Chloride stress triggers maturation and negatively affects the postharvest quality of persimmon fruit. Involvement of calyx ethylene production

Slight Changes in Fruit Firmness at Harvest Determine the Storage Potential of the ‘Rojo Brillante’ Persimmon Treated with Gibberellic Acid

Today, the ‘Rojo Brillante’ persimmons undergoing prolonged storage are treated with giberellic acid, which allows the delay of the harvesting to November-December. Although during this period the fruit maintained high commercial firmness, practical experience indicates very different behavior during the posterior cold storage, depending on the harvest moment. To explain what leads to these differences, an in-depth study of the physicochemical and microstructural changes occurring in the fruit during five commercial harvest times from November to December was carried out. During this period, slight variations in firmness occurred, ranging from 48 to 40 N. Nevertheless, the fruit behavior under cold storage was strongly influenced by the harvest date, which was explained by the degradation of cell wall, cell membrane and tonoplast, mainly noted in fruit from the latest harvests. Therefore, the fruit harvested with firmness close to 48 N had a highly structured cell, which maintained firmness during cold storage for up to 90 days. The fruit harvested with 43 N presented a more degraded structure, while the fruit with initial firmness around 40 N underwent major ultrastructure cell wall and membranes modifications, which led to greater firmness loss. Therefore, the fruit firmness at harvest is decisive for its storage potential.

MBW complexes impinge on anthocyanidin reductase gene regulation for proanthocyanidin biosynthesis in persimmon fruit

MBW protein complexes containing MYB, bHLH and WD40 repeat factors are known transcriptional regulators of secondary metabolites production such as proanthocyanidins and anthocyanins, and developmental processes such as trichome formation in many plant species. DkMYB2 and DkMYB4 (MYB-type), DkMYC1 (bHLH-type) and DkWDR1 (WD40-type) factors have been proposed by different authors to take part of persimmon MBW complexes for proanthocyanidin accumulation in immature fruit, leading to its characteristic astringent flavour with important agronomical and ecological effects. We have confirmed the nuclear localization of these proteins and their mutual physical interaction by bimolecular fluorescence complementation analysis. In addition, transient expression of DkMYB2, DkMYB4 and DkMYC1 cooperatively increase the expression of a persimmon anthocyanidin reductase gene (ANR), involved in the biosynthesis of cis-flavan-3-ols, the structural units of proanthocyanidin compounds. Collectively, these data support the presence of MBW complexes in persimmon fruit and suggest their coordinated participation in ANR regulation for proanthocyanidin production.

A cross population between D. kaki and D. virginiana shows high variability for saline tolerance and improved salt stress tolerance

Persimmon (Diospyros kaki Thunb.) production is facing important problems related to climate change in the Mediterranean areas. One of them is soil salinization caused by the decrease and change of the rainfall distribution. In this context, there is a need to develop cultivars adapted to the increasingly challenging soil conditions. In this study, a backcross between (D. kaki x D. virginiana) x D. kaki was conducted, to unravel the mechanism involved in salinity tolerance of persimmon. The backcross involved the two species most used as rootstock for persimmon production. Both species are clearly distinct in their level of tolerance to salinity. Variables related to growth, leaf gas exchange, leaf water relations and content of nutrients were significantly affected by saline stress in the backcross population. Water flow regulation appears as a mechanism of salt tolerance in persimmon via differences in water potential and transpiration rate, which reduces ion entrance in the plant. Genetic expression of eight putative orthologous genes involved in different mechanisms leading to salt tolerance was analyzed. Differences in expression levels among populations under saline or control treatment were found. The ‘High affinity potassium transporter’ (HKT1-like) reduced its expression levels in the roots in all studied populations. Results obtained allowed selection of tolerant rootstocks genotypes and describe the hypothesis about the mechanisms involved in salt tolerance in persimmon that will be useful for breeding salinity tolerant rootstocks.

Friend or Foe? Chloride Patterning in Halophytes

In this opinion article, we challenge the traditional view that breeding for reduced Cl^- uptake would benefit plant salinity tolerance. A negative correlation between shoot Cl^- concentration and plant biomass does not hold for halophytes - naturally salt tolerant species. We argue that, under physiologically relevant conditions, Cl^- uptake requires plants to invest metabolic energy, and that the poor selectivity of Cl^--transporting proteins may explain the reported negative correlation between Cl^- accumulation and crop salinity tolerance. We propose a new paradigm: salinity tolerance could be achieved by improving the selectivity of some of the broadly selective anion-transporting proteins (e.g., for NO₃^->Cl^-), alongside tight control of Cl^- uptake, rather than targeting traits mediating its efflux from the root.

Review on the significance of chlorine for crop yield and quality

The chloride concentration in the plant determines yield and quality formation for two reasons. First, chlorine is a mineral nutrient and deficiencies thereof induce metabolic problems that interfere with growth. However, due to low requirement of most crops, deficiency of chloride hardly appears in the field. Second, excess of chloride, an event that occurs under chloride-salinity, results in severe physiological dysfunctions impairing both quality and yield formation. The chloride ion can effect quality of plant-based products by conferring a salty taste that decreases market appeal of e.g. fruit juices and beverages. However, most of the quality impairments are based on physiological dysfunctions that arise under conditions of chloride-toxicity: Shelf life of persimmon is shortened due to an autocatalytic ethylene production in fruit tissues. High concentrations of chloride in the soil can increase phyto-availability of the heavy metal cadmium, accumulating in wheat grains above dietary intake thresholds. When crops are cultivated on soils that are moderately salinized by chloride, nitrate fertilization might be a strategy to suppress uptake of chloride by means of an antagonistic anion-anion uptake competition. Overall, knowledge about proteins that catalyse chloride-efflux out of the roots or that restrict xylem loading is needed to engineer more resistant crops.

Determination of persimmon leaf chloride contents using near-infrared spectroscopy (NIRS)

Early diagnosis of specific chloride toxicity in persimmon trees requires the reliable and fast determination of the leaf chloride content, which is usually performed by means of a cumbersome, expensive and time-consuming wet analysis. A methodology has been developed in this study as an alternative to determine chloride in persimmon leaves using near-infrared spectroscopy (NIRS) in combination with multivariate calibration techniques. Based on a training dataset of 134 samples, a predictive model was developed from their NIR spectral data. For modelling, the partial least squares regression (PLSR) method was used. The best model was obtained with the first derivative of the apparent absorbance and using just 10 latent components. In the subsequent external validation carried out with 35 external data this model reached r(2) = 0.93, RMSE = 0.16% and RPD = 3.6, with standard error of 0.026% and bias of -0.05%. From these results, the model based on NIR spectral readings can be used for speeding up the laboratory determination of chloride in persimmon leaves with only a modest loss of precision. The intermolecular interaction between chloride ions and the peptide bonds in leaf proteins through hydrogen bonding, i.e. N-H···Cl, explains the ability for chloride determinations on the basis of NIR spectra.