Alleviating Chilling Injury in Stored Pomegranate Using a Single Intermittent Warming Cycle: Fatty Acid and Polyamine Modifications.

Pomegranate is a perishable superfruit with important human health-promoting phytochemicals. The use of cold storage is inevitable for its long-term preservation. As pomegranate is sensitive to temperatures below 5°C, it is therefore necessary and worthwhile to introduce a postharvest technique that is safe, applicable, and commercially acceptable to maintain the fruit quality under a cold storage condition. The efficacy of intermittent warming (IW) in the form of a single warming period (1 day at 20°C with 70% relative humidity (RH) before returning the treated fruit to storage) during the cold storage of 'Rabab-e-Neyriz' pomegranate (70 days at 2 ± 0.5°C and 90 ± 5% RH) was evaluated. To find the best treatment time, warming was performed at 4 temporary interruption points in storage (after 15, 25, 35, or 45 days of storage). For each interruption date, the treated fruit were compared to the controls twice, once immediately after treatment and once at the end of the storage period. It was founded that a single warming period at the right time during cold storage (before irreversible damage occurs) activated multiple mechanisms and physiological responses in pomegranate fruit peel that are significantly responsible for alleviating the severity of chilling damage to this commodity. In other words, warming on the 15th day was the most efficient treatment, resulting in better preservation of unsaturated fatty acids from peroxidation, lower malondialdehyde (MDA) production, and preservation of the unsaturated/saturated fatty acids (UFAs/SFAs) ratio (membrane integrity index) in the peel during storage and lower chilling injury symptoms. Moreover, the content of spermine (Spm) and putrescine (Put) (as important antioxidants acting as membrane safety agents) was significantly increased immediately after treatment, followed by a continuous increase in Spm and a higher level of Put compared to control until the end of storage.

Flowering in Persian walnut: patterns of gene expression during flower development.

BACKGROUND: Flower development and sufficient fruit set are important parameters with respect to walnut yield. Knowledge about flowering genes of fruit trees can help to conduct better molecular breeding programs. Therefore, this study was carried out to investigate the expression pattern of some flowering genes (FT, SOC1, CAL, LFY and TFL1) in Persian walnut (cv. Chandler) during the growing season and winter dormancy. RESULTS: The results showed that walnut flower induction and initiation in Shahmirzad, Iran occurred in early June and late September, respectively. After meeting chilling and heat requirement, flower differentiation and anthesis occurred in late-March and mid-April to early-May, respectively. Study of flowering gene expression showed that the expression of the FT gene increased in three stages including before breaking of bud dormancy, from late March to late April (coincided with flower differentiation and anthesis) and from late May to mid-June (coincided with flower induction). Like FT, the expression of SOC1 gene increased during flower induction and initiation (mid-May to early-August) as well as flower anthesis (mid-April to early-May). LFY and CAL genes as floral meristem identity genes are activated by FT and SOC1 genes. In contrast with flowering stimulus genes, TFL1 showed overexpression during winter dormancy which prevented flowering. CONCLUSION: The expression of FT gene activated downstream floral meristem identity genes including SOC1, CAL and LFY which consequently led to release bud dormancy as well as flower anthesis and induction. Also, TFL1 as a flowering inhibitor gene in walnut showed overexpression during the bud dormancy. Chilling accumulation reduced TFL1 gene expression and increased the expression of flowering genes which ultimately led to overcome dormancy.

Comparing Kinetics of Xylem Ion Loading and Its Regulation in Halophytes and Glycophytes.

Although control of xylem ion loading is essential to confer salinity stress tolerance, specific details behind this process remain elusive. In this work, we compared the kinetics of xylem Na+ and K+ loading between two halophytes (Atriplex lentiformis and quinoa) and two glycophyte (pea and beans) species, to understand the mechanistic basis of the above process. Halophyte plants had high initial amounts of Na+ in the leaf, even when grown in the absence of the salt stress. This was matched by 7-fold higher xylem sap Na+ concentration compared with glycophyte plants. Upon salinity exposure, the xylem sap Na+ concentration increased rapidly but transiently in halophytes, while in glycophytes this increase was much delayed. Electrophysiological experiments using the microelectrode ion flux measuring technique showed that glycophyte plants tend to re-absorb Na+ back into the stele, thus reducing xylem Na+ load at the early stages of salinity exposure. The halophyte plants, however, were capable to release Na+ even in the presence of high Na+ concentrations in the xylem. The presence of hydrogen peroxide (H2O2) [mimicking NaCl stress-induced reactive oxygen species (ROS) accumulation in the root] caused a massive Na+ and Ca2+ uptake into the root stele, while triggering a substantial K+ efflux from the cytosol into apoplast in glycophyte but not halophytes species. The peak in H2O2 production was achieved faster in halophytes (30 min vs 4 h) and was attributed to the increased transcript levels of RbohE. Pharmacological data suggested that non-selective cation channels are unlikely to play a major role in ROS-mediated xylem Na+ loading.

Postharvest treatments with γ-aminobutyric acid, methyl jasmonate, or methyl salicylate enhance chilling tolerance of blood orange fruit at prolonged cold storage.

BACKGROUND: Blood orange is sensitive to chilling injury (CI) depending on cultivar and storage temperature. Postharvest treatments with γ-aminobutyric acid (GABA), methyl jasmonate (MeJA), or methyl salicylate (MeSA) are known to alleviate CI. γ-Aminobutyric acid aqueous solution, applied at 20 and 40 mM, was vacuum-infiltrated at 30 kPa for 8 min at 20 °C. Methyl jasmonate or MeSA vapor treatments were applied separately at 50 and 100 µM by putting the fruit in 20 L plastic containers for 18 h at 20 °C. There have been no reports about postharvest treatments of GABA, MeJA, or MeSA on enhancing the tolerance of 'Moro' blood orange to chilling during long-term cold storage at 3 °C for 150 days, which was the subject of this study. RESULTS: All treatments significantly alleviated CI symptoms of blood orange manifested by lower electrolyte leakage (EL), malondialdehyde (MDA), hydrogen peroxide (H2 O2 ) concentrations, and higher proline content in flavedo during storage. The largest effects were obtained with 100, 50 µM, and 40 mM for MeSA, MeJA, and GABA, respectively, which enhanced the activity of the antioxidant enzymes catalase (CAT), ascorbate peroxidase (APX) and superoxide dismutase (SOD), and phenylalanine ammonia-lyase (PAL). On the other hand, these treatments suppressed peroxidase (POD) and polyphenol oxidase (PPO) activities. CONCLUSION: The mechanisms involved in enhancing the tolerance of 'Moro' blood orange to chilling could involve scavenging H2 O2 by increasing the activity of antioxidant enzymes, higher PAL/PPO activity ratio, and osmoregulation by increasing proline content. These changes led to the maintenance of the epidermis structure. This was confirmed by scanning electron microscopy (SEM) micrographs. © 2019 Society of Chemical Industry.

Responses of pomegranate cultivars to severe water stress and recovery: changes on antioxidant enzyme activities, gene expression patterns and water stress responsive metabolites.

The biochemical and molecular responses of five commercially well-known pomegranate cultivars to severe water stress were studied. The cultivars were subjected to 14-day water stress by withholding irrigation, followed by re-watering for 7 days. Results showed clear differences in metabolites contents and activities of antioxidant enzymes among various pomegranate cultivars during severe water stress and recovery. According to our results, increased accumulation of proline in pomegranate was not related to osmotic adjustment during severe water stress. Except for 'Ghojagh', leaves grown under severe water stress conditions showed symptoms of oxidative stress such as reduced chlorophyll concentration. The improved performance of 'Ghojagh' under drought stress may be associated with an efficient osmotic adjustment. The up- or down regulated expression of cytosolic glutathione reductase (cytosolic GR) and glutathione peroxidase were observed under drought conditions. Moreover, the suppressed expression of cytosolic GR was also noted. Comparatively, 'Rabab' exhibited higher antioxidant capacity and an efficient ROS-scavenging mechanism under drought stress. Lower levels of membrane lipid peroxidation in 'Ghojagh' and 'Rabab' under drought stress and the marked reduction of malondialdehyde concentration after re-watering represents that these cultivars have a good tolerance to drought stress. As a first step towards the study of the biochemical and molecular responses of pomegranate plants to water stress, this research provides new information into the mechanisms of drought tolerance in the plants.

Enzyme activity and biochemical changes of three date palm cultivars with different softening pattern during ripening.

The physicochemical composition changes during palm ripening were studied. The activities of invertase and cell wall-modifying enzymes, namely pectin methylesterase (PME), ß-galactosidase (ß-Gal), endo-1,4-ß-D-glucanase (EGase), and cellulase were monitored during growth and ripening of Shahani, Piarom and Deiry cultivars with different textures. Also, we estimated the concentrations of six organic acids by HPLC. Reducing sugars, most of organic acid, pH and TSS increased up to the full-ripe stage of all date types. On the contrary, moisture, macro and microelements and proteins decreased during the same period. Despite a considerable rise in invertase activity (200 units) during ripening of Shahani, no significant trend could be discerned in Deiry cultivar (8 units) at different stages. Our results also showed that cell wall enzymes were increased in activity during ripening and these increases were coincident with fruit softening. Furthermore, our results showed that the composition and the variation of the chemical compositions mainly depended on the cultivar and maturity stage.

The application of polyamines by pressure or immersion as a tool to maintain functional properties in stored pomegranate arils.

Pomegranate fruits were treated with putrescine (Put) or spermidine (Spd) at 1 mM either by pressure infiltration or by immersion and then were stored at 2 degrees C for 60 days. Samples were taken biweekly and were further stored 3 days at 20 degrees C for shelf life study. The treatments were effective on maintaining the concentration of ascorbic acid, total phenolic compounds, and total anthocyanins in arils at higher levels than in control samples. In addition, the two ways of polyamine application increased the levels of total antioxidant activity (TAA) during storage, especially when polyamines were applied by pressure infiltration. Moreover, Spd showed the best results on increasing TAA through maintenance of total phenolic compounds.

Prestorage heat treatment to maintain nutritive and functional properties during postharvest cold storage of pomegranate.

Heat treatments have been used to extend storability of several fruits, although no information is available about their effects on nutritive and functional properties in pomegranates, which was the objective of this research. Thus, pomegranate fruits were heat treated (dips at 45 degrees C for 4 min) and stored at 2 degrees C for 90 days. Every 15 days, samples were taken and further stored 2 days at 20 degrees C for shelf life study. Arils from heat-treated pomegranates exhibited higher total antioxidant activity than controls, which was correlated primarily to the high levels of total phenolics and to lesser extent to ascorbic acid and anthocyanin contents. Additionally, the levels of sugars (glucose and fructose) and organic acids (malic, citric, and oxalic acids) remained also at higher concentrations in arils from treated fruits. With this simple and non-contaminant technology, the functional and nutritive properties, after long periods of storage, could then be even greater than in recently harvested fruits, thus providing a high content in health-beneficial compounds to consumers after the intake of these fruits.