Metabolomics and Transcriptomics Analysis of Pollen Germination Response to Low-Temperature in Pitaya (Hylocereus polyrhizus)

Abstract

Cross-pollination can improve the percentage of fruit set and fruit weight for most red flesh varieties in pitaya. The technology of pollen storage was very important for successful cross-pollination. However, till present, the technology of pollen storage is unsatisfactory in pitaya production. In this study, pitaya pollen stored at low temperature was taken as the research object, and its physicochemical indexes, metabolomics, and transcriptomics were studied. The results showed that in vitro pollen germination rate decreased significantly with the increase in storage time. Soluble sugar and soluble protein content of pollen peaked on the first day of storage, whereas its relative conductivity, and manlondialdehyde (MDA) and proline contents increased gradually during storage. At the same time, the antioxidant enzyme system of pollen was also affected. Superoxide dismutase (SOD) activity decreased, while the activities of catalase (CAT) and peroxidase (POD) increased and superoxide anion generation rate increased gradually during storage. According to the metabolomics results, amino acid, peptide, nucleotide, plant hormone, terpene, alcohol, phenol, flavonoid, sterol, vitamin, ester, sphingolipid, and ketone contents increased significantly during storage, whereas flavonoid and pigment contents declined gradually. During pollen storage, the gene expressions related to carbohydrate metabolism, protein metabolism, acid and lipid metabolism, sterol metabolism, plant hormone metabolism, and signal transductions were significantly downregulated. With KEGG pathway analysis, isoquinoline alkaloid biosynthesis, tyrosine metabolism, alanine, aspartate, and glutamate metabolism of pollen were affected significantly during low-temperature storage. Correlation analysis showed that the gene expression patterns of HuRP2, HuUPL1, and HuAAT2 had significant effects on pollen germination. D-arabinose 5-phosphate and myricetin were positively correlated with pollen germination rate, which was valuable for studying preservation agents. In this study, the changes in pollen during low-temperature storage were described from the level of metabolites and genes, which could provide theoretical support for the research and development of pollen long-term storage technology in pitaya.

Advances in the Understanding of Postharvest Physiological Changes and the Storage and Preservation of Pitaya

“…Additionally, the content of betaine decreased with senescence, but bio-preservatives prevented their degradation and maintained the fruit's nutritional quality throughout storage [52]. Low temperatures, heat treatment, phytohormones, and biochemical preservatives effectively delay decomposition of vitamin C, acid, sugar, phenolics, and others in fruits [53,54]. However, further in-depth studies are needed to address the regulation of synthesis and catabolism of pitaya fruit nutrients at the molecular level during postharvest storage, which will help solve the problem of postharvest nutrient depletion in pitaya fruit at the molecular level.…”

Research on Phenolic Content and Its Antioxidant Activities in Fermented Rosa rugosa ‘Dianhong’ Petals with Brown Sugar

“…The darker the color of the reaction solution, the lower the activity of SOD, and vice versa. In this study, the SOD activity of unfermented and fermented R. rugosa 'Dianhong' methanol extracts (UFR, NFR, and YFR) were determined according to the test kit (D799593, Sangon Biotech Co., Ltd., Shanghai, China) used and described in Dai et al [28]. To measure SOD activity, 90 µL of extract dilution (1 mg/mL) was centrifuged at 4200 r/min for 10 min, and the supernatant was collected on ice to be measured.…”

In Vitro and In Vivo Performance of Plum (Prunus domestica L.) Pollen from the Anthers Stored at Distinct Temperatures for Different Periods

“…Namely, pollen grain can germinate, as the germination test has shown, but could not achieve fertilization. In different plant species, during low-temperature storage, free radicals accumulate due to disorders of the oxidative system which leads to the low energy of pollen and ultimately to the inhibition of pollen germination [47,48]. Furthermore, it is found that during pollen storage, the content of glucose and proline increased when pollen germination decreased.…”