Release Of Buds Research Articles

Current perspectives on shoot branching regulation

Shoot branching is regulated by the complex interactions among hormones, development, and environ- mental factors. Recent studies into the regulatory mecha- nisms of shoot branching have focused on strigolactones, which is a new area of investigation in shoot branching regulation. Elucidation of the function of the D53 gene has allowed exploration of detailed mechanisms of action of strigolactones in regulating shoot branching. In addition, the recent discovery that sucrose is key for axillary bud release has challenged the established auxin theory, in which auxin is the principal agent in the control of apical dominance. These developments increase our understan- ding of branching control and indicate that regulation of shoot branching involves a complex network. Here, we first summarize advances in the systematic regulatory network of plant shoot branching based on current information. Then we describe recent developments in the synthesis and signal transduction of strigolactones. Based on these considerations, we further summarize the plant shoot branching regulatory network, including long distance systemic signals and local gene activity mediated by strigolactones following perception of external envi- ronmental signals, such as shading, in order to provide a comprehensive overview of plant shoot branching.

Cytokininy a polární transport auxinu v axilárních pupenech hrachu

The influence of cytokinin on auxin transport during release of axillary buds from apical dominance was studied. Expression of auxin-carrier coding genes PsAUX1 (AUXIN RESISTANT 1) and PsPIN1 (PIN-FORMED 1) was explored in axillary buds of the 2nd node of 7-day pea plants (Pisum sativum L.) cv. Vladan after decapitation or after exogenous application of benzyladenine (6-benzylaminopurine) onto axillary buds of intact plants. Localization of the PsPIN1 protein, the key factor for polar transport of auxin in axillary buds, was visualised by immunohistochemistry. After exogenous application of cytokinin the expression of PsAUX1 and PsPIN1 rapidly increased with a simultaneous rapid decrease in PsDRM1 and PsAD1 expression – genes related to bud dormancy. The same changes in expression were observed after decapitation, however they were markedly slower. The PsPIN1 auxin efflux carrier in the inhibited axillary buds of intact plants was localised in a non-polar manner. After exogenous application of cytokinin gradual polarisation of the PsPIN1 protein occurred on the basal pole of polar auxin transport competent cells. Despite the fact that direct auxin application to buds of intact plants led to an increase in PsAUX1 and PsPIN1 expression, the buds remained dormant (non-growing) what was accompanied by persistent expression of the dormancy markers PsDRM1 and PsAD1. The results indicate a possible effect of cytokinins on biosynthesis, and/or transport of auxin in axillary buds and they highlight the importance of auxin-cytokinin crosstalk in the regulation of bud outgrowth after breaking of apical dominance.

Sugars take a central position in plant growth, development and, stress responses. A focus on apical dominance.

Sugars take a central position in plant growth, development and, stress responses. A focus on apical dominance.

EFFECT OF UNICONAZOLE ON FLOWERING, YIELD AND FRUIT QUALITY ON DURIAN

This study was aimed to investigate the effect of uniconazole (UCZ) on inducing early flowering, fruit yield and quality in durian cultivar ‘Monthong’. In the 1st year, a single foliar spray at a high concentration of 2,500 mg L-1 UCZ was made, compared to multiply sprays of 1.5 mg L-1 brown seaweed extracts, a conventionally used solution. The results showed that UCZ sprayed at mature leaf stage after 2nd leaf flushing could hasten flower emergence. UCZ very strongly inhibited inflorescence length, shortening the fruit stalk. There was no significant effect of UCZ on fruit yield but UCZ reduced fruit size. Analysis of fresh fruit showed that UCZ decreased both fresh weight and normal seeds. In vivo pollen germination, observation showed that UCZ delayed pollen tube growth. In the 2nd year, the experiment was conducted to find a suitable concentration for early durian fruiting. Lower concentrations of UCZ could induce both early flowering and more flowering branches than non-chemical application. All lower concentrations of UCZ had no effect on fruit yield. Spraying of 100 mg L-1 UCZ had no effect on suppression of inflorescence elongation and fruit size. UCZ at 250 and 500 mg L-1 inhibited only fruit width, whereas no other fruit size characteristics were suppressed. All lower concentration of UCZ decreased both fresh weight and the number of normal seeds. These results suggest that UCZ promoted flowering in durian by shortening the time of bud release. The reduction of pollen tube growths caused by UCZ could be attributed to the inhibition of normal seed development. We recommended the lower concentration of UCZ at 100 mg L-1 for early durian production.

The dormancy-breaking stimuli “chilling, hypoxia and cyanamide exposure” up-regulate the expression of α-amylase genes in grapevine buds

It has been suggested that respiratory stress is involved in the mechanism underlying the dormancy-breaking effect of hydrogen cyanamide (H2CN2) and sodium azide in grapevine buds; indeed, reductions in oxygen levels (hypoxia) and inhibitors of respiration promote bud-break in grapevines. In this study, we showed that, hypoxia increased starch hydrolysis soluble sugar consumption and up-regulated the expression of α-amylase genes (Vvα-AMYs) in grapevine buds, suggesting that these biochemical changes induced by hypoxia, may play a relevant role in the release of buds from endodormancy (ED). Three of the four Vvα-AMY genes that are expressed in grapevine buds were up-regulated by hypoxia and a correlation between changes in sugar content and level of Vvα-AMY gene expression during the hypoxia treatment was found, suggesting that soluble sugars mediate the effect of hypoxia on Vvα-AMY gene expression. Exogenous applications of soluble sugars and sugar analogs confirmed this finding and revealed that osmotic stress induces the expression of Vvα-AMY1 and Vvα-AMY3 and that soluble sugars induces Vvα-AMY2 and Vvα-AMY4 gene expression. Interestingly, the plant hormone gibberellic acid (GA3) induced the expression of Vvα-AMY3 and Vvα-AMY4 genes, while dormancy breaking stimuli, chilling and cyanamide exposure, mainly induced the expression of Vvα-AMY1 and Vvα-AMY2 genes, suggesting that these two α-amylase genes might be involved in the release of grapevine buds from the ED.

Rhizobium-induced elevation in xylem cytokinin delivery in pigeonpea induces changes in shoot development and leaf physiology.

Inoculation with Rhizobium strain IC3342 induces in pigeonpea (Cajanus cajan (L) Millsp.) a leaf curl syndrome and elevated cytokinin levels in the xylem sap. High nitrogen (N) nutrition was found to inhibit onset of the syndrome which could then be induced by N-free nutrient after development of seven trifoliate leaves. This provided a new system to study the role of xylem cytokinin in shoot development and yielded plants suitable for determining the rate of delivery of xylem cytokinin to the shoot which for IC3342-inoculated plants was found to be three times that of control plants. Relative to leaves of control plants, the non-curled leaves of these IC3342 plants exhibited higher nitrogen and chlorophyll content and greater photosynthetic rate and stomatal conductance. Induction of the syndrome increased leaf thickness in developing leaves but not in expanded leaves already formed. Diameter of stems and number of laterals were also increased markedly by IC3342 inoculation which in addition induced leaf hyponasty. Exogenous cytokinins when applied directly to control leaves induced leaf curl and increased leaf thickness. The present studies are discussed in relation to the role of xylem cytokinins in plant development and especially the release of lateral buds from apical dominance.

Is GABA-shunt functional in endodormant grapevine buds under respiratory stress?

It has been suggested that a respiratory stress is part of the mechanism through which the dormancy-breaking compounds, hydrogen cyanamide (HC) and sodium azide, induce the release of buds from the endodormancy (ED) in grapevines. The accumulation of metabolites like succinate, alanine (Ala) and γ-amino butyric acid (GABA), together with the activation of the GABA-shunt pathway, is a general feature of plants in response to oxygen deprivation and to respiratory stress. Unexpectedly, in a previous study, we found that GABA applied exogenously to grapevine buds, down-regulated the expression of most genes encoding for antioxidant enzymes, suggesting that its accumulation under respiratory stress conditions could be deleterious for the bud. In order to analyze whether GABA accumulates under respiratory stress conditions in grapevine buds, we analysed in this study, the effect of hypoxia, the respiration inhibitor KCN and the dormancy breaker compound HC, on the level of GABA, and on the expression levels of the GABA-shunt genes (VvGAD, VvGABA-T, VvSSADH). Additionally, genes from the Ala fermentative pathway (VvAlaAT, VvAspAT) were also analysed. The results revealed that although the three treatments mentioned above, up-regulated the expression of VvGAD1, the content of GABA remained constant, while Ala content increased. The lack of GABA accumulation under respiratory stress is an important physiological fact in grapevine buds, since it avoids the down-regulation of antioxidant genes, and promotes the incorporation of succinate into the TCA cycle, a fact that would be important in the release of buds from the ED.

RATIONALIZATION OF CAMELLIA JAPONICA L. POT CULTIVATION: A MULTIDISCIPLINARY APPROACH

Camellia japonica L. is an evergreen flowering perennial with more than 3,000 named cultivars of great ornamental value. These are nowadays traded worldwide as containerized small sized plants. Cultivation of ornamental plants is strongly oriented to sustainable production on the one hand and on a consumer-oriented high quality product on the other hand. In this context, the present work concerned a series of critical points of the cultivation cycle of potted C. japonica: the reduction of fertilization; the choice of a peat alternative substrate; the regulation of plant growth for size and flowering control; the control of the dormancy release of flower buds. Experiment 1 concerned the application of commercial biofertilizer inocula which included a specific arbuscular mycorrhizal fungus (AMF) isolate or a consortium of microorganisms (AMF, saprophytic fungi and helper bacteria) as alternatives to inorganic fertilization of pot cultivated C. japonica. To deepen AMF role, Experiment 2 evaluated potential specific isolates associated with camellia roots (active population) or surrounding soil (potential and soil exploring population) of centennial specimens found in natural or semi-natural ecosystems. Experiment 3 assessed the efficacy of flurprimidol and three peat alternatives (nutshells, rice husk, coconut fiber) on camellia growth control. Finally, Experiment 4 used a multidisciplinary approach to describe and characterize the effects of cold treatments on the dormancy release of flower buds. Overall, the results highlighted that C. japonica is susceptible to AMF inoculation and that a series of benefits can be achieved by inoculating pots with specific symbiotic fungi. Moreover, two newly tested materials (nutshells and rice husk) were suitable as partial peat alternatives (30% v/v), and the efficacy of very low concentrations of flurprimidol to control growth and enhance flowering was underlined. Lastly, the use of cold treatment allowed the achievement of an earlier, uniform and enhanced flowering.

Viperin: a radical response to viral infection.

One of the first lines of defense of the host immune response to infection is upregulation of interferons, which play a vital role in triggering the early nonspecific antiviral state of the host. Interferons prompt the generation of numerous downstream products, known as interferon-stimulated genes (ISGs). One such ISG found to be either directly induced by type I, II, and III interferons or indirectly through viral infection is the 'virus inhibitory protein, endoplasmic reticulum-associated, interferon-inducible' protein, or viperin. Not only is viperin capable of combating a wide array of viral infections but its upregulation is also observed in the presence of endotoxins, various bacterial infections, or even in response to other immune stimuli, such as atherosclerotic lesions. Recent advances in the understanding of possible mechanisms of action of viperin involve, but are perhaps not limited to, interaction with farnesyl pyrophosphate synthase and disruption of lipid raft domains to prevent viral bud release, inhibition of hepatitis C virus secretory proteins, and coordination to lipid droplets and inhibition of viral replication. Unexpectedly, new insight into the human cytomegalovirus induction of this antiviral protein demonstrates that mitochondrial viperin plays a necessary and beneficial role for viral propagation.

Hypoxia and hydrogen cyanamide induce bud-break and up-regulate hypoxic responsive genes (HRG) and VvFT in grapevine-buds

It has been reported that dormancy-breaking compound hydrogen cyanamide (HC) stimulates the fermentative pathway and inhibits respiration in grapevine-buds, suggesting in this way, that a respiratory stress must be involved in the release of buds from dormancy. Here, we tested low-oxygen effect (hypoxia) on the bud-break response of endodormant grapevine buds, and HC and hypoxia effects on the expression of hypoxic responsive genes (HRG) PYRUVATE DECARBOXYLASE (VvPDC), ALCOHOL DEHYDROGENASE (VvADH2), SUCROSE SYNTHASE (VvSUSY), non-symbiotic HEMOGLOBIN (VvnsHb), and on FLOWERING LOCUS T (VvFT), a transcription factor related to dormancy release in Vitis. Hypoxia as HC, induce transiently the expression of HRG and VvFT and hasten the sprouting of endodormant grapevine-buds. During the first 24 h after treatment, HRG and VvFT were strongly induced by hypoxia, subsequently, their expressions fell, and 14 days post-treatment increased again above control levels. These results indicate that in the short-term, a respiratory stress, caused either by oxygen deprivation or by inhibitors of respiration, induces transiently the expression of HRG and VvFT, and in the long-term, along with the advancement of bud-break, the expression of these genes move forward in treated buds, suggesting that these second induction that occurs just before bud-break is developmentally regulated.

Changes in nitrogen and polyamines during breaking bud dormancy in “Anna” apple trees with foliar application of some compounds

The capacity of hydrogen cyanamide (Dormex), potassium nitrate (KNO3) and mineral oil for breaking of dormancy in buds of “Anna” apple (Malus sylvestris, Mill) trees, and their effects on metabolic changes of nitrogen (N) and polyamines (PAs) in buds during bud break were determined. Our results showed that the capacity to release of buds from dormancy was noticed in varying degrees with these compounds. Breaking bud dormancy was correlated with the early date of bud break, the short duration of flowering, the high percentages of bud break and fruit-set, and the high contents of soluble N and PAs. The best results were obtained with Dormex; therefore we recommend using this compound for reaching the bud break as early as possible, the short period of flowering and the high percentages of bud break and fruit-set by regulating the contents of N and PAs in buds.

Determining the growth responses of Phyla canescens to shoot and root damage as a platform to better-informed weed-management decisions

Understanding the responses of invasive plants to control methods is important in developing effective management strategies. Lippia (Phyla canescens (Kunth) Greene : Verbenaceae) is an invasive, perennial, clonal forb for which few control options exist for use in the Australian natural and agro-ecosystems it threatens. To help inform management decisions, lippia’s growth responses to damage it may experience during proposed control measures, i.e. cutting, crushing, twisting, were assessed in three glasshouse experiments using either whole plants or plant pieces. Plants quickly recovered from severe damage through growth from shoot and root buds at stem nodes. After shoot and root removal, the relative growth rate of the remaining plant was twice that of controls, suggesting tolerance to damage. Lacking buds, root pieces and isolated stem internodes were incapable of responding. Crushing and cutting individual ramets and plant pieces induced the largest responses, including release of axillary buds on damage or removal of apical buds, but full recovery was not achieved. Lippia will be difficult to control because of its ability to rapidly propagate from stem fragments possessing undamaged or damaged nodes; thus, the full impact of control methods that increase fragmentation (e.g. grazing) should be assessed before implementation. Our results also suggest that the most effective biological agents will be those that limit lippia’s vegetative growth and spread, such as shoot- or crown-feeding insects.

Developmental variation in DNA methylation in poplar (Populus trichocarpa)

Using methylated DNA immunoprecipitation followed by high-throughput sequencing (MeDIP-seq), we analyzed DNA methylation patterns in the P. trichocarpa genome in relation to four biological processes: bud dormancy and release, mature organ maintenance, in vitro organogenesis, and methylation suppression. Here, we report results from Illumina sequencing of nine sampled tissues, each representing 1 to 2 biological replicates. We sequenced 26M – 97M reads per tissue type, and validated our MeDIP-seq results using bisulfite sequencing of selected targets. Unique MeDIP-seq reads covered ~30-60% of genome space at an average depth of 4 to 12 reads/nucleotide. Transposons and other repeat elements were enriched within the methylated fraction of the genome. The pattern of gene model methylation showed higher methylation at promoters, in the middle of coding regions, and 3’ to ends of genes, similar to that observed in other plant and animal species. Numbers of methylated genes identified varied widely by tissue type. We produced summary data for genome methylation in P. trichocarpa, including the distribution of methylation across chromosomes (Fig. 1) and in and around genes. The intensity of methylation was highly heterogeneous within and between chromosomes. One-third of the genome, analyzed as 1 kb tiled windows, was differentially methylated among tissues. An example of a chromosomal region with differential methylation is shown in Fig. 2. Promoter methylation was more frequent than gene body methylation. Male catkins differed from the other tissues in that gene body methylation was more prevalent than promoter methylation, and two

Association of the Endosomal Sorting Complex ESCRT-II with the Vps20 Subunit of ESCRT-III Generates a Curvature-sensitive Complex Capable of Nucleating ESCRT-III Filaments

The scission of membranes necessary for vesicle biogenesis and cytokinesis is mediated by cytoplasmic proteins, which include members of the ESCRT (endosomal sorting complex required for transport) machinery. During the formation of intralumenal vesicles that bud into multivesicular endosomes, the ESCRT-II complex initiates polymerization of ESCRT-III subunits essential for membrane fission. However, mechanisms underlying the spatial and temporal regulation of this process remain unclear. Here, we show that purified ESCRT-II binds to the ESCRT-III subunit Vps20 on chemically defined membranes in a curvature-dependent manner. Using a combination of liposome co-flotation assays, fluorescence-based liposome interaction studies, and high-resolution atomic force microscopy, we found that the interaction between ESCRT-II and Vps20 decreases the affinity of ESCRT-II for flat lipid bilayers. We additionally demonstrate that ESCRT-II and Vps20 nucleate flexible filaments of Vps32 that polymerize specifically along highly curved membranes as a single string of monomers. Strikingly, Vps32 filaments are shown to modulate membrane dynamics in vitro, a prerequisite for membrane scission events in cells. We propose that a curvature-dependent assembly pathway provides the spatial regulation of ESCRT-III to fuse juxtaposed bilayers of elevated curvature.

Expression analysis of PpDAM5 and PpDAM6 during flower bud development in peach ( Prunus persica)

We previously reported transcript amounts of peach PpDAM5 and PpDAM6 ( Prunus persica Dormancy- Associated MADS 5 and 6 ) were negatively correlated with endodormancy release of peach vegetative buds ( Yamane et al., 2011). We here investigated PpDAM5 and PpDAM6 expressions in lateral flower buds of peach in relation to seasonal flower bud development by using peach cultivars differing in their chilling requirements, and thus, in their flowering time. Up-regulation of PpDAM5 and PpDAM6 during the flower organ differentiation stage was followed by down-regulation during the flower organ enlargement stage. Furthermore, artificial cold temperature treatments in winter simultaneously induced down-regulation of PpDAM5 and PpDAM6 and flower organ enlargement. Based on these results, we discuss a possible involvement of PpDAM5 and PpDAM6 in the phenological control of peach flower bud development.

Gene level responses of shortleaf pine and loblolly pine to top removal

Young shortleaf pine sprouts prolifically after death of the stem due to top removal or fire damage. Considerable interest has been shown in shortleaf pine restoration due to continually declining native populations. Shortleaf pine’s strong sprouting ability has tremendous potential in promoting its regeneration. However, little is known about its sprouting mechanisms at the molecular level. We designed a microarray experiment to study genes responsible for sprouting ability. In this study, 1-year-old shortleaf pine and loblolly pine seedlings’ tops were removed mechanically and the remaining stem tissues collected just before sprouting. Shortleaf pine showed an extraordinarily strong sprouting ability. Large numbers of sprouts were seen within 2 days after top removal. However, loblolly pine developed only a few sprouts about 1 week following top removal. Using microarray gene profiling with about 2,400 cDNA clones obtained from suppression subtractive hybridization, 139 differentially expressed genes were found to be associated with the sprouting response, including genes functioning in reserve (carbohydrates, protein, and fatty acid) mobilization, transcriptional regulation, stress response, plant development, signal transduction, and hormone regulation. Shortleaf pine responds actively to top removal at the molecular level, while loblolly pine apparently does not. As reported for dormancy release of buds of other perennial plants, oxidative stress might be the major cause of dormancy release of axillary buds of shortleaf pine. Apparent cross talk between plant hormones (gibberellins, auxins, and ethylene), carbohydrates, and other players of signal transduction leads to the cooperative promotion of sprouting of shortleaf pine after top removal.

Short Exposure to Sublethal Heat Shock Facilitates Dormancy Release in Grapevines

A wet heat shock (WHS) treatment in a water bath at 50°C for 1 hr is a powerful stimulus for grapevine budbreak. However, this treatment is not feasible as a horticultural practice in commercial vineyards. The development of an effective horticultural dormancy release practice favors a short, intense heat shock that combines convenient application and effective stimulation of budbreak. Thus, the influence of heat shock temperature and duration on dormancy release of grapevine buds was studied. Results suggested that in both WHS and dry heat shock (DHS) treatments, increased temperature can compensate for shortened shock duration. In addition, it appeared that buds better tolerate DHS than WHS. Based on these results, we analyzed the effect of short and intense heat shock on budbreak. A DHS of 10 to 30 sec at the sublethal temperature of 150°C served as a powerful stimulus of dormancy release. This short shock induced production of acetaldehyde and ethylene from the buds, as follows application of hydrogen cyanamide. This similarity suggests that analogous mechanisms are activated by the short, sublethal temperature pulse and the commercially used chemical stimulus. The efficiency of short and intense heat shock, which has not been previously documented, will aid the development of a feasible and practical treatment in commercial vineyards.

An FTIR study of the induction and release of kiwifruit buds from dormancy

Many deciduous, perennial fruit crops require winter chilling for adequate budbreak and flowering. Recent research has shown that changes in sugar and amino acid profiles are associated with the release of buds from dormancy. This paper uses FTIR spectrometry to provide an alternative mechanism for tracking metabolic changes in the meristems of kiwifruit buds during winter dormancy. The results suggest that the application of multivariate analysis to FTIR spectra has the potential to be a reliable and fast method for detecting structural and compositional changes in fruit crops. Ten wave numbers of the FTIR spectra are used to calculate a bud development function. This function has been validated using data from two seasons and four orchards, and by monitoring the effects of hydrogen cyanamide application, sugar concentrations and soil temperatures on this function. These wave numbers appear to be associated with carbohydrate, pectin and cellulose levels in the meristems. It is expected that this FTIR signature can be used to advance our understanding of the influence of the various environmental and physiological factors on the breaking of bud dormancy and shoot outgrowth, including the optimum timing and concentrations of applications of budbreak regulators, such as hydrogen cyanamide.

Bamboo, fire and flood: consequences of disturbance for the vegetative growth of a clumping, clonal plant

The clumping growth form of tropical bamboos suggests a consolidator strategy in the face of intense competition rather than an ability to exploit disturbance. We investigated the annual growth and culm demographic responses to disturbance by fire and flood of vegetatively mature clumps of a riparian stand of Bambusa arnhemica. Linear-mixed models were employed to control for the non-independence of culm fates within clumps and clump growth among years. As the stand was monodominant and the species is gregariously monocarpic, responses can be interpreted independently of interspecific competition and trade-offs with sexual reproduction. Disturbance depressed clump growth but the culm demographic responses to fire and flood were quite different. Few culms were destroyed during the fire but damage depressed their subsequent survival, leading to declines in clump basal area. Fire also triggered the release of ramet buds, but the additional recruits were small and short-lived. Prolonged and early flooding in one of the study years depressed culm recruitment in clumps low on the lagoon bank but there was possible compensatory recruitment in the following year. There was no convincing evidence that sparse clumps recruited culms better than dense clumps, though culm recruitment was negatively correlated with culm survival. Fire and prolonged flooding are inevitable elements of the environment occupied by B. arnhemica, but we interpret the species’ response as persisting in the face of disturbance rather than exploiting the opportunities created by it.

Computational modeling and molecular physiology experiments reveal new insights into shoot branching in pea.

Bud outgrowth is regulated by the interplay of multiple hormones, including auxin, cytokinin, strigolactones, and an unidentified long-distance feedback signal that moves from shoot to root. The model of bud outgrowth regulation in pea (Pisum sativum) includes these signals and a network of five RAMOSUS (RMS) genes that operate in a shoot-root-shoot loop to regulate the synthesis of, and response to, strigolactones. The number of components in this network renders the integration of new and existing hypotheses both complex and cumbersome. A hypothesis-driven computational model was therefore developed to help understand regulation of shoot branching. The model evolved in parallel with stepwise laboratory research, helping to define and test key hypotheses. The computational model was used to verify new mechanisms involved in the regulation of shoot branching by confirming that the new hypotheses captured all relevant biological data sets. Based on cytokinin and RMS1 expression analyses, this model is extended to include subtle but important differences in the function of RMS3 and RMS4 genes in the shoot and rootstock. Additionally, this research indicates that a branch-derived signal upregulates RMS1 expression independent of the other feedback signal. Furthermore, we propose xylem-sap cytokinin promotes sustained bud outgrowth, rather than acting at the earlier stage of bud release.