Nicholas H. Battey

Exocytosis and endocytosis

Exocytosis is a general term used to denote vesicle fusion at the plasma membrane, and it is the final step in the secretory pathway that typically begins in the endoplasmic reticulum (ER), passes through the Golgi apparatus, and ends at the outside of the cell. Endocytosis refers to the recovery of

Annexins: multifunctional components of growth and adaptation

Plant annexins are ubiquitous, soluble proteins capable of Ca(2+)-dependent and Ca(2+)-independent binding to endomembranes and the plasma membrane. Some members of this multigene family are capable of binding to F-actin, hydrolysing ATP and GTP, acting as peroxidases or cation channels. These multifunctional proteins are distributed throughout the plant and throughout the life cycle. Their expression and intracellular localization are under developmental and environmental control. The in vitro properties of annexins and their known, dynamic distribution patterns suggest that they could be central regulators or effectors of plant growth and stress signalling. Potentially, they could operate in signalling pathways involving cytosolic free calcium and reactive oxygen species.

Ca2+, Annexins, and GTP Modulate Exocytosis from Maize Root Cap Protoplasts

Protoplasts isolated from root cap cells of maize were shown to secrete fucose-rich polysaccharides and were used in a patch–clamp study to monitor changes in whole-cell capacitance. Ca2+ was required for exocytosis, which was measured as an increase in cell capacitance during intracellular dialysis with Ca2+ buffers via the patch pipette. Exocytosis was stimulated significantly by small increases above normal resting [Ca2+]. In the absence of Ca2+, protoplasts decreased in size. In situ hybridization showed significant expression of the maize annexin p35 in root cap cells, differentiating vascular tissue, and elongating cells. Dialysis of protoplasts with maize annexins stimulated exocytosis at physiological [Ca2+], and this could be blocked by dialysis with antibodies specific to maize annexins. Dialysis with millimolar concentrations of GTP strongly inhibited exocytosis, causing protoplasts to decrease in size. GTPγS and GDPβS both caused only a slight inhibition of exocytosis at physiological Ca2+. Protoplasts were shown to internalize plasma membrane actively. The results are discussed in relation to the regulation of exocytosis in what is usually considered to be a constitutively secreting system; they provide direct evidence for a role of annexins in exocytosis in plant cells.

Reversion of flowering

Reversion from floral to vegetative growth is under environmental control in many plant species. However the factors regulating floral reversion, and the events at the shoot apex that take place when it occurs, have received less attention than those associated with the transition to flowering.Reversions may be categorized as flower reversion, in which the flower meristem resumes leaf production, or inflorescence reversions, in which the meristem ceases to initiate bracts with flowers in their axils and begins instead to make leaves with vegetative branches in their axils. Related to these two types of reversion, but distinct from them, are examples of partial flowering, when non-floral meristems grow out so that the plant begins to grow vegetatively again. Anomalous or proliferous flowers may form as a result of unfavourable growth conditions or viral infection, but these do not necessarily involve flower reversions.There are many examples of inflorescence reversion but fewer clearly defined cases of flower reversion. In flower reversion the meristem of the flower itself reverts to vegetative growth so that flowers with basal floral organs and distal leaves on the same axis are formed successively by the apical meristem. InPharbitis nil, Anagallis arvensis, andImpatiens balsamina flower reversions have been caused by defined environmental conditions. However, only inImpatiens has detailed study of the changes in growth and development at the shoot apex during reversion been carried out. These studies show that changes in apical growth and phyllotaxis that typically accompany flowering can be separated from the development of floral organs and suggest that the floral stimulus plays a role throughout flower morphogenesis. The occurrence of reverting organs intermediate between leaves and petals is of particular interest in allowing experiments to be done on the progress of determination at the cell, tissue and organ levels. Reversion indicates that the flowering process must be regarded as a continuum, with physiological stages such as commitment to flower, and even morphological stages such as different floral organ types, being to varying extents artificial. Further study of the regulation of floral morphogenesis, and of the events associated with reversion, may provide important information on the nature of the factors that bring about the onset of flowering itself.ResuméChez de nombreuses espèces végétales, la réversion de l’état floral vers l’état végétatif est controlée par l’environnement. Cependent, alors que beaucoups de recherches ont été consacrées à la transition vers la mise à fleur, peu d’études concernant les facteurs régulateurs de la réversion florale et les évènements survenant à l’apex de la tige lors de cette réversion ont été réalisées.On peut distinguer deux types de réversion: la réversion de la fleur, et dans ce cas le méristème floral se met à produire des feuilles; la réversion de l’inflorescence, où le méristème de l’inflorescence cesse l’initiation des bractées avec des fleurs axillaires et se met à initier des feuilles avec des tiges végétatives axillaires. Tout en differant de ces deux types de réversion, la floraison partielle ou incomplète, qui se traduit par la croissance des méristèmes non-floraux (c’est à dire une croissance encore végétative de la plante qui a déjà formé des fleurs), leurs est liée. Des fleurs anomales ou prolifères peuvent se former lorsque les conditions de croissance sont peu favourables ou lors d’une infection virale, mais sans que la réversion florale soit nécessairement impliquée.On connait de nombreuses exemples de réversion de l’inflorescence, mais peu d’examples de réversion de la fleur. La réversion de la fleur se traduit par la réversion du méristème floral vers une croissance végétative. Dans ce cas, les fleurs possèdent des pièces florales basales et des feuilles distales, toutes portées par le même axe, et formées successivement par l’action du méristème apical. On sait que les conditions de l’environnement causent des réversions de la fleur chezPharbitis nil, Anagallis arvensis etImpatiens balsamina. Chez l’Impatiens, les changements de la croissance et du développement du méristème apical pendant la réversion ont été étudiés en détail. Ces études montrent que les changements survenant dans la croissance apicale et la phyllotaxie, qui accompagnent typiquement la mise à fleurs, peuvent être expérimentalement séparés du mode de développement des organes floraux. Ceci suggère que le stimulus floral joue un rôle continu pendant la morphogénèse florale. L’existence d’organes intermédiaires entre des feuilles et des petales est très intéressante, puisqu’elle permet de réaliser des experiences pour suivre la progression de la détermination aux niveaux des cellules, des tissus, et des organes. L’existence de la réversion florale indique que l’on peut considérer la mise à fleur et la floraison comme des processus continus, avec des étapes physiologiques (par exemple l’engagement à la floraison), et morphologiques (par exemple la formation des différents types de pièces florales), même si cette classification est dans une certaine measure artificielle. Des études plus approfondies de la régulation de la morphogénèse florale et des évènements associés à la réversion pourraient apporter d’importantes informations sur la nature des facteurs qui contrôlent la mise à fleur.

Zea mays Annexins Modulate Cytosolic Free Ca2+ and Generate a Ca2+-Permeable Conductance

Regulation of reactive oxygen species and cytosolic free calcium ([Ca2+]cyt) is central to plant function. Annexins are small proteins capable of Ca2+-dependent membrane binding or membrane insertion. They possess structural motifs that could support both peroxidase activity and calcium transport. Here, a Zea mays annexin preparation caused increases in [Ca2+]cyt when added to protoplasts of Arabidopsis thaliana roots expressing aequorin. The pharmacological profile was consistent with annexin activation (at the extracellular plasma membrane face) of Arabidopsis Ca2+-permeable nonselective cation channels. Secreted annexins could therefore modulate Ca2+ influx. As maize annexins occur in the cytosol and plasma membrane, they were incorporated at the intracellular face of lipid bilayers designed to mimic the plasma membrane. Here, they generated an instantaneously activating Ca2+-permeable conductance at mildly acidic pH that was sensitive to verapamil and Gd3+ and had a Ca2+-to-K+ permeability ratio of 0.36. These results suggest that cytosolic annexins create a Ca2+ influx pathway directly, particularly during stress responses involving acidosis. A maize annexin preparation also demonstrated in vitro peroxidase activity that appeared independent of heme association. In conclusion, this study has demonstrated that plant annexins create Ca2+-permeable transport pathways, regulate [Ca2+]cyt, and may function as peroxidases in vitro.

Arabidopsis Annexin1 Mediates the Radical-Activated Plasma Membrane Ca2+- and K+-Permeable Conductance in Root Cells

The Arabidopsis thaliana root cell plasma membrane contains a calcium channel that is activated by oxidizing conditions and operates in cell growth. It was identified here as the most abundant member of the Arabidopsis annexins. These are soluble proteins that can undergo conditional attachment to or insertion into membranes. Plant cell growth and stress signaling require Ca2+ influx through plasma membrane transport proteins that are regulated by reactive oxygen species. In root cell growth, adaptation to salinity stress, and stomatal closure, such proteins operate downstream of the plasma membrane NADPH oxidases that produce extracellular superoxide anion, a reactive oxygen species that is readily converted to extracellular hydrogen peroxide and hydroxyl radicals, OH•. In root cells, extracellular OH• activates a plasma membrane Ca2+-permeable conductance that permits Ca2+ influx. In Arabidopsis thaliana, distribution of this conductance resembles that of annexin1 (ANN1). Annexins are membrane binding proteins that can form Ca2+-permeable conductances in vitro. Here, the Arabidopsis loss-of-function mutant for annexin1 (Atann1) was found to lack the root hair and epidermal OH•-activated Ca2+- and K+-permeable conductance. This manifests in both impaired root cell growth and ability to elevate root cell cytosolic free Ca2+ in response to OH•. An OH•-activated Ca2+ conductance is reconstituted by recombinant ANN1 in planar lipid bilayers. ANN1 therefore presents as a novel Ca2+-permeable transporter providing a molecular link between reactive oxygen species and cytosolic Ca2+ in plants.

Mutation in TERMINAL FLOWER1 reverses the photoperiodic requirement for flowering in the wild strawberry, Fragaria vesca

Photoperiodic flowering has been extensively studied in the annual short-day and long-day plants rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana), whereas less is known about the control of flowering in perennials. In the perennial wild strawberry, Fragaria vesca (Rosaceae), short-day and perpetual flowering long-day accessions occur. Genetic analyses showed that differences in their flowering responses are caused by a single gene, SEASONAL FLOWERING LOCUS, which may encode the F. vesca homolog of TERMINAL FLOWER1 (FvTFL1). We show through high-resolution mapping and transgenic approaches that FvTFL1 is the basis of this change in flowering behavior and demonstrate that FvTFL1 acts as a photoperiodically regulated repressor. In short-day F. vesca, long photoperiods activate FvTFL1 mRNA expression and short days suppress it, promoting flower induction. These seasonal cycles in FvTFL1 mRNA level confer seasonal cycling of vegetative and reproductive development. Mutations in FvTFL1 prevent long-day suppression of flowering, and the early flowering that then occurs under long days is dependent on the F. vesca homolog of FLOWERING LOCUS T. This photoperiodic response mechanism differs from those described in model annual plants. We suggest that this mechanism controls flowering within the perennial growth cycle in F. vesca and demonstrate that a change in a single gene reverses the photoperiodic requirements for flowering.

Temperate flowering phenology

Individuals, families, networks, and botanic gardens have made records of flowering times of a wide range of plant species over many years. These data can highlight year to year changes in seasonal events (phenology) and those datasets covering long periods draw interest for their perspective on plant responses to climate change. Temperate flowering phenology is complex, using environmental cues such as temperature and photoperiod to attune flowering to appropriate seasonal conditions. Here we give an overview of flowering phenological recording, outline different patterns of flowering, and look at the interpretation of datasets in relation to seasonal and climatic change.

The potential of ISSR-PCR primer-pair combinations for genetic linkage analysis using the seasonal flowering locus in Fragaria as a model

Abstract ISSR-PCR has been widely used for genetic distance analysis and DNA fingerprinting but has been less well utilised for mapping purposes. A key limitation lies in the small number of primer designs available to generate useful polymorphisms. In this study, the potential of paired combinations of ISSR primers is evaluated using a test cross mapping population of 168 BC1 individuals between Fragaria vesca f. vesca and a closely related line F. vesca f. semperflorens. Ten ISSR primers and all possible pairwise combinations between them were used to generate markers potentially linked to the locus controlling seasonal flowering in F. vesca. Band profiles of individual primers were found to be highly reproducible for band position and intensity, and only minor variation was noted in band intensity (but not in position) between different constituent mixes of primer-pair combinations. Overall, ISSR primers used in isolation produced 85 markers of which only five were specific to F. vesca. None of these markers were linked to the seasonal flowering locus. In contrast, the primer-pair combina-tions yielded 493 markers, including 14 specific to F. vesca. These markers included two located within 2.2 cM of the seasonality locus. The strengths and limitations of using pairs of ISSR primers in combination for mapping and other genetic analyses are briefly explored.

Molecular control and variation in the floral transition

The common controls that are involved in both vegetative and floral development are becoming apparent at the molecular level. Intriguing links are also emerging between developmental events during the juvenile/adult and floral transitions. This progress has made it possible to test the annual model of floral transition in a wide range of plant species, including those that flower perennially.