Bud Content and its Relation to Shoot Size and Structure in Nothofagus pumilio(Poepp. et Endl.) Krasser (Nothofagaceae)

Buds of shoots from the trunk, main branches, secondary branchesand short branches of 10–21 year-old Nothofagus pumiliotrees were dissected and their contents recorded. The numberof differentiated nodes in buds was compared with the numberof nodes of sibling shoots developed at equivalent positionsduring the following growing season. Axillary buds generallyhad four cataphylls, irrespective of bud position in the tree,whereas terminal buds had up to two cataphylls. There were morenodes in terminal buds, and the most distal axillary buds, oftrunk shoots than in more proximal buds of trunk shoots, andin all buds of shoots at all other positions. The highest numberof nodes in the embryonic shoot of a bud varied between 15 and20. All shoots had proximal lateral buds containing an embryonicshoot with seven nodes, four with cataphylls and three withgreen leaf primordia. The largest trunk, and main branch, shootswere made up of a preformed portion and a neoformed portion;all other shoots were entirely preformed. In N. pumilio, theacropetally-increasing size of the sibling shoots derived froma particular parent shoot resulted from differences in: (1)the number of differentiated organs in the buds; (2) the probabilityof differentiation of additional organs during sibling shootextension; (3) sibling shoot length; (4) sibling shoot diameter;and (5) the death of the apex and the most distal leaves ofeach sibling shoot. Copyright 2000 Annals of Botany Company Axis differentiation, branching, bud structure, leaf primordia, neoformation, Nothofagus pumilio, preformation, size gradient     

Periods of organogenesis in shoots of Nothofagus dombeyi (Mirb.) oersted (Nothofagaceae)

The organogenetic cycle of main-branch shoots of Nothofagus dombeyi (Nothofagaceae) was studied. Twelve samples of 52-59 parent shoots were collected from a roadside population between September 1999 and October 2000. Variations over time in the number of nodes of terminal and axillary buds, and the length, diameter and number of leaves of shoots derived from these buds (sibling shoots) were analysed. The number of nodes of buds developed by parent shoots was compared with the number of nodes of buds developed, I year later, by sibling shoots. The length, diameter and number of leaves of sibling shoots increased from October 1999 to February 2000 in those shoots with a terminal bud. However, extension of most sibling shoots, including the first five most distal leaf primordia, ceased before February due to abscission of the shoot apex. Axillary buds located most distally on a shoot had more nodes than both terminal buds and more proximal axillary buds. The longest shoots included a preformed part and a neoformed part. The organogenetic event which initiated the neoformed organs continued until early autumn, giving rise to the following year's preformation. The absence of cataphylls in terminal buds could indicate a low intensity of shoot rest. The naked terminal bud of Nothofagus spp. could be interpreted as a structure less specialized than the scaled bud found in genera of Fagaceae and Betulaceae.     

Analysing branching pattern in plantations of young red oak trees (Quercus rubra L., Fagaceae)

Branching patterns of the growth units of monocyclic or bicyclic annual shoots on the main axis of 5-year-old red oaks were studied in a plantation in south-western France. For each growth unit, the production of axillary structures associated with each node was described in the form of a sequence. For a given category of growth units, homogeneous zones (i.e. zones in which composition in terms of type of axillary production does not change substantially) were identified on such sequences using a dedicated statistical model called a hidden semi-Markov chain. For instance, on the first growth unit of bicyclic annual shoots, a zone with 1-year-delayed branches was found systematically below a zone with buds and one-cycle-delayed branches. Branching patterns shown by the growth unit of monocyclic annual shoots and on the second growth unit of bicyclic annual shoots were very similar. Branches with a 1-year delay in development tended to be polycyclic at the top of the growth unit and monocyclic lower down. The number of nodes shown by the branched zone of the growth unit of monocyclic annual shoots was stable, irrespective of the total number of nodes of the growth unit. In contrast, the second growth unit of bicyclic annual shoots exhibited a correlation between the number of nodes in the branching zone and the total number of nodes. The contribution made by this method to understanding plant functioning is discussed.     

Growth Dynamics and Morphology of Annual Shoots, According to their Architectural Position, in Young Cedrus atlantica (Endl.) Manetti ex Carriere (Pinaceae)

The influence of shoot architectural position on growth andbranching pattern of young Cedrus atlantica (Endl.) Manettiex Carrière trees were studied. Extension growth andtype of axillary products (lateral bud, sylleptic short or longshoots) of annual shoots of increasing branching order (mainstem, branches and branchlets) were recorded weekly during the1993 growing season. Annual final shoot length, duration ofextension, and maximum extension rate decreased with increasingbranching order. Sylleptic axillary shoots occurred only onannual shoots of the main stem and branches and were producedwhen extension rate was at its highest. Differences in growthrate and final length of annual shoots, according to their architecturalposition, were related to differences in the total number anddiversity of types of sylleptic axillary shoots produced. Itis suggested that types and numbers of sylleptic axillary shootsproduced are linked with threshold values for both final lengthand extension rate of the parent shoot. Copyright 1999 Annalsof Botany Company Atlas cedar, extension growth, sylleptic branching, tree architecture, morphology.     

Bud Structure in Relation to Shoot Morphology and Position on the Vegetative Annual Shoots of Juglans regia L. (Juglandaceae)

The length and basal diameter of all lateral and terminal budsof vegetative annual shoots of 7-year-oldJuglans regia treeswere measured. All buds were dissected and numbers of cataphylls,embryonic leaves and leaf primordia were recorded. Each axillarybud was ranked according to the position of its associated leaffrom the apex to the base of its parent shoot. Bud size andcontent were analysed in relation to bud position and were comparedwith the size and number of leaves of shoots in equivalent positionswhich extended during the following growing season. Length andbasal diameter of axillary buds varied according to their positionon the parent shoot. Terminal buds contained more embryonicleaves than any axillary bud. The number of leaves was smallerfor apical and basal axillary buds than for buds in intermediatepositions on the parent shoot only. All new extended shootswere entirely preformed in the buds that gave rise to them.Lateral shoots were formed in the median part of the parentshoot. These lateral shoots derived from buds which were largerthan both apical and basal ones. Copyright 2001 Annals of BotanyCompany Juglans regia L., Persian walnut tree, branching pattern, preformation, bud content, shoot morphology     

Periods of organogenesis in mono- and bicyclic annual shoots of Juglans regia L. (Juglandaceae)

The organogenetic cycle of shoots on main branches of 4-year-old Juglans regia trees was studied. Mono- and bicyclic floriferous and vegetative annual shoots were analysed. Five parent annual shoot types were sampled between October 1992 and August 1993. Organogenesis of summer growth units was monitored between 16 Jun. and 3 Aug. 1993. Variations over time in the number of nodes, cataphylls and embryonic green leaves of terminal buds were studied. The number of nodes of parent shoot buds was compared with the number of nodes of shoots derived from parent shoot buds. The spring growth units of mono- and bicyclic shoots consist exclusively of preformed leaves which were differentiated, respectively, during the spring flush of growth (mid-April until mid-May) or the summer flush of growth (mid-June until early August) in the previous growing season. Thus, winter buds may consist of flower and leaf primordia differentiated in two different periods during annual shoot extension. The summer growth units of bicyclic shoots consist of preformed leaves that were differentiated in spring buds during the spring flush of growth in the current growing season. Bud morphology is compared between spring and summer shoots.     

Branching responses in Silphium integrifolium (Asteraceae) following mechanical or gall damage to apical meristems and neighbor removal

Branching in plants increases plant access to light and provides pathways for regrowth following damage or loss of the apical meristem. We conducted two experiments in an eastern Kansas tallgrass prairie to determine how apical meristem loss (by clipping), apical meristem damage (by insect galling), and increased light availability affected growth, reproduction, and branching in Silphium integrifolium (Asteraceae). The first experiment compared clipping with galling. Clipping increased axillary shoot numbers, while galling increased axillary shoot lengths, reflecting different allocation responses among damage types and inhibition of branching by galls. However, total capitulum production was less in all gall/clip treatments than in intact shoots. The second experiment compared clipping with mowing the surrounding vegetation to increase light availability. Mowing increased total leaf, total capitulum, and axillary shoot length and axillary capitulum production in clipped and unclipped plants and in large vs. small shoots. The presence of the neighboring canopy, not of an intact apical meristem, was therefore the stronger limitation on leaf and capitulum production. These experiments suggest that damage and light competition affected both branching frequency and the partitioning of resources among shoots, branches, and leaves. Because Silphium's growth form is widespread, similar responses may occur in other grassland forbs.     

Preformation and neoformation in shoots of Nothofagus antarctica (G. Forster) Oerst. (Nothofagaceae) shrubs from northern Patagonia

The size (length and diameter) and number of leaf primordia of winter buds of Nothofagus antarctica (G. Forster) Oerst. shrubs were compared with the size and number of leaves of shoots derived from buds in equivalent positions. Buds developed in two successive years were compared in terms of size and number of leaf primordia. Bud size and the number of leaf primordia per bud were greater for distal than for proximally positioned buds. Shoots that developed in the five positions closest to the distal end of their parent shoots had significantly more leaves than more proximally positioned shoots of the same parent shoots. The positive relationship between the size of a shoot and that of its parent shoot was stronger for proximal than for distal positions on the parent shoots. For each bud position on the parent shoots there were differences in the number of leaf primordia per bud between consecutive years. The correlations between the number of leaf primordia per bud and bud size, bud position and parent shoot size varied between years. Only shoots produced close to the distal end of a parent shoot developed neoformed leaves; more proximal sibling shoots consisted entirely of preformed leaves. Leaf neoformation, a process usually linked with high shoot vigour in woody plants, seems to be widespread among the relatively small shoots developed in N. antarctica shrubs, which may relate to the species' opportunistic response to disturbance.     

The origin, initiation and development of axillary shoot meristems in Lotus japonicus

BACKGROUND AND AIMS: Lotus japonicus 'Gifu' develops multiple axillary shoots in the cotyledonary node region throughout the growth of the plant. The origin, initiation and development of these axillary meristems were investigated. METHODS: Morphological, histological and mRNA in situ analyses were done to characterize the ontogeny of cotyledonary axillary shoot meristems in Lotus. Morphological characterization of a putative Lotus shoot branching mutant (super-accessory branches) sac, is presented. KEY RESULTS: By using expression of an L. japonicus STM-like gene as a marker for meristematic tissues, it was demonstrated that groups of cells maintained in the meristematic state at the cotyledonary axil region coincide with the sites where additional axillary meristems (accessory meristems) form. A Lotus shoot branching mutant, sac, is a putative Lotus branching mutant characterized by increased proliferation of accessory shoots in all leaf axils including the cotyledons. CONCLUSION: In Lotus, axillary shoot meristems continually develop at the cotyledonary node region throughout the growth of the plant. These cotyledonary primary and accessory axillaries arise from the position of a meristematic zone of tissue at the cotyledonary node axil region.     

Relative extents of preformation and neoformation in tree shoots: Analysis by a deconvolution method

BACKGROUND AND AIMS: Neoformation is the process by which organs not preformed in a bud are developed on a growing shoot, generally after preformation extension. The study of neoformation in trees has been hindered due to methodological reasons. The present report is aimed at assessing the relative importance of preformation and neoformation in the development of shoots of woody species. METHODS: A deconvolution method was applied to estimate the distribution of the number of neoformed organs for eight data sets corresponding to four Nothofagus species and a Juglans hybrid. KEY RESULTS: The number of preformed organs was higher and less variable than the number of neoformed organs. Neoformation contributed more than preformation to explain full-size differences between shoots developed in different positions within the architecture of each tree species. CONCLUSIONS: Differences between the distributions of the numbers of preformed and neoformed organs may be explained by alluding to the duration of differentiation and extension for each of these groups of organs. The deconvolution of distributions is a useful tool for the analysis of neoformation and shoot structure in trees.     

Preformation of Node Number in Vegetative and Reproductive Proleptic Shoot Modules of Persea (Lauraceae)

The numbers of nodes on single flush terminal and axillary shootmodules were determined in a range of Persea species and cultivars.They were compared with node numbers in apical and axillarybuds to investigate whether preformation or neoformation ofnodes occurred. Mean number of nodes on terminal shoots was14 for vegetative shoot modules and 21 for reproductive shootmodules, and was similar across species, cultivars, rootstocks,locations and climates. In the cultivar 'Hass', numbers of nodeson axillary shoot modules were variable, and lower than thosefor primary shoot modules forming the dominant growth axis ofannual growth modules. There was a mean of 12 nodes for vegetativeproleptic shoot modules, 15 for reproductive proleptic shootmodules and six for sylleptic shoot modules, which were invariablyvegetative. All nodes were preformed within both apical andaxillary proleptic buds. This was not the case in syllepticbuds, which burst contemporaneously with extension of the parentaxis. The majority (63%) of reproductive buds formed indeterminatecompound inflorescences. They carried six basal bud scales,six axillary inflorescences and their subtending bracts, andup to nine true leaves.Copyright 1994, 1999 Academic Press Persea Clus., avocado, Persea americana Mill., bud morphology, shoot growth, preformation, prolepsis     

Application of architectural analysis and AMAPmod methodology to study dwarfing phenomenon: the branch structure of 'Royal Gala' apple grafted on dwarfing and non-dwarfing rootstock/interstock combinations

Architectural analysis was applied to study branch development of 'Royal Gala' apple trees grafted with dwarfing and non-dwarfing rootstock/interstock combinations, which had been chosen to produce trees with a wide range of vigour. Using AMAPmod methodology, the structure of 3-year-old branches was described at four levels of representation: branch; annual shoot; growth unit; and node. Three types of growth units were distinguished: extension growth unit (vegetative unit with internode extension); vegetative spur with minimal internode extension; and fruiting spur or bourse. The aim of the analysis was to describe exactly how the rootstock/interstock combinations affected the structure building process. The number of extension growth units, vegetative spurs and fruiting spurs per annual shoot changed over the years, but this was not affected by rootstock/interstock combination. Compared with MM.106 rootstock, M.9 rootstock reduced the number of nodes per extension growth unit. In most cases, rootstock/interstock combination had no effect on the linear relationship between extension growth unit length and node number (R(2) = 0.88). Average internode length depended on unit node number, with internodes being shorter for units with fewer nodes. Thus the difference in apple branch size induced by the rootstock/interstock combinations was mainly due to a reduction in the length and number of neoformed nodes produced on extension growth units. As percentage budbreak of axillary buds on extension growth units was not affected by rootstock/interstock combination, differences in numbers of axillary annual shoots per branch were entirely due to differences in the total numbers of nodes extended during the previous year.     

Patterns of leaf size and morphology in relation to shoot length in Tsuga canadensis

Summary Pattern of change in leaf character was assessed along the length and around the circumference of Tsuga canadensis (L.) Carr. shoots of different length classes. Leaf size decreased, and number of leaves per unit length of shoot increased, with decrease in shoot length. Acropetally along the shoots, lamina length and width decreased, relative petiole length increased, apices became more pointed, and leaf margins bore more teeth. Around the shoot, from upper to side, and to lower surfaces, leaf size and number of marginal teeth in the proximal halves of leaves increased. These patterns were related both to production of preformed versus neoformed leaves, though their separation was indistinct, and to secondary orientation of leaves by twisting in their petiolar regions into two major bi-lateral ranks. An additional minor rank occurred along the upper surfaces of the shoots where secondary orientation of the leaves was minimal. Surface features of leaves did not differ in any obvious manner. Leaves on sylleptic shoots, which by definition were all neoformed, exhibited similar patterns, but were generally smaller than those on their parent shoots.     

Preformed and neoformed extension of shoots and sylleptic branching in relation to shoot length in Tsuga canadensis

Summary Shoot systems developed over 3 successive years were investigated on 55 understorey Tsuga canadensis (L.) Carr. trees. Paired comparisons of preformed-leaf content of terminal buds and numbers of leaves produced on new shoots showed that neoformed leaves were produced in large numbers. Parent-shoot character was not useful in predicting numbers of preformed leaves, was better related to total leaves produced, but left the majority of the variation unexplained. This reflected the capacity of any terminal bud to produce a shoot with more or less neoformation, depending on conditions for growth. All shoots over 6 cm long produced sylleptic shoots that bore from two to many leaves and were arranged in a mesitonic pattern along the parent. Some of the longer sylleptic shoots produced lateral buds or second-order sylleptic shoots. Monopodial second-year extensions of sylleptic-shoot axes followed an acrotonic pattern, as did proleptic shoots from the few lateral buds borne on the parent shoots. Such lateral buds were more frequent on shorter parent shoots: they typically occurred near the proximal and distal ends. Duration of shoot extension was positively correlated with shoot length: terminal buds became evident as shoot extension neared cessation.     

Relationship between reproductive behavior and new shoot development in 5-year-old branches of olive trees (Olea europaea L.)

The development of new shoots plays a central role in the complex interactions determining vegetative and reproductive growth in woody plants. To explore this role we evaluated the new shoots in the olive tree, Olea europaea L., and the effect of fruiting on new shoot growth and subsequent flowering. Five-year-old branches served as canopy subunits in order to obtain a global, whole-tree view of new shoot number, size and morphological origin. The non-bearing trees had many more shoots than the fruit-bearing trees, and a greater number of longer shoots. In both bearing conditions, however, the majority of shoots were less than 4 cm long, with shoots of progressively longer lengths present in successively decreasing frequencies. Six major shoot types were defined on the basis of apical or lateral bud origin and of parent shoot age. On fruit-bearing trees, the new shoots originated predominantly from the shoot apex, while on non-fruiting trees, they formed mainly from axillary buds, but in both cases, they tended to develop on younger parent shoots. The previous bearing condition of the tree was the main determinant for subsequent inflorescence development, which was independent of both shoot type and length. Thus, reproductive behavior strongly affected both the amount and type of new branching, but subsequent flowering level was more influenced by previous bearing than by the potential flowering sites on new shoots.     

Development of shoot inHydrangea macrophylla II. sequence and timing

The development of axillary buds, terminal buds, and the shoots extended from them was studied inHydrangea macrophylla. The upper and lower parts in a nonflower-bearing shoot are discernible; the preformed part of a shoot develops into the lower part and the neoformed part into the upper part (Zhou and Hare, 1988). These two part are formed by the different degrees of internode elongation at early and late phases during a growth season, respectively. Leaf pairs in the neoformed part of the shoot are initiated successively with a plastochron of 5–20 days after the bud burst in spring. The upper axillary buds are initiated at approximately the same intervals as those of leaf pairs, but 10–30 days later than their subtending leaves. Changes in numbers of leaf pairs and in lengths of successive axillary buds show a pattern similar to the changes in internode lengths of the shoot at the mature stage. The uppermost axillary buds of the flower-bearing shoot often begin extending into new lateral shoots when the flowering phase has ended. The secondary buds in terminal and lower axillary buds are initiated and developed in succession during the late phase of the growth season. Internode elongation seems to be important in determining the degrees of development of the axillary buds. Pattern of shoot elongation is suggested to be relatively primitive. Significances of apical dominance and environmental conditions to shoot development are discussed.     

Micropropagation of <Emphasis Type="Italic">Pongamia pinnata</Emphasis> through enhanced axillary branching

A complete protocol is presented for the first time for the micropropagation of Pongamia pinnata, a biofuel tree, using cotyledonary nodes derived from axenic seedlings. Multiple shoots were induced in vitro from nodal segments through forced axillary branching. Murashige and Skoog (MS) medium supplemented with 7.5 μM benzylaminopurine (BAP) induced up to 6.8 shoots per node with an average shoot length of 0.67 cm in 12 d. Incorporation of 2.5 μM gibberellic acid (GA₃) in the medium during the first subculture after establishment and initiation of shoot buds significantly improved the shoot elongation. Single use of GA₃ during the first subculture eliminated the need for prolonged culturing on BAP medium. Further use of GA₃ in the medium was not useful. Shoot culture was established for at least two subcultures without loss of vigor by repeatedly subculturing the original cotyledonary node on shoot multiplication medium followed by shoot elongation medium after each harvest of the newly formed shoots. Thus, from a single cotyledonary node, about 16–18 shoots were obtained in 60 d. Shoots formed in vitro were rooted on full-strength MS medium supplemented with 1.0 μM indole butyric acid (IBA). Plantlets were successfully acclimated, established in soil, and transferred to the nursery.     

Architectural analysis of 1-year-old apple seedlings according to main shoot growth and sylleptic branching characteristics

Main shoot and sylleptic shoot growth characteristics were measured during and after the first year of growth of 255 Telamon x Braeburn apple seedlings. Although mean main shoot growth characteristics between branched and non-branched trees were significantly different, many non-branched trees expressed similar main shoot growth to branched trees. The variables describing length, number and position of the sylleptic shoots were used to classify branched trees into architecturally different groups. A continuum from trees with few and short shoots to trees with many long shoots is observed. The release of axillary buds from apical dominance is not under complete control by the apical meristem. Genetic seedling difference at the level of roots presumably plays an important role in sylleptic branching. Genetic variation in terms of number, position, and subsequent elongation of sylleptic shoots is clearly observed.     

Winter bud content according to position in 3-year-old branching systems of 'Granny Smith' apple

An investigation was made of the number of preformed organs in winter buds of 3-year-old reiterated complexes of the 'Granny Smith' cultivar. Winter bud content was studied with respect to bud position: terminal buds were compared on both long shoots and spurs according to branching order and shoot age, while axillary buds were compared between three zones (distal, median and proximal) along 1-year-old annual shoots in order 1. The percentage of winter buds that differentiated into inflorescences was determined and the flowers in each bud were counted for each bud category. The other organ categories considered were scales and leaf primordia. The results confirmed that a certain number of organs must be initiated before floral differentiation occurred. The minimum limit was estimated at about 15 organs on average, including scales. Total number of lateral organs formed was shown to vary with both bud position and meristem age, increasing from newly formed meristems to 1- and 2-year-old meristems on different shoot types. These differences in bud organogenesis depending on bud position, were consistent with the morphogenetic gradients observed in apple tree architecture. Axillary buds did not contain more than 15 organs on average and this low organogenetic activity of the meristems was related to a low number of flowers per bud. In contrast, the other bud categories contained more than 15 differentiated organs on average and a trade-off was observed between leaf and flower primordia. The ratio between the number of leaf and flower primordia per bud varied with shoot type. When the terminal buds on long shoots and spurs were compared, those on long shoots showed more flowers and a higher ratio of leaf to flower primordia.     

Apple shoot architecture: evidence for strong variability of bud size and composition and hydraulics within a branching zone

* In the apple tree (Malus domestica), shoot architecture - the distribution of lateral bud types and growth along the parent shoot - has been extensively investigated. The distal zone of a shoot is characterized by a high proportion of vegetative or floral axillary branches mixed with latent buds and aborted laterals. The hypothesis tested here was that bud development was related to hydraulic conductance of the sap pathway to the bud, independently of an acrotonic (proximal vs distal) effect. * The distal zone of 1-yr-old shoots was studied on five cultivars for bud size and composition (number of appendages) and hydraulic conductance before bud burst. * Bud size, composition and hydraulic conductance were highly variable for all cultivars. A positive correlation was demonstrated between both the number of cataphylls and green-leaf primordia, and hydraulic conductance. Cultivar and bud size affected the intercept of these relationships more than the slope, suggesting similar scaling between these variables, but different hydraulic efficiencies. A great proportion of small buds were also characterized by null values of hydraulic conductance. * This study suggests that hydraulically mediated competition exists between adjacent buds within the same branching zone, prefiguring the variability of lateral types in the following growing season. It is hypothesized that this developmental patterning is driven by hydraulic characteristics of the whole metamer, including the subtending leaf, during bud development.