Differential effects of postharvest application of ethylene inhibitors on guava stored under ambient conditions

Aim: To assess the efficiency of ethylene synthesis and action inhibitors on postharvest shelf life of guava fruits under ambient conditions. Methodology: Mature green guava fruits (P. guajava L. cv. Arka Mridula) were harvested and treated with ethylene inhibitors. Various physiological, physical and nutritional changes of the treated fruits in comparison with untreated ones were monitored during ambient temperature storage. Multivariate analysis approach was used for interpreting the data on quality changes during storage. Results: Significant positive correlation (p<0.01) was observed among rates of ethylene production, respiration, ripening and Hunter’s a* value. Biplot from principal component analysis of eleven parameters showed that 1-MCP (500 ppb) treated fruits were grouped together with freshly harvested fruits throughout storage period, and proved superior over other treatments in delaying ripening and quality maintenance. Seven days stored 3.0 mM Salicylic acid and 1.5 mM Sodium nitroprusside treated fruits were grouped together with 5 days stored control fruits, suggesting their effectiveness in extending the shelf life by additional two days. Interpretation: Postharvest application of 1-MCP on guava fruits can extend the shelf life by four days when compared with control. Even PCA indicated that the study of major ripening attributes (L*, a*, b*, Hue, texture, acidity, ethylene rate and respiration rate) was quite sufficient to know the ripening status of the fruits.

Transcriptional and Hormonal Responses in Ethephon-Induced Promotion of Femaleness in Pumpkin

The number and proportion of female flowers per plant can directly influence the yield and economic benefits of cucurbit crops. Ethephon is often used to induce female flowers in cucurbits. However, the mechanism through which it affects floral sex differentiation in pumpkin is unknown. We found that the application of ethephon on shoot apical meristem of pumpkin at seedling stage significantly increased the number of female flowers and expedited the appearance of the first female flower. These effects were further investigated by transcriptome and hormone analyses of plants sprayed with ethephon. A total of 647 differentially expressed genes (DEGs) were identified, among which 522 were upregulated and 125 were downregulated. Gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) analysis indicated that these genes were mainly enriched in plant hormone signal transduction and 1-aminocyclopropane-1-carboxylate oxidase (ACO). The results suggests that ethylene is a trigger for multiple hormone signaling, with approximately 4.2% of the identified DEGs involved in ethylene synthesis and multiple hormone signaling. Moreover, ethephon significantly reduced the levels of jasmonic acid (JA), jasmonoyl-L-isoleucine (JA-ILE), and para-topolin riboside (pTR) but increased the levels of 3-indoleacetamide (IAM). Although the level of 1-aminocyclopropanecarboxylic acid was not changed, the expression of ACO genes, which code for the enzyme catalyzing the key rate-limiting step in ethylene production, was significantly upregulated after ethephon treatment. The results indicate that the ethephon affects the transcription of ethylene synthesis and signaling genes, and other hormone signaling genes, especially auxin responsive genes, and modulates the levels of auxin, jasmonic acid, and cytokinin (CK), which may together contribute to femaleness.

Effects of Exogenous Regulation of Ethylene and Abscisic Acid on Grain-Filling and Endosperm PCD of Wheat Under Drought Stress After Anthesis

Although studies have shown that grain-filling and programmed cell death of wheat endosperm are affected by drought stress, which is closely related to ethylene and abscisic acid.The mechanism of ethylene and abscisic acid regulate grain-filling and endosperm PCD under drought stress is remains unclear. In this study, we regulated the production of ethylene and abscisic acid in wheat grains under drought stress at filling stage by chemicals. The results showed that spraying ethylene synthesis inhibitor enhanced endosperm cell viability, delayed nuclear deformation, and decreased ACC content. Compared with the CK, the CN significantly decreased the DNA hydrolase activity and significantly increased the DNA content. In addition, the CN treatment reduced the expression of four genes related to ethylene receptors (ers1, ers2 etr1, etr2) and increase the expression of dad1. Under CN treatment, the process of endosperm PCD was delayed, the duration of high grouting rate was prolonged, and the grain weight was increased, in contrast, the opposite result was obtained after spraying abscisic acid synthesis inhibitor. The production of abscisic acid and ethylene in grains determines the fate of endosperm cells. A new model of artificial regulation of abscisic acid and ethylene, delaying endosperm PCD process and increasing grain weight under post-anthesis drought was proposed.

OsNAC2 Is Involved in Multiple Hormonal Pathways to Mediate Germination of Rice Seeds and Establishment of Seedling

The germination of seeds and establishment of seedling are the preconditions of plant growth and are antagonistically regulated by multiple phytohormones, e.g., ethylene, abscisic acid (ABA), and gibberellic acid (GA). However, the interactions between these phytohormones and their upstream transcriptional regulation during the seed and seedling growth in rice remain poorly understood. Here, we demonstrated a rice NAC (NAM-ATAF-CUC) transcription factor, OsNAC2, the overexpression of which increases the ethylene sensitivity in rice roots during the seedling period. Further study proved that OsNAC2 directly activates the expressions of OsACO and OsACO3, enhancing ethylene synthesis, and then retards seedling establishment. Moreover, OsNAC2 delays the germination of seeds and coleoptile growth through the ABA pathway instead of the ethylene and GA pathway, by targeting the promoters of OsNCED3, OsZEP1, and OsABA8ox1. We also found that OsNAC2 regulates downstream targets in a time-dependent manner by binding to the promoter of OsKO2 in the seedling period but not in the germination stage. Our finding enriched the regulatory network of ethylene, ABA, and GA in the germination of rice seeds and seedling growth, and uncovered new insights into the difference of transcription factors in targeting their downstream components.

Emission Patterns of Esters and Their Precursors Throughout Ripening and Senescence in ‘Redchief Delicious’ Apple Fruit and Implications Regarding Biosynthesis and Aroma Perception

The volatile profile of ‘Redchief Delicious’ apple (Malus ×domestica Borkh.) fruit was evaluated at 18 time points from 3 weeks before to 8 weeks after onset of autocatalytic ethylene production to capture the dynamics associated with development from mature green to senescent fruit. Minor amounts of ester production began several days before the onset of ethylene production. Ester production rose rapidly as internal ethylene levels increased beyond 22 nmol·L−1 (0.5 µL·L−1). Peak ester production roughly coincided with maximum ethylene synthesis, declining thereafter. Ester production was further evaluated according to the acid- (alkanoate) and alcohol- (alkyl) derived portions of the ester. The maximum rate of production for a given ester tended to occur later in development as the chain length of the alcohol-derived portion declined. The production rate for many esters paralleled the rate of emanation of their respective alcohol substrates, suggesting that availability of the alcohols limits ester production more than availability of the acid substrates. Combining production rates with sensory descriptors and human sensitivity to individual volatiles permitted approximations of aroma sensations likely engendered by the fruit throughout ripening. Overripe and alcoholic sensations are predicted to increase 2 weeks after the initiation of ripening in response to an increase in the production of ethyl esters. Acetate esters predominated, comprising 50% to 80% of esters throughout maturation and ripening, indicating that the substrate acetyl-CoA may be at saturating levels for alcohol acyl transferase (AAT) at the final step of ester formation. Acetate feeding did not enhance ester production, although label from 13C-acetate was extensively incorporated into esters. The data are consistent with the action of multiple AAT isozymes differing in activity and substrate preference. Incorporation of labeled 13C-acetate into precursors of esters, alcohols, and acids, reflected ester biosynthesis via 1- and 2-carbon chain elongation pathways in ripening ‘Redchief Delicious’ apple fruit.

Desiccation-driven senescence and its repression in Xerophyta schlechteri are regulated at extremely low water contents

Vegetative desiccation tolerance, the ability to survive loss of over 90% of cellular water, is an extremely rare trait in Angiosperms. Xerophyta schlechteri survives such extreme water deficit by entering prolonged quiescence and suppressing drought-induced senescence in most of the leaf area, except the apical tip. Information on the molecular regulation of senescence in such plants is scarce and this is the first study to investigate such regulation in senescing and non-senescing tissues of the same leaf. Genome-wide RNA sequencing enabled comparison of senescent and non-senescent tissues during desiccation and early rehydration, establishment of the water content range in which senescence is initiated and identification of molecular mechanisms employed to bring about cellular death. Senescence-associated genes (XsSAG) specific to this species were identified and two potential regulatory sites were enriched in regions upstream to these XsSAGs, allowing us to create a model of senescence regulation in X. schlechteri based on homology with known Arabidopsis senescence regulators. We hypothesise that desiccation-driven senescence occurs as a result of a convergence of signals around MAPK6 to trigger WRKY-mediated ethylene synthesis and XsSAG expression, not unlike aging and stress-related senescence in Arabidopsis, but at remarkably lower water contents (<35% RWC).

Proteomic analysis reveals key proteins involved in ethylene-induced adventitious root development in cucumber (Cucumis sativus L.)

The mechanisms involved in adventitious root formation reflect the adaptability of plants to the environment. Moreover, the rooting process is regulated by endogenous hormone signals. Ethylene, a signaling hormone molecule, has been shown to play an essential role in the process of root development. In the present study, in order to explore the relationship between the ethylene-induced adventitious rooting process and photosynthesis and energy metabolism, the iTRAQ technique and proteomic analysis were employed to ascertain the expression of different proteins that occur during adventitious rooting in cucumber (Cucumis sativus L.) seedlings. Out of the 5,014 differentially expressed proteins (DEPs), there were 115 identified DEPs, among which 24 were considered related to adventitious root development. Most of the identified proteins were related to carbon and energy metabolism, photosynthesis, transcription, translation and amino acid metabolism. Subsequently, we focused on S-adenosylmethionine synthase (SAMS) and ATP synthase subunit a (AtpA). Our findings suggest that the key enzyme, SAMS, upstream of ethylene synthesis, is directly involved in adventitious root development in cucumber. Meanwhile, AtpA may be positively correlated with photosynthetic capacity during adventitious root development. Moreover, endogenous ethylene synthesis, photosynthesis, carbon assimilation capacity, and energy material metabolism were enhanced by exogenous ethylene application during adventitious rooting. In conclusion, endogenous ethylene synthesis can be improved by exogenous ethylene additions to stimulate the induction and formation of adventitious roots. Moreover, photosynthesis and starch degradation were enhanced by ethylene treatment to provide more energy and carbon sources for the rooting process.

Application of 1-Methylcyclopropene (1-MCP) for Delaying the Ripening of Banana: A Review

1- Methylcyclopropene (1-MCP) has been identified as a safe chemical tested successfully in extending shelf life while maintaining quality of plant products. 1-MCP, at very low concentrations, usually blocks ethylene receptors and then inhibits the action of ethylene delaying further ripening and senescence. Several studies have been conducted elsewhere for delaying ripening of different banana cultivars such as Cavendish, Prata, Tella Chakkerakeli, Beragan and Kolikuttu. Physiological reactions related with ripening of banana are delayed by inhibition of ethylene perception, while ethylene synthesis of banana fruit can be regulated at suppressed levels of ACS and ACO by 1-MCP. The effectiveness of 1-MCP on bananas varies with the maturity of the fruit. Fumigation, the conventional application method, has some limitations, particularly long exposure duration, uneven ripening and green ripening in bananas. Application of 1-MCP in aqueous form is recently developed to minimize these limitations. Micro-bubbling and controlled release packaging technologies are effective tools of application of 1-MCP on bananas. This review compiles and critically analyses the existing knowledge on the technological use of 1-MCP, clarifies inconsistencies in different publications.

Reduced ethylene synthesis of mangoes under high CO2 atmosphere storage

. High CO2 atmospheres have been reported to be accountable for slower ripening processes of many fruit species. In modified or controlled atmosphere storage of mangoes (Mangifera indica L.) delayed ripening is attributed to the effects of CO2 on ethylene biosynthesis, which is reduced under CO2 concentrations beyond 10%. In the present work the objective was to determine if those elevated CO2 atmospheres on ethylene synthesis could be attributed to the action of CO2 upon ACC oxidase. Mature green or tree ripe `Tommy Atkins` mangoes were, in four experiments, held in a flow through system of either 10 or 25% CO2 mixed to 5% O2 or only air for 14 or 21 days at 5, 8 or 12°C. Mangoes in the 25% CO2 atmosphere did not produce detectable levels of ethylene, whereas under 10% CO2 the production rates were significantly suppressed at 5 or 8°C. However, 1-aminocyclopropane-1-carboxylic acid (ACC) concentrations in mango mesocarp tissue at retrieval from storage were similar to the air controls and ACC synthase activity was not completely inhibited. The direct effects of CO2 concentrations on ACC oxidase activity is to be considered the most important factor in inhibiting ethylene biosynthesis of mangoes under 25% CO2 atmospheres.