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Floral senescence or petal abscission that determine cut flower quality and longevity are primarily caused by the regulation of endogenous ethylene and perception of endogenous and exogenous ethylene in floral organs (such as the petals and gynoecium), in ethylene-sensitive species. Several attempts have been made to prolong flower quality and longevity using silver ions and other chemicals that inhibit ethylene production and perception in floral organs. Among the available compounds, 1-methylcyclopropene (1-MCP) has been increasingly used as ethylene-action/perception inhibitor because of its ability to inhibit ethylene action/perception and it is environmentally safe. Although 1-MCP has been used in several cut flower crops for about 25 years, there has been no review yet that critically emphasizes the benefits or difficulties of using this compound for the prolongation of cut flower quality and longevity. Here, we outline the role of 1-MCP in inhibiting ethylene action/perception and petal senescence in cut flowers through the blocking of receptor binding sites, and we discuss how various factors affecting efficacy of 1-MCP (such as concentration, treatment time and temperature, genotype, and flower stage) are involved in the achievement of flower longevity. Moreover, we highlight the advantages of applying nonvolatile and liquid 1-MCP formulation types, as opposed to using the conventional 1-MCP treatment (powder formulation type). We expect that this review will provide useful information for the future utilization of 1-MCP for the maintenance of cut flower longevity.

Editing of ACO genes involved in ethylene biosynthesis pathway reduces ethylene production in petunia seeds and inhibits seed germination. Ethylene production in the seeds of Petunia hybrida cv. ‘Mirage Rose’ was associated with expression of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACO) genes (PhACO1, PhACO3, and PhACO4). Suppression of their expression by ethylene inhibitor silver thiosulphate (STS) significantly reduced ethylene production and inhibited seed germination. When it was combined with ethylene precursor ACC, ethylene production was re-promoted via activation of the genes and higher seed germination was restored. This was confirmed using the mutants editing the genes and WT. In the present study, compared with wild type plants, three different mutants (phaco1, phaco3, and phaco4) showed significantly decreased germination percentages as well as delayed germination time and seedling growth. These reductions were associated with lighter seed weight, lower ACO transcript levels, and lower ethylene production in mutants. Inhibited seed germination owing to reduced ethylene production was further verified by the supplementation of exogenous ACC and gibberellic acid (GA3) to growth medium, which restored high seed germination activity in all mutants via enhanced ethylene production. In this study, we reported a key regulatory role of ethylene in seed germination mechanisms in petunia. Further, we highlighted on need to consider the negative effects of ethylene reduction in seed germination and plant growth when editing genes in the ethylene biosynthesis pathway for the maintenance of postharvest fruit, vegetable, and flower quality.

Global climate change results in frequent occurrences and/or long durations of abiotic stress. Field grown plants are affected by abiotic stress, and they modulate ethylene in response to abiotic stress exposure and use it as a signaling molecule in stress tolerance mechanisms. However, frequent occurrences and/or long durations of stress conditions can cause plants to induce ethylene levels higher than their thresholds, resulting in a reduction of plant growth and crop productivity. The use of plant growth-promoting bacteria (PGPB) that produce 1-aminocyclopropane-1-carboxylate (ACC) deaminase has increased in various plant species to ameliorate the deleterious effects of stress-induced ethylene and promote plant growth despite abiotic stress conditions. Unfortunately, there are restrictions that limit the use of ACC deaminase-producing PGPB to protect plants from abiotic stresses. This review describes how abiotic stress induces ethylene and how stress-induced ethylene adversely affects plant growth. In addition, this review emphasizes the importance of the compatibility of PGPB strains and specific host plants and ACC deaminase activities in the reduction of stress ethylene and the promotion of plant growth, based on the research published in the last 10 years. Moreover, due to the restrictions in PGPB use, this review highlights the potential generation of transgenic plants expressing the AcdS gene that encodes the ACC deaminase enzyme as a substitute for PGPB in the future to support and uplift agricultural sustainability and food security globally.

Abiotic stresses, such as heat, drought, salinity, low temperature, and heavy metals, inhibit plant growth and reduce crop productivity. Abiotic stresses are becoming increasingly extreme worldwide due to the ongoing deterioration of the global climate and the increase in agrochemical utilization and industrialization. Plants grown in fields are affected by one or more abiotic stresses. The consequent stress response of plants induces reactive oxygen species (ROS), which are then used as signaling molecules to activate stress-tolerance mechanism. However, under extreme stress conditions, ROS are overproduced and cause oxidative damage to plants. In such conditions, plants produce anthocyanins after ROS signaling via the transcription of anthocyanin biosynthesis genes. These anthocyanins are then utilized in antioxidant activities by scavenging excess ROS for their sustainability. In this review, we discuss the physiological, biochemical, and molecular mechanisms underlying abiotic stress-induced anthocyanins in plants and their role in abiotic stress tolerance. In addition, we highlight the current progress in the development of anthocyanin-enriched transgenic plants and their ability to increase abiotic stress tolerance. Overall, this review provides valuable information that increases our understanding of the mechanisms by which anthocyanins respond to abiotic stress and protect plants against it. This review also provides practical guidance for plant biologists who are engineering stress-tolerant crops using anthocyanin biosynthesis or regulatory genes.

In this study, we sought to optimize the isolation of protoplasts from chrysanthemums by manipulating the mannitol and cellulase levels, the incubation period, and the purification method, followed by the conversion of the protoplasts into calli and shoots. A high protoplast yield was achieved using 0.5 M mannitol, 1.5% cellulase, and a 4 h incubation period. Cell wall regeneration was observed after 3 days, with the first cell division occurring approximately 4–5 days after culturing. The addition of sucrose to the culture media was more beneficial than glucose; in sucrose media the protoplasts grew more rapidly and successfully reached the colony and microcalli stage. The addition of activated charcoal to the culture improved colony and microcalli formation. Greater proliferation of microcalli was also achieved using solid Murashige & Skoog (MS) media supplemented with 1 mg l−1 6-Benzylaminopurine (BA) and 2 mg l−1 Naphthaleneacetic acid (NAA). The calli produced shoots THE on media supplemented with 2 mg l− 1 BA and 0.5 mg l−1 NAA. These findings could facilitate further chrysanthemum protoplast-based research. The regeneration of chrysanthemum protoplasts into whole plants is difficult due to the recalcitrant nature of these plants and because of their genotype-dependent response. This study is appropriate for protoplast isolation and callus formation of Chrysanthemum cv. White ND, and it also achieved regenerating chrysanthemum protoplasts-derived calli into whole plants.

Abiotic stress induces the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) in plants, which consequently enhances ethylene production and inhibits plant growth. The bacterial ACC deaminase enzyme encoded by theacdSgene reduces stress-induced ethylene production and improves plant growth in response to stress. In this study, overexpression ofacdSinPetunia hybrida(‘Mirage Rose’) significantly reduced expression of the ethylene biosynthesis gene ACC oxidase 1 (ACO1) and ethylene production relative to those in wild type (WT) under various abiotic stresses (cold, drought, and salt). The higher reduction of stress-induced ethylene in the transgenic plants, which was due to the overexpression ofacdS, led to a greater tolerance to the stresses compared to that in the WT plants. The greater stress tolerances were proven based on better plant growth and physiological performance, which were linked to stress tolerance. Moreover, expression analysis of the genes involved in stress tolerance also supported the increased tolerance of transgenics relative to that with the WT. These results suggest the possibility thatacdSis overexpressed in ornamental plants, particularly in bedding plants normally growing outside the environment, to overcome the deleterious effect of ethylene on plant growth under different abiotic stresses. The development of stress-tolerant plants will be helpful to advance the floricultural industry.

The efficacy of 1-methylcyclopropene (1-MCP) in maintenance of apple fruit quality can differ depending on apple cultivar, ethylene content at harvest, 1-MCP concentration, the interval between harvest and 1-MCP application, and the number of applications. In this study, we investigated whether the 1-MCP concentration and its application frequency differently affected fruit quality attributes of the two new apple cultivars ‘Arisoo’ and ‘Picnic’. The fruits were treated with 1-MCP (as single or double treatments) at the rate of 0 μL L−1 (control), 0.5 μL L−1, 1 μL L−1, 0.5 + 0.5 μL L−1, and 1 + 1 μL L−1 for 18 h, and they were stored at 0 °C up to six months. Comparatively, the fruit qualities of 1-MCP treated fruits were higher than that of the control during cold storage, with a higher suppression of internal ethylene content and a slower reduction of titratable acidity in 1-MCP treatments than the controls throughout the cold storage in both cultivars, regardless of the concentration and number of applications. Reduction of fruit firmness and soluble solid contents were maintained by single application of 0.5 μL L−1 1-MCP in ‘Arisoo’ apple, while double application of 0.5 + 0.5 μL L−1 was needed in ‘Picnic’ cultivar. The effective concentration for weight-loss reduction was found to be the single application of 1 μL L−1 1-MCP in both ‘Arisoo’ and ‘Picnic’. Conclusively, 1-MCP as single treatment at the rate of 0.5 μL L−1 could be sufficient in inhibiting ethylene action and maintaining fruit quality losses during cold storage, particularly in ‘Arisoo’. However, double application of 1-MCP might be necessary for some quality attributes in ‘Picnic’ apple.

This study investigated whether ethylene is involved in the stem-bending mechanism of three different snapdragon cultivars ‘Asrit Red’, ‘Asrit Yellow’, and ‘Merryred Pink’, by treating their cut stems with an ethylene-releasing compound (ethephon), an ethylene-action inhibitor [silver thiosulfate (STS)], and distilled water (as the control). Ethephon completely prevented stem bending in all cultivars, whereas STS exhibited a higher bending rate compared with the control. The bending rates were influenced by several factors, such as the degree of stem curvature, relative shoot elongation, ethylene production, and lignin content, indicating their involvement in the stem-bending mechanism of the cultivars. The analysis of the expression of genes involved in the ethylene and lignin biosynthetic pathways also supported the importance of lignin and ethylene in the stem-bending mechanism. Taken together, as ethephon completely prevented stem bending of the three snapdragon cultivars, this study suggested that ethylene acts as a negative regulator of the stem-bending mechanism of snapdragon cultivars, and the information will be valuable for the prevention of stem bending in other commercially important ornamental flowers.

Chionanthus retusus is a small deciduous tree that is widely used in landscaping due to its beautiful white spring flowers and ornamental value. Conventional propagation through seeds requires one to two years of breaking dormancy. The objective of this study was to determine the conditions of in vitro germination in C. retusus. In vitro embryo culture was carried out to investigate the effects of six factors: basal media (McCown Woody Plant Medium (WPM) and Murashige and Skoog (MS)); plant growth regulators (different combinations and concentrations of naphthaleneacetic acid (NAA), 6-Benzylaminopurine (BA), and gibberellic acid (GA₃)); embryo age (collected weekly beginning 36 days after fruit setting); low temperature pretreatment (storing 4°C for 1, 2, 3, and 4 weeks); coconut additives (100, 200, and 300 ml·L-1); and genotype (grouping plants depending on their flowering nature). The basal medium used in this study was WPM with 2 mg·L-1-1 GA₃, 20 g·L-1 sucrose, and 6 g·L-1 Agar. WPM medium mixed with GA₃, resulted in higher germination rate as compared to when using a combination of auxin and cytokinin. GA₃ at 2 mg·L-1 was the most effective of all combinations and concentrations of PGRs. WPM medium with 2 mg·L-1 GA₃ resulted in better and faster germination (75.93%). Embryos collected at 57 days after fruit setting had the highest percent of germinated seeds (87.04%) while low-temperature pretreatment of fruits at 4°C for two weeks produced the highest germination (95.37%). These results of this study could be an open ground for development of an efficient protocol for commercial production of the ornamental tree.

The generation of transgenic floricultural crops for flower color modification requires a transgene that enhances anthocyanin accumulation and a flower-specific promoter with stable expression throughout flowering stage. Here, the anthocyanin regulatory R2R3-MYB transcription factor (TF) RsMYB1 was placed under the control of the stable flower-specific promoter (InMYB1) to enhance anthocyanin accumulation in Petunia hybrida cv. Mirage Rose. RsMYB1 overexpression with the flower-specific promoter enhanced anthocyanin accumulation only in floral tissues via the upregulation of key anthocyanin biosynthetic genes. The target gene introgression to another Petunia hybrida cv. White Hawaiian lacking anthocyanins also changed the flower color from white to intense pink in the F1 hybrids by upregulating the biosynthetic genes. Target gene inheritance in the F2 hybrids also produced diverse flower colors, redder than those of non-inheritance F2 hybrids. RsMYB1 overexpression using the flower-specific promoter (InMYB1) enhanced anthocyanin levels in the petals of transgenic Petunia and its related hybrids. Thus, this system can be used as a promising tool for intensifying the flower color of other commercially important floricultural crops. In addition, the obtained F2MW11 and F2MW12 lines are potential commercial cultivars for the floriculture and landscape industries due to its attractive flower color pattern.

This study was conducted to investigate the efficacy of shoot regeneration from different leaf types (normal leaves and vitrified leaves) from three different carnation cultivars &lsquo, Kumbuyl&rsquo, &lsquo, Denev&rsquo, and &lsquo, Jinju&rsquo, using different combinations of 3-indole butyric acid (IBA) and thidiazuron (TDZ) concentrations. The shoot tips cultured on Murashige and Skoog (MS) basal media (Type 1 media) produced normal leaves, while those cultured-on media supplemented with plant growth regulators and/or vitamin (Type 2 media and Type 3 media) produced vitrified leaves for all cultivars. Culture of normal leaf segments on MS medium containing different combinations of IBA and TDZ concentrations induced callus in all treatments, however, the callus was unable to induce shoots and finally became necrotic. In contrast, no callus induction was observed in the control (hormone-free treatment). When vitrified leaf segments underwent the same treatments, shoots were induced from the vitrified leaves (derived from Type 2 media) but were unhealthy and gradually died, whereas those induced from Type 3 media were vitrified and healthy. The optimal combination for the best shoot regeneration and number of shoots per explants varied depending on the genotypes used. The vitrified shoots induced from the leaves of Type 3 media transformed into normal shoots and survived well under greenhouse conditions. According to the results of random amplified polymorphic DNA (RAPD) analysis, the banding patterns of twelve primers that were detected in vitrified leaf-induced normalized shoots were identical to those of normal in vitro grown plants, indicating that no genetic variation had occurred during the procedure. Taken together, this study indicates that vitrified leaves can be used for shoot regeneration of recalcitrant carnation cultivars, regardless of the genotypes and types of vitrified leaves. However, as the number of shoots per explants was still low, further investigation is warranted to obtain a more efficient shoot regeneration protocol for genetic transformation of the cultivars.

This review contains functional roles of MYB transcription factors in the transcriptional regulation of anthocyanin biosynthesis in horticultural plants. This review describes potential uses of MYB TFs as tools for metabolic engineering for anthocyanin production. Anthocyanins (ranging from red to blue) are controlled by specific branches of the anthocyanin biosynthetic pathway and are mostly visible in ornamentals, fruits, and vegetables. In the present review, we describe which R2R3-MYB transcription factors (TFs) control the transcriptional regulation of anthocyanin structural genes involved in the specific branches of the anthocyanin biosynthetic pathway in various horticultural plants (e.g., ornamentals, fruits, and vegetables). In addition, some MYBs responsible for anthocyanin accumulation in specific tissues are described. Moreover, we highlight the phylogenetic relationships of the MYBs that suppress or promote anthocyanin synthesis in horticultural crops. Enhancement of anthocyanin synthesis via metabolic genetic engineering of anthocyanin MYBs, which is described in the review, is indicative of the potential use of the mentioned anthocyanin-related MYBs as tools for anthocyanin production. Therefore, the MYBs would be suitable for metabolic genetic engineering for improvement of flower colors, fruit quality, and vegetable nutrients.

We established an in vitro system to investigate transcription levels of the RsMYB1 gene expressed in T2 20-day-old transgenic Petunia plants (three independent lines: PhRs1, PhRs2, and PhRs3), and the association between those transcription levels and anthocyanin production at various pH values (3.0 to 8.0) for a period of 10 days. All the lines treated with pH 5.0-7.0 exhibited increased anthocyanin content and delays in growth compared to the wild-type (WT) seedlings. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis confirmed that the enhancement of anthocyanin production in the transgenic lines was due to the upregulation of RsMYB1 transcription at various pH values. The results suggest that pH value can control expression of RsMYB1 which is associated with anthocyanin production.

Despite an increase in the use of 1-methylcyclopropene (1-MCP) to delay fruit softening, the role of 1-MCP in the modification of cell wall pectin to maintain apple fruit firmness during storage is poorly understood. Hence, in this study, we investigated whether 1-MCP treatment delayed fruit softening through pectin modification, in “Hwangok” and “Picnic” apple cultivars, stored up to six months at 0 °C. In both cultivars, 1-MCP-treated apples maintained firmness and exhibited lower internal ethylene concentrations compared with untreated fruit. The depolymerization of pectin in all pectin fractions was attenuated in 1-MCP-treated fruit compared with untreated fruit. In addition, a peak location shift was observed in the molecular mass profile of untreated fruit. Neutral sugar contents (arabinose and galactose), which typically change as fruit ripen, were effectively maintained in 1-MCP-treated fruit. The activity of four important enzymes involved in pectin modification (exo-polygalacturonase, pectin methylesterase, β-galactosidase, and α-L-arabinofuranosidase) was reduced in treated fruit compared to the control. Furthermore, 1-MCP treatment reduced the expression of pectin-degrading candidate genes (MdPG1, MdPME1, Mdβ-GAL1, Mdβ-GAL2, and Mdα-ARF2). This study suggests that 1-MCP maintains cell wall pectin and delays the softening of the two apple cultivars by reducing the solubilization of polyuronides and neutral sugars, and limiting the activities of cell wall hydrolysis.

Flower senescence in three carnation cultivars (‘Koba Kabana,’ ‘Purple Sky,’ and ‘Lufa’) was associated with increased ethylene production in floral tissues (petals and gynoecia). Treatment with silver nanoparticles (NAg) significantly reduced ethylene production in petals and gynoecia and significantly delayed petal senescence compared with that in control (untreated) flowers, as indicated by higher relative fresh weight. Gene expression analyses performed on petals and gynoecia from initial flower opening through senescence indicated that the expression levels of ethylene biosynthesis genes (ACS1 and ACO1) and a petal senescence-related gene (CP1) were significantly higher in control flowers than in NAg-treated flowers. In contrast, the expression level of the petal senescence inhibitor gene CPi was more upregulated in NAg-treated flowers than in control flowers. The expression levels of EIL1/2, ERS2, and EBF1 were significantly higher in control flowers, in which ethylene was highly produced, than in NAg-treated flowers, whereas the expression levels of CTR1 and ETR1 were lower. This indicates that EIL1/2, ERS2, and EBF1 positively regulate and CTR1 and ETR1 negatively regulate the ethylene signal transduction pathway in carnations. In addition, NAg can inhibit the expression of these positive regulator genes in carnations. Therefore, this study suggests that NAg is helpful in significantly repressing ethylene production and delaying petal senescence in carnations via the suppression of ethylene biosynthesis genes, a petal senescence-related gene, and genes positively regulating ethylene signaling in petals and gynoecia.

We examined the effects of different sucrose concentrations (3%, 5%, and 7%) on anthocyanin accumulation and plant growth in wild type (WT) and transgenic (T2) torenia cultivar “Kauai Rose” overexpressing the anthocyanin regulatory transcription factors B-Peru + mPAP1 or RsMYB1. Sucrose increased anthocyanin production in both WT and transgenic plants, with higher anthocyanin production in transgenic plants compared to WT plants. Higher sucrose concentrations increased production of anthocyanin in transgenic and WT plants, with increased anthocyanin production associated with increased expression of anthocyanin biosynthesis genes. Higher sucrose concentrations reduced growth of WT and transgenic plants. Our results indicate that sucrose enhances anthocyanin production in torenia by regulating anthocyanin biosynthesis genes.

In this study, whether the addition of antifreeze protein (AFP) to a cryopreservative solution (plant vitrification solution 2 (PVS2)) is more effective in reducing freezing injuries in Hosta capitata than PVS2 alone at different cold exposure times (6, 24, and 48 h) is investigated. The upregulation of C-repeat binding factor 1 (CBF1) and dehydrin 1 (DHN1) in response to low temperature was observed in shoots. Shoots treated with distilled water (dH2O) strongly triggered gene expression 6 h after cold exposure, which was higher than those expressed in PVS2 and PVS2+AFP. However, 24 h after cold exposure, gene expressions detected in dH2O and PVS2 treatments were similar and higher than PVS2 + AFP. The expression was highest in PVS2+AFP when the exposure time was extended to 48 h. Similarly, nitric reductase activities 1 and 2 (Nia1 and Nia2) genes, which are responsible for nitric oxide production, were also upregulated in low-temperature-treated shoots, as observed for CBF1 and DHN1 expression patterns during cold exposure periods. Based on the gene expression patterns, shoots treated with PVS2+AFP were more likely to resist cold stress, which was also associated with the higher cryopreservation efficiency of PVS2+AFP compared to PVS2 alone. This finding suggests that the improvement of cryopreservation efficiency by AFP could be due to the transcriptional regulation of CBF1, DHN1, Nia1, and Nia2, which might reduce freezing injuries during cryopreservation. Thus, AFP could be potentially used as a cryoprotectant in the cryopreservation of rare and commercially important plant germplasm.

Anthocyanin production enhanced by heterologous expression of R2R3 MYB transcription factors has been studied. However, little is known about validated information on the ability of RsMYB (an MYB gene from radish) to enhance anthocyanin production in a heterologous system. In the present study, heterologous expression of RsMYB1 in Petunia hybrida ‘Mirage Rose’ enhanced anthocyanin production in vegetative and floral tissues such as leaves, stems, roots, and petals by transcriptional activation of anthocyanin biosynthetic genes and endogenous antocyanin regulatory genes. Line PM6 expressed higher transcript levels of RsMYB1 than line PM2 and regulated transcript levels of the investigated genes largely than line PM2, whereas those regulated in wild type (WT) plants were the lowest. In addition, transcript levels of the genes detected using qualitative real-time polymerase chain reaction were found to be higher in petals, followed by leaves, stems and roots. Taken together, our results suggest that RsMYB1 enhances anthocyanin production in vegetative and floral tissues of this cultivar, thus, we expect that heterologous expression of RsMYB1 would help to modify flower color of other ornamental plants as well.

Cold temperatures are a major source of stress for plants and negatively impact crop yield. A possible way to protect plants is to treat them with antifreeze proteins (AFPs). Here, we investigated whether fish AFPs can shield the rare ornamental species Hosta capitata from low-temperature stress. We elucidated the expression patterns of the cold-inducible genes C-repeat binding factor 1 (CBF1) and dehydrin 1 (DHN1), as well as the antioxidant genes superoxide dismutase (SOD) and catalase (CAT). All were upregulated at low temperature (4 °C). With increasing exposure time, CBF1 and DHN1 expression generally rose (except CBF1 at 48 h). In contrast, SOD and CAT expression gradually declined from 6 to 48 h. Depending on exposure duration, AFP regulation of gene transcription varied with concentration. However, compared with other concentrations, 100 µg/L AFP reduced CBF1 and DHN1 expression and increased SOD and CAT expression in plants, regardless of exposure time. Both AFP I and III were likely to be most effective at protecting plants against cold stress at concentrations of 100 µg/L. Their involvement in H. capitata cold-stress treatment occurred through regulating the expression of important stress-response genes.

Background As strawberries are susceptible to somaclonal variation when propagated by tissue culture techniques, it is challenging to obtain the true-to-type plants necessary for continuous production of fruits of stable quality. Therefore, we aimed to develop an in vitro propagation method for the production of true-to-type plants of five different strawberry cultivars from meristems cultured in media containing different concentrations of kinetin (Kn). Results For all the cultivars, shoot induction was successful only in the meristems cultured in the medium without Kn and the medium containing 0.5 mg L−1 Kn. The shoots obtained from explants cultured in media supplemented with 0.5 mg L−1 Kn exhibited better plant growth parameters than those cultured in media without Kn and were genetically stable when compared with conventionally propagated plants for all the cultivars. Vegetative and sexual characters and fruit quality attributes observed in the plants derived from meristems cultured on 0.5 mg L−1 Kn and the conventionally propagated plants were not significantly different when grown for three continuous growing seasons under greenhouse conditions. Conclusion The culture of meristems in the medium containing 0.5 mg L−1 Kn is suitable for the efficient propagation of true-to-type plants of different strawberry cultivars and continuous production of fruits with stable quality. Hence, we expect that the method presented in this study will be helpful for the commercial production of true-to-type plants generated in vitro for other strawberry cultivars. Electronic supplementary material The online version of this article (10.1186/s13007-019-0421-0) contains supplementary material, which is available to authorized users.

This study was conducted to examine the role of the transcription factors (TFs), RsMYB1 and mPAP1 together with B-Peru (mPAP1 + B-Peru), in regulating anthocyanin biosynthesis in the ornamental torenia (Torenia fournieri) cultivar Kauai Rose using Agrobacterium-mediated transformation. Expression levels of RsMYB1 were the highest in the lines RS5 and RS3, followed by RS4, RS2, and RS1, while transcript levels of mPAP1 + B-Peru increased in the order of PB-6 > PB-5 > PB-7 > PB-8 > PB-2. Moreover, transcript levels of the anthocyanin structural genes in transgenic lines were significantly higher than those in wild-type (WT) plants. Anthocyanin structural gene expression was specifically altered by TF overexpression: the highest expression of anthocyanidin synthase (ANS) was observed in transgenic lines with RsMYB1, while expression of dihydroflavonol-4-reductase (DFR) was the highest in lines with mPAP1 + B-Peru. We expect that enhanced expression of these anthocyanin structural genes will improve anthocyanin content in the flowers of transgenic torenia. Moreover, these results indicate that RsMYB1 and mPAP1 + B-Peru can be exploited as anthocyanin regulatory TFs to enhance anthocyanin content in other horticultural plants. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s13205-018-1505-7) contains supplementary material, which is available to authorized users.

This study was conducted to investigate the in vitro influence of ethylene on shoot branching and leaf yellowing in the rose cultivar Tineke by using different compounds that regulate ethylene inhibition and stimulation. Aminoethoxy vinyl glycine (AVG), silver thiosulfate (STS), and sodium nitroprusside (SNP) caused enhanced apical shoot initiation and reduced leaf yellowing, via inhibition of ethylene production, in the following order: AVG > SNP > STS. In contrast, the addition of 1-aminocyclopropane-1-carboxylic acid (ACC) or 3-indoleacetic acid (IAA) stimulated ethylene production and had greater negative effects on the studied parameters than the control; the negative effects of IAA were further confirmed in combination with AVG, STS, or SNP. The effects of ethylene on apical shoot initiation and leaf yellowing in Tineke were confirmed in another rose cultivar, Innocence. Hence, this study provides strong support for the hypothesis that ethylene-inhibiting agents have beneficial effects on apical shoot initiation and reduction of leaf yellowing in other rose cultivars.

This study aimed to determine ways to improve the growth and salt tolerance of petunia. Effects of polyamines (PAs; spermidine [Spd], spermine [Spm], and putrescine [Put]) and a nitric oxide (NO) donor (sodium nitroprusside [SNP]) were investigated. Initially, we screened petunia cultivars against sodium chloride (0–125 mM). The petunia cultivar Hurrah Red was identified as salt-sensitive cultivar in the basis of salt-effect on seed germination, fresh weight, and root length of seedlings. Treatment of Hurrah Red shoots with nitrogenous compounds improved the number, length, and fresh weight of roots, as well as the length and fresh weight of shoots over those of the control. Furthermore, plantlets rooted in an optimal concentration of Spd (34.5 µM), Spm (24.8 µM), Put (62.1 µM), and SNP (3.9 µM) were treated with 200 mM NaCl for 3 days to assess their tolerance level. Salt-affected plantlets showed higher level of lipid peroxidation, reduced catalase (CAT), peroxidase (POD), polyphenol oxidase (PP...

The effects of supplementary lighting with high-pressure sodium (HSP) lamps alone or in combination with carbon dioxide (CO2) on the growth, yield, and flower stem quality of two rose cultivars (‘Loving Heart’ and ‘Top Grace’) were studied. Compared to natural lighting (control), supplementary lighting alone was beneficial for plant growth, and it increased plant height, stem diameter, and the number of axillary shoots. Furthermore, increases in flower stem yield (>70 cm), flower stem diameter, fresh weight, and the number of petals per flower were also observed. The combination of supplementary lighting and CO2 significantly enhanced all of the studied parameters compared to supplementary lighting alone. Moreover, stomatal density and chlorophyll fluorescence were seemingly affected by either supplementary lighting alone or in combination with CO2. This is the first study to examine the beneficial effects of combined supplementary lighting and CO2 conditions, and the resulting information is essential to rose growers and commercial production.

Anthocyanin accumulation and plant growth were examined in petunia (NT and transgenic plants) by determining the effects of different sources of light and varying light/dark cycles. Red light significantly enhanced anthocyanin content of B-peru+mPAP1; however, it had a negative effect on anthocyanin production in RsMYB1 plants. In general, white light was found to be reasonable for anthocyanin accumulation in all plants. In case of light/dark cycles, application of seven days of light:14 days of dark significantly enhanced anthocyanin content. We found that anthocyanin content detected in transgenic plants expressing anthocyanin regulatory transcription factor genes (B-peru+mPAP1 or RsMYB1) was higher than that in NT plants in all treatments. Plant growth was also influenced by the different light sources and dark/light cycles. Taken together, our results suggest that light source and light/dark cycle play an important role in anthocyanin production and plant growth. The choice of the optimal conditions is also important for anthocyanin production and plant growth depending on NT or transgenic plants carrying anthocyanin regulatory transcription factors.

The present study aimed to determine the role of transcription factors (bHLH and MYB) in enhancing anthocyanin production in Petunia ‘Mirage rose’. Initially, we optimized an Agrobacterium-mediated transformation protocol to over-express transcription factors (B-Peru, mPAP1, and B-Peru + mPAP1) in Petunia. Phosphinothricin (PPT) concentrations of 0.5, 1.0, and 1.5 mg l−1 were found to be ideal for the selection and regeneration of transformed shoots at different developmental stages. Clavamox (250 mg l−1) efficiently eliminated Agrobacterium after co-cultivation (2 days) and favored maximum shoot regeneration. In addition, incubation for 30 min in Agrobacterium suspension increased the number of transformed cells and resulted in improved regeneration in the selection medium. The transformed plants were successfully developed through a direct organogenesis system. The transformed plants were selected using BASTA® and the presence of transgenes was assessed using PCR. Visible anthocyanin accumulation was evident only in plantlets (shoots, stem, leaves, and roots) carrying the gene combination B-Peru + mPAP1. The expression of biosynthetic genes involved in the flavonoid pathway was analyzed using quantitative real-time PCR. Expression levels of PAL, CHS, CHI, F3H, DFR, and ANS were higher in the young and mature leaves of plants transformed with B-Peru + mPAP1 compared to those transformed with B-Peru, mPAP1, and/or non-transformed plants. Furthermore, the highest level of anthocyanin was recorded in the leaves, stem, and roots of plants transformed with B-Peru + mPAP1. These results validate the combinatorial requirement of B-Peru and mPAP1 to enhance anthocyanin content in Petunia hybrida ‘Mirage rose’.

The postharvest longevity and quality of cut flowers are affected by floral senescence and petal abscission, which primarily result from both ethylene production in the floral organs (such as the petals and gynoecium) and microbial growth in the xylem vessels in ethylene-sensitive flowers, while microbial growth plays a more crucial role in ethylene-insensitive flowers. Several approaches have been proposed to improve these postharvest traits, many of which use chemicals to inhibit ethylene biosynthesis and bacterial growth. However, the use of nanotechnology in the agricultural industry has been increasing in the last decade due to its ability to increase agricultural production and reduce postharvest waste. In particular, nano-silver (NS) particles have been used as ethylene inhibitors and antimicrobial agents in packaging to extend the vase life of horticultural products (i.e., fruits, vegetable, and flowers). In this review, we outline the role of NS particles in the suppression of ethylene production and microbial growth in cut flowers and discuss how the concentration and size of NS particles, incubation time, and plant genotype affect postharvest longevity. In addition, we highlight recent results on the application of biologically synthesized NS particles in packaging and postharvest management within the horticultural industry. We expect that this review will provide useful information on the benefits of using NS particles to control the postharvest biology of horticultural products, particularly with respect to improving the vase life of cut flowers.

The RsMYB1 transcription factor (TF) controls the regulation of anthocyanin in radishes (Raphanus sativus), and its overexpression in tobacco and petunias strongly enhances anthocyanin production. However, there are no data on the involvement of RsMYB1 in the mechanisms underlying abiotic stress tolerance, despite strong sequence similarity with other MYBs that confer such tolerance. In this study, we used the anthocyanin-enriched transgenic petunia lines PM6 and PM2, which overexpress RsMYB1. The tolerance of these lines to heavy metal stress was investigated by examining several physiological and biochemical factors, and the transcript levels of genes related to metal detoxification and antioxidant activity were quantified. Under normal conditions (control conditions), transgenic petunia plants (T2-PM6 and T2-PM2) expressing RsMYB1, as well as wild-type (WT) plants, were able to thrive by producing well-developed broad leaves and regular roots. In contrast, a reduction in plant growth was observed when these plants were exposed to heavy metals (CuSO4, ZnSO4, MnSO4, or K2Cr2O7). However, T2-PM6 and T2-PM2 were found to be more stress tolerant than the WT plants, as indicated by superior results in all analyzed parameters. In addition, RsMYB1 overexpression enhanced the expression of genes related to metal detoxification [glutathione S-transferase (GST) and phytochelatin synthase (PCS)] and antioxidant activity [superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX)]. These results suggest that enhanced expression levels of the above genes can improve metal detoxification activities and antioxidant activity, which are the main components of defense mechanism included in abiotic stress tolerance of petunia. Our findings demonstrate that RsMYB1 has potential as a dual-function gene that can have an impact on the improvement of anthocyanin production and heavy metal stress tolerance in horticultural crops.

We investigated whether the presence of anthocyanins in plants could contribute to low pH stress tolerance using anthocyanin-enriched transgenic petunia lines (PM2, PM6, and PM8) expressing RsMYB1 and wild-type (WT) plants. We examined several physiological and biochemical factors and the transcript levels of genes involved in abiotic stress tolerance. A reduction in plant growth, including plant height and fresh weight, was observed when plants (PM2, PM6, PM8, and WT) were exposed to low pH (pH 3.0) conditions compared to growth under normal (pH 5.8) conditions. A small reduction in the growth of PM6 was observed, followed by that in PM2, PM8, and WT, reflecting the anthocyanin levels in the plants (PM6 > PM2 and PM8 > WT). An analysis of physiological and biochemical factors also supports the degree of low pH tolerance in the plants (PM6 > PM2 and PM8 > WT). In addition, an enhanced expression of the genes [superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), osmotin, and vacuolar H+-ATPase (V-ATPase)] was observed in the transgenic lines (PM2, PM6, and PM8). The resultant of the enhanced transcript levels of the genes could promote antioxidant activities, proline content, and pH homeostasis involved in the mechanisms underlying abiotic stress tolerance in plants. These results suggest that anthocyanin-enriched plants overexpressing RsMYB1 enhances low pH stress tolerance by elevating the transcript levels of the relevant genes.

We investigated the expression of anthocyanin structural genes and transcription factors (TFs) associated with varying anthocyanin content during different developmental stages (S1–S4) of the gerbera cultivars ‘Nathasha’ and ‘Rosalin’. Accumulation of anthocyanin started at S1 and reached a maximum at S3 in both cultivars. Enhancement of anthocyanin content in ‘Nathasha’ was associated with upregulation of ANS and MYB10, whereas in ‘Rosalin’, upregulation was associated with CHS1, MYB10, and MYC1. Low-temperature exposure (6 °C) enhanced anthocyanin content to a greater extent than that at 22 °C via stronger upregulation of CHS1 and MYB10 in ‘Nathasha’ and CHS1 in ‘Rosalin’, irrespective of flower developmental stage. However, differences in anthocyanin content between the two cultivars were found to be influenced by the expression levels of all structural genes and TFs, irrespective of flower developmental stage and temperature conditions. We suggest that differences in the regulation mechanisms of anthocyanin biosynthesis and coloration pattern between ‘Nathasha’ and ‘Rosalin’ are related to differences in the expression patterns of structural genes and TFs; however, further functional studies of the key genes in anthocyanin biosynthesis are needed.

We analyzed the expression of anthocyanin biosynthesis genes and transcription factors (TFs) in the Gerbera hybrida cultivars ‘Bintang’ and ‘Alliance’ that exhibit different coloration patterns. Differential expression of biosynthesis genes and TFs was associated with variable anthocyanin content at different flower developmental stages (S1–S3) in both cultivars; higher anthocyanin content was correlated with higher levels of gene expression. Exposure to different temperatures (6 and 22 °C) also resulted in different anthocyanin content levels: the lower temperature (6 °C) enhanced anthocyanin content compared to the higher temperature (22 °C). However, the increased anthocyanin content of ‘Bintang’ compared to ‘Alliance’ was the result of higher levels of expression of all detected genes, regardless of flower stage and temperature conditions. Therefore, we conclude that transcriptional control of the detected genes is associated with the mechanisms of anthocyanin biosynthesis and coloration patterns in gerberas; however, further studies of the key genes are needed.

Factors affecting shoot regeneration were optimized in order to develop an efficient protocol for shoot regeneration in leaf explants of the chrysanthemum (Chrysanthemum morifolium Ramat) cultivar Shinma. The maximum number of shoots per explant (9.7) was regenerated in leaf explants of 6-week-old donor plants cultured on Murashige–Skoog medium containing a combination of 0.5 mg L−1 6-benzyladenine and 0.5 mg L−1 α-naphthaleneacetic acid with initial dark treatment for 7 days. Among the different auxins tested, indolebutyric acid was the most effective for root induction and development, whereas the presence of ethylene inhibitors strongly suppressed shoot regeneration. Ploidy levels were analyzed by flow cytometry: there was no ploidy variation between the regenerated plants and the mother plant grown under greenhouse conditions. The new protocol will facilitate genetic transformation and micropropagation of chrysanthemum cv. Shinma.

We investigated the effects of sucrose and Nano-silver (NAg) on extending the vase life of cut carnation flowers ‘Edun’. Sucrose suppressed ethylene production by downregulating the genes that code for its biosynthesis. Relative to the control, however, sucrose significantly increased bacterial proliferation on cut stem surfaces and reduced relative fresh weight (RFW), antioxidant activity, and cysteine proteinase inhibitor gene (DcCPi) expression. Consequently, the sucrose-treated flowers had shorter vase lives than the control. In contrast, NAg suppressed ethylene production in the petal, prevented bacterial blockage in the cut stem surface, and improved all the aforementioned parameters. Therefore, NAg increased flower longevity. The most effective treatment in terms of longevity extension and parameter improvement, however, was the combination of NAg and sucrose. These results suggest that sucrose can suppress ethylene production but does not necessarily extend the vase life of the flower cultivar, which is partially or totally insensitive to ethylene. The role of NAg in increasing cut carnation longevity is mainly to inhibit xylem blockage rather than suppress ethylene production, and the combined effect of NAg and sucrose is most effective at prolonging cut carnation vase life, likely due to their synergetic effects on multiple modes of action.

We investigated the role of nano-silver (NAg) and the bacterial strain Enterobacter cloacae in increasing the vase life of cut carnation flowers ‘Omea’. NAg treatment extended vase life of the flowers by increasing relative fresh weight, antioxidant activities, and expression level of the cysteine proteinase inhibitor gene (DcCPi), and by suppressing bacterial blockage in stem segments, ethylene production and expression of ethylene biosynthesis genes and DcCP1 gene, compared with the control. Out of all the treatments, administration of 25 mg L-1 NAg gave the best results for all the analyzed parameters. Interestingly, application of E. cloacae also extended the vase life of cut flowers by three days in comparison with control flowers, and overall, showed better results than the control for all the analyzed parameters. Taken together, these results demonstrate the positive role of NAg and E. cloacae in increasing the longevity of cut carnation flowers, and indicate that this effect is brought about through multiple modes of action.

The objective of this research was to develop an efficient protocol for shoot regeneration from leaf segments of the Chrysanthemum cv. Vivid Scarlet by examining the effects of plant growth regulators, dark incubation period, gelling agents, and silver nitrate. The highest number of shoots per explant (12.3) was regenerated from leaf explants cultured on Murashige and Skoog (MS) medium supplemented with a combination of 1 mgL(-1) of 6-benzyladenine (BA) and 2 mgL(-1) of α-naphthaleneacetic acid (NAA) under light conditions without any initial dark period. Gelrite was the most effective gelling agent for shoot regeneration among those tested, whereas the presence of silver nitrate distinctly inhibited shoot regeneration. Superior plant growth and rooting was observed on a hormone-free MS medium solidified with Gelrite. Flow cytometry analysis revealed no ploidy variation between the regenerated plants and the mother plant grown under greenhouse conditions. The established protocol was applicable to shoot regeneration for four out of six cultivars tested. This research will facilitate the genetic transformation and micropropagation of Chrysanthemum cultivars.

Tetraploids were successfully produced from diploid seeds obtained through interspecific crossing between Calanthe discolor and Calanthe sieboldii by treating with colchicine or oryzalin. Colchicine was tested at concentrations of 0.05 and 0.1 % for 0, 3, or 7 days and oryzalin was tested at a concentration of 0.003 % for 1, 2, 4, and 7 days, and the ploidy of the seedlings was determined by flow cytometry. Tetraploids (4×) were obtained from the interspecific hybrid seeds treated with all colchicine and oryzalin concentrations. The most efficient condition for inducing tetraploids seemed to be treated with 0.003 % oryzalin for 1 or 2 days. Cytological and morphological evidence confirmed the results of flow cytometric analysis. The stomatal density and sizes of the tetraploid plants were significantly higher and larger than those of the diploid plants. Differences in leaf shape were found between the tetraploid and diploid plants under the same growing conditions: the leaves of the diploids were elongated and those of the tetraploids were round.

The research was conducted to investigate the capacity for shoot regeneration of leaf (apical, middle, and basal parts) and stem (internodal and nodal segments) of Lilium longiflorum hybrid “Bright Tower”. When the explants were examined on the Murashige and Skoog medium containing different concentrations of naphthaleneacetic acid and 6-benzyladenine combinations, only nodal explant induced shoots on plant growth regulator (PGR)-free medium, while the other explant sources induced shoots on the media containing PGRs. However, no shoot formation was observed in the apical parts of leaves. Of the different explants used, in general, nodal segments exhibited the highest frequencies of shoot formation and mean number of shoots per explant followed by middle parts of leaves, internodal segments, and basal parts of leaves regardless of PGRs. Ploidy analysis of regenerated plants using flow cytometer also revealed the same ploidy level (diploid). This study will be useful for Agrobacterium-mediated transformati...

Somatic embryogenesis was induced from in vivo grown leaf explants of Chrysanthemum cv. Euro incubated on Murashige and Skoog (MS) medium supplemented with 2.0 mg/L 2,4-dichlorophenoxyacetic acid and 2.0 mg/L Kinetin, yielding the highest mean number of embryos (42 ± 5.97) per explant after 5 weeks of culture. We evaluated the effects of basal medium, various concentrations of sucrose, and timentin on the proliferation of secondary somatic embryos. MS medium was observed to be the more effective in promoting the proliferation of somatic embryos than half-strength Murashige and Skoog (1/2MS). In addition, timentin was also more efficient in induction of secondary embryogenesis than sucrose. Whole plantlets were obtained by culturing of secondary embryos on hormone-free MS medium and successfully acclimated in the green house.

The effects of three different sucrose concentrations on plant growth and anthocyanin accumulation were examined in non-transgenic (NT) and transgenic (T2) specimens of the Petunia hybrida cultivar 'Mirage rose' that carried the anthocyanin regulatory transcription factors B-Peru+mPAP1 or RsMYB1. Anthocyanin accumulation was not observed in NT plants in any treatments, whereas a range of anthocyanin accumulation was observed in transgenic plants. The anthocyanin content detected in transgenic plants expressing the anthocyanin regulatory transcription factors (B-Peru+mPAP1 or RsMYB1) was higher than that in NT plants. In addition, increasing sucrose concentration strongly enhanced anthocyanin content as shown by quantitative real-time polymerase chain reaction (qRT-PCR) analysis, wherein increased concentrations of sucrose enhanced transcript levels of the transcription factors that are responsible for the induction of biosynthetic genes involved in anthocyanin synthesis; this pattern was not observed in NT plants. In addition, sucrose affected plant growth, although the effects were different between NT and transgenic plants. Taken together, the application of sucrose could enhance anthocyanin production in vegetative tissue of transgenic Petunia carrying anthocyanin regulatory transcription factors, and this study provides insights about interactive effects of sucrose and transcription factors in anthocyanin biosynthesis in the transgenic plant.

A MYB transcription factor gene, RsMYB1, from radish was introduced into the chrysanthemum cultivars 'Peach ND', 'Peach Red', and 'Vivid Scarlet' under the control of the cauliflower mosaic virus 35S promoter. Presence of RsMYB1 in transgenic lines was confirmed using polymerase chain reaction (PCR). Results of reverse-transcription-PCR analysis revealed that the expression of RsMYB1 was stable in all transgenic lines and could enhance the expression levels of three key biosynthetic genes (F3H, DFR, and ANS) involved in anthocyanin production. Accordingly, anthocyanin content was significantly higher in transgenic lines than in control of all the cultivars, although the increasement was not visually observed in any of the transgenic lines. Therefore, these results demonstrate that RsMYB1 has potential to enhance anthocyanin content in the chrysanthemums.

Chrysanthemum cultivar Shinma is a standard cultivar and has a large flower size, long vase life, and strong resistance to the white rust disease; thus, it is an important commercial cut flower in the flower markets of Korea. However, its flower color (white) is simple, so variation in flower color by using genetic transformation is necessary to increase its value in flower markets worldwide. Success of genetic transformation in chrysanthemum is dependent on many factors. In this study, factors that affect the efficient genetic transformation of this chrysanthemum were assessed, transgenic plants with the RsMYB1 anthocyanin regulatory gene were produced, and the presence of the transgene and its stable expression were confirmed using PCR and reverse transcription-PCR. Co-cultivation temperature and Agrobacterium strains were observed to be the main factors that affected higher transformation efficiency. However, the protocol developed by a combination of all optimized factors yielded eight- or fourfold higher transformation efficiency than the simple (un-optimized) protocol or individually optimized factors. The herbicide resistance assay revealed that PCR-positive transgenic shoots have stronger resistance to Basta™ than the wild type (WT). We expect that the efficient protocol developed in this study will facilitate the genetic transformation of genes of interest in this cultivar and that the anthocyanin regulatory gene will help in modifying the flower color.

Background: Several MYB genes belonging to R2R3 MYB transcription factors have been used in several plant species to enhance anthocyanin production, and have shown various expression or regulation patterns. This study focused on the effect of ectopic expression of an RsMYB1 isolated from radish (Raphanus sativa) on chrysanthemum cv. 'Shinma'. Results: The RT-PCR results confirmed that RsMYB1 regulated the expression of three key biosynthetic genes (CmF3H, CmDFR, and CmANS) that are responsible for anthocyanin production in transgenic chrysanthemum, but were not detected in the non-transgenic line. In all transgenic plants, higher expression levels of key biosynthetic genes were observed in flowers than in leaves. However, the presence of RsMYB1 in chrysanthemum did not affect any morphological characteristics, such as plant height, leaf shape or size, and number of flowers. Furthermore, no anthocyanin accumulation was visually observed in the leaves and floral tissue of any of the transgenic lines, which was further confirmed by anthocyanin content estimation. Conclusion: To our knowledge, this is the first time the role of an MYB transcription factor in anthocyanin production has been investigated in chrysanthemum. (C) 2015 Pontificia Universidad Catolica de Valparaiso. Production and hosting by Elsevier B.V. All rights reserved.

Background Rosea1 ( Ros1 ) and Delila ( Del ) co-expression controls anthocyanin accumulation in snapdragon flowers, while their overexpression in tomato strongly induces anthocyanin accumulation. However, little data exist on how Del expression alone influences anthocyanin accumulation. Results In tobacco ( Nicotiana tabacum ‘Xanthi’), Del expression enhanced leaf and flower anthocyanin production through regulating NtCHS , NtCHI , NtF3H , NtDFR , and NtANS transcript levels. Transgenic lines displayed different anthocyanin colors (e.g., pale red: T 0 -P, red: T 0 -R, and strong red: T 0 -S), resulting from varying levels of biosynthetic gene transcripts. Under salt stress, the T 2 generation had higher total polyphenol content, radical (DPPH, ABTS) scavenging activities, antioxidant-related gene expression, as well as overall greater salt and drought tolerance than wild type (WT). Conclusion We propose that Del overexpression elevates transcript levels of anthocyanin biosynthetic and antioxidant-related genes, leading to enhanced anthocyanin production and antioxidant activity. The resultant increase of anthocyanin and antioxidant activity improves abiotic stress tolerance.