Epibrassinolide enhanced chilling tolerance of postharvest banana fruit by regulating energy status and pyridine nucleotide homeostasis

The regulation of postharvest strawberry quality mediated by abscisic acid under elevated CO2 stress

Elevated CO2 was a potential strategy for strawberry preservation. However, the regulatory mechanism remained unclear. In current study, transcriptome analysis showed that elevated CO2 played important roles in regulating strawberry fruit quality at the transcriptional level, and plant hormones metabolism at least partially involved in the regulatory process. Further, ABA was demonstrated to play important roles in the response to elevated CO2. Elevated CO2 inhibited the accumulation of ABA, which was 61% lower than that in control. Elevated CO2 repressed ABA synthesis by inhibiting NCED activity and the expression of FaNCED1/2, leading to the reduction of ABA accumulation as a result. Meanwhile, elevated CO2 also decreased ABA sensitivity by down-regulating FaSnRK2.4/2.6 and FaABI5 expression. The dual down-regulation of ABA signaling accounted for the regulation of fruit quality under elevated CO2 treatment. These results provide new insights into the mechanism of strawberry fruit response to elevated CO2.

DNP and ATP modulate the pulp softening and breakdown in fresh longan by acting on the antioxidant system and the metabolisms of membrane lipids and cell wall polysaccharides

Compared to the control longan, DNP treatment elevated pulp breakdown index, reduced the values of pulp firmness, CSP, ISP, cellulose, and hemicellulose by enhancing the activities of PE, PG, Cx, XET, and β-Gal. Additionally, DNP treatment increased the levels of PLD, lipase, LOX, PA, and SFA, and decreased the values of PC, PI, USFA, U/S, and IUFA, displaying higher cell membrane permeability and more severe cell membrane damage in longan pulp. Furthermore, DNP treatment weakened the levels of SOD, CAT, APX, AsA, GSH, TP, and TF, thereby exacerbating ROS outbreak and MDA production. These results indicate that DNP treatment destroyed the antioxidant system to cause ROS eruption. This disruption further disturbed the metabolisms of membrane lipids and cell wall polysaccharides, leading to the breakdown of cell membrane and cell wall, and eventually aggravated longan pulp softening and breakdown. However, ATP treatment exhibited the opposite effects of DNP treatment.

Regulation of Embden-Meyerhof-Parnas (EMP) Pathway and Tricarboxylic Acid (TCA) Cycle Concerning Aberrant Chilling Injury Behavior in Postharvest Papaya (Carica papaya L.)

Postharvest abnormal chilling injury (CI) behavior in papaya (Carica papaya L.) fruit is a rare phenomenon that may be associated with respiratory metabolism. This study thus aimed to investigate the impacts of storage temperatures (1 and 6 °C) on the respiratory metabolism of postharvest papaya and its impact on CI development. Results demonstrated that 1 °C storage reduced the activities of hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), citrate synthase (CS), and α-ketoglutarate dehydrogenase (α-KGDH) and regulated the expression of corresponding enzymes in the Embden-Meyerhof-Parnas (EMP) pathway and tricarboxylic acid (TCA) cycle compared with 6 °C storage, resulting in a lower respiration rate of the EMP-TCA pathway and mitigating the development of CI. Meanwhile, lower contents of nicotinamide adenine dinucleotide (hydrogen) (NAD(H)) were observed in papaya fruit stored at 1 °C. Notably, papaya fruit stored at 1 °C maintained higher activity and transcriptional levels of SDH and IDH during the whole storage period. These findings suggest that 1 °C storage reduced the respiration rate of the EMP-TCA pathway by reducing the expression level and activity of related enzymes, which is conducive to the reduction of respiration substrate consumption and finally alleviating the occurrence of CI.

PpBZR1, a BES/BZR transcription factor, enhances cold stress tolerance by suppressing sucrose degradation in peach fruit

Brassinosteroids (BRs) are phytohormones that play numerous roles in a plant's response to environmental stress. While BES/BZR transcription factors are essential components in BR signaling, their role in regulating postharvest fruit responses to cold stress is largely unknown. In this study, the application of 24-epibrassinolide (EBR) to peaches alleviated chilling injury (CI) during postharvest cold storage. We further characterized a key BES/BZR gene, PpBZR1, which regulates peach cold resistance. Transient expression PpBZR1 in peaches showed that PpBZR1 inhibits PpVIN2 expression and VIN activity, resulting in an elevated level of sucrose, which protects fruit from CI. Arabidopsis thaliana expressing PpBZR1 that had a high germination and seedling survival rate at low temperatures, which may be due to higher level of sucrose and lower oxidative damage. Mechanistically, we confirmed that PpBZR1 directly binds to the PpVIN2 promoter and functions as a negative regulator for sucrose metabolism. In addition, PpCBF1/5/6 were induced by EBR treatment and AtCBFs were upregulated in PpBZR1 transgenic Arabidopsis thaliana. Combined with previous findings, we hypothesize that PpBZR1 regulates PpVIN2 and may also be mediated by CBF. In conclusion, PpBZR1 expression is induced by EBR treatment during cold storage, which futher inhibite sucrose degradation gene PpVIN2 transcription via direct binding its promoter and indirectly regulating PpVIN2, resulting in slower sucrose degradation and higher chilling tolerance of peach.