Dormant Axillary Buds Research Articles

A Conserved Carbon Starvation Response Underlies Bud Dormancy in Woody and Herbaceous Species.

Plant shoot systems give rise to characteristic above-ground plant architectures. Shoots are formed from axillary meristems and buds, whose growth and development is modulated by systemic and local signals. These cues convey information about nutrient and water availability, light quality, sink/source organ activity and other variables that determine the timeliness and competence to maintain development of new shoots. This information is translated into a local response, in meristems and buds, of growth or quiescence. Although some key genes involved in the onset of bud latency have been identified, the gene regulatory networks (GRNs) controlled by these genes are not well defined. Moreover, it has not been determined whether bud dormancy induced by environmental cues, such as a low red-to-far-red light ratio, shares genetic mechanisms with bud latency induced by other causes, such as apical dominance or a short-day photoperiod. Furthermore, the evolution and conservation of these GRNs throughout angiosperms is not well established. We have reanalyzed public transcriptomic datasets that compare quiescent and active axillary buds of Arabidopsis, with datasets of axillary buds of the woody species Vitis vinifera (grapevine) and apical buds of Populus tremula x Populus alba (poplar) during the bud growth-to-dormancy transition. Our aim was to identify potentially common GRNs induced during the process that leads to bud para-, eco- and endodormancy. In Arabidopsis buds that are entering eco- or paradormancy, we have identified four induced interrelated GRNs that correspond to a carbon (C) starvation syndrome, typical of tissues undergoing low C supply. This response is also detectable in poplar and grapevine buds before and during the transition to dormancy. In all eukaryotes, C-limiting conditions are coupled to growth arrest and latency like that observed in dormant axillary buds. Bud dormancy might thus be partly a consequence of the underlying C starvation syndrome triggered by environmental and endogenous cues that anticipate or signal conditions unfavorable for sustained shoot growth.

Genetic stability of physiological responses to defoliation in a eucalypt and altered chemical defence in regrowth foliage.

Defoliation may initiate physiological recovery and chemical defence mechanisms that allow a plant to improve fitness after damage. Such responses may result in changes in plant resource allocation that influence growth and foliar chemistry. In this study, we investigated the nature and stability of the defoliation response of juvenile plants from three divergent populations of Eucalyptus globulus Labill. A partial defoliation treatment that removed all upper crown leaves and the apical buds was applied to plants sourced from eight families from each of three populations representing contrasting chemical resistance to mammalian herbivory. Growth, photosynthetic rate and chlorophyll content were assessed pre-defoliation and periodically up to 12 weeks post-defoliation. The content of key plant primary and secondary metabolites was assessed pre-defoliation, at 12 weeks post-defoliation in the old foliage (positioned below the point of defoliation) and in the new foliage of the control plants and regrowth (from axillary buds) on the defoliated plants. There were clear treatment impacts on physiological responses, growth and foliar chemical traits, but despite significant constitutive differences in physiology, growth and chemistry the three E. globulus populations did not vary in their response to foliage loss. Distinct physiological responses to defoliation were observed with treatment plants showing significant up-regulation of photosynthetic rate and increased chlorophyll content in the old foliage remaining in the lower crown. There was a significant increase in the concentrations of a number of foliar chemical compounds in the regrowth arising from previously dormant axillary buds compared with new growth derived from apical meristems. There were changes in biomass allocation; defoliated plants had increased branching and leaf biomass, with changes in regrowth morphology to increase light capture. This study argues for multiple responses of E. globulus juveniles to defoliation involving apical bud loss, including elevated chemical defences matched with increased growth. From a chemical defence perspective, these responses create an enhanced chemical mosaic to the herbivore, with leaves remaining after partial browsing potentially being more palatable than the regrowth. This study demonstrates the multiple independent strategies plants may use to respond to partial defoliation and emphasizes the dynamic interplay between growth and defence in the recovery response.

Improved Micropropagation of Plantlets from Nodal Explants of Anchote (Coccinia abyssinica)—A Calcium- and Protein-rich Tuber

The effect of phytohormones on breaking of dormancy of axillary buds in anchote and their subsequent shoot proliferation were examined. Anchote is an annual trailing endemic plant with high calcium content grown for its edible tuberous roots in Ethiopia. Nodal explants harvested from the greenhouse were sterilized using various concentrations of a commercial bleach (JIK) which contains 3.85% sodium hypochlorite (NaOCl) and time duration. The highest (85%) clean explants were obtained when 5% JIK was used for 15 minutes. The explants were cultured on Murashige and Skoog (MS) medium supplemented with various concentrations of benzylaminopurine (BAP), kinetin, and thidiazuron (TDZ). The highest frequency of microshoot induction (84%) and mean number of microshoots (3.4) were recorded from explants cultured on medium supplemented with TDZ 0.025 µm. Hyperhydrated shoots were observed on media supplemented with high concentrations of BAP and kinetin but interestingly not on TDZ media. Induction of roots was highest (86%; 4.6 roots per shoot) when shoots were transferred to half strength MS medium containing 0.5 μm α-naphthalene acetic acid (NAA) after 12 days. A survival rate of 83% was recorded in the greenhouse and the plantlets appeared to be morphologically normal. This is the first report on use of TDZ for in vitro propagation of anchote.

Short day transcriptomic programming during induction of dormancy in grapevine.

Bud dormancy in grapevine is an adaptive strategy for the survival of drought, high and low temperatures and freeze dehydration stress that limit the range of cultivar adaptation. Therefore, development of a comprehensive understanding of the biological mechanisms involved in bud dormancy is needed to promote advances in selection and breeding, and to develop improved cultural practices for existing grape cultivars. The seasonally indeterminate grapevine, which continuously develops compound axillary buds during the growing season, provides an excellent system for dissecting dormancy, because the grapevine does not transition through terminal bud development prior to dormancy. This study used gene expression patterns and targeted metabolite analysis of two grapevine genotypes that are short photoperiod responsive (Vitis riparia) and non-responsive (V. hybrid, Seyval) for dormancy development to determine differences between bud maturation and dormancy commitment. Grapevine gene expression and metabolites were monitored at seven time points under long (LD, 15 h) and short (SD, 13 h) day treatments. The use of age-matched buds and a small (2 h) photoperiod difference minimized developmental differences and allowed us to separate general photoperiod from dormancy specific gene responses. Gene expression profiles indicated three distinct phases (perception, induction and dormancy) in SD-induced dormancy development in V. riparia. Different genes from the NAC DOMAIN CONTAINING PROTEIN 19 and WRKY families of transcription factors were differentially expressed in each phase of dormancy. Metabolite and transcriptome analyses indicated ABA, trehalose, raffinose and resveratrol compounds have a potential role in dormancy commitment. Finally, a comparison between V. riparia compound axillary bud dormancy and dormancy responses in other species emphasized the relationship between dormancy and the expression of RESVERATROL SYNTHASE and genes associated with C3HC4-TYPE RING FINGER and NAC DOMAIN CONTAINING PROTEIN 19 transcription factors.

Secondary Growth of the Leaf and Bud Traces in Hylocereus undatus (Cactaceae) during the Formation of Branches or Flowers

Premise of research. Hylocereus undatus produces two different types of woody structures supporting its lateral shoots. Although a branch and a flower both derive from the same initials, the dormant axillary buds (in cacti aka areoles), the fully developed support structures within the succulent cortex of the parental shoot differ significantly in their macroscopic and microscopic anatomy. The objective of our research was to analyze the secondary growth of these two structures as they develop from their initial state as leaf/bud traces that connect the axillary bud with the stele of the parental shoot.Methodology. Macroscopic anatomy was visualized by a staining and clearing technique for lignified elements of whole-plant organs. The microscopic anatomy was investigated with microtome sections of samples embedded in wax and stained with safranin and fast green.Pivotal results. The vascular tissue of both support structures has a wood dimorphism consisting of an early parenchymatous phase followed later b...

Physiological Response of In Vitro Cultured MAGNOLIASP. to Nutrient Medium Composition

Abstract The objective of this study was to assess the regeneration response of in vitro cultured Magnolia × soulangeana ‘Alexandrina’ and Magnolia liliiflora ‘Nigra’ to nutrient medium composition. In the primary culture (initiated from dormant axillary buds) combinations of Murashige and Skoog (MS) basal salts with 6-benzylaminopurine and α-naphthaleneacetic acid were tested. The primary explants of cv. ‘Alexandrina’ expressed higher regeneration rate than cv. ‘Nigra’. For both species, the regen eration was most strongly potentiated at addition of 0.25 mg dm−3 of the cytokinin alone. The auxin exerted undesir–able effects. Several basal salts media were applied in proliferation stage and their physiological effects were evaluated in reference to traditionally used MS. At culturing on Chée & Pool C2d Vitis Medium (VM) that is for the first time introduced to magnolia and on MS, M. liliiflora formed more but less elongated shoots than M. soulangeana. However, on VM, substantial increase (25-30%) of the number of axillary shoots and leaves, shoot length and fresh and dry weights over MS was established for both species. This suggested VM as promising composition of nutrients in multiplication stage. Microshoots obtained on MS, VM, Rugini Olive Medium and DKW Juglans Medium were successfully rooted in vitro and subsequently established ex vitro. The findings expand the information on magnolia response to culture conditions and contribute to elaboration of innovative elements of protocols for establishing tissue cultures with high regeneration capacity.

Identification of differential gene expression profiles between winter dormant and sprouting axillary buds in tea plant (Camellia sinensis) by suppression subtractive hybridization

Tea plant (Camellia sinensis (L.) O. Kuntze) is an important cash crop. In temperate regions, bud dormancy in winter and budbreak in spring are important biological phenomena for the tea plant life cycle. To understand the molecular mechanism of dormancy maintenance and release in tea plant, the differentially expressed genes in dormant and sprouting axillary buds were investigated in two cultivars (special early-sprouting tea cultivar ‘Camellia sinensis cv. Longjing 43’ (‘LJ’) and late-sprouting tea cultivar ‘C. sinensis cv. Zhenghe Dabaicha’ (‘ZD’)), using suppression subtractive hybridization (SSH) approach. Four high performance complementary DNA (cDNA)-SSH libraries (‘LJ’ sprouting bud library, ‘LJ’ dormant bud library, ‘ZD’ sprouting bud library and ‘ZD’ dormant bud library) were constructed, and 1,736 valid ESTs were obtained, in which 1,242 ESTs were unique to the sprouting bud libraries and 494 ESTs were unique to the dormant bud libraries. Based on sequence matching and gene ontology analysis, 1,287 unigenes consisting of 208 contigs and 1,079 singletons were identified, in which 995 had Blast hits. The putative functions of differentially regulated sequences were involved in most aspects of plant biological processes. The quality and expression patterns of partial ESTs from these four libraries were validated by qRT-PCR. We identified numerous differentially expressed genes mainly involved in stress response, water metabolism, cell division regulation, energy metabolism and hormone regulation from dormant and sprouting bud libraries. This study provides general information on tea plant axillary bud dormancy and release at the transcriptional level and provides some hypotheses for further exploration on the mechanism of bud dormancy and budbreak in tea plant.

Roles of DgBRC1 in Regulation of Lateral Branching in Chrysanthemum (Dendranthema ×grandiflora cv. Jinba)

The diverse plasticity of plant architecture is largely determined by shoot branching. Shoot branching is an event regulated by multiple environmental, developmental and hormonal stimuli through triggering lateral bud response. After perceiving these signals, the lateral buds will respond and make a decision on whether to grow out. TCP transcriptional factors, BRC1/TB1/FC1, were previously proven to be involved in local inhibition of shoot branching in Arabidopsis, pea, tomato, maize and rice. To investigate the function of BRC1, we isolated the BRC1 homolog from chrysanthemum. There were two transcripts of DgBRC1 coming from two alleles in one locus, both of which complemented the multiple branches phenotype of Arabidopsis brc1-1, indicating that both are functionally conserved. DgBRC1 was mainly expressed in dormant axillary buds, and down-regulated at the bud activation stage, and up-regulated by higher planting densities. DgBRC1 transcripts could respond to apical auxin supply and polar auxin transport. Moreover, we found that the acropetal cytokinin stream promoted branch outgrowth whether or not apical auxin was present. Basipetal cytokinin promoted outgrowth of branches in the absence of apical auxin, while strengthening the inhibitory effects on lower buds in the presence of apical auxin. The influence of auxin and strigolactons (SLs) on the production of cytokinin was investigated, we found that auxin locally down-regulated biosynthesis of cytokinin in nodes, SLs also down-regulated the biosynthesis of cytokinin, the interactions among these phytohormones need further investigation.

BRANCHED1 promotes axillary bud dormancy in response to shade in Arabidopsis.

Plants interpret a decrease in the red to far-red light ratio (R:FR) as a sign of impending shading by neighboring vegetation. This triggers a set of developmental responses known as shade avoidance syndrome. One of these responses is reduced branching through suppression of axillary bud outgrowth. The Arabidopsis thaliana gene BRANCHED1 (BRC1), expressed in axillary buds, is required for branch suppression in response to shade. Unlike wild-type plants, brc1 mutants develop several branches after a shade treatment. BRC1 transcription is positively regulated 4 h after exposure to low R:FR. Consistently, BRC1 is negatively regulated by phytochrome B. Transcriptional profiling of wild-type and brc1 buds of plants treated with simulated shade has revealed groups of genes whose mRNA levels are dependent on BRC1, among them a set of upregulated abscisic acid response genes and two networks of cell cycle- and ribosome-related downregulated genes. The downregulated genes have promoters enriched in TEOSINTE BRANCHED1, CYCLOIDEA, and PCF (TCP) binding sites, suggesting that they could be transcriptionally regulated by TCP factors. Some of these genes respond to BRC1 in seedlings and buds, supporting their close relationship with BRC1 activity. This response may allow the rapid adaptation of plants to fluctuations in the ratio of R:FR light.

Micropropagation and Microrhizome Induction in Costus pictus D. Don Using In Vitro and Ex Vitro Nodal Segments as Explant

Costus pictus D. Don is a potent anti-diabetic plant used in folk, ayurvedic and homeopathic system of medicine. Gene and protein expression of key targets in insulin signaling pathway have revealed that methyl tetracosonoate, a bio-active molecule from Costus pictus extract has anti-diabetic activity. The axillary buds of Costus pictus are dormant. The dormancy of axillary buds were broken when cultured in Murashige and Skoog (MS) medium supplemented with 3-4 μM 6-benzylaminopurine (BAP) in combination with 0.21 μM naphthalene acetic acid (NAA). The highest bud-break percentage was achieved in those supplemented with 0.6 μM NAA and 3 μM BAP. The sprouted axillary buds were transferred onto medium supplemented with 0.6 μM NAA and 6-10 μM BAP for shoot multiplication. The maximum average number of shoot was achieved in medium supplemented with 0.6 μM NAA and 8 μM BAP. The shoots were successfully rooted when transferred onto media supplemented with 1-12 μM NAA or indole-3-acetic acid (IAA) and 3 μM BAP. The maximum number of roots was found in 8 μM NAA and 3 μM BAP. The dormancy of in vitro axillary buds were also successfully broken in stems from which shoot apex were decapitated and cultured in MS medium with 0.6 μM NAA, 7 μM BAP and 5-13% sucrose. These sprouted in vitro axillary buds could be used as secondary explants for shoot multiplication. The maximum was in medium supplemented with 9% sucrose. Rhizomes were successfully induced when 4-month old plantlets were cultured on 1⁄2 strength MS medium supplemented with 2.4 μM NAA, 32 μM BAP and 5-13% sucrose. Microrhizomes formed in 9% sucrose was largest in size with highest average fresh weight.

Micropropagation of Costus speciosus (Koen.) Sm. Using Nodal Segment Culture

Nodal segments of Costus speciosus (Koen.) Sm. containing single axillary buds were cultured on Murashige and Skoog medium (MS medium) supplemented with plant growth regulators for inducing plantlets. For breaking of axillary bud dormancy, nodal segments were cultured on 40-70gl-1 sucrose or 1-13 μM adenine sulphate (AdS) supplemented MS basal medium containing 5 μM 6-benzylaminopurine (BAP) and 1μM α-naphthalene acetic acid (NAA). The nodal segments cultured on 1-13 μM AdS, 5 μM BAP, 1 μM NAA and 50gl-1 sucrose showed simultaneous production of shoots and roots while those cultured on 5 μM BAP, 1 μM NAA and 40-70gl-1 sucrose produced shoots only. The most effective media for breaking axillary bud dormancy was 5 μM BAP, 1 μM NAA, 50 gl-1 sucrose and 10 μM AdS supplemented medium. The propagules from 40-70gl-1 sucrose produced roots in shoot multiplication medium, i.e.,10 μM AdS, 1 μM NAA, 50gl-1 sucrose and 3-11 μM BAP supplemented medium. The best response for shoot multiplication was on 10 μM AdS, 1 μM NAA, 50gl-1 sucrose and 7 μM BAP. The well-rooted shoots were hardened and transferred to the soil where they showed 95% survival rate. Results show that axillary bud can be used for micropropagation of Costus speciosus.

Vegetative axillary bud dormancy induced by shade and defoliation signals in the grasses

Vegetative axillary bud dormancy and outgrowth is regulated by several hormonal and environmental signals. In perennials, the dormancy induced by hormonal and environmental signals has been categorized as eco-, endo- or para-dormancy. Over the past several decades para-dormancy has primarily been investigated in eudicot annuals. Recently, we initiated a study using the monoculm phyB mutant (phyB-1) and the freely branching near isogenic wild type (WT) sorghum (Sorghum bicolor) to identify molecular mechanisms and signaling pathways regulating dormancy and outgrowth of axillary buds in the grasses. In a paper published in the January 2010 issue of Plant Cell and Environment, we reported the role of branching genes in the inhibition of bud outgrowth by phyB, shade and defoliation signals. Here we present a model that depicts the molecular mechanisms and pathways regulating axillary bud dormancy induced by shade and defoliation signals in the grasses.

Leaf Axil Anatomy and Bud Reserves in 21 Myrtaceae Species from Northern Australia

Dormant axillary buds allow plants to repair minor damage to their canopies. In woody plants, these buds subsequently develop into epicormic structures that may allow vegetative recovery after major disturbances. They are an essential but little‐studied part of the persistence niche. We wondered what bud reserves were present in the leaf axils of northern Australian myrtaceous species, what levels of protection they have, and how this relates to the ecology of these species. Axillary buds of 21 species from 10 genera of northern Australian Myrtaceae were examined anatomically. All species possessed axillary buds in all axils examined, and accessory buds were recorded in 86% of species. The species exhibited an extremely wide range of variation—from axillary buds that consisted of only an apical dome with no leaf primordia (Calytrix exstipulata) to axils with a complex array of accessory buds and meristems located beneath the axil surface (Corymbia and Eucalyptus). The axils of the Eucalyptus and Corymbia species had a greater number of and better protected axillary buds and meristems than the other species studied, including some of their closest relatives, Arillastrum, Allosyncarpia, and Stockwellia. All investigated species had an excellent meristem reserve for recovery of photosynthetic capacity after minor canopy damage and for developing epicormic structures for sprouting after more severe damage. The complex and well‐protected axillary bud or meristem structures of Corymbia and Eucalyptus may be an important component of the success of these genera in Australia.

Genetic stability of micropropagated ginger derived from axillary bud through cytophotometric and RAPD analysis.

A protocol was developed for the in vitro propagation of ginger (Zingiber officinale) cv. Suprava using dormant axillary buds from unsprouted rhizomes. The dormant axillary buds embedded in the rhizome nodes were induced to sprout when cultured on MS medium supplemented with 6-benzyladenine (BA) alone (1-6 mg/1) or with a combination of BA (1-6 mg/1) and indole-3-acetic acid (IAA) (0.5, 1 mg/l). In vitro sprouted buds were transferred to the multiplication medium containing various combinations of auxins and cytokinins. MS basal medium supplemented with BA (1 mg/l), IAA (1 mg/l) and adenine sulfate (100 mg/l) was found optimum for the in vitro multiplication of shoots producing (8.2 +/- 0.2) shoots from a single explant within 30 days of culture. The multiplication rate remained unchanged in subsequent subcultures. Rooting of shoots occurred in the same multiplication media. Upon transfer of the in vitro culture to ex vitro in pots, 96% of plants survived and established successfully under natural conditions. Tissue culture-raised plantlets of ginger could be conserved in vitro through subculturing at an interval of 4 months. The genetic stability of micropropagated clones was evaluated at regular intervals of 6 months up to 24 months in culture using cytophotometric estimation of 4C nuclear DNA content and random amplified polymorphic DNA (RAPD) analysis. Cytophotometric analysis revealed a unimodal distribution of the DNA content with a peak corresponding to the 4C value (23.1 pg), and RAPD analysis revealed monomorphic bands showing the absence of polymorphism in all fifty regenerants analyzed, thus confirming the genetic uniformity among in vitro grown somaclones of Z. officinale. This study is of commercial significance as axillary bud explants are available throughout the year for initiating a fresh culture of the elite ginger cv. Suprava to be used as a source of true-to-type disease-free planting material thereby minimizing the adverse effect of repeated subculturing from the same explant source.

Micropropagation of Salix pseudolasiogyne from nodal explants

The effect of phytohormones on the breaking of dormancy of axillary buds in Salix pseudolasiogyne and their subsequent proliferation from nodal explants were examined. Nodal explants obtained from a 20–year-old S. pseudolasiogyne tree were cultured either on woody plant basal medium (WPM) or WPM supplemented with benzyladenine (BA, 2.2/4.4 μM), zeatin (1.1/2.2 μM), gibberillic acid (GA3, 2.9 and 14.5 μM), and GA3 + BA (2.9 + 4.4 μM). Although axillary shoots developed in all the media, a higher percentage bud break occurred on BA supplemented media. To corroborate the results, endogenous levels of cytokinins [Cks, N 6-isopentenyladenine (iP), zeatin riboside (t-ZR), dihydrozeatinriboside (DHZR)] and abscisic acid (ABA) were determined. On BA supplemented media, the levels of zeatin type (Z-type) of Cks were higher than those of isopentenyladenine type of Ck in the explants, while the ABA level was low. Axillary shoots did not grow well and became necrotic upon subculture to fresh basal WPM. In order to improve shoot growth, they were subcultured twice at a 4-week interval on to WPM supplemented with BA (2.2/4.4 μM), GA3 (1.4 μM), or GA3 + BA (1.4 + 4.4/2.9 + 4.4 μM). Maximal shoot growth (93%) was achieved on WPM supplemented with 2.2 μM BA. Comparative analyses of endogenous Cks revealed that higher Cks (Z-type Cks) were present in actively growing shoots. Rooting was readily achieved when the shoots were subcultured to WPM without phytohormones. The rooted plants were acclimatized well upon transplantation.

PsRBR1 encodes a pea retinoblastoma-related protein that is phosphorylated in axillary buds during dormancy-to-growth transition.

In intact plants, cells in axillary buds are arrested at the G1 phase of the cell cycle during dormancy. In mammalian cells, the cell cycle is suppressed at the G1 phase by the activities of retinoblastoma tumor suppressor gene (RB) family proteins, depending on their phosphorylation state. Here, we report the isolation of a pea cDNA clone encoding an RB-related protein (PsRBR1, Accession No. AB012024) with a high degree of amino acid conservation in comparison with RB family proteins. PsRBR1 protein was detected as two polypeptides using an anti-PsRBR1 antibody in dormant axillary buds, whereas it was detected as three polypeptides, which were the same two polypeptides and another larger polypeptide 2 h after terminal decapitation. Both in vitro-synthesized PsPRB1 protein and lambda protein phosphatase-treated PsRBR1 protein corresponded to the smallest polypeptide detected by anti-PsRBR1 antibody, suggesting that the three polypeptides correspond to non-phosphorylated form of PsRBR1 protein, and lower- and higher-molecular mass forms of phosphorylated PsRBR1 protein. Furthermore, in vivo labeling with [32P]-inorganic phosphate indicated that PsRBR1 protein was more phosphorylated before mRNA accumulation of cell cycle regulatory genes such as PCNA. Together these findings suggest that dormancy-to-growth transition in pea axillary buds is regulated by molecular mechanisms of cell cycle control similar to those in mammals, and that the PsRBR1 protein has an important role in suppressing the cell cycle during dormancy in axillary buds.

A review of the ecology and management of Ranunculus acris subsp. acris in pasture

Summary Ranunculus acris subsp. acris is widespread in pastures across Europe. In New Zealand, it persists in dairy pastures throughout the country, despite the annual use of herbicides, causing a loss in the national yield of milk solids estimated at NZ$156 million in the 2001–2002 milking season. Its persistence appears to be due in part to the production of a blistering agent, protoanemonin, which deters grazing animals, combined with evolved resistance to herbicides and a resilience imparted by a stout rhizome supporting dormant axillary buds. The latter enables regeneration after damage inflicted by herbicides, fungi and other control agents, and facilitates lateral spread and asexual reproduction. Its persistence in dairy pastures may also be influenced by plants recruiting from seeds which are formed annually subject to the availability of insect pollinators. Based on a review of observations and experiments conducted mainly in Europe and New Zealand, we propose a detailed life‐cycle model for R. acris. This provides the basis for a matrix population model that will identify the life‐cycle stages that contribute most to population growth and, hence, the extent to which each of these would need to be targeted for improved management in dairy pastures in New Zealand.

In vitro culture of rose species (Rosa spp.) via axillary bud growth

The utilization of nodal stem cuttings containing dormant axillary buds as explants for plant production of two rose species; Rosa chinensis cv.‘Old Blush’ and R. centifolia cv. ‘Petite de Hollande’ was demonstrated in this study. This propagation technique required the breaking of dormant axillary buds by aseptically culturing them in agarsolidified Woody Plant Medium (WPM) added with 0.5, 1.0, and 2.0 mg l-1 of 6benzylaminopurine (BAP) or, a combination of 2.0 mg l-1 BAP and 0.01 mg l-1 naphthalene acetic acid (NAA). Production of multiple adventitious shoots from one nodal stem explant was obtained after three months of culture in medium supplemented with 1.0 or 2.0 mg l-1 BAP. Four types of plant morphology; single shoot (type 1), multiple shoots with normal leaves (type 2), cluster of tiny shoots with curly leaves (type 3), and single shoot with callus at the base (type 4) were observed from the axillary bud-derived plantlets. The rooting of plantlets was induced in WPM containing 0.25 to 1.0 mg l-1 of indole-butyric acid (IBA) or, 2.0 mg l-1 of indole-3-acetic acid (IAA).

Redesign of the castorbean plant body plan for optimal combine harvesting

SummaryThe seed oil of castorbean (Ricinus communis, Euphorbiaceae) is highly appreciated in several sectors of the chemical industry. A tropical perennial, with sympodial branching, this plant presents, at the same time, both vegetative shoots and inflorescences, as well as racemes with ripe seeds. This architecture is an obstacle to harvesting the plants using the standard combine harvester which requires, as with any other seed crop, that the plants be dry. One agronomic solution is to spray the plants with desiccants. However, in this paper a genetic solution is suggested, that is, an annual plant. This model is discussed within the present knowledge of plant monocarpic senescence. A mutation that changes the quantity and/or the quality of cambial activity could reduce the secondary growth in castorbean, thus favouring the plants death. Moreover, to stop iterative growth which is at the base of the perennial form of castorbean, a non‐branching model is also proposed. The occurrence of this phenotype in some crops (maize and sunflower) and mutants (tomato, barley, etc.) is examined. Considering apical dominance as the primary mechanism at the base of a non‐branching form, a mutation capable of inducing permanent dormancy of axillary buds is discussed. Both mutation breeding and genetic engineering are suggested as major tools to obtain an annual plant of castorbean.

Control of Outgrowth and Dormancy in Axillary Buds

Control of Outgrowth and Dormancy in Axillary Buds