Subtending Leaf Research Articles

The Role of Leaf Petiole in Photoperiodic Induction of Flowering

Explants of Chenopodium rubrum, a short-day plant, were decapitated and exposed to floral inductive treatment, and the extent of flowering of axillary buds was afterwards assessed. Isolated buds never responded to induction, whereas the presence of the petiole of the subtending leaf already assured a high degree of flowering. We may assume either that the petiole is the receptor organ of the photoperiodic signal or that its transporting role is indispensable.

Shoot Axillary Bud Morphogenesis in Kiwifruit (Actinidia deliciosa)

The annual cycle of kiwifruit [Actinidia deliciosa(A. Chev.) C. F. Liang et A. R. Ferguson var.deliciosacv. Hayward] shoot axillary bud (first-order axillary bud, FOAB) morphogenesis is described. FOABs developed quickly with the majority of bud scales and leaf primordia present approx. 125 d after budbreak (dab). Mature FOABs had, on average, 23.2 bud scales and leaf primordia. Most second-order axillary structures were also present approx. 125 dab. During the growing season, the second-order structures developed into second-order axillary buds (SOABs) or remained as simple, dome-shaped meristems (SDSMs). At maturity, nearly all FOABs had four SOABs and, on average, 12.4 SDSMs. Most SDSMs were fused to the subtending leaf primordia, but some SDSMs developed so that they were ‘free’ from the subtending leaf primordia. Third-order axillary meristems (third-order SDSMs) were observed in the axils of most SOABs, and, on average, there were 20.6 per FOAB. Our observations on the development of second-order axillary structures are consistent with evocation in kiwifruit occurring earlier than the generally-accepted time of late summer.

The pattern of14C-assimilate distribution in chrysanthemum cv. Red Delano with particular reference to branch interrelations

SummaryThe physiological organization of pinched plants of chrysanthemum was investigated by following the pattern of 14C-assimilate allocation from individual leaves on the main stem and uppermost branch, and from selected branches. In vegetative plants almost all of the assimilate imported by a developing branch was obtained from its subtending leaf and the three uppermost branches became virtually independent components of the plant within three weeks from pinching. The root system was the major sink for assimilate exported by main stem leaves and branches. Only a very small proportion of assimilate was distributed generally throughout the shoot and there was evidence that this followed a sectorial pattern. There was no interbranch exchange of assimilate. In flowering plants the flowers were the major sink for assimilate produced within the flowering branch. The results are discussed in relation to competition for assimilate between various plant components and in terms of the physiological status of b...

Sectoriality and physiological organisation in herbaceous plants: an overview

The physiological organisation of plants is considered in relation to the carbon economy of plant parts. Although assimilate is partitioned according to the relative strength of sinks, in many species there is also a very close relationship between partitioning and shoot phyllotaxy, giving rise to sectorial patterns of allocation whereby only certain sinks are supported by any source leaf. Essentially these sinks are in the same orthostichy as the source leaf. This constraint of the vascular architecture on assimilate distribution to developing sinks such as leaves, flowers and fruits is not always absolute, as following the loss of their principal source leaves these sinks can in many cases be supplied with assimilate by other leaves via new inter-orthostichy pathways. The supply of assimilate to major sinks such as developing fruits becomes more and more localised with time so that a fruit in an axillary position becomes largely supported by its subtending leaf; the reproductive node—a metamer-can thus be regarded as a relatively autonomous unit of the plant (an IPU). Similary, once established after a developmental phase of assimilate import, tiller ramets and branches in unitary plants tend to become physiologically autonomous modules. However, the functional autonomy of tillers is reversed following defoliation or shading as they are then sustained by the import of assimilate, subject to its availability, from unaffected tillers. Consequently the plant becomes physiologically integrated by the flow of assimilate from one part to another. The mainly autonomous ramets of many stoloniferous and rhizomatous species display a similar pattern of physiological integration in response to source manipulation, but in some species the ramets appear to maintain their independent functioning as a normal feature of the carbon allocation within the clone. In other clonal species, as the clone develops and becomes more structurally complex, vascular constraints start to restrict the movement of resources, and the clone becomes composed of a number of semi-autonomous IPUs. In unitary plants branches appear to remain very physiologically isolated in terms of their carbon economy once they become established, irrespective of a range of source-sink manipulations. These different patterns of physiological integration and organisation are discussed in relation to different strategies of assimilate utilisation and conservation.

Drought effects on the water relations of cotton fruits, bracts, and leaves during ontogeny

Cotton ( Gossypium hirsutum L.) yields are strongly influenced by water-deficit stress, but the effects of drought on the water relations of cotton fruits have not been documented. Field and greenhouse studies were conducted to investigate the effects of water deficit on the water status of cotton leaves, bracts, and fruits. Water potential (Ψ) of the capsule wall did not react to drought during the period of fruit expansion. Cotton fruits generally had higher water and osmotic potential, and their water status was less sensitive to drought than that of the subtending leaf and bracts. The insensitivity of cotton fruit water potential to drought can be explained by their isolation from the apoplast of the rest of the plant and their high hydraulic capacitance. The lower Ψ of the leaves may have been the result of the much higher transpiration rate of leaves compared with fruits. Transpiration and stomatal conductance of the sympodial leaf decreased during fruit development. Since gradients in water potential are the driving force for water transport through the xylem, it seems unlikely that cotton fruits receive water through the xylem. The results from this study are in agreement with our earlier hypothesis that the phloem plays an important role in water transport to developing cotton fruits.

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 shoot and the fates of the axillary meristems (developing in the axils of the leaves) borne by that shoot were studied, on first-order shoots of young peach trees. A comprehensive picture of those relationships was obtained by a discriminant analysis. Shoot growth at meristem emergence date was characterized by internode length, leaf-production rate and leaf-unfolding duration. All possible fates of axillary meristems at the end of the growing season (i.e. blind nodes, single vegetative or flower bud, bud associations, sylleptic or proleptic shoots) were considered. Shoot-elongation rate determined meristem fates quantitatively. The number of buds produced by a meristem increased when the shoot-elongation rate increased.Qualitatively, the fate of axillary meristems was related to the balance between shoot-growth components. If the subtending leaf unfolded slowly, sylleptic or proleptic shoots were more likely to develop than bud associations, for high shoot-elongation rates; and flower buds were more frequent than vegetative buds, for low shoot-elongation rates. Compared to flower buds, blind nodes appeared for similar shoot-elongation rates but longer internodes and lower leaf-production rates. The emergence date slightly modified the relation between shoot growth and axillary-meristem fates, but the main features held true throughout the growing season.The relationships between shoot growth and meristem fates may result from competitive interactions between the growing subtending leaf and the developing axillary meristem. Growing conditions might also influence both shoot growth and meristem fates by favouring either cell enlargement or cell division.

Phalaenopsis Orchid Light Requirement during the Induction of Spiking

Potted mature Phalaenopsis `Joseph Hampton' orchid (clone Diane) plants were placed in each of four growth chambers with 0, 8, 60, or 160 μmol·m–2·s–1 photosynthetic photon flux (PPF) for 12 hours daily and at 20C day/15C night air. Plants under 160 or 60 μmol·m–2·s–1 PPF began spiking (an elongating reproductive bud protruding through the base of its subtending leaf) in an average of 28 or 34 days, respectively. None of the plants placed under 0 or 8 μmol·m–2·s–1 PPF started spiking within 6 weeks. These plants, following return to a greenhouse, spiked and flowered 8 weeks later than those receiving 160 μmol·m–2·s–1. In a second experiment, plants were placed in each of three growth chambers and kept in complete darkness at 20C day/15C night for 2, 4, or 6 weeks before exposure to 160 μmol·m–2·s–1 PPF. Air was maintained at 20C day/15C night for an additional 6 weeks and then raised to 25C day/20C night to accelerate flowering. Plants exposed to 2, 4, or 6 weeks of darkness required 45, 60, or 77 days, respectively, to reach spiking. However, all plants spiked at similar times (31 to 35 days) after lighting began. Anthesis occurred at progressively later dates for plants placed in darkness for increasing durations, but plants in all treatments required 123 days to reach anthesis following their exposure to light. Flower count and size were not affected in both experiments.

Effect of light quality (red: far-red ratio) and defoliation treatments applied at a single phytomer on axillary bud outgrowth in Trifolium repens L.

We studied the effects of light quality and defoliation on the rate of phytomer appearance and axillary bud outgrowth in white clover. The treatments were applied to one phytomer, a phytomer being defined as the structural unit comprising a node, internode, axillary bud, subtending leaf and two nodal root primordia. Light of a low red:far-red (R:FR) ratio (0.27) was applied to a "target" phytomer either (i) within the apical bud and then to the axillary bud after emergence of the phytomer from the apical bud, or (ii) to the axillary bud only after emergence. The light conditions were directed to these specific parts of the plant by collimating light from small FR light-emitting diodes; with this technique we were able to change the light quality without any change in the level of photosynthetically active radiation. The subtending leaf of the target phytomer was retained or defoliated when it had emerged from the apical bud. FR light applied from the time the phytomer was within the apical bud caused a delay in branch appearance at the target phytomer. In contrast, direct treatment of the axillary bud with FR light after it had emerged from the apical bud did not result in any delay in branch appearance. As the light treatment of the apical bud may have changed the light environment of any of the organs contained in the bud we were unable to ascribe the delay in branch appearance to light perception by any particular organ. However, indirect evidence leads to the conclusion that the likely site of light perception was the developing leaf subtending the axillary bud while it was the outermost phytomer within the apical bud. These results do not support the hypothesis that the R:FR ratio of light incident at an axillary bud site is the environmental factor that controls bud development. Defoliation of the unfolding leaf reduced the rate of phytomer appearance on the main stolon but had no immediate effect on branch appearance. As a consequence there was a reduction in the number of phytomers between the stolon apical meristem and the first phytomer with a branch. This is frequently taken to indicate a relaxation of apical dominance, but in this case was found not to involve a direct effect on bud activity. A current model of white clover growth suggests that there is integration of activity between apical meristems but independence of activity and response to the local micro-environment by axillary buds. In contrast, we found that (i) defoliation reduced phytomer appearance only at the main stolon apical meristem and not at all the meristems in the plant and (ii) that a change in the local light environment of an axillary bud had no discernible effect on bud activity once the bud had emerged from the apical bud but could delay branching if applied before emergence. These results are at variance with the predictions of the model.

Reduction in vigour of leafless potato cuttings in vitro

Removing the leaves from single node potato cuttings in vitro allows propagules to be placed in culture vessels at increased densities with the intent of saving resources and space. Under light intensities of 22 wattsm−2, the removal of the subtending leaf resulted in fewer nodes, shorter plantlets, smaller leaf area, and lower fresh and dry weights of 4-week-old plantlets of cvs Atlantic, Kennebec, Russet Burbank and Shepody. Fewer nodes and reduced plantlet height may result in inefficient multiplication protocols because fewer propagules are available and shorter internodes make dissection more difficult. The coefficient of variation for the various growth parameters was greater when propagules lacked leaves, indicating that the variability of the plant material for propagation was increased. A reduction of vigour and growth was still evident when plantlets of cv. Shepody were grown for 6–8 weeks.

Development and Growth Potential of Axillary Buds in Roses as Affected by Bud Age

The effect of axillary bud age on the development and potential for growth of the bud into a shoot was studied in roses. Age of the buds occupying a similar position on the plant varied from 'subtending leaf just unfolded' up to 1 year later. With increasing age of the axillary bud its dry mass, dry-matter percentage and number of leaves, including leaf primordia, increased. The apical meristem of the axillary bud remained vegetative as long as subjected to apical dominance, even for 1 year.The potential for growth of buds was studied either by pruning the parent shoot above the bud, by grafting the bud or by culturing the bud in vitro. When the correlative inhibition (i.e. domination of the apical region over the axillary buds) was released, additional leaves and eventually a flower formed. The number of additional leaves decreased with increasing bud age and became more or less constant for axillary buds of shoots beyond the harvestable stage, while the total number of leaves preceding the flower increased. An increase in bud age was reflected in a greater number of scales, including transitional leaves, and in a greater number of non-elongated internodes of the subsequent shoot. Time until bud break slightly decreased with increasing bud age; it was long, relatively, for 1 year old buds, when they sprouted attached to the parent shoot. Shoot length, mass and leaf area were not clearly affected by the age of the bud that developed into the shoot. With increasing bud age the number of pith cells in the subsequent shoot increased, indicating a greater potential diameter of the shoot. However, final diameter was dependent on the assimilate supply after bud break. Axillary buds obviously need a certain developmental stage to be able to break. When released from correlative inhibition at an earlier stage, increased leaf initiation occurs before bud break.

Modeling Inflorescence Development of the African Violet (Saintpaulia ionantha Wendl.)

The effects of temperature and daily-integrated photosynthetic photon flux (PPFDI) on African violet (Saintpaulia ionantha Wendl.) flower initiation and development were quantified to provide the basis for an inflorescence development model. The percentage of leaf axils in which an inflorescence initiated and continued development increased as the PPFDI increased from 1 to 4 mol·m-2·day-1, while the rate of inflorescence development was a function of the average daily temperature (ADT). The appearance of a visible flower bud (VB) in a leaf axil was related to the growth of the subtending leaf blade. A polynomial model based on ADT and PPFDI was used to describe leaf blade length at visible bud (LBLVB). A nonlinear model was used to describe the influence of ADT on leaf expansion rate (LER). Inflorescence appearance in the leaf axil was predicted by measuring LBL and estimating the time for the leaf blade to develop to the length required for VB. A phasic-development scale was developed to quantify inflorescence development. Days required for an inflorescence to develop from VB to first open flower was described as a function of ADT and either inflorescence height or inflorescence development stage (IDS). Days from leaf emergence to first open flower for the inflorescence initiated in that leaf axil decreased from 86 to 55 as ADT increased from 18 to 26C.

Contributions of the leaves and axillary shoots to rooting inEucalyptus granáisHill ex Maid, stem cuttings

In one-node stem cuttings of Eucalyptus granais the absence of leaves was fatal. The optimum leaf area per leaf for rooting was 2-5 cm2, and in this range rooting was higher in one-leaf than in two-leaf cuttings. Axillary shoots started to develop soon after the cuttings were set and their growth was promoted by the presence of the subtending leaf. Thus, in one-leaf cuttings the shoot in the leafy axil grew, at the expense of the shoot in the defoliated axil, while in two-leaf cuttings the shoot in the upper (sub-opposite) axil tended to grow more quickly. Axillary shoots were also vigorous in cuttings from decapitated and disbudded mother plants. Rapid shoot growth was associated with low rates of abscission of the subtending leaf and relatively high rooting ability. Removing axillary shoots from cuttings accelerated leaf abscission and reduced rooting. The stem of the cutting often swelled and discoloured from the base, apparently due to the demand of the cutting for water. Additional leaf wounds had no...

High Carbohydrate Content in Snap Bean Leaves Stimulates Chinese Rose Beetle Feeding

Chinese rose beetle (CRB) (Adoretus sinicus Burmeister) preferential feeding based on leaf carbohydrate content was determined using `Hawaiian Wonder' snap bean (Phaseohs vulgaris L.) plants exposed to 0% ,40%, or 80% shade for 2 days. Plants exposed to 0% shade before CRBs fed had 8.5% leaf area consumed compared with 2.8% and 3.6% for 40% and 80% shade, respectively. Leaves exposed to 0% shade had a higher carbohydrate content than leaves exposed to 40% and 80% shade. Darkening the apical and subtending leaf with aluminum foil for 1 day before CRBs fed shifted CRB feeding from heavy feeding on the apical leaf and light feeding on the subtending leaves to a reversed feeding pattern-light feeding on the apical leaf and heavy feeding on the subtending leaves. Three snap bean cultivars grown under similar environmental conditions were compared to `Hawaiian Wonder' using a unifoliate split-leaf technique. Cultivars with a high endogenous carbohydrate content in their leaves had a higher percentage of leaf area consumed by CRBs than cultivars with low endogenous carbohydrates. This report suggests that high endogenous carbohydrate content in leaves stimulates CRB feeding.

Determination of the time of flower evocation in kiwifruit vines

Abstract The timing of flower evocation in kiwifruit (Actinidia deliciosa) was determined by defoliating shoots on several occasions during two growing seasons, and measuring the percentage of shoots that produced flowers in the following spring. The results obtained using this technique were not as clear as those reported for other crops, possibly because some of the axillary buds on defoliated shoots commenced growth in the current season. The effects of this regrowth on evocation are not known. Furthermore, since shoots were kept defoliated for the rest of the season, early defoliation is necessarily linked with a long period of defoliation. In view of these problems any deductions based on data obtained using the defoliation technique must be considered tentative. Our results suggest that, for most shoots in the Bay of Plenty, New Zealand, evocation occurs during December and January. However, shoots which develop late in the season may also be evoked later. Within each shoot, evocation appears to occur progressively, from the base of the shoot to the apex, and evocation of each axillary bud occurs at about the time that the subtending leaf ceases expansion. Girdling shoots in either January or March resulted in a higher budburst and c. 50% more flowers per cane in the following spring. However, covering axillary buds with aluminium foil from January to July did not reduce the percentage of shoots which produced flowers.

The Effects of Plant Density on Shoot and Leaf Lamina Angles in Lolium multiflorum and Paspalum dilatatum

The effects of plant density on shoot -and leaf lamina zenith angles (i.e. the angles with respect to the vertical) were investigated in Lolium multiflorum and Paspalum dilatatum plants grown in pots either outdoors or in Tillers appeared above the ligule of their subtending leaf with a small zenith angle but, in plants grown at low densities, gradually adopted a more horizontal position. In plants grown at high densities this gradual increase in shoot zenith angle with age was strongly reduced. The average shoot zenith angle at a given time was lower (i.e. tillers were more erect) at high

A fate map of the Arabidopsis embryonic shoot apical meristem

ABSTRACT We have mapped the fate of cells in the Arabidopsis embryonic shoot apical meristem by irradiating seed and scoring the resulting clonally derived sectors. 176 white, yellow, pale green or variegated sectors were identified and scored for their position and extent in the resulting plants. Most sectors were confined to a fraction of a leaf, and only occasionally extended into the inflorescence. Sectors that extended into the inflorescence were larger, and usually encompassed about a third to a half of the inflorescence circumference. We also find that axillary buds in Arabidopsis are clonally related to the subtending leaf. Sections through the dry seed embryo indicate that the embryonic shoot apical meristem contains approximately 110 cells in the three meristematic layers prior to the formation of the first two leaf primordia. The histological analysis of cell number in the shoot apical meristem, in combination with the sector analysis have been used to construct a map of the probable fate of cells in the embryonic shoot apical meristem.

Cell fate in the shoot apical meristem of Arabidopsis thaliana

ABSTRACT Seeds of Arabidopsis thaliana, heterozygous for the alb1 mutation were treated with X-rays to generate sectors of albino tissue in the mature plants. Sectors were observed in tissues derived from L2 and L3 layers of the shoot meristem. Altogether 324 sectors were obtained affecting 512 leaves or the inflorescence. The majority of sectors affected only one or other of the first leaf pair. In later leaves, sectors were less frequent, and often affected more than one leaf. Sectors seen in the flowers almost invariably included some of the cauline leaves. Sectors in any region of the plant were of variable length and width. The axillary meristems of Arabidopsis were found to be clonally related to two or more cells near the centre of the subtending leaf. Overall the data are compatible with the idea that there are few, if any, restrictions on cell fate within the cell layers of the dry seed meristem. As in other higher plants, developmental fate could only be predicted in a general and probabilistic way. Such a pattern might be generated if the acquisition of cell fate occurred continuously as the plant grows, in a position-dependent, lineage-independent fashion. A general model of the meristem has been produced to accommodate the observations concerning the great majority of the sectors.

Morphology and Axillary Shoot Formation in the Anisocladous Shoot of Stellaria media L.

Stellaria media is a creeping herb with isophyllous leaves that are irregularly placed, approaching decussate but more often pseudobijugate. A single lateral shoot occurs most frequently at a node, two less frequently, and nodes without buds only rarely. Shoot placement tends to show spiral anisoclady, but the spirals are frequently reversed or otherwise disturbed. Axillary shoots are generally initiated in the axils of p3 primordia. Their development, which is preceded by the differentiation of an oblique procambial strand to the subtending leaf, occurs in cells that are undergoing vacuolation. These shoots are not initially connected to the parent shoot axis and undergo considerable development before procambial connection occurs.

MODELING INFLORESCENCE DEVELOPMENT OF AFRICAN VIOLETS

The effects of temperature and irradiance on flower initiation and development were quantified to provide a basis for an inflorescence development model. The percentage of leaf axils forming an inflorescence increased as the daily integrated PPF increased from 1 to 4 mol m-2 d-1, while the rate of inflorescence development was a linear function of temperature from 18 to 26C. The appearance of a visible flower bud in the leaf axil was correlated with leaf blade length of the subtending leaf. Mathematical functions were used to describe leaf blade length at the time of visible flower bud as a function of temperature and irradiance, and also to describe the influence of temperature on the rate of leaf extension. The time of visible flower bud in the leaf axil was then predicted by measuring the current length of the subtending leaf blade and estimating the time required for the leaf blade to extend to the length required for visible flower bud appearance. A phasic development scale was used to describe the developmental status of an inflorescence from visible flower bud to anthesis. A model was then created which predicted time to anthesis based upon temperature and the current stage of inflorescence development.

Influence of defruiting on the abscisic acid and indole-3-acetic acid contents of cotton leaves

A field experiment was conducted to test the hypothesis that young cotton ( Gossypium hirsutum L.) fruits (bolls) serve as sinks for ABA, or that they are a source of IAA for subtending leaves. Cotton was grown in eight four-row plots in Phoenix during the summer of 1989 and irrigated about every two weeks. In one test, flowers at anthesis were removed on 22 and 29 June and on 7 and 14 July from the first node of fruiting branches of one center row, but not the other row, in each of four replications. Subtending leaves were harvested seven days after deflowering for ABA and IAA analyses. Removal of one flower per plant had no consistent effect on the concentrations of ABA and IAA in the subtending leaf. In another test, all flowers and bolls were removed from all plants of one center row, but not the other row, of four replications on 30 June and 5 and 13 July. Uppermost fully expanded mainstem leaves were harvested from the same plots on 20, 25, and 27 July, and on 9 August (7, 12, 14, and 27 days after final defruiting) for ABA and IAA analyses. Removal of all fruits apparently caused a slight increase in ABA concentration in mainstem leaves, but the effect disappeared with time after defruiting. The ability of leaves to accumulate ABA apparently decreased slightly as boll load increased. Complete fruit removal did not, however, affect the IAA content of leaves.