under different degrees of low temperature stress, observed their growth conditions, and discussed the effects of trehalose on cold resistance of Gardenia from the perspectives of phenotype, photosynthesis, active oxygen species, antioxidant system, endogenous hormones and respiratory metabolic products. To provide a theoretical basis for trehalose to improve cold resistance of plants. The results show that: Low temperature stress at − 3℃ significantly inhibited the growth of Gardenia, while trehalose at 15 mmol/L restored plant height, number of leaves, total plant weight, fresh weight of above ground and underground parts to 88.10%, 81.05%, 98%, 87.61% and 96.68% of the normal temperature conditions at 20℃. The total length of root, number of lateral roots, total root surface area and root volume recovered to 88.48%, 74.08%, 104.03% and 83.77% under normal temperature at 20℃. The chlorophyll content, chlorophyll fluorescence parameters and photosynthetic intensity parameters in leaves of gardenia jasminoides were significantly decreased under low temperature stress at − 3℃, while the contents of chlorophyll a, chlorophyll b and total chlorophyll were significantly increased under 15 mmol/L trehalose treatment (by 90.56%, 45.16% and 74.39%, respectively). Meanwhile, chlorophyll fluorescence parameters (φPSII, Fv '/Fm' and qP increased by 18.60%, 73.17% and 81.82%, respectively) and photosynthetic intensity parameters (Pn, Gs, Ci and Tr increased by 33.33%, 70.86%, 14.83% and 116.50%, respectively) were also increased. At -3℃, trehalose treatment at 15 mmol/L could significantly increase the activities of SOD, POD and CAT in roots of Gardenia (increased by 12.76%, 32.64% and 10.69%, respectively), and reduce the content of reactive oxygen species (H2O2 and superoxide anion radical decreased by 20.49% and 3.39%, respectively). At the same time, the contents of root osmotic regulatory substances (proline and malondialdehyde) were decreased by 15.16% and 12.65%, respectively. At -3℃, trehalose treatment at 15 mmol/L significantly increased root auxin content (32.03%) and significantly decreased trans-zeanoside content (14.92%), but had no significant effects on gibberellin and abscisic acid contents. 15 mmol/L trehalose can also regulate the content of root respiratory metabolites under low temperature stress, and increase malic acid content by 96.77% under -3℃ low temperature stress, while decrease succinic acid content by 56.34%. In conclusion, low temperature stress inhibited the growth of Gardenia. Trehalose could increase chlorophyll content and chlorophyll fluorescence parameters in leaves of Gardenia and enhance photosynthesis to promote the growth of Gardenia. Under low temperature stress, trehalose can reduce the content of active oxygen by improving the antioxidant capacity of roots of gardenia seedlings, so as to reduce the damage of active oxygen, maintain the level of active oxygen metabolism and enhance the cold resistance of plants. Trehalose also enhanced the osmoregulation ability and the stability of cell membrane by reducing the content of root osmoregulation substances, and enhanced the cold resistance of Gardenia by regulating the content of root hormones and aerobic respiratory metabolites.

Arbuscular Mycorrhizal Fungi (AMF) can form symbiotic relationships with most plants. They can alleviate the toxic effects of heavy metals on plants. This study analyzed the effects of AMF (Diversispora versiformis, D.v.) on the physiological responses and root organic acid secretion of tomato (Solanum lycopersicum L.) under cadmium (Cd) stress, in order to elucidate how AMF enhance Cd tolerance. The results indicated that when the AMF inoculation rate of tomato seedlings ranged from 26.75% to 38.23%, the AMF treatment significantly promoted tomato growth. Cd significantly reduced the agronomic traits of tomato. However, AMF inoculation dramatically lowered the Cd level from 19.32 mg/kg to 11.54 mg/kg in tomato roots, and effectively reduced the negative effect of Cd toxicity on seedling growth. Cd stress also significantly reduced the chlorophyll fluorescence parameters, chlorophyll contents, and photosynthetic intensity parameters in seedling leaves, while the AMF treatment significantly increased these indicators. Under Cd stress, the AMF treatment significantly increased the activities of SOD, POD, and CAT, and reduced the levels of reactive oxygen species and the contents of osmotic regulatory substances in roots. Under Cd stress conditions, the AMF treatment also significantly increased the auxin level (57.24%) and reduced the abscisic acid level (18.19%), but had no significant effect on trans-zeatin riboside and gibberellin contents in roots. Cd stress markedly reduced the content of malic acid and succinic acid by 17.28% and 25.44%, respectively; however, after the AMF inoculation, these indicators only decreased by 2.47% and 2.63%, respectively. Under Cd stress, AMF could increase tomato roots’ antioxidant capacity to reduce ROS level, thereby alleviating the toxicity induced by ROS and maintaining reactive oxygen metabolism, enhancing the plant’s stress resistance. In summary, the AMF treatment enhances the osmotic regulation capacity and maintains the stability of cell membranes by reducing the levels of osmotic regulatory substances in roots. It also enhances the Cd tolerance of tomato plants by regulating the contents of root hormones and aerobic respiration metabolites, among other pathways. Therefore, inoculating plants with AMF is a prospective strategy for enhancing their adaptive capacity to Cd-polluted soils.

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.

Melatonin is a small-molecule indoleamine compound that is essential to life. It is widely present in plants and plays an extremely important role in plant growth and fruit quality. This article summarizes the role of melatonin synthesis in plants, its distribution in some fruits, and its impact on post-harvest fruit quality. The mechanisms by which melatonin regulates post-harvest fruit quality are discussed in depth from the perspectives of respiratory metabolism, ethylene metabolism, sugar metabolism, reactive oxygen species (ROS), and antioxidant systems. Finally, we analyze the existing problems in the current research field of melatonin in post-harvest fruit preservation and look toward the application prospects of melatonin synthesis, metabolism, and the mechanisms for regulating fruit quality. This article provides a reference for further exploring the role of melatonin and increasing the endogenous content of melatonin in fruits, as well as post-harvest preservation techniques, with the aim of promoting the application of melatonin in post-harvest preservation.

The plant-specific INDETERMINATE DOMAIN (IDD) gene family is important for plant growth and development. However, a comprehensive analysis of the IDD family in orchids is limited. Based on the genome data of Phalaenopsis equestris, the IDD gene family was identified and analyzed by bioinformatics methods in this study. Ten putative P. equestris IDD genes (PeIDDs) were characterized and phylogenetically classified into two groups according to their full amino acid sequences. Protein motifs analysis revealed that overall structures of PeIDDs in the same group were relatively conserved. Its promoter regions harbored a large number of responsive elements, including light responsive, abiotic stress responsive elements, and plant hormone cis-acting elements. The transcript level of PeIDD genes under cold and drought conditions, and by exogenous auxin (NAA) and abscisic acid (ABA) treatments further confirmed that most PeIDDs responded to various conditions and might play essential roles under abiotic stresses and hormone responses. In addition, distinct expression profiles in different tissues/organs suggested that PeIDDs might be involved in various development processes. Furthermore, the prediction of protein-protein interactions (PPIs) revealed some PeIDDs (PeIDD3 or PeIDD5) might function via cooperating with chromatin remodeling factors. The results of this study provided a reference for further understanding the function of PeIDDs.