MeJA induces chilling tolerance in loquat fruit by regulating proline and γ-aminobutyric acid contents

Loquat fruit were pretreated with 10 μmol l⁻¹ methyl jasmonate (MeJA) for 24 h at 20 °C and then stored at 1 °C for 35 days to investigate the effect of MeJA treatment on chilling injury (CI) and changes in the contents of proline and γ-aminobutyric acid (GABA). The control fruit exhibited severe flesh leatheriness, a specific CI symptom, after 21 days of storage at 1 °C, but it was reduced in MeJA-treated fruit. During the development of CI in fruit, proline and GABA accumulated with the storage time, while MeJA treatment enhanced the increases in proline and GABA contents. The MeJA-treated fruit exhibited higher activities of Δ¹-pyrroline-5-carboxylate synthetase (P5CS), ornithine δ-aminotransferase (OAT) and glutamate decarboxylase (GAD), and lower proline dehydrogenase (PDH) activity than control during storage. These results suggest that the reduction in CI in loquat fruit by MeJA may be due to the increased proline and GABA contents.     

Changes in physiology and quality of peach fruits treated by methyl jasmonate under low temperature stress

The quality and physiological changes were determined in peach (Prunus persica L. cv. Jiubao) fruits in low temperature storage with or without methyl jasmonate (MeJA) treatment. Peach fruits stored for 3 weeks at 5 °C and following 3 d shelf life intervals at 20 °C appeared chilling injury (CI) symptom, expressed as flesh browning. MeJA treatment decreased the CI index, which was possibly attributed to higher activity of peroxidase and lower content of phenolic compounds than that without MeJA treatment. Moreover, MeJA treatment not only enhanced the rate of SSC/TA in peach fruits by mainly restraining the decrease of the SSC in peach, but also affected the degradation of cell wall, perhaps by regulation of cell wall modifying enzymes and the calcium content in cell wall of flesh. The results suggested that MeJA treatment was beneficial for maintaining quality owing to reducing chilling injury of peach fruits under low temperature stress.     

Reducing Chilling Injury of Loquat Fruit by Combined Treatment with Hot Air and Methyl Jasmonate

The effects of a combined treatment of hot air (HA, 38 °C for 6 h) and methyl jasmonate (MeJA, 16 μmol L^?1) on chilling injury, fruit quality, and physiological changes in loquat fruit stored at 1 °C were investigated. The results showed that treatment with HA or MeJA alone both significantly alleviated chilling injury in loquat fruit compared with the control, while their combination had the lowest level of chilling injury symptoms and highest quality. The activities of antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, and catalase were enhanced by the combination of HA and MeJA. In addition, the combined treatment significantly inhibited the activities of phenylalanine ammonia-lyase, peroxidase, and polyphenol oxidase, which resulted in lower lignin content. Highest level of polygalacturonase activity and water-soluble pectin content and lowest level of protopectin content were also observed in the combined treatment. These results suggested that the enhanced chilling tolerance by combination of HA and MeJA treatment in loquat fruit was related to the induction of antioxidant enzymes and the inhibition of lignin biosynthesis. The combination of HA and MeJA treatment could be a useful technique to alleviate chilling injury and maintain quality of loquat fruit during cold storage.     

Sugar metabolism in relation to chilling tolerance of loquat fruit

The relationship between chilling injury and sugar metabolism was investigated in loquat fruit stored at 1 °C for 35 days. No symptoms of chilling injury occurred in the fruit, of ‘Ninghaibai’ cultivar, during the whole storage whereas, in ‘Dahongpao’ fruit, severe chilling symptoms were observed after 20 days of storage at 1 °C. ‘Ninghaibai’ fruit had higher levels of glucose and fructose and higher activities of sucrose hydrolyzing enzymes, such as sucrose synthase-cleavage and invertase, than had ‘Dahongpao’. Furthermore, the chilling resistant ‘Ninghaibai’ fruit also showed higher activities of hexokinase and fructokinase, involved in hexose phoshorylation and sugar signal generation. These results suggest that the higher content of hexoses and activities of hexose sensors were likely part of the mechanism for chilling tolerance of loquat fruit.     

Fatty acid composition and antioxidant system in relation to susceptibility of loquat fruit to chilling injury

Two cultivars of loquat fruit with contrasting chilling resistance were stored at 1 °C for 35 days to investigate the relationship between chilling injury and fatty acid composition and its antioxidant system. No symptoms of chilling injury occurred in the fruit of ‘Qingzhong’ cultivar during the whole storage, whereas in ‘Fuyang’ fruit, chilling injury increased sharply after 21 days of storage at 1 °C. ‘Qingzhong’ fruit had lower levels of superoxide radical and H₂O₂, in addition to lower lipoxygenase activity, but higher membrane lipid unsaturation and higher activities of superoxide dismutase and catalase than ‘Fuyang’. Furthermore, the chilling resistant ‘Qingzhong’ fruit also showed higher activities of antioxidant enzymes involved in ascorbate–glutathione cycle and higher levels of ascorbate acid and reduced glutathione. These results suggest that the higher membrane lipid unsaturation and the more efficient antioxidant system were both beneficial in enhancing resistance of loquat fruit to chilling injury.     

Peach fruit acquired tolerance to low temperature stress by accumulation of linolenic acid and N-acylphosphatidylethanolamine in plasma membrane

Peach fruit (Prunuspersica L. cv. Beijing 33) did not show symptoms of chilling injury in 0 °C-Air or 0 °C-CA, but did in 5 °C-Air after 21 d. The mechanisms by which 0 °C storage could activate chilling tolerance of peach fruit were investigated by analysing characteristics of plasma membrane. We found that peach fruit stored in 0 °C-Air and 0 °C-CA had much higher linolenic acid content and unsaturation degree of plasma membrane than did that in 5 °C-Air. In addition, the fruits stored in 0 °C-CA showed a higher membrane fluidity and membrane integrity than did that in 0 °C-Air, which was related to the accumulation of N-acylphosphatidylethanolamine (NAPE) of peach fruits stored in 0 °C-CA. Based on these results, it appears that a higher unsaturation degree of membrane lipid and NAPE accumulation are beneficial for maintaining membrane fluidity, leading to an enhanced tolerance of peach fruit to chilling stress.     

茉莉酸处理对采后葡萄果实贮藏期间落粒的影响

以"巨峰"葡萄果实为试材,研究了茉莉酸甲酯(methyl jasmonate,MeJA)处理对采后葡萄果实在1℃贮藏期间落粒的影响。结果显示:10μmol/L MeJA处理可显著降低葡萄果实贮藏期间落粒率和腐烂率,并延缓果穗离区组织中脱落酸(ABA)含量和乙烯释放量的上升、赤霉素(GA3)含量的下降以及ABA/GA3比值的增长,并显著抑制离区果胶甲酯酶(Pectinesterase,PME)活性的下降和多聚半乳糖醛酸酶(Golygalacturonase,PG)活性的上升。同时,经MeJA处理的果穗离区细胞壁中胶层中乙醇不溶物(AIR)和Na2CO3溶性果胶含量也明显高于对照水平,而水溶性和环己二胺四乙酸(CDTA)溶性果胶含量却低于对照水平。实验表明,MeJA处理可通过调控葡萄果穗离区组织中内源激素水平来平衡细胞壁水解酶PME和PG的活性,从而抑制离区细胞壁中胶层的水解,维持细胞壁结构的完整,最终降低采后葡萄果实的落粒率,起到改善果实贮藏品质的效果。     

γ-Aminobutyric acid treatment reduces chilling injury and activates the defence response of peach fruit

Peach fruit were immersed in 5 mM γ-aminobutyric acid (GABA) solution for 10 min at 20 °C and then stored at 1 °C for 5 weeks to investigate the effect of GABA treatment on chilling injury (CI), antioxidant enzymes and energy status in peach fruit. The results showed that GABA treatment significantly inhibited CI incidence of peaches and enhanced activities of antioxidant enzymes, such as superoxide dismutase, catalase, ascorbate peroxidase, glutathione peroxidase, glutathione S-transferase, monodehydroascorbate reductase and dehydroascorbate reductase. The treatment also increased contents of adenosine triphosphate and adenosine diphosphate, but lowered adenosine monophosphate content, which resulted in a higher level of energy charge in treated fruit. These results indicated that GABA increased chilling tolerance of peach fruit through enhancing its enzymatic antioxidant system and maintaining energy status in peach fruit.     

Postharvest quality of arazá fruit during low temperature storage

Arazá (Eugenia stipitata Mc Vaugh) fruits at breaker stage of maturity were stored at 7, 10, 12, or 20 °C and 85-90% RH for 2 weeks, with or without an additional simulated shelf-life period (3 days at 20 °C and 70% RH). Some half-yellow (turning) arazá fruit were also stored at 7 or 12 °C. Respiration rate, ethylene production, quality traits and physiological disorders and decay were monitored. Arazá fruit of both stages of maturity showed a climacteric pattern of ripening, with the maximum levels of respiration being reached after 5 days at 20 °C for breaker fruit, while half-yellow fruit ripened totally after one day. Weight loss was the most limiting quality trait for arazá fruit. Chilling injury symptoms included skin scald (only at 7 °C), uneven ripening (at 7 or 10 °C, including uneven softening during storage, particularly in breaker fruit), and slight acidification at 7 °C. Decay in the post-storage shelf-life periods (mainly Gloesporium sp.) was particularly high after storage at 7 °C in breaker fruit. The storage of breaker arazá fruit at 12 °C is recommended because this prevents chilling injury and flesh acidification, and allows normal fruit ripening during a post-storage shelf-life at 20 °C, as revealed by the lower organic acids (mainly malic) content and increased sugar (glucose, fructose and sucrose) content.