Exogenous Application Of Cytokinin Research Articles

Genome-wide identification and expression analysis of the TaRRA gene family in wheat (Triticum aestivum L.).

Cytokinin is an important endogenous hormone in plants performing a wide spectrum of biological roles. The type-A response regulators (RRAs) are primary cytokinin response genes, which are important components of the cytokinin signaling pathway and are involved in the regulation of plant growth and development. By analysis of the whole genome sequence of wheat, we identified 20 genes encoding RRAs which were clustered into eight homologous groups. The gene structure, conserved motifs, chromosomal location, and cis-acting regulatory elements of the TaRRAs were analyzed. Quantitative real-time polymerase chain reaction (qRT-PCR) results showed that the expression levels of most of the TaRRAs increased rapidly on exogenous cytokinin application. Moreover, the TaRRA family members displayed different expression profiles under the stress treatments of drought, salt, cold, and heat. This study provides valuable insights into the RRA gene family in wheat and promotes the potential application of these genes in wheat genetic improvement.

OsDOF11 Promotes Crown Root Formation via Cytokinin in Oryza Sativa.

Crown root is the main part of root system, which performs an important role in rice growth and development, especially in nutrition and water assimilation. Previously, we reported negative feedback regulation loop between Oryza sativa DNA BINDING WITH ONE FINGER 11 (OsDOF11) and cytokinin by Oryza sativa CYTOKININ OXIDASE/DEHYDROGENASE 4 (OsCKX4) in rice development. Reverse transcription quantitative RT-PCR analyses was used to analyze the related gene transcript level. Nitrogen and hormone were measured by CHN-Nitrogen analyser and Liquid chromatography mass spectrometer, respectively. Exogenous application of cytokinin and [13C] sucrose labeled stable isotope uptake experiments help us to explain the relationship between OsDOF11 and cytokinin. We demonstrate the role of OsDOF11 in root development. We note that the loss function of OsDOF11 displays the reduced crown roots number, low activity of nitrogen assimilation and low content of cytokinin and auxin. The expression level of WUSCHEL-related homeobox (OsWOX11), A-type response regulator 2 (OsRR2), OsRR3, and OsCKX4 were decreased in osdof11-1, as well as in OsDOF11 RNA interference 9 mutants (RNAi-9 lines). Through Exogenous application of multiple concentrations of cytokinin as treatment to osdof11-1 mutant, RNAi-9 lines, and wild type (WT). We found that the crown roots number of osdof11-1 plants were rescued as the cytokinin concentration increased gradually from 1 μM to 10 μM, but the effect was weaker in RNAi-9 line. And cytokinin inhibited sucrose uptake activity from Murashige-Skoog medium with 3.0% sucrose (MS30) by OsDOF11 in rice root. OsDOF11 promotes crown root formation via cytokinin in oryza sativa. These results provide a physiological basis for further analysis of the OsDOF11 function of in rice root development.

Influence of 2iP and 2,4-D Concentrations on Accumulation of Biomass, Phenolics, Flavonoids and Radical Scavenging Activity in Date Palm (Phoenix dactylifera L.) Cell Suspension Culture

Plant hormones are chemical compounds that serve as crucial signal molecules. The growth and induction of bioactive compounds in plant suspension cultures depend on the exogenous application of auxins and cytokinins at different concentrations. In this study, date palm (Phoenix dactylifera L., cv. Shishi) cell suspension cultures initiated in Murashige and Skoog (MS) medium were treated with 2.5 and 5 mg/L 2-isopentenyladenine (2-iP) in combinations with 1, 2.5, 5 and 10 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D), and compared to the standard cell multiplication medium as the control, which contained 1.5 mg/L 2iP and 10 mg/L naphthaleneacetic acid (NAA). The optimum biomass accumulation, based on the packed cell volume and dry weight, was found in the cell suspension culture augmented with 1 mg/L 2,4-D + 5 mg/L 2iP followed by 5 mg/L 2,4-D + 2.5 mg/L 2-iP. In addition, the study assessed the total phenolic, flavonoid and radical scavenging activity, and high performance liquid chromatography (HPLC) was also used to determine the content of polyphenols (apigenin, caffeic acid, catechin and kaempferol) quantitatively. Cell suspension cultures containing 5 mg/L 2,4-D and 2.5 mg/L 2iP yielded the maximum accumulation of phenolics, flavonoids and radical scavenging activity (90.65%), and also a significantly higher content of caffeic acid (37.1 µg/g DW). The present finding facilitates the scaling up and commercial production of polyphenols from date palm cell suspension culture.

Heavy metal induced regulation of plant biology: Recent insights.

The presence of different forms of heavy metals in the earth crust is very primitive and probably associated with the origin of plant life. However, since the beginning of human civilisation, heavy metal use and its contamination to all living systems on earth have significantly increased due to human anthropogenic activities. Heavy metals are nonbiodegradable, which directly or indirectly impact photosynthesis, antioxidant system, mineral nutrition status, phytohormones and amino acid-derived molecules. Due to the toxic behaviour of some heavy metals, the endogenous status of chemical messengers like phytohormones may get significantly influenced, leading to harmful impacts on plant growth, development and overall yield of the plants. It has been noticed that exogenous application of phytohormones, that is, abscisic acid, salicylic acid, auxins, brassinosteroids, cytokinins, ethylene and gibberellins can positively regulate the heavy metal toxicity in plants through the regulation of the ascorbate-glutathione cycle, nitrogen metabolism, proline metabolisms, transpiration rate, and cell division. Furthermore, it may also restrict the entry of heavy metals into the plant cells, which aids in the recovery of plant growth and productivity. Besides these, some defence molecules also assist the plant in dealing with heavy metal toxicity. Therefore, the present review aims to bridge the knowledge gap in this context and present outstanding discoveries related to plant life supportive processes during stressful conditions including phytohormones and heavy metal crosstalk along with suggestions for future research in this field.

Cytokinin increases vegetative growth period by suppressing florigen expression in rice and maize.

Increasing the vegetative growth period of crops can increase biomass and grain yield. In rice (Oryza sativa), the concentration of trans -zeatin, an active cytokinin, was high in the leaves during vegetative growth and decreased rapidly upon induction of florigen expression, suggesting that this hormone is involved in the regulation of the vegetative phase. To elucidate whether exogenous cytokinin application influences the length of the vegetative phase, we applied 6-benzylaminopurine (BAP) to rice plants at various developmental stages. Our treatment delayed flowering time by 8-9 days when compared with mock-treated rice plants, but only at the transition stage when the flowering signals were produced. Our observations also showed that flowering in the paddy field is delayed by thidiazuron, a stable chemical that mimics the effects of cytokinin. The transcript levels of florigen genes Heading date 3a (Hd3a) and Rice Flowering locus T1 (RFT1) were significantly reduced by the treatment, but the expression of Early heading date 1 (Ehd1), a gene found directly upstream of the florigen genes, was not altered. In maize (Zea mays), similarly, BAP treatment increased the vegetative phage by inhibiting the expression of ZCN8, an ortholog of Hd3a. We showed that cytokinin treatment induced the expression of two type-A response regulators (OsRR1 and OsRR2) which interacted with Ehd1, a type-B response regulator. We also observed that cytokinin did not affect flowering time in ehd1 knockout mutants. Our study indicates that cytokinin application increases the duration of the vegetative phase by delaying the expression of florigen genes in rice and maize by inhibiting Ehd1.

Grain yield and nitrogen use efficiency are increased by exogenous cytokinin application through the improvement in root physiological traits of rice

Grain yield and nitrogen use efficiency are increased by exogenous cytokinin application through the improvement in root physiological traits of rice

Evolutionary and functional analysis of two-component system in chickpea reveals CaRR13, a TypeB RR, as positive regulator of symbiosis.

SummaryThe critical role of cytokinin in early nodulation in legumes is well known. In our study, exogenous cytokinin application to roots of the important crop legume, chickpea (Cicer arietinum L.), led to the formation of pseudo‐nodules even in the absence of rhizobia. Hence, a genome‐wide analysis of the cytokinin signalling, two‐component system (TCS) genes, was conducted in chickpea, Medicago and Cajanus cajan. The integrated phylogenetic, evolutionary and expression analysis of the TCS genes was carried out, which revealed that histidine kinases (HKs) were highly conserved, whereas there was diversification leading to neofunctionalization at the level of response regulators (RRs) especially the TypeB RRs. Further, the functional role of the CaHKs in nodulation was established by complementation of the sln1Δ mutant of yeast and cre1 mutants of (Medicago) which led to restoration of the nodule‐deficient phenotype. Additionally, the highest expressing TypeB RR of chickpea, CaRR13, was functionally characterized. Its localization in the nucleus and its Y1H assay‐based interaction with the promoter of the early nodulation gene CaNSP2 indicated its role as a transcription factor regulating early nodulation. Overexpression, RNAi lines and complementation of cre1 mutants with CaRR13 revealed its critical involvement as an important signalling molecule regulating early events of nodule organogenesis in chickpea.

Effects of Exogenous Trans-Zeatin and Lovastatin on Abortion of Small Seeds in ‘Dawuxing’ Loquat (Eriobotrya Japonica Lindl.)

The small seeds of loquat possess very rich and diverse genetic characteristics which can potentially serve as precious resources for plant breeding. However, they are often aborted during the seed development. Cytokinin, as an important signaling mediator, plays a pivotal regulatory role in seed development. However, the effects of exogenous cytokinin application on the development of loquat seeds are poorly understood. In this study, we analyzed the potential effects of exogenous cytokinin on the abortion of small seeds of loquat. Cytokinin (20 mg/L trans-zeatin) and cytokinin inhibitor (60 mg/L lovastatin) were sprayed on the fruits of ‘Dawuxing’ loquat during an early stage of fruit expansion. The clean water treatment was used as the control group. The results showed that exogenous trans-zeatin significantly increased the weight of small seeds, the levels of soluble sugar and starch, as well as peroxidase (POD) and superoxide dismutase (SOD) activities. It also promoted a substantial increase in the expression of POD- and SOD-related genes during the process of small seed abortion. Moreover, trans-zeatin treatment significantly increased the content of endogenous trans-zeatin in the small seeds, and this increase in content showed a trend opposite to that of control (CKA). Cytokinin dehydrogenase related genes were found to be down-regulated after trans-zeatin treatment. It was found that exogenous cytokinin inhibitor (lovastatin) treatment could induce the anti-stress reaction in the small seeds during the early stage of treatment by significantly increasing the activities of POD and SOD, and the weight of small seeds at the early stage of treatment was significantly lower than that of the control group, but reverted to the level of the control group during the late stage of the treatment. Therefore, a specific concentration of trans-zeatin treatment can promote the development of small loquat seeds, while cytokinin inhibitor (lovastatin) can significantly inhibit the development of small seeds during the early stage of treatment. In summary, this study reports for the first time that application of exogenous trans-zeatin could effectively promote the development of small loquat seeds by significantly increasing the metabolism of small seeds. The small seeds which contained rich and diverse genetic characteristics often aborted during seed development. Our study thus established a foundation for the rescue of new germplasm resources of loquat by promoting the development of small loquat seeds.

CYTOKININ AND GIBBERELLIC ACID ALLEVIATE THE EFFECT OF WATERLOGGING IN MUNGBEAN (VIGNA RADIATA L. WILCZEK)

Recently, waterlogging damage of mungbean is most common in many mungbean growing areas of the world. The exogenous application of phytohormones cytokinin (CK) and gibberellic acid (GA) could be an effective way of managing mungbean under waterlogging stress. Therefore, we applied different levels of CK and GA at the onset of waterlogging and ten days after waterlogging, and the results were observed in waterlogged plants as compared to control. The CK and GA application showed much improvement in depressed morpho-physiological and yield-related traits and seed yield. However, the responses varied depending on the types and doses of CK and GA. The plant height and the number of leaves were higher in GA-applied plants than CK-treated plants. The GA responded more in shoot growth, whereas CK in root development under waterlogged situations. The application of CK at 150 mg/L displayed the highest 33.9% yield advantage. It reveals that exogenous CK could be a good management practice in areas prone to waterlogging stress for attaining better yield in mungbean.

Quantitative proteomics analysis reveals the response mechanism of peanut (Arachis hypogaea L.) to imbibitional chilling stress.

Imbibitional chilling stress inhibits normal seed germination and seedling establishment and leads to large losses in peanut production. This is a major limiting factor when sowing peanut earlier and further north. To reveal the response mechanism of peanut to imbibitional chilling stress, a Tandem Mass Tag (TMT)-based quantitative proteomics analysis was conducted to identify differentially accumulated proteins (DAPs) under imbibitional chilling stress. Hormone profiling and transcriptional analysis were performed to confirm the proteomics data. Further seed priming analysis with exogenous cytokinins was conducted to validate the role of cytokinins in alleviating imbibitional chilling injury. A total of 5029 proteins were identified and quantified in all of the experimental groups. Among these, 104 proteins were DAPs as compared with the control. Enrichment analysis revealed that these DAPs were significant in various molecular functional and biological processes, especially for biosynthesis and metabolism of plant hormones. Hormone profiling and transcription analysis suggested that the reduced abundance of cytokinin oxidase may be caused by down-regulation of gene expression of the corresponding genes and leads to an elevated content of cytokinins under chilling stress. Seed priming analysis suggested that exogenous application of cytokinins may alleviate injury caused by imbibitional chilling. Our study provides a comprehensive proteomics analysis of peanut under imbibitional chilling stress, suggesting the role of plant hormones in the response mechanism. The results provide a better understanding of the imbibitional chilling stress response mechanism in peanut that will aid in peanut production.

Mitigation of salinity stress by exogenous application of cytokinin in faba bean (Vicia faba L.)

Soil salinity limits agricultural land use and crop productivity, thereby a major threat to global food safety. Plants treated with several phytohormones including cytokinins were recently proved as a powerful tool to enhance plant’s adaptation against various abiotic stresses. The current study was designed to investigate the potential role of 6-benzyladenine (BA) to improve broad bean (Vicia faba L.) salinity tolerance. The salt-stressed broad bean plantlets were classified into two groups, one of which was sprayed with water and another was sprayed with 200 ppm of BA. Foliar applications of BA to salt-exposed plants promoted the growth performance which was evidenced by enhanced root-shoot fresh and dry biomass. Reduced proline was strongly connected to the enhanced soluble proteins and free amino acids contents, protecting plant osmotic potential following BA treatment in salt-stressed broad bean. BA balanced entire mineral homeostasis and improved mineral absorption and translocation from roots to shoots, shoots to seeds and roots to seeds in salt-stressed plants. Excessive salt accumulation increased malondialdehyde level in leaves creating oxidative stress and disrupting cell membrane whereas BA supplementation reduced lipid peroxidation and improved oxidative defence. BA spray to salinity-stressed plants also compensated oxidative damage by boosting antioxidants defence mechanisms, as increased the enzymatic activity of superoxide dismutase, catalase, peroxidase and ascorbate peroxidase. Moreover, clustering heatmap and principal component analysis revealed that mineral imbalances, osmotic impairments and increased oxidative damage were the major contributors to salts toxicity, on the contrary, BA-augmented mineral homeostasis and higher antioxidant capacity were the reliable markers for creating salinity stress tolerance in broad bean. In conclusion, the exogenous application of BA alleviated the antagonistic effect of salinity and possessed broad bean to positively regulate the osmoprotectants, ion homeostasis, antioxidant activity and finally plant growth and yield, perhaps suggesting these easily-accessible and eco-friendly organic compounds could be powerful tools for the management of broad bean growth as well as the development of plant resiliency in saline prone soils.

Cytokinin and auxin modulate cucumber parthenocarpy fruit development

Parthenocarpy (fruit development without pollination) is an important agricultural trait, which determines the production of horticultural crops like tomato, eggplant and cucumber. Parthenocarpy ability varies widely among cucumber lines. To better understand the genetic regulators underlying this variation, hormone and transcriptome profiles and the expressions of hormone-related genes in non-pollinated fruit of a highly parthenocarpic line DDX and a weakly parthenocarpic line ZK were compared at 1 day after anthesis. The cytokinin and gibberellic acid contents were higher in DDX than in ZK, while the abscisic acid content was less. Exogenous application of cytokinins, auxin and gibberellic acid 4 + 7 successfully induced the parthenocarpic fruit set of ZK. The transcript levels of several cytokinin biosynthesis genes (CsCYP735A1, CsCYP735A2 and CsLOG1), cytokinin-responsive genes (CsRR8/9b, CsRR8/9d, CsRR8/9e and CsRR16/17) and auxin signal transduction genes (Aux/IAAs) were greater in DDX than in ZK, while the level of an abscisic acid receptor (CsPYR1) was lower. These results suggest that high expression levels of cytokinin- and auxin-related genes in DDX contribute to its high parthenocarpy ability.

Function of histone H2B monoubiquitination in transcriptional regulation of auxin biosynthesis in Arabidopsis

The auxin IAA is a vital plant hormone in controlling growth and development, but our knowledge about its complicated biosynthetic pathways and molecular regulation are still limited and fragmentary. cytokinin induced root waving 2 (ckrw2) was isolated as one of the auxin-deficient mutants in a large-scale forward genetic screen aiming to find more genes functioning in auxin homeostasis and/or its regulation. Here we show that CKRW2 is identical to Histone Monoubiquitination 1 (HUB1), a gene encoding an E3 ligase required for histone H2B monoubiquitination (H2Bub1) in Arabidopsis. In addition to pleiotropic defects in growth and development, loss of CKRW2/HUB1 function also led to typical auxin-deficient phenotypes in roots, which was associated with significantly lower expression levels of several functional auxin synthetic genes, namely TRP2/TSB1, WEI7/ASB1, YUC7 and AMI1. Corresponding defects in H2Bub1 were detected in the coding regions of these genes by chromatin immunoprecipitation (ChIP) analysis, indicating the involvement of H2Bub1 in regulating auxin biosynthesis. Importantly, application of exogenous cytokinin (CK) could stimulate CKRW2/HUB1 expression, providing an epigenetic avenue for CK to regulate the auxin homeostasis. Our results reveal a previously unknown mechanism for regulating auxin biosynthesis via HUB1/2-mediated H2Bub1 at the chromatin level.

Polyamine Metabolism Is Involved in the Direct Regeneration of Shoots from Arabidopsis Lateral Root Primordia.

Plants can be regenerated from various explants/tissues via de novo shoot meristem formation. Most of these regeneration pathways are indirect and involve callus formation. Besides plant hormones, the role of polyamines (PAs) has been implicated in these processes. Interestingly, the lateral root primordia (LRPs) of Arabidopsis can be directly converted to shoot meristems by exogenous cytokinin application. In this system, no callus formation takes place. We report that the level of PAs, especially that of spermidine (Spd), increased during meristem conversion and the application of exogenous Spd improved its efficiency. The high endogenous Spd level could be due to enhanced synthesis as indicated by the augmented relative expression of PA synthesis genes (AtADC1,2, AtSAMDC2,4, AtSPDS1,2) during the process. However, the effect of PAs on shoot meristem formation might also be dependent on their catabolism. The expression of Arabidopsis POLYAMINE OXIDASE 5 (AtPAO5) was shown to be specifically high during the process and its ectopic overexpression increased the LRP-to-shoot conversion efficiency. This was correlated with Spd accumulation in the roots and ROS accumulation in the converting LRPs. The potential ways how PAO5 may influence direct shoot organogenesis from Arabidopsis LRPs are discussed.

Application of Exogenous Phytohormones at Silking Stage Improve Grain Quality under Post-Silking Drought Stress in Waxy Maize.

The application of exogenous plant growth regulator can improve plant resistance to drought stress. The effects of application of exogenous cytokinin (CTK), brassinolide (BR), or gibberellic acid (GA) at the silking time on the grain quality of two waxy maize hybrids under drought stress at grain formation stage were studied. Grain weight of both hybrids was unaffected by exogenous phytohormones under control conditions but increased under drought conditions with the application of BR. The grain starch content in response to drought varied with hybrid and phytohormone. Starch granule size and protein content in grains were increased by drought under all conditions, but various phytohormones exerted different forms of influence. The starch λmax in Yunuo7 was unaffected by single or interaction of phytohormones and water deficit, λmax in Jingkenuo2000 with BR was unaffected but with CTK or GA increased by drought. Relative crystallinity was reduced by drought without the application of phytohormone, but with phytohormones in response to drought it was different. Flour peak viscosity was reduced by drought. The value was increased with BR spraying under control and drought conditions. Retrogradation percentage under drought conditions was unaffected by exogenous phytohormones in Jingkenuo2000. In Yunuo7, retrogradation percentage was unaffected by BR but reduced by CTK and GA. In conclusion, spraying phytohormones at the silking stage can affect grain weight and starch quality, grains with a sticky taste can be improved by applying BR, and grains with low retrograde tendency can be produced by applying CTK.

OsWUS promotes tiller bud growth by establishing weak apical dominance in rice

Two branching strategies are exhibited in crops: enhanced apical dominance, as in maize; or weak apical dominance, as in rice. However, the underlying mechanism of weak apical dominance remains elusive. OsWUS, an ortholog of Arabidopsis WUSCHEL (WUS) in rice, is required for tiller development. In this study, we identified and functionally characterized a low-tillering mutant decreased culm number 1 (dc1) that resulted from loss-of-function of OsWUS. The dc1 tiller buds are viable but repressed by the main culm apex, leading to stronger apical dominance than that of the wild-type (WT). Auxin response is enhanced in the dc1 mutant, and knocking out the auxin action-associated gene ABERRANT SPIKELET AND PANICLE 1 (ASP1) de-repressed growth of the tiller buds in the dc1 mutant, suggesting that OsWUS and ASP1 are both involved in outgrowth of the rice tiller bud. Decapitation triggers higher contents of cytokinins in the shoot base of the dc1 mutant compared with those in the WT, and exogenous application of cytokinin is not sufficient for sustained growth of the dc1 tiller bud. Transcriptome analysis indicated that expression levels of transcription factors putatively bound by ORYZA SATIVA HOMEOBOX 1 (OSH1) are changed in response to decapitation and display a greater fold change in the dc1 mutant than that in the WT. Collectively, these findings reveal an important role of OsWUS in tiller bud growth by influencing apical dominance, and provide the basis for an improved understanding of tiller bud development in rice.

The Anti-Senescence Activity of Cytokinin Arabinosides in Wheat and Arabidopsis Is Negatively Correlated with Ethylene Production.

Leaf senescence, accompanied by chlorophyll breakdown, chloroplast degradation and inhibition of photosynthesis, can be suppressed by an exogenous application of cytokinins. Two aromatic cytokinin arabinosides (6-benzylamino-9-β-d-arabinofuranosylpurines; BAPAs), 3-hydroxy- (3OHBAPA) and 3-methoxy- (3MeOBAPA) derivatives, have recently been found to possess high anti-senescence activity. Interestingly, their effect on the maintenance of chlorophyll content and maximal quantum yield of photosystem II (PSII) in detached dark-adapted leaves differed quantitatively in wheat (Triticum aestivum L. cv. Aranka) and Arabidopsis (Arabidopsis thaliana L. (Col-0)). In this work, we have found that the anti-senescence effects of 3OHBAPA and 3MeOBAPA in wheat and Arabidopsis also differ in other parameters, including the maintenance of carotenoid content and chloroplasts, rate of reduction of primary electron acceptor of PSII (QA) as well as electron transport behind QA, and partitioning of absorbed light energy in light-adapted leaves. In wheat, 3OHBAPA had a higher protective effect than 3MeOBAPA, whereas in Arabidopsis, 3MeOBAPA was the more efficient derivative. We have found that the different anti-senescent activity of 3OHBAPA and 3MeOBAPA was coupled to different ethylene production in the treated leaves: the lower the ethylene production, the higher the anti-senescence activity. 3OHBAPA and 3MeOBAPA also efficiently protected the senescing leaves of wheat and Arabidopsis against oxidative damage induced by both H2O2 and high-light treatment, which could also be connected with the low level of ethylene production.

The pre-mRNA splicing factor RDM16 regulates root stem cell maintenance in Arabidopsis.

Pre-mRNA (messenger RNA) splicing participates in the regulation of numerous biological processes in plants. For example, alternative splicing shapes transcriptomic responses to abiotic and biotic stress, and controls developmental programs. However, no study has revealed a role for splicing in maintaining the root stem cell niche. Here, a screen for defects in root growth in Arabidopsis thaliana identified an ethyl methane sulfonate mutant defective in pre-mRNA splicing (rdm16-4). The rdm16-4 mutant displays a short-root phenotype resulting from fewer cells in the root apical meristem. The PLETHORA1 (PLT1) and PLT2 transcription factor genes are important for root development and were alternatively spliced in rdm16-4 mutants, resulting in a disordered root stem cell niche and retarded root growth. The root cap of rdm16-4 contained reduced levels of cytokinins, which promote differentiation in the developing root. This reduction was associated with the alternative splicing of genes encoding cytokinin signaling factors, such as ARABIDOPSIS HISTIDINE PHOSPHOTRANSFER PROTEIN5 and ARABIDOPSIS RESPONSE REGULATORS (ARR1, ARR2, and ARR11). Furthermore, expression of the full-length coding sequence of ARR1 or exogenous cytokinin application partially rescued the short-root phenotype of rdm16-4. This reveals that the RDM16-mediated alternative splicing of cytokinin signaling components contributes to root growth.

Acid invertase activities of dahlia ‘Kokucho’ petals during flower opening and following cutting and treatment with 6-benzylaminopurine

Extending the vase life of cut dahlia ‘Kokucho’ flowers through enhanced activities of acid invertases (cell wall, CWIN and vacuolar, VIN) on flower opening and senescence after harvest was investigated. The activities of CWIN and VIN were very low in the outer petals at the tight bud stage (stage 1), increased markedly at the half-open stage (stage 2), and decreased at the fully open stage (stage 3) to levels lower than at stage 2. Glucose and fructose concentrations were very low at stage 1, markedly increased at stage 2, and further increased at stage 3. These results suggest that acid invertase activities play a very important role in increasing soluble sugars of petals during flower opening. Following harvest at stage 3, florets or cut flowers were treated with 50 μmol L−1 6-benzylaminopurine (BA) by dipping or spraying, respectively. These treatments extended vase life longer than in the controls. In the florets experiment, CWIN and VIN activities were significantly higher with a BA dip than in the control for petals at 3 and 6 d, but there were no significant differences in sugar concentrations between the control and BA dip groups. In cut flowers at 3 d after cutting, VIN activity and glucose concentration were higher in the outer petals treated with BA spray than in control petals. From these results, application of exogenous cytokinin has some effect of maintaining high acid invertase activity, and high invertase activity itself may be important for delaying senescence in cut dahlia flowers. BA application is useful for extending petal longevity and is expected to be a popular post-harvest treatment in cut dahlia flowers.

Modifying Effects of Some Plant Hormones on Zucchini Cotyledons Subjected to High Temperature and Excess Copper

AbstractThe aim of the study was to investigate the potential beneficial effects of exogenous application of methyl jasmonate (MeJa) and phenylurea cytokinin (4PU-30) on zucchini (Cucurbita pepo L.) cotyledons subjected to high temperature (HT) and combined HT plus excess copper (Cu2+) stress. Compared to HT stressed zucchini cotyledons, exposure to excess Cu2+ prior to HT treatment inhibited the growth, decreased superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione reductase (GR) activities, increased glutathione-Stransferase (GST) and peroxidase (Px) total activities, and induced new enzyme isoforms (GST4, GST8, and Px4). The effect of MeJa on the double-stressed plants was to increase SOD, GPx and Px total activities and stimulate the activity of GST8, GST9, GST10, SOD5, Px3 and Px8 isoenzymes. In addition to SOD, GPx and Px, 4PU-30 increased GST total activity, up-regulated Px1 and GR1, and had a higher stimulatory effect on SOD5, Px3, GPx3, GST9 and GST10 activities. Copper, 4PU-30 and MeJa treatments changed the abundance and pattern (MeJa) of soluble zucchini polypeptides in a specific manner. MeJa and especially 4PU-30 applied alone, or in combination, stimulated the growth of later HT-treated cotyledons. 4PU-30 counteracted better than MeJa in the HT+heavy metal-caused inhibition of the growth. The data indicated that both MeJa and 4PU- 30 may protect the zucchini plants from high temperature and combined high temperature plus excess copper stress, but 4PU-30 was more effective; the protective effect was related to the changes in the gene expression, total antioxidant enzyme activities and the activity of individual isoforms of the enzymes.