Effect of jasmonates on coloration and quality of the‘Christmas Rose’ grape berry

Objective:

TheChristmas Rosegrape is a type of the late-maturing cultivars which is widely planted in China. It is favored by consumers because of its delicate fleshresistance to storage and transportationand high quality. Howeverin some areasthe coloration of theChristmas Rosegrape was not very good because of high temperature and humiditywhich affected its internal and external qualities. In recent yearsresearchers found that jasmonateswhich widely exist in plantscould improve coloration of fruit by promoting the accumulation of anthocyanin. This study is to explain the effect of different concentrations of exogenous prohydrojasmon(PDJ)methyl jasmonate(MeJA) on the coloration and quality of theChristmas Rosegrape so as to provide some theoretical evidence to improve coloration and quality of this grape berry.

Methods:

The trial was conducted at the experimental farm of the Zheng⁃zhou Fruit Research InstituteCAASon uniform 6- year- oldChristmas Rosegrapevines. All treatments were applied in three replications and arranged in a complete randomized block designwith a single grapevine for each replication. Two different concentrations (10 mg·L– 150 mg·L– 1) of prohydrojasmonmethyl jasmonate were respectively applied to theChristmas Rosegrape berries. The aqueous solutions of both treatments and control involved 0.1% Tween-80 and 1% ethanol. The experimental grape berries were sprayed uniformly with aqueous solution twice at the beginning of veraison and 7 days later after the first application. After the first treatmentsamples were taken every 10 days until the fruit was ripe when the seeds were completely brown and the soluble solids content no longer increased. A total of 40 single berries from the topmiddle and bottom parts of randomly selected 10 grape bunches were picked and brought to the laboratory for analysis. The coloration of the grape berry was measured by a Minolta colorimeter and expressed as the value (the fruit surface light brightness) value (color component of red and green) value (color component of yellow and blue) and CIRG value (color index of red grape). Anthocyanin content in the skin extraction was measured by the pH differential method. The contents of chlorophyll a and chlorophyll b in the skin extraction were tested according to the Arnons method. The soluble solids content of the fruit was measured by a PR-101 refractometer. The titratable acid in the grape juice was titrated by 0.1 mol·L– 1 NaOH according to the Gaos method. The total phenolicsand flavonoids in the skin extraction were determined respectively according to the Jia and Meyers method. The pedicel endurable pulling force and berry endurable pressing force were measured by a Digital Push & Pull Tester. In additionthe berry weightberry lengthberry diameterand the content of vitamin C were also determined. All analyses were performed using Excel and SPSS software.

Results:

During the ripening period of the grapes that were treated or not treatedthe L valueand b value decreasedwhile the a valueand CIRG value increasedthe brightness of the grape skin declined and the coloration of the grape skin was transformed from green to red. The grape berries treated with PDJand MeJA had a higher valueCIRG value and a lower value value than the control. The highest valueCIRG value and the lowest value value were found in the grapes treated with 50 mg·L-1 PDJ. At harvestthe CIRG value of 50 mg·L-1 PDJ-MeJA- treated grapes reached 4.61 and 4.50 respectively while the CIRG value of the untreated grapes was only 4.04. During the ripening period of the grapesthe anthocyanin content rose graduallyin contrast to chlorophyll a and chlorophyll b which declined gradually in the grape skin. The content of anthocyanin in the grape skin treated with PDJand MeJA was obviously higher than the control. The 50 mg·L-1 PDJand MeJA treated grapes presented a higher an⁃ thocyanin content than the 10 mg·L-1 PDJand MeJA- treated grapes. The PDJ treatment had a better effect than the MeJA treatment under the same concentration on increasing the content of anthocyanin. At harvestthe anthocyanin content in the grape skin treated with 50 mg·L-1 PDJand 50 mg·L-1 MeJA was respectively 31.2%and 20.0% higher than the control. The content of chlorophyll a and chlorophyll b in the grape skins treated with PDJand MeJA were lower compared with the control. The PDJand MeJA treatments promoted the synthesis of anthocyanin while enhanced the degradation of chlorophyll a and chlorophyll band the coloration of the grape berry improved. The 50 mg·L– 1 PDJ treatment performed best in improving the coloration of the grape berries among all of the treatments. During the period of maturationthe soluble solids content of grapes treated with PDJand MeJA were obviously higher compared with the grapes that were untreated. The 50 mg·L-1 PDJand MeJA treatments were more effective in increasing the content of soluble solids than the 10 mg·L-1 PDJand MeJA treatments. There were no obvious differences between the treated and untreated grapes on the titratable acid content. The application of PDJand MeJA promoted the accumulation of total phenolicsand flavonoids in the skin at harvestand total phenolics in the skin treated with 50 mg·L-1 PDJand MeJA were respectively 36.4%and 29.0% higher than the control. The application of PDJand MeJA significantly enhanced the content of vitamin C in the fruithoweverthe berry weightberry length and berry diameter were not influenced. The grape treated with PDJand MeJA had a higher nutritional qualityin additionthe PDJand MeJA treatment did not have a negative effect on fruit yield. The pedicel endurable pulling force and berry endurable pressing force were not influenced by the PDJand MeJA treatment. The phenomenon of berry drop did not happen in the treated grapes. There was no difference between the treated and untreated grapes on resistance to storage and transportation.

Conclusion:

Two different concentrations of exogenous PDJand MeJA improved coloration and quality of theChristmas Rosegrape berry compared with the control. Under the same concentrationthe PDJ treatment had a better effect than the MeJA treatment on improving coloration and the quality of grapes; the 50 mg·L-1 PDJand MeJA treatment showed a better effect than the 10 mg·L-1 PDJand MeJA treatment. Among all of the treatmentsthe 50 mg·L-1 PDJ treatment was the most effective in improving the coloration and quality of grapes in the trial.

By  SUN XiaowenGAO DengtaoWEI ZhifengGUO Jingnan*CAO Meng
Zhengzhou Fruit Research InstituteCAASZhengzhou 450009HenanChina

Gibberellin Localization

The fact that the biosynthesis of active GAs (see Glossary) is a complex, multistepped process with diverse intermediates (Figure 1) makes it difficult to pinpoint the exact tissue or organ in which GAs are synthesized and localize to. Studies focusing on the spatial organization of the GA biosynthesis pathway, characterizing the expression patterns of different GA biosynthetic enzymes using GUS as a reporter, have led to several insights. First, GA biosynthesis genes are differentially expressed among different tissues, cell types, and developmental stages . Second, several members of the GA3ox family, which catalyze the final step in the synthesis of bioactive GAs, are expressed in growing and elongating shoot and root organs . Third, although there are several examples of tissues in which the expression of GA biosynthesis genes co-localizes with GA perception genes (e.g., in inflorescence meristem and developing leaves), there are also examples where these two groups do not overlap (e.g., GA-biosynthesis genes are not expressed in the aleurone cells of the endosperm but GA signaling genes are) . Such spatial separation between genes involved in GA biosynthesis and perception suggests the requirement for GA movement. Finally, levels of expression of genes constituting the GA biosynthetic pathway itself do not always coincide . For example, the expression of the late stage GA biosynthesis genes AtGA3ox1 and AtGA3ox2 in germinating embryos is spatially different from that of the early GA biosynthesis gene AtCPS. This and other examples suggest that the location of GA precursors could play an important role in regulating GA responses.

Figure 1

Figure 1. Gibberellins are Mobile Signaling Molecules in Plants. Illustration of a schematic plant (left) and gibberellin (GA) biosynthesis pathway (right). Arrows indicate documented long-distance movement of mobile GAs. The arrows are color-coded to correlate with GA forms shown in the biosynthetic pathway. Root-to-shoot and shoot-to-root movement of GA12 in Arabidopsis and GA20 in Pisum sativum (blue) . GA9 movement from the ovaries to the sepals and petals was shown in Cucumis sativus flowers (red) . Movement of GA from leaves to stem was demonstrated in tobacco and Arabidopsis and from stamens to petals in Arabidopsis and Petunia (black); in these cases, the exact form of mobile GA is not clear.

A recent study, combining mathematical and experimental approaches, compared the putative GA response, represented by the expression pattern of the SCR3 GA responsive gene (pSCR3:GUS reporter) and GA perception sites, represented by the expression pattern of GA perception proteins (GID1 and DELLA). The study demonstrated that alternating temperatures act as an instructive signal in the embryonic root tip in Arabidopsis dormant seeds . The modeling nicely showed that the process of dormancy break in the seed is defined by the distribution of the plant hormones GA and abscisic acid (ABA) . This spatial separation of ABA and GA responses suggests that crosstalk between ABA and GA is non-cell-autonomous and is controlled at the level of hormone movement between spatially separated signaling centers .

It should be noted that the observations and interpretations regarding GA localization are limited by several factors. First, the spatiotemporal resolution of the studies, using GUS reporters or mRNA expression, is relatively low. It would be constructive to increase the resolution of such studies through dynamic monitoring of fluorescent reporters. Second, only a few of the GA biosynthesis genes families, and only a few members from those families, have been analyzed so far. In order to draw a comprehensive map of the spatial distribution of GA biosynthesis, a concurrent characterization of the whole pathway will be required. Third, studies to date have usually analyzed expression of GA biosynthetic genes at the mRNA level. As it is possible that these enzymes are subjected to post-translational modifications and non-cell-autonomous movement, it will be important to examine their localization as translational fusions. The ultimate goal should be to generate specific sensors that will provide a readout for the enzyme family activity. This would allow a specific readout of the final enzymatic biochemical activity and overcome redundancies. It is reasonable to assume that GA localization is also regulated by catabolism, conjugation, and transport steps . Thus, expression patterns of GA biosynthesis genes will not necessarily enable identification of all sites of active GA localization and response.

In order to overcome several of the limitations illustrated above, a novel fluorescence resonance energy transfer-based GA biosensor (termed GPS1) was developed. The GPS1 biosensor, constructed by fusing GID1 variants to the DELLA N-termini, showed an increased emission ratio in response to nanomolar concentrations of GA4. With the exception of a few limitations such as nonreversible response to GA4, phenotypic hypersensitivity to a GA biosynthesis inhibitor, and a limited response to GA3 and GA1, this biosensor should be a useful new tool for identifying GA response sites. For example, GPS1 revealed that GA response is higher in the elongation zone compared with the root meristematic zone. GA localization correlated with cell length when GA4 was exogenously applied, suggesting that rapid transport or catabolism of GA in the root may generate local GA gradients independently of GA biosynthesis. In addition, the GPS1 sensor indicated that high levels of GA4 in the elongating hypocotyl depend on darkness . GPS1 should find broad utility in exploration of GA distribution and transport mechanisms and is expected, for example, to shed light on GA distribution in known and novel GA transporter loss-of-function and gain-of-function lines reported for the nitrate transporter 1/peptide transporter family (NPF) and SWEET families  (further discussed below).

A different approach to address the question of GA distribution and accumulation sites utilized fluorescently labeled versions of GA3 and GA4 (termed GA-Fl). Combining imaging of GA-Fl localization with information on transporter expression levels and genetics showed that the TEMPRANILLO (TEM) proteins play an essential role not only in GA biosynthesis but also in regulating GA distribution in the mesophyll, which, in turn, regulates epidermal trichome formation . In roots, GA-Fl accumulated specifically in the elongating endodermal cells of Arabidopsis roots. The localization of GA-Fl in the elongating cells is consistent with GFP-RGA levels and with other studies indicating that GA activity is necessary for root elongation and gravitropic response , but only partially overlaps with GPS1 signal, which was not restricted to the endodermis. Since GA-Fl is highly specific to NPF3 , it is possible that it represents only a subset of GA forms. Alternatively, it is possible that GPS1 and GA-Fl report on GA levels on different sites within the cell; whereas GPS1 mainly responds to nuclear GA4 levels, the fluorescent GA4 reports on transport and localization of exogenously applied GA that eventually localizes to the vacuole. Since the GA response was shown to be restricted to the root endodermis cell layer,  it will be important to evaluate the distribution of active GA and its precursors at a cellular resolution, as has been successfully carried out for the plant hormones auxin and cytokinin .

Cells entering the elongation zone increase in length by approximately 10-fold over 5 hours. Such a rapid expansion is expected to result in a rapid intracellular dilution of GA, practically reducing its effective concentration. Modeling of this process suggests a correlation between GA distribution and root cell growth, and the study authors posit that cellular GA levels decrease at the elongation zone due to cytosolic dilution . Independent analyses of the GPS1 sensor response and GA-Fl distribution indicate that GA levels are higher in the root elongation zone compared with the meristematic zone; therefore, GA is probably either synthesized locally or imported from surrounding tissues to compensate for dilution.

The Plant Hormone Gibberellin

Gibberellin (GA) was first identified in the pathogenic fungus Gibberella fujikuroi, which causes a disease in rice called ‘foolish-seedling’.

By producing large quantities of GA, the plants become long and slender, are incapable of supporting their own weight, and are chlorotic and partially infertile .

Further research established GA as a hormone that is essential for many developmental processes in plants, among them are seed germination; organ elongation and expansion through cell growth; trichome development; transition from vegetative to reproductive growth; and flower, seed, and fruit development .

GA manipulation in agriculture is common practice; the best-known contribution of GA manipulations to agriculture is the introduction of dwarfing alleles into staple crops. This manipulation resulted in one of the cornerstones of the so-called ‘green revolution’ and led to a massive increase in global wheat and rice yields. Identification of the genes responsible for these traits showed that the encoded proteins interfere with the action or production of GA .

Among more than 130 GAs identified in plants, fungi, and bacteria to date, only a subset, namely GA1, GA3, GA4, and GA7 are thought to function as bioactive hormones .

Additional forms of GA that exist in plants are precursors of the bioactive forms or deactivated metabolites .

Effects of gibberellin A3 and cytokinins on natural and post‐harvest, ethylene‐induced pigmentation of Satsuma mandarin peel

Natural and post-harvest ethylene-induced pigment changes in the rind of Satsuma mandarin (Citrus unshiu Marc.) fruits respond differently to the exogenous application of growth regulators.

Both gibberellin A3 and the synthetic cytokinins N6-benzyladenine and kinetin opposed the ethylene-induced chlorophyll destruction, while the loss of chlorophyll during natural maturation was retarded by the gibberellin but not by the cytokinins.

This different behaviour suggests that ethylene may not be playing a central role in the endogenous control of ripening.

Carotenoid accumulation during natural maturation is apparently controlled through a different mechanism than chlorophyll loss since it is reduced both by the cytokinins and gibberellin A3.

Kinetin and gibberellin A3 increased to a similar extent the accumulation of reducing sugars and free amino acids, and reduced that of non-reducing sugars in the peel during natural maturation.

Their differential effect on chlorophyll loss may not be explained through their effects on sugar accumulation.

Gibberellic acid

Gibberelin Gibberellic acid (also called Gibberellin A3, GA, and GA3) is a hormonefound in plants and fungi .

Its chemical formula is C19H22O6. When purified, it is a white to pale-yellow solid. Plants in their normal state produce large amounts of GA3.

It is possible to produce the hormone industrially using microorganisms. Nowadays, it is produced by submerse fermentation, but this process presented low yield with high production costs and hence higher prices.

One alternative process to reduce costs of the GA3 production is Solid-State Fermentation (SSF) that allows the use of agro-industrial residues.

Gibberellic acid is a simple gibberellin, a pentacyclic diterpene acid promoting growth and elongation of cells. It affects decomposition of plants and helps plants grow if used in small amounts, but eventually plants develop tolerance to it. GA stimulates the cells of germinating seeds to produce mRNA molecules that code for hydrolytic enzymes.

Gibberellic acid is a very potent hormone whose natural occurrence in plants controls their development. Since GA regulates growth, applications of very low concentrations can have a profound effect while too much will have the opposite effect. It is usually used in concentrations between 0.01 and 10 mg/L.

GA was first identified in Japan in 1926, as a metabolic by-product of the plant pathogen Gibberella fujikuroi (thus the name), which afflicts rice plants; fujikuroi-infected plants develop bakanae (“foolish seedling”), which causes them to grow so much taller than normal that they die from no longer being sturdy enough to support their own weight.Gibberellins have a number of effects on plant development.

They can stimulate rapid stem and root growth, induce mitotic division in the leaves of some plants, and increase seed germination rate.Gibberellic acid is sometimes used in laboratory and greenhouse settings to trigger germination in seeds that would otherwise remain dormant.

It is also widely used in the grape-growing industry as a hormone to induce the production of larger bundles and bigger grapes, especially Thompson seedless grapes.

In the Okanagan and Creston valleys, it is also used as a growth replicator in the cherry industry.

It is used on Clementine Mandarin oranges, which may otherwise cross-pollinate with other citrus and grow undesirable seeds.

Applied directly on the blossoms as a spray, it allows for Clementines to produce a full crop of fruit without seeds.