Determination for inflorescence development is a stable state,separable from determination for flower development in Pisum sativum L. buds

Terminal meristems of Pisum sativum (garden pea) transit from vegetative to inflorescence development, and begin producing floral axillary meristems. Determination for inflorescence development was assessed by culturing excised buds and meristems. The first node of floral initiation (NFI) for bud expiants developing in culture and for adventitious shoots forming on cultured meristems was compared with the NFI of intact control buds. When terminal buds having eight leaf primordia were excised from plants of different ages (i.e., number of unfolded leaves) and cultured on 6-benzylaminopurine and kinetin-supplemented medium, the NFI was a function of the age of the source plant. By age 3, all terminal buds were determined for inflorescence development. Determination occurred at least eight nodes before the first axillary flower was initiated. Thus, the axillary meristems contributing to the inflorescence had not formed at the time the bud was explanted. Similar results were obtained for cultured axillary buds. In addition, meristems excised without leaf primordia from axillary buds three nodes above the cotyledons of age-3 plants gave rise to adventitious buds with an NFI of 8.3 ±0.3 nodes. In contrast seed-derived plants had an NFI of 16.5 ±0.2. Thus cells within the meristem were determined for inflorescence development. These findings indicate that determination for inflorescence development in P. sativum is a stable developmental state, separable from determination for flower development, and occurring prior to initiation of the inflorescence at the level of meristems.     

Floral determination in the terminal and axillary buds of Nicotiana tabacum L

The terminal and axillary buds of the day-neutral plant, Nicotiana tabacum cv. Wisconsin 38, become determined for floral development during the growth of the plant. This state of determination can be demonstrated with a simple experiment: buds determined for floral development produce the same number of nodes in situ and if rooted. After several months of growth and the production of many leaves, the terminal bud became determined for floral development within a period of about 2 days. After the terminal bud became florally determined, it produced four nodes and a terminal flower. The buds located in the axils of leaves borne just below the floral branches became florally determined 5 to 9 days after the terminal bud became florally determined. Since florally-determined axillary buds were not clonally derived from a florally-determined terminal meristem, axillary buds and the terminal bud acquired the state of floral determination independently. These data indicate that a pervasive signal induced a state of floral determination in competent terminal and axillary buds.     

Erratum

The number of nodes produced by a bud meristem before differentiation into a flower is defined as its developmental potential. Decapitation, rooting, and grafting experiments were used to measure the developmental potential of the vegetative axillary bud meristems on Nicotiana tabacum. Decapitation experiments measure the in situ developmental potential while rooting and grafting experiments measure developmental potential in isolation and at a new location on the organism, respectively. A rooted or grafted bud exhibits one of two patterns of development: (1) It develops like an in situ bud or (2) It develops according to its new environment. For example, second axillary buds below the inflorescence produced 18.8 ± 0.8 nodes in situ, 17.9 ± 0.9 or 39.8 ± 1.1 nodes when rooted, and 22.2 ± 0.6 or 34.2 ± 0.7 nodes when grafted to the base of the plant. These results suggest that the buds which develop like in situ buds are developmentally determined while buds that develop according to their new environment are undetermined. On an individual plant, determined and undetermined buds are separated by one internode and only first, second, and third buds below the inflorescence exhibit determination.     

The maryland mammoth allele and rooting both perturb the fate of florally determined apices in Nicotiana tabacum.

The stability of the florally determined state in terminal and axillary buds of two tobacco cultivars was studied. We used Hicks and Hicks Maryland Mammoth, near-isogenic cultivars of Nicotiana tabacum differing at the recessive maryland mammoth locus which confers short-day behavior. The experimental design consisted of growing plants in short-day conditions and subjecting them to three bioassays in long-day conditions: in vitro culture of apices consisting of meristems and three to four leaf primordia; rooting of buds consisting of meristems and 8 to 12 leaves, leaf primordia, and internodes; and release from apical dominance of axillary buds in situ. Cultured terminal and axillary apices expressed floral determination, indicating that meristems can be florally determined. Two lines of evidence indicate that rooting destabilizes an already acquired florally determined state: cultured apices from both axillary and terminal buds produced fewer nodes after excision than homologous buds which were rooted; and a lower percentage of rooted axillary buds from Hicks Maryland Mammoth plants expressed floral determination than did homologous axillary buds grown out in situ in noninductive conditions. Rooted buds from the two genotypes expressed floral determination at different frequencies, but produced abnormal inflorescences at similar frequencies, indicating that roots and the maryland mammoth allele influence common as well as unique processes associated with floral determination.     

NODE COUNTING IN AXILLARY BUDS OF NICOTIANA TABACUM CV. WISCONSIN 38, A DAY-NEUTRAL PLANT

A mature, quiescent, primary axillary bud on the main axis of a flowering Nicotiana tabacum cv. Wisconsin 38 plant, when released from apical dominance and before forming its terminal flower, produced a number of nodes which was dependent upon its position on the main axis. Each bud produced about one more node than the next bud above it. The total number of nodes produced by an axillary bud was about 6 to 8 greater than the number of nodes present above this bud on the main axis. At anthesis of the terminal flower on the main axis, mature, quiescent, primary axillary buds had initiated 7 to 9 leaf primordia while secondary axillary buds, sometimes present in addition to the primary ones, had initiated 4 to 5 leaf primordia. When permitted to grow out independently, primary and secondary axillary buds located at the same node on the main axis produced the same number of nodes before forming their terminal flowers. In contrast, immature primary axillary buds which had produced only 5 leaf primordia and which were released from apical dominance prior to the formation of flowers on the main axis produced only as many nodes as would be produced above them on the main axis by the terminal meristem, i.e., “extra” nodes were not produced. Therefore, it is the physiological status of the plant and not the number of nodes on the bud at the time of release from apical dominance that influenced the node-counting process of a bud. When two axillary buds were permitted to develop on the same main axis, each produced the same number of nodes as single axillary buds developing at these nodes. Thus, the counting process in an axillary bud of tobacco is independent of other buds. Axillary buds on main axes of plants that had been placed horizontally produced the same number of nodes as identically-positioned axillary buds on vertical plants, indicating that gravity does not play a major role in the counting, by an axillary bud, of the nodes on the main axis.     

Floral determination in the terminal bud of the short-day plant Pharbitis nil

Temporal and spatial aspects of floral determination in seedling terminal buds of the qualitative short-day plant Pharbitis nil were examined using a grafting assay. Floral determination in the terminal buds of 6-day-old P. nil seedlings is rapid; by 9 hr after the end of a 14-hr inductive dark period more than 50% of the induced terminal buds grafted onto uninduced stock plants produced a full complement of flower buds. When grafted at early times after the end of the dark period the terminal buds of induced plants produced three discrete populations of plants: plants with no flowers, plants with two axillary flowers at nodes 3 and 4 and a vegetative terminal shoot apex, and plants with five to seven flowers including a terminal flower. The temporal relationship among these populations of plants produced by apices grafted at different times indicates that under our conditions, the region of the terminal bud that will form the axillary buds at nodes 3 and 4 becomes florally determined prior to floral determination of the region of the terminal bud giving rise to the nodes above node 4.     

Growth Context and Fate of Axillary Meristems of Young Peach Trees. Influence of Parent Shoot Growth Characteristics and of Emergence Date

The relationship between several growth components of a shootand the fates of the axillary meristems (developing in the axilsof the leaves) borne by that shoot were studied, on first-ordershoots of young peach trees. A comprehensive picture of thoserelationships was obtained by a discriminant analysis. Shootgrowth at meristem emergence date was characterized by internodelength, leaf-production rate and leaf-unfolding duration. Allpossible fates of axillary meristems at the end of the growingseason (i.e. blind nodes, single vegetative or flower bud, budassociations, sylleptic or proleptic shoots) were considered.Shoot-elongation rate determined meristem fates quantitatively.The number of buds produced by a meristem increased when theshoot-elongation rate increased. Qualitatively, the fate of axillary meristems was related tothe balance between shoot-growth components. If the subtendingleaf unfolded slowly, sylleptic or proleptic shoots were morelikely to develop than bud associations, for high shoot-elongationrates; and flower buds were more frequent than vegetative buds,for low shoot-elongation rates. Compared to flower buds, blindnodes appeared for similar shoot-elongation rates but longerinternodes and lower leaf-production rates. The emergence dateslightly modified the relation between shoot growth and axillary-meristemfates, but the main features held true throughout the growingseason. The relationships between shoot growth and meristem fates mayresult from competitive interactions between the growing subtendingleaf and the developing axillary meristem. Growing conditionsmight also influence both shoot growth and meristem fates byfavouring either cell enlargement or cell division.Copyright1995, 1999 Academic Press Peach tree, Prunus persica (L.) Batsch, axillary meristem, meristem fate, branching, flowering, shoot growth, discriminant analysis, exploratory analysis     

Induction and floral determination in the terminal bud of Nicotiana tabacum L. cv. Maryland Mammoth,a short-day plant

Floral determination in the terminal bud of the short-day plant Nicotiana tabacum cv. Maryland Mammoth has been investigated. Plants grown continuously in short days flowered after producing 31.4±1.6 (SD) nodes while plants grown continuously in long days did not flower and produced 172.5±9.5 nodes after one year. At various ages, expressed as number of leaves that were at least 1.0 cm in length above the most basal 10-cm leaf, one of three treatments was performed on plants grown from seed in short days: 1) whole plants were shifted from short days to long days, 2) the terminal bud was removed and then rooted and grown in long days, and 3) the terminal bud was removed and then rooted and grown in short days. Whole plants flowered only when shifted from short days to long days at age 15 or later. Only rooted terminal buds from plants at age 15 or older produced plants that flowered when grown in long days. Only terminal buds from plants at age 15 or older that were rooted and grown in short days produced the same number of nodes as they would have produced in their original locations while buds from younger plants produced more nodes than they would have in their original locations. Thus, determination for floral development in the terminal bud, as assayed by rooting, is simultaneous with the commitment to flowering as assayed by shifting whole plants to non-inductive conditions.Abbreviations LD long day(s) - SD short day(s) - DN dayneutral     

Developmental events in differentiating floral buds of four olive (Olea europaea L.) cultivars during late winter to early spring

The olive tree (Olea europaea L.) is a very important evergreen fruit tree because of the high interest of olive oil and table olives in the human diet. Differentiation of olive floral buds during winter is strictly related to flowering during spring and finally to fruit production during autumn–winter. In order to determine which are the developmental events in differentiating olive floral buds we studied in four olive cultivars “Amfissis”, “Kalamon”, “Manzanillo” and “Chalkidikis” the anatomical progress of the ontogeny using median longitudinal sections of floral buds (cutting odd nodes), in weekly intervals from early February (initiation of differentiation) to mid-April (one week after floral bud burst) keeping the cultivars under the same environmental conditions. At the same time, we determined the changes in their water extractable proteins, as an index of the meristematic activity. At the beginning of differentiation, floral buds consisted of the apical and one pair of developed (odd) axillary meristems which were covered with the corresponding bracts. Floral buds showed a slow gradual enlargement in all cultivars. The sequence of the developmental events (initiation of intense mitotic activity in the apical and the first axillary meristems, initiation of mitotic activity in the second axillary meristem, development of the third pair of bracts (except from cv. Chalkidikis), appearance of mitotic activity in the third axillary meristem, swelling of apical and axillary meristems and appearance of primordial whorls) are presented comparatively. All cultivars showed similar ontogenetic trends but there were temporal differences in the initiation, the progress and the completion of the process. Cv. Amfissis initiated differentiation one week later compared to the other cultivars, also delaying the development of the second and the third axillary meristems. On the other hand, cvs. Kalamon and Chalkidikis delayed one week to complete the process when compared to cvs. Amfissis and Manzanillo.     

Partial shoot reiteration in Wollemia nobilis (Araucariaceae) does not arise from 'axillary meristems'

Background and Aims

Conifers are characterized by the paucity of axillary buds which in dicotyledonous trees usually occur at every node. To compensate, conifers also produce ‘axillary meristems’, which may be stimulated to late development. In juvenile material of Wollemia nobilis (Araucariaceae: Massart''s model) first-order (plagiotropic) branches lack both axillary buds and, seemingly, axillary meristems. This contrasts with orthotropic (trunk) axes, which produce branches, either within the terminal bud or as reiterated orthotropic axes originating from axillary meristems. However, plagiotropic axes do produce branches if they are decapitated. This study investigated how this can occur if axillary meristems are not the source.

Methods

The terminal buds of a series of plagiotropic branches on juvenile trees were decapitated in order to generate axillary shoots. Shoots were culled at about weekly intervals to obtain stages in lateral shoot development. Serial sections were cut with a sliding microtome from the distal end of each sample and scanned sequentially for evidence of axillary meristems and early bud development.

Key Results

Anatomical search produced no clear evidence of pre-existing axillary meristems but did reveal stages of bud initiation. Buds were initiated in a group of small starch-rich cortical cells. Further development involved de-differentiation of these small cells and the development of contrasting outer and inner regions. The outer part becomes meristematic and organizes the apex of the new branch. The inner part develops a callus-like tissue of vacuolated cells within which vascular cambia are developed. This kind of insertion of a branch on the parent axis seems not to have been described before.

Conclusions

Axillary meristems in Wollemia characterize the leaf axils of trunk axes so that the origin of reiterated shoots is clear. Plagiotropic axes seemingly lack axillary meristems but still produce axillary branches by distinctive developmental processes. These observations demonstrate limited understanding of branch initiation in trees generally.     

Shoot morphogenesis associated with flowering in Populus deltoides (Salicaceae)

Temporal and spatial formation and differentiation of axillary buds in developing shoots of mature eastern cottonwood (Populus deltoides) were investigated. Shoots sequentially initiate early vegetative, floral, and late vegetative buds. Associated with these buds is the formation of three distinct leaf types. In May of the first growing season, the first type begins forming in terminal buds and overwinters as relatively developed foliar structures. These leaves bear early vegetative buds in their axils. The second type forms late in the first growing season in terminal buds. These leaves form floral buds in their axils the second growing season. The floral bud meristems initiate scale leaves in April and begin forming floral meristems in the axils of the bracts in May. The floral meristems subsequently form floral organs by the end of the second growing season. The floral buds overwinter with floral organs, and anthesis occurs in the third growing season. The third type of leaf forms and develops entirely outside the terminal buds in the second growing season. These leaves bear the late vegetative buds in their axils. On the basis of these and other supporting data, we hypothesize a 3-yr flowering cycle as opposed to the traditional 2-yr cycle in eastern cottonwood.     

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.     

Florigen is involved in axillary bud development at multiple stages in Arabidopsis

The wide variety of plant architectures is largely based on diverse and flexible modes of axillary shoot development. In Arabidopsis, floral transition (flowering) stimulates axillary bud development. The mechanism that links flowering and axillary bud development is, however, largely unknown. We recently showed that FLOWERING LOCUS T (FT) protein, which acts as florigen, promotes the phase transition of axillary meristems, whereas BRANCHED1 (BRC1) antagonizes the florigen action in axillary buds. Here, we present evidences for another possible role of florigen in axillary bud development. Ectopic overexpression of FT or another florigen gene TWIN SISTER OF FT (TSF) with LEAFY (LFY) induces ectopic buds at cotyledonary axils, confirming the previous proposal that these genes are involved in formation of axillary buds. Taken together with our previous report that florigen promotes axillary shoot elongation, we propose that florigen regulates axillary bud development at multiple stages to coordinate it with flowering in Arabidopsis.     

Influence des corrélations entre organes sur la croissance et le développement floral des bourgeons cotylédonaires chez leScrofularia arguta Sol.

The importance of various correlative influences on growth and vegetative or floral development of cotyledonary buds inScrofularia arguta Sol. is shown. The terminal bud, on the one hand, inhibits growth of cotyledonary buds and, on the other hand, induces their early flowering. The cotyledon stimulates growth of its axillary bud, but has no action on its floral development. Leaves above the cotyledonary node have the same effect as the cotyledon. Finally, roots stimulate vegetative growth of cotyledonary buds and suppress floral expression, but only when apical dominance has been removed at an early stage of development.     

Revisiting the fate of buds: size and position drive bud mortality and bursting in two coexisting Mediterranean Quercus species with contrasting leaf habit

Understanding the relationships between bud size and position and bud fate through time is crucial for identifying and subsequently modeling the mechanisms underlying tree architecture. However, there is a lack of information on how bud size drives crown architectural patterns in coexisting tree species. We studied bud demography in two coexisting Mediterranean oak species with contrasting leaf habit (Quercus ilex, evergreen; Q. faginea, deciduous). The main objective was to analyse the effect of bud size on the fate of buds with different positions along the shoot (apical, leaf axillary and scale-cataphyll axillary buds). The number, length and position of all buds and stems were recorded in marked branches during 4 years. Study species presented different strategies in bud production and lifespan. The evergreen species showed greater mortality rate than the deciduous one, which produced larger buds. Bud size and position were highly related since apical buds where longer than axillary ones and bud length declined basipetally along the stem. Apical buds had also higher chances of bursting than axillary ones. Within positions, longer buds presented a higher probability of bursting than shorter ones, although no absolute size threshold was found below which bud bursting was impaired. In Q. ilex, four-year-old buds were still viable and able to burst, whereas in Q. faginea practically all buds burst in their first year or died soon after. Such different bud longevities may indicate contrasting strategies in primary growth between both species. Q. ilex is able to accumulate viable buds for several ages, whereas Q. faginea seems to rely on the production of large current-year buds with high bursting probability under favourable environmental conditions.     

Ontogeny of the proventitious epicormic buds in Quercus petraea.

In the present work, we described the fate of proventitious epicormic buds on the trunks of 40-year-old Quercus petraea trees and in parallel the vascular trace they produced in the wood. Our results show that small and large individual epicormic buds can survive as buds for 40 years and that both are composed of a terminal meristem and scales. Meristematic areas are detected in the scale axils of small buds; in addition to these meristems the large buds also have secondary bud primordia. The small buds are connected to the pith of the main stem by a unique trace, whereas the large buds are connected by one or multiple traces. A single trace might imply that the whole bud is still alive and multiple traces might indicate that the terminal meristem has died. In the latter case, each trace is connected to a secondary bud of the large bud. The buds found in a cluster are composed of a terminal meristem and scales with axillary meristems in the scale axils. A cluster is connected to the pith of a stem either by a unique trace when it seems to be the result of partial abscission of an epicormic shoot or multiple traces when it might have originated from an epicormic bud in which the terminal meristem has died. Whatever the type of the bud, the vascular trace in the bark is composed of a cambium, secondary xylem and parenchyma cells and the trace present in the wood had parenchyma cells with vestiges of secondary xylem. Each year, the vascular trace should be produced in the bark by the cambium of the tree but not by the bud itself. On 40-year-old Q. petraea, we observed a proliferation of epicormic buds and in parallel a multiplication of the number of vascular traces in the trunk, but the knots caused by the traces of epicormic buds in the wood, either as individuals or in clusters, are minor since their colours are only slightly darker than those of woody rays and they are less than 2 mm in diameter. The knots will appear when epicormic buds develop into shoots. Received: 30 March 1999 / Accepted: 09 June 1999     

Localization of axillary meristems of short day plantChenopodium rubrum L.

Axillary meristems of short day plantChenopodium rubrum are localized as caulinar, foliar or axillar. The localization of axillary meristems and axillary buds of 14 day old plants varied in similar pattern as in other plant species so far investigated: after several nodes with foliar axillary meristems the caulinar ones were produced. However, unlike in other species, in C.rubrum a very high percentage of caulinar meristem is produced also on the first node. In this case, like in the case of its later differentiation at higher nodes, the formation of caulinar meristem is confined also to the vegetative state. It was found that the caulinary position coincides with higher responsiveness to photoperiodic induction. The developmental significance of such behaviour is discussed.     

Early inflorescence and floral development in Cocos nucifera L. (Arecaceae: Arecoideae)

Palms are generally characterized by a large structure with a massive crown that creates difficulties in anatomical studies. The flowering behaviour of palm species may be a useful indicator of phylogenetic relationships and therefore evolutionary events. This paper presents a detailed histological study of reproductive development in coconut (Cocos nucifera L.), from initiation up to maturation of staminate and pistillate flowers. Reproductive development in coconut consists of a sequence of individual events that span more than two years. Floral morphogenesis is the longest event, taking about one year, while sex determination is a rapid process that occurs within one month. The inflorescence consists of different ultimate floral structural components. Pistillate flowers are borne in floral triads that are flanked by two functional staminate flowers. The staminate flowers are born in floral diads towards the base of the rachilla followed by solitary flowers in the middle to top of the rachilla. Three primary phases were identified in reproductive development, namely, transition of axillary bud into inflorescence bud, formation of floral buds, and sexualisation of individual flower buds. All developmental events with respect to stage or time of occurrence were determined.