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The fruit and seed produced by a small number of crop plants provide the majority of food eaten across the world. Given the growing global population, there is a pressing need to increase yields of these crops without using more land or more chemical inputs. Many of these crops display prominent 'fruit–flowering feedbacks', in which fruit produced early in sexual reproductive development can inhibit the production of further fruit by a range of mechanisms. Understanding and overcoming these feedbacks thus presents a plausible route to increasing crop yields 'for free'. In this review, we define three key types of fruit–flowering feedback, and examine how frequent they are and their effects on reproduction in a wide range of both wild and cultivated species. We then assess how these phenomenologically distinct phenomena might arise from conserved phytohormonal signalling events, particularly the export of auxin from growing organs. Finally, we offer some thoughts on the evolutionary basis for these self-limiting sexual reproductive patterns, and whether they are also present in the cereal crops that fundamentally underpin global diets. [ABSTRACT FROM AUTHOR]

In established vineyards, node number retention at winter pruning is the first step to achieving and maintaining vine balance. Balanced vines exhibit timely and quasi-uniform 100 percent budburst. To understand how vine capacity and balance are expressed before flowering, mature Sauvignon blanc vines were pruned according to a 5 [total node numbers on canes: 10, 20, 30, 40, 50] x 3 [total node numbers on spurs: 1, 2, 3] factorial design in one site, and in two other sites according to a 5 [total node numbers on canes: 10, 20, 30, 40, 50] x 2 [total node numbers on spurs: 1, 2] factorial design. Two spurs of one, two or three nodes each were retained on either side of the vine. The number of canes laid down per vine was one, two, three and four canes each of 10 nodes for the 10-, 20-, 30- and 40-node treatments, and four canes averaging 12.5 nodes for the 50-node treatment. The budburst percentage was calculated on the whole vine, canes, and spurs. Blind nodes, count shoots, non-count shoots and double shoots were counted and mapped along canes and spurs. Many non-count shoots were measured on the vine head of 10-node vines (29.5 ± 3.0 shoots, p

The interactions of branches in relation to the transports of IAA export activity (IEA) were studied in pea plants of the semidwarf cv. Adagumsky having a strong apical dominance (AD) and the dwarf cv. Porta with a weakened AD. In a model system of two-branched seedlings, the branches of cv. Adagumsky competitively suppressed the growth and IEA of each other, but that is not the case with cv. Porta. The root supply with GA3 inhibits the outgrowth of axillary buds at basal node 2 in cv. Porta seedlings, thus enhancing AD, and led to establishing a 1.5 fold different IEA in the shoots between two-branched and one-branched seedlings, making it similar to cv. Adagumsky. Thus, the emerging role of GAs as a systemic signal in regulation of AD and correlative inhibition is suggested. Molecular mechanisms of GA involvement in these processes are discussed. [ABSTRACT FROM AUTHOR]

Between-branch nitrogen competition is expected to be important during spring in temperate deciduous trees as nitrogen allocation would be higher in branches from earlier budburst than in those from later budburst. Such phenology-induced branch interaction would influence plant photosynthesis, but this has not been evaluated. Warming experiments were conducted on whole crowns (warmed trees; trunks and all branches of the same tree were warmed) or parts of the crowns (warmed branches with unwarmed control branches in the same tree), with unwarmed control trees, in saplings of the deciduous species Fraxinus lanuginosa. Spring leaf phenology and leaf photosynthetic traits were investigated to determine how the difference in temperature affects leaf phenology and photosynthetic traits. The timing of budburst was influenced by temperature—budburst was earlier in warmed trees and warmed branches than in control trees and control branches, but budburst timing did not differ between control trees and control branches or between warmed trees and warmed branches. In contrast, leaf traits were affected by the variation in phenology within crowns—nitrogen content and photosynthetic capacity were greater in the leaves of the warmed branches than in the control branches, but they did not differ between the leaves of warmed trees and control trees. Thus, branch warming altered the distribution of nitrogen between warmed and unwarmed branches as warmed branches developed faster, resulting in intracrown variation in leaf photosynthetic traits. [ABSTRACT FROM AUTHOR]

Limited information exists regarding the dormancy of secondary and tertiary buds within the compound bud of grapevines. We were interested to evaluate how extended chilling duration would affect the budbreak percentage of all three bud orders within the compound bud. Dormant potted 'Shiraz' grapevines, with thirty retained buds per vine, were placed in a cool room at 4 °C over a 20-month period to extend dormancy. Vines were then systematically removed over five dates and placed in a controlled growth environment to assess budbreak percentages and cane tissue concentrations of abscisic acid and cytokinins. Budbreak was hastened by at least 13 d with vines receiving any extra chilling compared to no initial chilling. Furthermore, the firstly observed correlative inhibition of basal buds was apparently removed with chilling. Removal of correlative inhibition within the compound bud with increased chilling duration was also observed with the increases of secondary (doubles) and tertiary (triples) buds breaking simultaneously with the primary bud at each node. This resulted in 91 % of the nodes having two developing shoots and 56 % of the nodes presenting three developing shoots by the end of the experiment. Furthermore, a sigmoidal relationship between percent secondary buds and chilling duration was observed. Possible phytohormone connections were observed with the decline of ABA as secondary and tertiary buds broke at 414 d of chilling and depletion of the CKs, which coincided with the greatest rate of primary bud break after 242 d of chilling. Other possible involvement of ABA and Cis-type cytokinin interactions with secondary and tertiary bud dormancy is discussed. The results suggest future investigations into secondary and tertiary bud release within the grapevine using similar techniques may help to better understand the biochemical mechanisms associated with dormancy. [ABSTRACT FROM AUTHOR]

The contributions of strigolactones (SLs), cytokinins (CKs), and indole-3-acetic acid (IAA) to the regulation of correlative inhibition (CI) in two-branched 10-day-old (2-B) pea seedlings were studied in different cultivars in comparison with single-shoot seedlings (1-B). The first group of cultivars (Adagumsky and Torsdag) was characterized by a tall phenotype, strong apical dominance, and CI between branches, with IAA export activity (IEA) being almost 1.5–2 times lower in the shoots of 2-B plants than in 1-B plants. Branching IAA-response (rms2-1) and SL response/deficient (rms4-1/rms1) mutants of Torsdag also displayed CI at the level of the shoot IEA. In Torsdag, vascular supply of 6-benzylaminopurine in the hypocotyl, which led to an increase in IEA, equalized IEA differences between the 2-B and 1-B shoots, thus overcoming CI. In 1-B plants of these cultivars, the levels of xylem-CK were three-fold higher than that of 2-B plants, suggesting a key role for xylem-CK in establishing CI. The previously proposed dynamic model, where IAA and CK interact in interlocking feedback loops, can account for the regulation of CI in these cultivars. By contrast, both the growth and IEA of shoots in the second group of cultivars (Térèse and Porta), which displayed a dwarf phenotype and weakened apical dominance, were similar between 2-B and 1-B plants. Porta had an increased shoot IEA, but low xylem-CK levels as compared to Adagumsky, with both cultivars showing a similar response to CK. Therefore, we assume that in the second cultivar group, the shoot IAA synthesis/export is probably independent from xylem-CK, and further studies are needed to find a factor responsible for loss of CI in these cultivars. [ABSTRACT FROM AUTHOR]

Key message: This study proves the existence of correlative inhibition, and demonstrates that role of light intensity in the growth and death varies among different levels of branching units.Abstract: Within a tree crown, local light conditions vary within a branch and among different branches. Although the role of light intensity in the growth and survival of branches has been studied extensively, the effects of the spatial heterogeneity of light intensity on different levels of branching units are poorly understood. We investigated the effects of light intensity on the growth and death of primary branches (those branching off from the main stem) and secondary branches (those branching off from the primary branches) in the whole crown of Sakhalin spruce (Picea glehnii). The growth of shoot extension on a primary branch or secondary branch may be inhibited on sunlit trees compared to shaded trees when branches under relatively low local light intensity (rPPFD) levels, but it was increased with increasing rPPFD more rapidly on sunlit trees than on shaded trees. A relative importance analysis showed that, in the primary branches, branch growth was mainly influenced by rPPFD, and less influenced by its vertical position within the crown. However, the probability of death of a primary branch was equally influenced by its position within the crown and rPPFD. In contrast, rPPFD played a dominant role in both the growth and death of secondary branches. The results of our study suggest that local light intensity alone cannot fully explain the growth and survival of primary branches simultaneously, and the effects of light intensity vary among different levels of branching units. [ABSTRACT FROM AUTHOR]

A model system of 10-12 day-old, two-branched (2-B) pea (Pisum sativum L. cv. Adagumsky) seedlings was used to study the roles of endogenous auxin indole-3-acetic acid (IAA) and cytokinins (CKs) in the interaction between the shoots. The IAA export activity (IEA) from shoots was 2-fold higher in one-branched (1-B) plants with one shoot removed than in the 2-B plants, while tZ-type cytokinin contents in xylem sap were 4-fold greater in the 1-B plants than in 2-B plants. Exogenous 6-benzylaminopurine introduced into the vascular stream of one shoot enhanced its IEA. Therefore, xylem cytokinin appears to control both growth and IEA in branches. In the hypocotyls of 1-B and 2-B plants, IAA contents were equal in both cases, while the levels of tZ-type cytokinins were different. These data do not agree with the well-supported role of auxin in down-regulating CK content. The observed paradox may be explained by assuming that a steady-state IAA level in the hypocotyls is feedback regulated via xylem cytokinin, which controls the delivery of IAA from the shoots. As a result, the level of IAA in the hypocotyl is most likely maintained at a threshold below which a decrease in auxin content can switch on CK synthesis that will increase xylem cytokinin levels, thereby stabilizing the level of IAA in the hypocotyl. Therefore, our results suggest that correlative inhibition in the 2-B pea system is a function of an IAA/CK feedback loop, in which cytokinin essentially acts as a second messenger for IAA. [ABSTRACT FROM AUTHOR]

This study examined whether the strong inhibitory influences of basal branches on axillary bud outgrowth seen in Trifolium repens L. similarly occur in Pisum sativum L. Mechanisms by which basal branches in P. sativum suppress bud outgrowth were assessed using treatment combinations of main stem decapitation and excision, girdling, and (or) disbudding of basal branches. The combination of decapitation with basal branch excision provided a new avenue for the investigation of correlative suppression of bud outgrowth. The results revealed a dual suppressive action of basal branch buds: girdling of basal branches confirmed they act via export of an inhibitory influence, but also demonstrated, for the first time in P. sativum, their role as competitive sinks for bud outgrowth stimulus. Although all of the axillary buds on the main stem had similar intrinsic potential for outgrowth, sensitivity to these suppressive influences varied with position on the stem. This suppressive influence of basal branches was, like apical dominance, a major influence on the regulation of bud outgrowth. The finding in P. sativum that basal branches suppress bud outgrowth via their action as competitive sinks for an outgrowth stimulus, as they do in nodally rooting clonal herbs, suggests further investigation of this process is warranted. [ABSTRACT FROM AUTHOR]

Large trees are the most prominent structural features of old-growth forests, which are considered to be globally important carbon sinks. Because of their large size, estimates of biomass and growth of large trees are often based on ground-level measurements (e.g., diameter at breast height, DBH) and little is known about growth dynamics within the crown. As trees increase in size, growth of the crown may not be reflected in DBH measurements contributing to inaccuracy of aboveground forest productivity. Here we present data from a 10-yr re-measurement of crown structure and branch/trunk growth of 400-year-old Pseudotsuga menziesii trees in an old-growth forest in western Washington, USA. In six study trees, 40–60% of branches occurred in the upper third of the live crown. Branch mortality over 10 years was highest in the lower third of the crown. Of live-branch mass (including leaf mass), 41–78% occurred in the middle third of the live crown. During the study period, live-branch mass increased in the upper half of the crown and there was little loss due to fragmentation or death. In contrast, increment of live-branch mass was negligible and live-branch mass decreased in the lower half of the crown. On average, 70–99% of the increment of live-branch mass per tree occurred in the upper half of the crown. Core samples taken from various heights indicated that trunks became less tapered with increasing age as a result of greater increments of upper-trunk radius during the most recent 10 years. Increment of live-branch mass contributed 42 and 66% of the whole-tree and upper-crown increments of mass, respectively, and its vertical distribution corresponded to that of leaf mass density. Increments of trunk mass contributed 88% of the lower-crown increment. Growth increments of the crown were not reflected in core samples taken at lower heights. Our estimates of trunk, branch, and leaf mass were consistently smaller than those calculated using empirical allometric equations based on tape-wrap measurements of DBH. Moreover, leaf mass decreased in four trees, whereas allometric equations predicted increases. Our results indicate that large P. menziesii trees can sustain wood mass production, especially in trunk and branches of the upper crown, while leaf mass change can be more dynamic, and that such growth dynamics of the crown are difficult to detect via DBH-based measurements. [ABSTRACT FROM AUTHOR]

The development of crown architecture strongly affects tree growth and survival. Growth and death of primary branches (those branching off from the main stem) and secondary branches (those from a primary branch) in the lowest part of the crown were investigated for Picea glehnii in an even-aged plantation. Probability of death of a primary branch decreased as the length between its basal location and the crown base (LCB) increased (p = 0.04), but this probability was not significantly related to the relative photosynthetic photon flux density (rPPFD) above the primary branch (p = 0.18). The probability of producing one or more current-year shoots on a primary branch increased with increasing rPPFD above the primary branch (p = 0.01); however, this probability was unrelated to LCB (p = 0.29). Secondary branches at the distal part of a primary branch produced more current-year shoots and exhibited a lower probability of death than proximal branches (p < 0.01), probably because rPPFD above the distal secondary branches was greater than the proximal branches (p < 0.01). Our results suggest that, while local light conditions are relevant to shoot production and shoot death on a primary branch, the death of an entire primary branch may be related to some morphological attributes concerning the length to the crown base. [ABSTRACT FROM AUTHOR]

In Trifolium repens the decline in bud outgrowth that occurs with distance from basal root systems is due to correlative inhibition by the first-formed basal branches. The apical and axillary buds on these basal branches are the source of the inhibitory effect, but their mode of action is unclear. Inhibition might occur via basal branches being a sink for xylem-transported branching stimulants or alternatively by providing a source of inhibitory signals, or by both mechanisms. To distinguish between these mechanisms, four experiments were conducted on plants varying in initial growth stage from 10 to 19 nodes along their main stems to determine any variation in the relative importance of the operative mechanisms of correlative inhibition. Inhibitory signal exported into the main stem, detected as a branching response to girdling of basal branches, was relatively more significant in smaller (initially with 10-15 nodes on the main stem) than in larger (>19 nodes on main stem) plants. This signal was shown not to involve auxin fluxes, and is unidentified. However, across all stages of growth, the predominant mechanism driving correlative inhibition was the action of axillary and apical buds of basal branches as sinks for the stimulatory signal. This study indicates that the relative importance of the mechanisms regulating bud outgrowth in T. repens varies with growth stage and that, during intermediate stages, regulation has some similarity to that in Pisum. [ABSTRACT FROM AUTHOR]

Key message: In two apple cultivars, fruit set was due to primigenic dominance within the annual shoot in areas with insufficient winter chilling while positional dominance took precedence when chilling was sufficient. Abstract: The purpose of our study was to use fruit set and inflorescence size to characterize the positional (position along the shoot) and/or temporal (relative time of budburst and flowering) influences on competition between reproductive laterals within an annual shoot. The relative time of budburst and flowering, and the relative position within the shoot of reproductive buds were recorded on 2-year-old shoots of 'Granny Smith' and 'Golden Delicious' apple ( Malus × domestica (Borkh.)) trees. The trees were grown at two locations in South Africa, a cool area, Koue Bokkeveld, and a warm area, Warm Bokkeveld, with sufficient and insufficient winter chilling, respectively. Inflorescence size (leaf number, leaf area, and flower number) did not differ temporally or with position. For both cultivars, fruit set in the cool area was acrotonic and independent of relative flowering time, while it was more influenced by temporal (primigenic) dominance in the warm area. Therefore, there is a clear positional advantage within the shoot to fruit set in cool areas (i.e., better local climate conditions for the growing fruit), while there is a clear temporal advantage (first bud to burst sets a fruit), or a 'first come, first serve' approach to fruit set, in warm areas, which have limited and delayed budbreak. Inflorescence size and fruit set indicate a separation of environmental (degree of winter chilling) and innate factors in competition among reproductive buds along the 2-year-old annual shoot. [ABSTRACT FROM AUTHOR]

The progression of the dormancy of apricot (Prunus armeniaca L.) vegetative and reproductive buds in the summer-winter period (June-March) was analysed with the single-node cutting method during two consecutive years in a Mediterranean climate. The progression of the mean time to budbreak (MTB) was studied. Low MTB values were obtained, which show endodormancy intensity under climatic conditions in the South East of Spain only reached a shallow level in apricot. The onset of bud dormancy occurred prior to the advent of chilling accumulation. Although an oscillating pattern on dormancy progression was observed, MTB increased progressively from summer until January and declined rapidly thereafter coinciding with dormancy breaking, although in 2006-2007, maximum endodormancy intensity was observed at beginning of October. Vegetative and reproductive buds showed a similar pattern of seasonal progression of MTB, although after flower differentiation (ca. September) vegetative buds always showed a deeper dormancy than reproductive buds. Autumn and early winter temperatures seem to play a crucial role over dormancy intensity and dormancy progression. A gradient of increasingly deep dormancy from shoot apex to base is suggested by the gradual increment of MTB in a basipetal direction, although it was influenced by the year. [ABSTRACT FROM AUTHOR]

In Trifolium repens removal of any number of existing branches distal to a nodal root stimulates development of axillary buds further along the stem such that the complement of branches distal to a nodal root remains constant. This study aimed to assess possible mechanisms by which existing branches correlatively inhibit the outgrowth of axillary buds distal to them. Treatments were applied to basal branches to evaluate the roles of three postulated inhibitory mechanisms: (I) the transport of a phloem-mobile inhibitory feedback signal from branches into the main stem; (II) the polar flow of auxin from branches into the main stem acting to limit further branch development; or (III) the basal branches functioning as sinks for a net root-derived stimulatory signal (NRS). Results showed that transport of auxin, or of a non-auxin phloem-mobile signal, from basal branches did not influence regulation of correlative inhibition and were consistent with the possibility that the intra-plant distribution of NRS could be involved in the correlative inhibition of distal buds by basal branches. This study supports existing evidence that regulation of branching in T. repens is dominated by a root-derived stimulatory signal, initially distributed via the xylem, the characterization of which will progress the generic understanding of branching regulation. [ABSTRACT FROM PUBLISHER]

Because light conditions in the forest understory are highly heterogeneous, photosynthetic acclimation to spatially variable irradiance within a crown is important for crown-level carbon assimilation. The effect of variation in irradiance within the crown on leaf nitrogen content and photosynthetic rate was examined for pinnate compound leaves in saplings of Cedrela sinensis, a pioneer deciduous tree. Five shading treatments, in which 0, 25, 50, 75 and 100% of leaves were shaded, were established by artificial heavy shading using shade screen umbrellas with 25% transmittance. Although the nitrogen content of leaves was constant regardless of shading treatment, ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) content and light-saturated photosynthetic capacity were lower in shade leaves within partially shaded crowns than within fully shaded crowns. Shade leaves within partially shaded crowns contained higher amount of amino acids. Most shade leaves died in partially shaded crowns, whereas more than half of shade leaves survived in totally shaded crowns. Assumptions on photosynthetic acclimation to local light conditions cannot explain why shade leaves have different photosynthetic capacities and survival rates in between partially and totally shaded crowns. Irradiance heterogeneity within the crown causes a distinct variation in photosynthetic activity between sun and shaded leaves within the crown. [ABSTRACT FROM AUTHOR]

The branch autonomy principle states that the critical characteristics of a branch's carbohydrate economy (photosynthesis, respiration, growth, etc.) are largely independent of the tree to which the branch is attached, as long as light is the primary factor limiting photosynthesis and growth. However, this may not be generally true because in the spring, photosynthates are translocated from a tree stem into branches, and the amount of photosynthate available for translocation should be a function of the tree's canopy status. And the correlative inhibition principle states that a branch's priority for allocation of carbon and other resources is controlled not only by its own environment, but also by its position relative to other branches on the same tree. A study of the lower limit of branch growth and survival in trees of different sizes shows that the latter principle is more important: even though dominant trees have more resources to allocate, branches on suppressed trees are able to grow and produce new foliage at solar irradiances where branches on dominant trees die. Thus branches are sufficiently interdependent that a positive carbon budget by itself does not ensure branch survival; branch position relative to other branches on the same tree is also important. Other findings indicate that this result is quite general: regardless of the stress involved, a stressed branch on a tree where all other branches are also stressed does better than a similarly stressed branch on a tree where some branches are relatively unstressed. Although branch autonomy is an important and useful principle, it is not an absolute rule governing branch growth. [ABSTRACT FROM PUBLISHER]

1 The morphological plasticity of sun and shade branches of Pinus sylvestris growing at the edge of a ‘tree-patch’ created in 1989, when surrounding trees were removed, was compared with that of branches of trees growing in the centre of the patch. 2 In 1992, we selected 10-year-old branches. Yearly growth increments (long-shoots) and emerging buds were individually marked, architectural parameters measured, the branch topology mapped, and the number of male and female cones counted. In 1993, the survival of growth increments and buds was recorded and the branches were harvested to determine dry mass of growth increments and needles. 3 The size of growth increments produced after 1989, i.e. their length, total dry mass and needle dry mass, decreased in the order sun branches of edge trees > branches of centre trees > shade branches of edge trees. Thus, the growth increments produced on the shade branches of trees that also had branches in the sun were consistently smaller than the growth increments on the branches of centre trees growing completely in the shade. 4 The number of new growth increments produced after 1989 was highest in sun branches and lowest in shade branches of edge trees. Survival of growth increments and buds was higher in edge than in centre trees; no difference was found between sun and shade branches of edge trees. 5 In shade branches of edge trees, branching angles between first- and second-order growth increments were highest and increased from older to younger growth increments. This was interpreted as ‘bending’ towards the edge of the patch. 6 Production of female cones was almost totally restricted to edge trees and higher in sun than in shade branches. 7 One prediction of an optimal foraging strategy, i.e. the production of more growth increments and buds in higher light, was supported by the data, whereas the other prediction, i.e. decreased length of growth increments, could only be supported when it was... [ABSTRACT FROM AUTHOR]

Root restriction may be of importance for productivity in both forestry and agriculture. To study the physiological effects of root restriction in European alder (Alnus glutinosa Gaertn.), seedlings were grown in aerated liquid culture under one of four root. volumes to induce the following levels of root restriction: 1.5, 6, 16 and 500 ml. Root restriction for 96 days reduced shoot elongation, plant dry weight, leaf area and chlorophyll, levels and increased leaf area/root dry weight ratio and correlative bud inhibition in seedlings. The initial reduction in root/shoot ratios of severely restricted seedlings was followed by a reduction in leaf water potential, the development of internal water deficits in the upper shoots, a reduction in stomatal opening and transpiration rates and, eventually, stomatal closure. Severe prolonged root restriction (1.5 ml root volume) resulted in a decline in seedling vigour and ultimately. senescence as determined by increased electrical impedance ratios, followed by visible leaf senescence and later, by whole plant senescence. Of the severely restricted seedlings, 40%. were dead after 96 days of restriction. The results suggest that imbalanced root/shoot ratios caused the development of internal water stress and the consequent reduction in stomatal aperture, culminating in leaf and whole plant senescence. [ABSTRACT FROM AUTHOR]

Indol-3yl-acetic acid (IAA) present in the rooting solution for 1-4 days appreciably decreased the number of roots subsequently formed in pea stem cuttings. Removal of the lowest 10 mm of the cutting base after IAA treatment abolished the inhibitory effect of IAA almost completely. The number of roots formed from the remaining part of the base internode after excision of the basal centimeter of the internode 4 days after the cuttings were taken was similar to that of the control. It is concluded that the first root primordia, which develop near the cut surface, have an inhibitory influence on development of further roots. The inhibitory effect of IAA may be explained as a strengthening of this dominance phenomenon. Addition of charcoal to the rooting solution delayed the appearance of roots but increased the number of roots developed during a standard rooting period. Adsorption of stimulatory and inhibitory compounds at the surface of the cutting base is believed to be the reason for these results as no evidence of accumulation of inhibitory compounds in the solution was obtained. Charcoal reversed the inhibitory effect of IAA if added after the IAA treatment. This reversal was almost complete if the IAA treatment lasted for one day only but decreased drastically if the IAA treatment was extended over 4 days. [ABSTRACT FROM AUTHOR]

Removing apical portions of current growth coppice shoots from field-grown, low-pruned stumps of mulberry (Morus alba L. cv. Shin-ichinose) caused sprouting of one or more upper main buds, almost concurrently with that of accessory buds. However, removal of the new sprouts, including those from accessory buds, slightly enhanced the sprouting of buds immediately below them, and did not affect buds lower down. In contrast, mature leaves inhibited the buds in their axils. Budless, leafy nodes on the upper part of pruned shoots tended to swell after treatment, perhaps due to the accumulation of substances translocated from the roots and possibly from the remaining leaves. Lateral buds at different positions along the shoot differed in their sprouting ability with buds lower on the shoot being more inhibited. This inhibition gradient dissappeared when all coppice shoots on one stump were pruned to the same bud position, suggesting inhibition from neighboring, actively growing shoots. These results demonstrate that acropetal influences are important in bud dominance relationships. [ABSTRACT FROM AUTHOR]

Plants of Pisum sativum var. arvense Poir. cv. Dun were grown with two equal shoots kept in different light conditions. In these plants a darkened shoot was inhibited and it eventually withered and died; it elongated and became etiolated only when the shoot in the stronger light was removed. A similar result was obtained in simulated ecological conditions, when the shoot in the inferior light was merely shaded: this shoot was severely inhibited, though it did survive. The inhibition of the shaded shoot was more pronounced when the plants were stressed by the removal of large parts of their cotyledonary reserves. These results demonstrate an integration of responses to the light environment with the correlative inhibition between shoots of the same plant. This integration enables the plant to use its developmental resources optimally in heterogeneous environments, rather than merely growing where conditions are 'appropriate'. [ABSTRACT FROM AUTHOR]

It was postulated that the release of lateral buds from apical dominance is triggered by the immediate increase in apoplastic water potential (hydrostatic pressure) that is produced by shoot decapitation and that is rapidly transmitted throughout the plant. In experiments conducted to test this hypothesis the use of a strain gauge transducer capable of measuring bud growth with an accuracy of ± 0.1 μm, showed that growth of the inhibited lateral bud at the primary leaf node of Phaseolus vulgaris (L.) ev. Canadian Wonder was initiated within 1 to 5 s following shoot decapitation or excision of the primary leaves. When only the apical bud was excised the lateral bud showed a brief, transitory growth response of ca 1 min duration, but the axillary buds of the first and second trifoliate leaves were released from inhibition. Decapitation of the shoot just below the first trifoliate leaf induced a lateral bud response characterized by three distinct stages: a) a rapid initial growth response with a mean duration of 4.9 min b) a period of arrested growth, which varied in duration from 2 min to 4 h and c) the subsequent resumption of growth. Excision of both primary leaves induced a rapid but transitory bud response of considerably greater duration than that induced by apical bud excision. Excision of the primary leaves prior to decapitation of the shoot eliminated the phase of arrested growth, which characterized the bud response to decapitation of the intact plant. The rapidity of the bud response to both shoot decapitation and leaf excision and the interaction between the effect of these two treatments are consistent with the hypothesis that competition for water plays a major role in the correlative inhibition of lateral buds. [ABSTRACT FROM AUTHOR]

A plant has a great excess of buds each with the potential of developing an entire shoot system. The general question tackled was to what extent shoot size and time of bud development are important for bud hierarcy. Pea seedlings with two shoots, which were either equal or unequal in size, were obtained by the early removal of the seminal shoot. When these two shoots were also removed, one of the two cotyledon buds next to the basis of the shoots developed into the new shoot system. The determination of which of the buds became dominant was studied as a function of the relative sizes of the two primary cotyledonary shoots, of differences in the timing of the removal of these shoots and of the size of the buds. The bud that became dominant was not necessarily the larger shoot. Instead, it was usually the bud that was inhibited for a shorter period by the shoot next to it. It is suggested that the fate of a bud is predominantly determined by developmental parameters, for example time of release, which are correlated with its developmental status and not necessarily with its physical size or with the past development of its shoot. [ABSTRACT FROM AUTHOR]

Roots are known to respond to favourable nutrient conditions by increased initiation and growth of lateral roots. The problem studied here was to what extent does this local developmental response depend on the environments of other roots on the same plant. Such dependence could a How for an optimal allocation of resources required for root growth in unpredictable, heterogeneous soils. Pea seedlings (Pisum sativum var. arvense cv. Dun) were pruned and grown to have two equal root systems, each in an individual container. As expected, these roots responded by increased development to a wide range of nutrient solution concentrations. The local development of these roots, expressed by their dry weight, was a function of the relative rather than the absolute conditions in which they were grown: roots in a given environment developed more rapidly if other roots on the same plant were in poorer than if they were in richer nutrient conditions. The number of lateral initials doubled within 3d after the roots were exposed to optimal nutrient conditions, before any dry weight differences could be detected. This rapid root initiation was also a function of the conditions other roots of the same plant were in. These results mean that root development and especially lateral root initiations depends on the integrated effects of the local environment and the internal correlative relations between the roots. [ABSTRACT FROM AUTHOR]

The transport and accumulation of P and [C] sucrose in decapitated and intact shoot segments of the fern Davallia were studied. The apical buds of intact shoots and the expanding buds of shoots decapitated 4 weeks before application are major sinks for these nutrients. Decapitation results in a shift of C accumulation from the apex to the lateral buds within 36 h. This shift can be reversed in shoots decapitated for 12 h by replacing the apex. Increased C accumulation into the stump region occurs when decapitated shoot segments are treated with indole-3-acetic acid, and decreased label accumulation into the apical region results when intact shoots are treated with 2,3,5-triiodobenzoic acid. [ABSTRACT FROM AUTHOR]