Little is known about how salinity affects ions distribution in root apoplast and symplast. Using x-ray microanalysis, ions distribution and the relative contribution of apoplastic and symplastic pathways for delivery of ions to root xylem were studied in sunflower plants exposed to moderate salinity (EC=6). Cortical cells provided a considerably extended Na(+) and Cl(-) storage facility. Their contents are greater in cytoplasm (root symplast) as compared to those in intercellular spaces (root apoplast). Hence, in this level of salinity, salt damage in sunflower is not dehydration due to extracellular accumulation of sodium and chloride ions, as suggested in the Oertli hypothesis. On the other hand, reduction in calcium content due to salinity in intercellular space is less than reduction in the cytoplasm of cortical cells. It seems that sodium inhibits the radial movement of calcium in symplastic pathway more than in the apoplastic pathway. The cell wall seems to have an important role in providing calcium for the apoplastic pathway. Redistribution of calcium from the cell wall to intercellular space is because of its tendency towards xylem through the apoplastic pathway. This might be a strategy to enhance loading of calcium to xylem elements and to reduce calcium deficiency in young leaves under salinity. This phenomenon may be able to increase salt tolerance in sunflower plants. Supplemental calcium has been found to be effective in reducing radial transport of Na(+) across the root cells and their loading into the xylem, but not sodium absorption. Supplemental calcium enhanced Ca(2+) uptake and influx into roots and transport to stele.
This study was conducted to elucidate the effect of calcium chloride (CaCl2) spraying times and number of sprays on the changes in biochemical compounds of “Hayward” kiwifruit (Actinidia deliciosa) during storage as well as at the shelf life. The vines in two different commercial kiwifruit orchards were sprayed with CaCl2 (15 g/L), one, two and three times in 35, 85 and 125 days after full bloom. Fruits were harvested at maturity stage and then were stored at 0C for 90 days and 5 additional days under simulated marketing conditions. The results showed that orchard location had significant effect on fruit biochemical compounds. With a few exceptions, one‐time (early‐, mid‐, late‐season) and twice CaCl2 sprays had no significant effects on kiwifruit quality characteristics. Thrice sprays significantly reduced respiration rate, ethylene production and polygalacturonase activity that lead to delay degradation of vitamin c, phenolic compounds and antioxidant activity, and maintained fruit sensory quality. Overall, thrice sprays of CaCl2 delayed fruit ripening processes and maintained fruit quality of “Hayward” kiwifruit.
Practical Applications
As the importance of phytochemical content in the health benefits of fruits and vegetables is recognized, interest in the antioxidant activity, enzymes, and polyphenolic and phytochemical contents of kiwifruit has increased significantly in recent years. During cold storage, many physicochemical changes occur that significantly affect fruit quality. Polygalacturonase (PG) is a cell wall‐bound enzyme which has been found to play a role in numerous plant developmental processes such as fruit ripening and softening. Considerable attention has been given to calcium (Ca) application to kiwifruit, since maintenance of relatively high Ca concentrations in fruit tissues results in better nutrients balance, maintaining cell wall stabilization and integrity, retards fruit respiration and ripening by lower rates of CO2 and C2H4 production, PG activity, softening, and finally extends storability. It should also be noted that the beneficial effects of preharvest Ca sprays depend on the time and number of treatments and orchard location.
The postharvest quality attributes of "Hayward" kiwifruit were investigated to find the optimum times and frequencies of calcium chloride (CaCl2) spray. The vines in two different commercial kiwifruit orchards were sprayed with CaCl2 (1.5%) one, two and three times in 35, 85 and 125 days after full bloom (DAFB). Fruits were harvested at the maturity stage and thereafter stored at 0C for 90 days and five additional days under marketing conditions as shelf life. The results showed that with a few exceptions, one time and two times CaCl2 sprays had no significant effect on kiwifruit postharvest quality. Thrice CaCl2 sprays (35 + 85 + 125 DAFB) significantly enhanced fruit Ca concentration and improved fruit quality such as firmness, total soluble solid, titratable acidity, total chlorophyll and carotenoid content, and reduced fruit weight loss and decay incidence during cold storage and shelf life. Overall, it is proposed that thrice CaCl2 (1.5%) spray in "Hayward" kiwifruit orchards could be more appropriate to improve fruit quality and storability.
PRACTICAL APPLICATIONSConsumer's acceptance for ripe "Hayward" kiwifruits is influenced by sugar content, sugar-to-acid ratio, green pulp color and the sensory properties such as texture and appearance. During cold storage, many physicochemical changes will occur in kiwifruits such as weight loss, increase in soluble solid contents, decline in ascorbic acid and cell wall degradation, which significantly affect fruit qualities. Softening plays an important role in textural qualities, consumer acceptability, shelf life and postharvest disease resistance. It is significantly influenced by different preharvest factors. Foliar application of CaCl2 has very important role in improving fruit quality. Calcium participates in cross-linking negative charges, especially on the carboxylic residues of pectin, imparting significant structural rigidity to the wall. Therefore, finding the optimum preharvest CaCl2 spraying time and frequency is very important for orchard management.
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