The Role of IP3 in NO-Enhanced Chilling Tolerance in Peach Fruit

Antioxidant Systems and Quality in Sweet Cherries Are Improved by Preharvest GABA Treatments Leading to Delay Postharvest Senescence

γ-Aminobutyric acid (GABA) plays important roles in plant development, including the maintenance of fruit quality when applied as postharvest treatment. However, little information is available about the effects of preharvest GABA treatments. Thus, GABA (10, 50 and 100 mM) was applied as foliar spray at key points of fruit development in three sweet cherry cultivars and over two years. The results show that quality parameters, such as total soluble solid content, titratable acidity and firmness were higher in the fruit from GABA-treated trees than in the controls, either at harvest or during four weeks of cold storage. In addition, the total phenolic and total and individual anthocyanin concentrations were also enhanced by GABA treatments and the fruit color was improved. The activities of the antioxidant enzymes catalase, ascorbate peroxidase and peroxidase were also enhanced by the GABA treatments. The most effective concentration was 50 mM, which led to extending the storage period of sweet cherries with high quality traits to up to four weeks, while for the controls this was two weeks. Thus, GABA treatment had a clear effect on delaying the postharvest ripening and senescence processes in sweet cherries, with an additional effect on enhancing the content of bioactive compounds, such as phenolics and anthocyanins, with antioxidant properties and health benefits.

Proteomic and metabolomic studies on chilling injury in peach and nectarine

Peaches and nectarines are temperate climate stone fruits, which should be stored at 0°C to prevent the ripening of these climacteric fruits. However, if stored for too long or if stored at a higher temperature (4 or 5°C), they develop chilling injury. Chilling injury damage includes (1) dry, mealy, wooly (lack of juice) fruits, (2) hard-textured fruits with no juice (leatheriness), (3) flesh browning, and (4) flesh bleeding or internal reddening. There are genetic components to these disorders in that early season fruits are generally more resistant than late season fruits, and white-fleshed fruits are more susceptible to internal browning than yellow-fleshed fruits. A recent review covered the recent research in genomic and transcriptomic studies, and this review examines findings from proteomic and metabolomics studies. Proteomic studies found that the ethylene synthesis proteins are decreased in cold compromised fruits, and this affects the processes initiated by ethylene including cell wall and volatile changes. Enzymes in metabolic pathways were both higher and lower in abundance in CI fruits, an indication of an imbalance in energy production. Stress proteins increased in both fruits with or without CI, but were higher in damaged fruits. Metabolomics showed the role of levels of sugars, sucrose, raffinose, galactinol, and glucose-6-phosphate in protection against chilling injury, along with other membrane stabilizers such as polyamines. Amino acid changes were inconsistent among the studies. Lipid species changes during storage could be correlated with sensitivity or resistance to CI, but more studies are needed.

Heterologous Expression and Characterization of Tea (Camellia sinensis) Polyamine Oxidase Homologs and Their Involvement in Stresses

Polyamine oxidase (PAO) is a key enzyme maintaining polyamine homeostasis, which affects plant physiological activities. Until now, the gene members and function of PAOs in tea (Camellia sinenesis) have not been fully identified. Here, through the expression in Escherichia coli and Nicotiana benthamiana, we identified six genes annotated as CsPAO in tea genome and transcriptome and determined their enzyme reaction modes and gene expression profiles in tea cultivar 'Yinghong 9'. We found that CsPAO1,2,3 could catalyze spermine, thermospermine, and norspermidine, and CsPAO2,3 could catalyze spermidine in the back-conversion mode, which indicated that the precursor of γ-aminobutyric acid might originate from the oxidation of putrescin but not spermidine. We further investigated the changes of CsPAO activity with temperature and pH and their stability. Kinetic parameters suggested that CsPAO2 was the major PAO modifying polyamine composition in tea, and it could be inactivated by β-hydroxyethylhydrazine and aminoguanidine. Putrescine content and CsPAO2 expression were high in tea flowers. CsPAO2 responded to wound, drought, and salt stress; CsPAO1 might be the main member responding to cold stress; anoxia induced CsPAO3. We conclude that in terms of phylogenetic tree, enzyme characteristics, and expression profile, CsPAO2 might be the dominant CsPAO in the polyamine degradation pathway.

Employing phytosulfokine α (PSKα) for delaying broccoli florets yellowing during cold storage

The yellowing of florets limits the economic and nutritional value of broccoli during postharvest. We investigated mechanisms of action of 150 nM phytosulfokine α (PSKα) for delaying florets yellowing in broccoli during cold storage. Our results showed that SUMO E3 ligase (SIZ1) gene expression was higher in florets treated with PSKα, which may prevent endogenous H₂O₂ accumulation, resulting from the higher activity of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase. Besides, higher expression of methionine sulfoxide reductase and cysteine peroxiredoxin genes, concomitant with higher expression of heat shock proteins 70/90 genes, may arise from higherexpression of SIZ1 gene. Lower expression and activity of phospholipase D and lipoxygenase may be liable for membrane integrity protection featured by lower malondialdehyde accumulation in florets treated with PSKα. Additionally,florets treated with PSKα exhibited higher endogenous cytokinin accumulation which may arise from higher expression of isopentenyl transferase gene, concomitant with lower expression of cytokinin oxidase gene.

A CCR4-associated factor 1, OsCAF1B, confers tolerance of low-temperature stress to rice seedlings

Rice is an important crop in the world. However, little is known about rice mRNA deadenylation, which is an important regulation step of gene expression at the post-transcriptional level. The CCR4-NOT1 complex contains two key components, CCR4 and CAF1, which are the main cytoplasmic deadenylases in eukaryotic cells. Expression of OsCAF1B was tightly coupled with low-temperature exposure. In the present study, we investigated the function of OsCAF1B in rice by characterizing the molecular and physiological responses to cold stress in OsCAF1B overexpression lines and dominant-negative mutant lines. Our results demonstrate that OsCAF1B plays an important role in growth and development of rice seedlings at low temperatures. Rice is a tropical and subtropical crop that is sensitive to low temperature, and activates a complex gene regulatory network in response to cold stress. Poly(A) tail shortening, also termed deadenylation, is the rate-limiting step of mRNA degradation in eukaryotic cells. CCR4-associated factor 1 (CAF1) proteins are important enzymes for catalysis of mRNA deadenylation in eukaryotes. In the present study, the role of a rice cold-induced CAF1, OsCAF1B, in adaptation of rice plants to low-temperature stress was investigated. Expression of OsCAF1B was closely linked with low-temperature exposure. The increased survival percentage and reduced electrolyte leakage exhibited by OsCAF1B overexpression transgenic lines subjected to cold stress indicate that OsCAF1B plays a positive role in rice growth under low ambient temperature. The enhancement of cold tolerance by OsCAF1B in transgenic rice seedlings involved OsCAF1B deadenylase gene expression, and was associated with elevated expression of late-response cold-related transcription factor genes. In addition, the expression level of OsCAF1B was higher in a cold-tolerant japonica rice cultivar than in a cold-sensitive indica rice cultivar. The results reveal a hitherto undiscovered function of OsCAF1B deadenylase gene expression, which is required for adaptation to cold stress in rice.