Effect of defoliation on tracheid production and the level of indole-3-acetic acid in Abies balsamea shoots

To simulate feeding by the spruce budworm ( Choristoneura fumiferana Clem.), the apical current-year shoots on 1-year-old branches in the uppermost whorl of 6-year-old balsam fir [ Abies balsamea (L.) Mill.] trees were either removed completely by debudding before the start of the growing season or defoliated 0, 50, 90 or 100% shortly after budbreak. Debudded branches were treated at the apical end with 0, 0.1 or 1.0 mg of indole-3-acetic acid (IAA) (g lanolin)⁻¹. Ninety % of the 1-year-old needles were also removed from some of the experimental branches. After ca 4 weeks of growth, the radial width of new xylem and the level of IAA were determined in the 1-year-old internode. The IAA content was measured by radioimmunoassay.
The removal or defoliation of current-year shoots inhibited tracheid production and decreased the IAA level. Exogenous IAA stimulated tracheid production and increased the IAA level in debudded branches. Current-year shoot defoliation also inhibited current-year shoot elongation. The inhibitory effect of current-year needle removal on all parameters generally increased with increasing intensity of defoliation. The removal of 1-year-old needles did not affect the IAA level or current-year shoot elongation, nor did it influence tracheid production in branches with current-year shoots. However, removal of 1-year-old needles inhibited tracheid production in debudded branches supplied with exogenous IAA. The results indicate that (1) IAA is involved in the control of tracheid production in the 1-year-old internode, (2) IAA is supplied primarily by current-year shoots, and (3) defoliation by the spruce budworm inhibits tracheid production partly by decreasing the supply of IAA.     

Vertical and radial profiles in tracheid characteristics along the trunk of Douglas-fir trees with implications for water transport

The main stems of three young Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirbel) Franco) trees were dissected to obtain samples of secondary xylem from internodes axially along the trunk and radially within each internode. From these samples, measurements were obtained of tracheid diameter, length, the number of inter-tracheid pits per tracheid, and the diameter of the pit membranes. In addition, samples were obtained along the trunks of three old growth trees and also a small sample of roots for measurement of tracheid diameter. A gradient was apparent in all measured anatomical characters vertically along a sequence among the outer growth rings. These gradients arose not because of a gradient vertically along the internodes, but because of the strong gradients present at each internode among growth rings out from the pith. Tracheid characteristics were correlated: wider and longer tracheids had more numerous pits and wider pits, such that total pit area was about 6% of tracheid wall area independent of tracheid size. A stem model combining growth rings in parallel and internodes in series allowed for estimates of whole trunk conductance as a function of tree age. Conductance of the stem (xylem area specific conductivity) declined during the early growth of the trees, but appeared to approach a stable value as the trees aged.     

Levels of endogenous indole-3-acetic acid in the vascular cambium region of Abies balsamea trees during the activity - rest - quiescence transition

Indole-3-acetic acid (IAA) levels in the cambial region were measured by radioimmunoassay during the annual cambial activity - rest - quiescence transition at the crown top (current-year shoots) and at the middle and base of the stem of two 21-year-old Abies balsamea (L.) Mill. trees about 7.5 m in height. The IAA level declined throughout the experimental period (July 24 - December 3) at all positions in both trees. The earlywood - latewood transition, which occurred throughout each tree about the end of July, was associated in time with the largest decrease in the absolute amount of IAA. Tracheid production ceased towards the end of September, the cessation occurring earlier at the top of the tree than at the base. The cessation of tracheid production was only poorly correlated in time and space with the decline in IAA level, and it was not prevented by exogenous IAA. The results suggest that IAA level is involved in the control of tracheid radial enlargement, but not in the regulation of the cessation of tracheid production.     

Polarity of IAA Effect on Sieve-Tube and Xylem Regeneration in Coleus and Tomato Stems

A technique is described for the processing of regenerated xylem and sieve tubes from the same wound area for microscopic and quantitative comparison.

Regeneration was examined in internodes of 2 developmental stages in Coleus: internode 2, elongating, characteristic of primary growth; and internode 5, non-elongating, characteristic of secondary growth.

Transport of indoleacetic acid (IAA) in excised number 5 internodes of Coleus is strictly polar, in a basipetal direction, judging by a regeneration bioassay involving both sieve tube strands and xylem cells. Similar results were obtained with tomato.

If isolated number 5 Coleus internodes are not treated with hormone, they regenerate no xylem cells and a small number of sieve tube strands. With increasing concentrations of IAA added apically, the number of regenerated sieve tube strands (and, with higher concentrations, of xylem cells) increases progressively up to 1% IAA, the highest concentration applied.

Internode 2 of Coleus regenerates fewer xylem cells or sieve tube strands than internode 5, whether on the otherwise intact plant or with a given concentration of IAA added apically. The amount of regenerated xylem increases with added apical IAA, except that the highest concentration gives no further increase. The number of xylem cells regenerated in intact plants occurs at the same interpolated IAA concentration as in number 5 internodes. No concentration of IAA tried provided replacement of intact number of sieve tube strands in internode 2.

IAA can exert a regenerative stimulus on both xylem and sieve tubes in the area immediately adjacent to the site of its application.

     

Effects of environmental factors on wood formation in Scots pine stems

Summary To find the optimal conditions for growth and development of tracheid walls in Scots pine stems the effects of temperature and precipitation on xylem cell production by the cambium, radial cell expansion and secondary wall thickening have been studied. The observations were carried out on 10 specially chosen 50 to 60-year-old trees, growing in central Siberia, over 2 seasons. The data on the number of cells in differentiation zones and mature xylem along radial rows of tracheids, radial and tangential sizes of tracheids and their lumens were used for calculating cambial activity, the rates and durations of cell development in the zones, and both the thickness and cross sectional areas of tracheid walls. The mean day, mean maximal diurnal and mean minimal nocturnal temperatures have been shown by correlation and regression analyses to affect differentially separate stages of cytogenesis. The temperature influenced the initial division the side of xylem and radial cell expansion mainly in May–June, while the influence of precipitation increased in July–August. Throughout all seasons it was the temperature that had the main influence on the biomass accumulation in cell walls. Optimal values of temperature and precipitation for cell production by cambium, radial cell expansion and secondary wall thickening have been calculated. The data are discussed in connection with productivity and quality of wood.     

The role of plant hormones in higher plant cellular differentiation. II. Experiments with the vascular cambium, and sclereid and tracheid differentiation in the pine, Pinus contorta

In sterile-cultured explants of stems of the pine Pinus contorta Dougl., fusiform cambial cells differentiated entirely into axial parenchyma cells when exogenous indol-3yl-acetic acid (IAA) was omitted. The normal appearance of the cambial zone was maintained when IAA was included in the medium. The IAA-maintained stability of cambial structure suggests physiological rather than epigenetic control over vascular cambium structure. IAA was essential for the occurrence of callus growth in stem explants. Callus growth was similar in appearance and extent in winter- and summer-explanted material. Tracheids differentiated in explants only when actively differentiating tracheids were already present at the moment of explanting, suggesting the absence of factors necessary for tracheid differentiation in over-wintering tissues. Sclereid differentiation, which normally does not occur in phloem or xylem development in P. contorta, occurred in callus derived from active cambial explants. The sclereids were identical to sclereids which differentiated in pith of intact stems. The possibility that sclereid and tracheid differentiation may be fundamentally similar types of gene expression is discussed. Growth of P. contorta trees in continuous darkness resulted in extensive compression-wood tracheid differentiation in the upright main stem. Normal-wood tracheids differentiated in similar trees grown in light. More tracheids differentiated in light than in darkness. This apparently is the first report of induction of compression-wood tracheid differentiation in the absence of hormone treatment or tilting of trees. Different types and numbers of tracheids differentiated at different position in two-year-old disbudded defoliated stem cuttings of P. contorta in response to apically supplied IAA. No evidence for new tracheid differentiation was seen in control cuttings; however, the results suggest that neither cambial cell division nor tracheid differentiation were actually initiated by IAA. Directed transport of additional regulatory factors toward areas of high IAA concentration is formulated as a hypothesis to explain these observations. Gibberellic acid, (S)-abscisic acid and IAA inhibited tracheid differentiation when individually supplied to basal ends of P. contorta cuttings predisposed to differentiate new tracheids. Experiments with single intact needles on Pinus cembroides var. monophylla cuttings confirmed a previous interpretation that the mature pine needle, rather than the short-shoot apical meristem at its base, promotes tracheid differentiation in the stem.     

Indole-3-Acetic Acid Controls Cambial Growth in Scots Pine by Positional Signaling

The vascular cambium produces secondary xylem and phloem in plants and is responsible for wood formation in forest trees. In this study we used a microscale mass-spectrometry technique coupled with cryosectioning to visualize the radial concentration gradient of endogenous indole-3-acetic acid (IAA) across the cambial meristem and the differentiating derivatives in Scots pine (Pinus sylvestris L.) trees that had different rates of cambial growth. This approach allowed us to investigate the relationship between growth rate and the concentration of endogenous IAA in the dividing cells. We also tested the hypothesis that IAA is a positional signal in xylem development (C. Uggla, T. Moritz, G. Sandberg, B. Sundberg [1996] Proc Natl Acad Sci USA 93: 9282–9286). This idea postulates that the width of the radial concentration gradient of IAA regulates the radial number of dividing cells in the cambial meristem, which is an important component for determining cambial growth rate. The relationship between IAA concentration in the dividing cells and growth rate was poor, although the highest IAA concentration was observed in the fastest-growing cambia. The radial width of the IAA concentration gradient showed a strong correlation with cambial growth rate. The results indicate that IAA gives positional information in plants.     

Effects of environmental factors on wood formation in larch (Larix sibirica Ldb.) stems

 Effects of temperature and precipitation on xylem cell production by the cambium, radial cell expansion and secondary wall thickening in larch stems have been studied. The observations were carried out over two seasons on ten 50- to 60-year-old trees, growing in central Siberia and chosen according to growth rate (the number of cells in radial rows of each of two of the preceding seasons was equal). The data on the number of cells in differentiation zones and mature xylem along radial rows of tracheids, radial and tangential sizes of tracheids and their lumina were used for calculating cambial activity, the rates and durations of cell development in the zones, and both the thickness and cross-sectional areas of tracheid walls. The mean day air temperature, mean maximum diurnal and mean minimum nocturnal temperatures as well as precipitation have been shown by correlation and regression analyses to affect differentially separate stages of tracheid differentiation. Throughout all the seasons it was temperature that had the main influence on the initial divisions in the xylem, radial cell expansion and biomass accumulation. However, the levels of such an effect on separate stages of cytogenesis were different, especially the influence of nocturnal temperature on xylem cell production by cambium and primary wall growth. The optimum values of temperature and precipitation for cell production by cambium, for radial cell expansion and secondary wall thickening have been calculated. These optimum values of the first and second processes proved to be practically equal, while the last differs considerably in response to temperature. The data are discussed in connection with formation of early and late tracheids. Received: 3 July 1996 / Accepted: 7 February 1997     

Some quantitative effects of indoleacetic acid on the wood production and tracheid dimensions of Picea

The diameter and wall thickness of tracheids produced after indoleacetic acid treatment were not significantly different from those of the intact controls, for the first few weeks after treatment of disbudded shoots of Picea abies Karst. and Picea sitchensis (Bong.) Carr. However, lateral application of indoleacetic acid (IAA) to intact shoots increased both tracheid diameter and wall thickness; it is suggested that IAA acted synergistically with another endogenous growth regulator, which was also removed by disbudding. Increase in wall thickness after exogenous IAA was associated with increase in duration of the wall thickening phase of tracheid differentiation; this is discussed in relation to the seasonal change from early to latewood. Cambial dormancy was induced by disbudding during active wood production. Since this occurred with or without the presence of current leaves, it is concluded that in Picea continued cambial activity depends upon supply of auxin from the buds, and cannot be supplied from expanded leaves or from the internode itself. Neither indoleacetic acid nor gibberellic acid stimulated renewed cambial activity when applied after the cessation of wood production. With both disbudded and intact shoots, the effectiveness of exogenous IAA declined with time, probably due to decreasing penetration through callus developing at the wounded surface. It is suggested that this apparent change in IAA effectiveness may explain some discrepancies between the results of previous observers.Abbreviations IAA Indoleacetic acid - GA₃ Gibberellic acid     

Daily dynamics in xylem cell radial growth of Scots pine (Pinus sylvestris L.)

Daily dynamics of radial cell expansion during wood formation within the stems of 25-year-old Scots pine trees (Pinus sylvestris L.), growing in field conditions, were studied. The samples of forming wood layers were extracted 4 times per day for 3 days. Possible variations in the growth on different sides of the stem, duration of cell development in radial cell expansion phase and dynamics of cell growth in this phase were taken into account. The perimeters of tracheid cross-sections as a reflection of primary cell wall growth were the criterion of growth in a radial direction. For the evaluation of growing cell perimeters a special system for digital processing and image analysis of tracheid cross-sections of the forming wood was used. Growth rate for certain time intervals was estimated by the change in the relation of the perimeter of each observed cell in each of ten tracheid rows in each of 12 trees to the perimeter of the xylem cell of the same row before the expansion. Temporal differences in average values of the relations were estimated by Analyses of Variance. The existence of daily dynamics of Scots pine xylem cell radial growth has been proved. Intensive growth of pine tracheids has been shown to occur at any time of the day and to depend on the temperature regime of the day and the night as well as water supply of stem tissues. Moreover, reliable differences (P = 0.95) in the increment of cell walls during tracheid radial expansion have been found. Pulsing changes of the water potentials both of the cell and the apoplast, as the reason for the fluctuations of radial cell growth rate, were discussed.     

Auxin-induced assimilate translocation in the bean stem (Phaseolus vulgaris L.)

Decapitation of the fully-elongated fourth internode of Phaseolus vulgaris plants resulted in the disappearance from the internode of soluble acid invertase (EC 3.2.1.26). This loss was prevented by local applications to the internode of indol-3yl-acetic acid (IAA) and, at the point of IAA application, the specific activity of the enzyme increased by up to 3 times its initial value within 48 h of treatment. IAA applications stimulated the acropetal translocation to the internode of ¹⁴C-sucrose applied to the subtending (second) trifoliate leaf 30 h after decapitation and the start of the auxin treatment. Labelled assimilates accumulated in the IAA-treated region of the internode. Following decapitation the concentration of hexose sugars in the internode fell and that of sucrose rose substantially, but these trends were reversed by IAA treatment. However, small local accumulations of sucrose occurred at the point of auxin application where tissue concentrations of IAA were greatest (determined using [1-¹⁴C] IAA).Considerable quantities of starch were present in the ground parenchyma of the internodes at the start of the experiment but, in the absence of IAA, this was remobilised within 48 h of decapitation. IAA prevented starch loss at and below its point of application to the internode, but not from more distal tissues. Cambial proliferation, radial growth and lignification were stimulated in and below IAA-treated regions of the internode. These observations are discussed in relation to the hormonal regulation of assimilate translocation in the phloem.     

Magnitude and Kinetics of Stem Elongation Induced by Exogenous Indole-3-Acetic Acid in Intact Light-Grown Pea Seedlings

Exogenously applied indole-3-acetic acid (IAA) strongly promoted stem elongation over the long term in intact light-grown seedlings of both dwarf (cv Progress No. 9) and tall (cv Alaska) peas (Pisum sativum L.), with the relative promotion being far greater in dwarf plants. In dwarf seedlings, solutions of IAA (between 10-4 and 10-3 M), when continuously applied to the uppermost two internodes via a cotton wick, increased whole-stem growth by at least 6-fold over the first 24 h. The magnitude of growth promotion correlated with the applied IAA concentration from 10-6 to 10-3 M, particularly over the first 6 h of application. IAA applied only to the apical bud or the uppermost internode of the seedling stimulated a biphasic growth response in the uppermost internode and the immediately lower internode, with the response in the latter being greatly delayed. This demonstrates that exogenous IAA effectively promotes growth as it is transported through intact stems. IAA withdrawal and reapplication at various times enabled the separation of the initial growth response (IGR) and prolonged growth response (PGR) induced by auxin. The IGR was inducible by at least 1 order of magnitude lower IAA concentrations than the PGR, suggesting that the process underlying the IGR is more sensitive to auxin induction. In contrast to the magnitude of the IAA effect in dwarf seedlings, applied IAA only doubled the growth in tall seedlings. These results suggest that endogenous IAA is more growth limiting in dwarf plants than in tall plants, and that auxin promotes stem elongation in the intact plant probably by the same mechanism of action as in isolated stem segments. However, since dwarf plants to which IAA was applied failed to reach the growth rate of tall plants, auxin cannot be the only limiting factor for stem growth in peas.     

A Radial Concentration Gradient of Indole-3-Acetic Acid Is Related to Secondary Xylem Development in Hybrid Aspen

The radial distribution pattern of indole-3-acetic acid (IAA) was determined across the developing tissues of the cambial region in the stem of hybrid aspen (Populus tremula L. x Populus tremuloides Michx). IAA content was measured in consecutive tangential cryo-sections using a microscale mass spectrometry technique. Analysis was performed with wild-type and transgenic trees with an ectopic expression of Agrobacterium tumefaciens IAA-biosynthetic genes. In all tested trees IAA was distributed as a steep concentration gradient across the developing tissues of the cambial region. The peak level of IAA was within the cambial zone, where cell division takes place. Low levels were reached in the region where secondary wall formation was initiated. The transgenic trees displayed a lower peak level and a wider radial gradient of IAA compared with the wild type. This alteration was related to a lower rate of cambial cell division and a longer duration of xylem cell expansion in the transgenic trees, resulting in a decreased xylem production and a larger fiber lumen area. The results indicate that IAA has a role in regulating not only the rate of physiological processes such as cell division, but also the duration of developmental processes such as xylem fiber expansion, suggesting that IAA functions as a morphogen, conveying positional information during xylem development.     

Role of Cytokinin in Vessel Regeneration in Wounded Coleus Internodes

Cytokinin was found to be a controlling or limiting factor invessel regeneration around a wound in internodes of Coleus blumeiBenth. in which the endogenous cytokinin level was minimized.The cytokinin was applied in aqueous solution to the base ofexcised, mature internodes that had an active vascular cambium.Each internode also received IAA in lanolin at its apical end.Under low (0.1 %, w/w) or high (10%, w/w) auxin concentrations,the control internodes (without exogenous cytokinin) exhibitedsmall amounts of vessel regeneration. At appropriate concentrationszeatin, kinetin and 6-benzylamino-purine (BAP) induced a significantincrease in vessel regeneration around the wound. The threecytokinins also induced novel patterns of supplementary regenerationfurther from the wound surface. Kinetin and BAP showed the strongestpromoting effect at 5 and 10 µg ml^–1, while zeatinwas most effective at 20 µg ml^–1. At a low (0.1%) auxin level zeatin was the most effective cytokinin, whereaskinetin was the most effective one at high (1 %) auxin. An inhibitoryeffect on vessel regeneration was observed at the highest kinetinconcentration tested (50 µg ml^–1). The regenerationof vessels induced by cytokinin was very polar. Many more regeneratedvessel members differentiated below the wound than above it,and the regeneration process proceeded acropetally from thebase of the internode to its upper parts. Our results implya basipetal polar increase in cambium responsiveness along thestem axis from internode 5 to 7. The possible significance ofsuch a basipetal increase in cambium sensitivity in wood formationin trees is discussed. Auxin, Coleus blumei, cytokinin, vascular differentiation, vessel regeneration, wound xylem     

Ascorbic acid and xylem development in trunks of the Siberian larch trees

The contents of ascorbic acid (AA) and its oxidized form, dehydroascorbic acid (DHA), were assessed as related to the tracheid differentiation in the course of early and late wood development in the Siberian larch (Larix sibirica Ldb.) trees. The samples of the cambium, cell enlargement zone and mature cells were collected at the successive developmental stages by scraping tissues off layer by layer from trunk segments of the 20-year-old trees according to anatomical and histochemical criteria. While cambium initials were rapidly dividing, the AA contents per dry weight and per cell considerably exceeded the corresponding values characteristic of the late xylem development; such difference corresponded to the higher number of early tracheids per annual ring, as compared to the late tracheids. The AA content decreased as cells enlarged. The radial growth of the early wood tracheids, as compared to the late wood tracheids, was accompanied with a threefold increase in the AA and a decline in the DHA contents. The AA/DHA ratio was in line with the early tracheid enlargement. The maximum AA content was observed at the early stage of the secondary cell wall thickening in the tracheids of early and late xylem preceding lignification. During this stage of early wood development, the DHA content exceeded sixfold the corresponding value in the late xylem; as a result, the initial rates of lignification were different in two tissues. The rate of lignification in a newly developing layer of the early xylem increased gradually and was the highest in the completely differentiated tracheids. In the late xylem, the lignification rate was at its highest at the very beginning and then declined in the course of tracheid maturation. The dissimilar patterns of lignification in the early and late xylem were primarily associated with the DHA content, which increased in the early xylem and decreased in the maturing late xylem. Thus, the AA content and its accessibility to oxidation in the growing and mature xylem cells exhibited the diverse developmental patterns in the early and late xylem: two tissues differed in the tracheid number and radial diameter as well as in the rate of lignification.Translated from Fiziologiya Rastenii, Vol. 52, No. 1, 2005, pp. 97–107.Original Russian Text Copyright © 2005 by Antonova, Chaplygina, Varaksina, Stasova.     

Tracheid production in response to changes in the internal level of indole-3-acetic Acid in 1-year-old shoots of scots pine

Different concentrations of indole-3-acetic acid (IAA) were applied in lanolin to 1-year-old shoots of Pinus sylvestris (L.) in a manner known to stimulate cambial activity. The internal concentration of free IAA was measured at a distance below the application point by combined gas chromatography-selected ion monitoring-mass spectrometry using [¹³C₆]IAA as a quantitative internal standard, and related to the production of tracheids at the same site. The experiment was performed with: (a) debudded cuttings, where the major source of endogenous IAA, the apical buds, were replaced with exogenous IAA, and (b) intact, attached shoots, where endogenous IAA was supplemented by applying IAA around the circumference of the shoot. In both experimental systems, an increase in the internal IAA level was positively related to increased tracheid production. It was also demonstrated that the concentration of internal IAA measured at the sampling site was comparable with endogenous IAA levels found in intact control shoots, and that a wide range of applied IAA concentrations was associated with a relatively small range of internal IAA levels.     

CAMBIAL ACTIVITY IN ALASKAN WHITE SPRUCE

Cambial activity in white spruce stems in Alaska was observed during a 2-year period in 50–60-year-old natural stands. Mitotic index was used as a measure of the rate of periclinal division of fusiform cells in the cambial zone. Anticlinal divisions were relatively rare, averaging only one per 27S periclinal divisions in most stems. Mitotic index, at any given time, appeared uniform throughout the cambial zone of an internode, among internodes of the same tree, and even among trees growing at markedly different rates. Diurnal variation in mitotic index was observed. There were three distinct growing season periods: early, grand, and late. Early period activity was characterized by reactivation of periclinal division, erratic mitotic indices, and an approximate doubling of the number of cambial zone cells per radial file (NCZ). Production of the first new xylem and phloem elements marked the beginning of the grand period. Rate of cell production in the cambial zone remained about equal to derivative production for the next 45–50 days, when about 80 % of annual xylem and phloem increment occurred. There was a drop in NCZ at the beginning of the late period coincident with a decline in mitotic index, and NCZ soon dropped to the dormant level. Complete termination of cambial activity was gradual, extending through late August and perhaps into September.     

A role for polar auxin transport in rhizogenesis

Internodal shoot sections of the easy-to-root Forsythia×intermedia cv. Lynwood, and the difficult-to-root Syringa vulgaris cv. Madame Lemoine were used in vitro to investigate the role of polar auxin transport (PAT) in rhizogenesis. Syringa internodes required the distal application of indole-3-acetic acid (IAA), indole-3-butyric acid (IBA) or naphthaleneacetic acid to induce rooting, while 2,4-dichlorophenoxyacetic acid was ineffective. In contrast, Forsythia internodes rooted equally well when IBA was applied at either end of the internode. Using [³H]IAA showed transport of exogenous auxin was basipetal, and that despite similar transport velocities, the intensity of auxin transport in Syringa was greater than in Forsythia. Basipetal transport of exogenous auxin was blocked using the PAT inhibitors 2,3,5-triiodobenzoic acid (TIBA) and naringenin (Nar); where Forsythia proved more sensitive to TIBA, but less so to Nar, in comparison with Syringa. In both species, percentage rooting and the number of roots formed were greater in 5-mm-long internodes than in shorter internodes. The results demonstrate the importance of PAT for root initiation in Syringa, whereas Forsythia tissue appears to be more sensitive to the direct application of auxin.     

Changes in diffusible indole-3-acetic acid from various parts of tulip plant during rapid elongation of the flower stalk

In order to chemically identify the putative indole-3-acetic acid (IAA) and to confirm the native source of auxins account for rapid elongation of the floral stalk of tulip, we examined diffusible IAA from various parts of tulip plant during rapid elongation of the flower stalk. IAA was identified in the diffusates collected from the leaves, internodes, and floral organs with gas chromatography (GC)–mass spectrometry. The amount of diffusible IAA from different plant organs followed the order of that the internodes > flower organs > leaves during the period of rapid elongation of the floral stalk. The diffusible IAA from internodes reached its peak amount at different time than did diffusible IAA from the flower. The results obtained indicated that the top internode is probably the major source of auxins account for rapid elongation of the flower stalk.     

The role of the leaves in the regulation of internode elongation in Phaseolus vulgaris

Time-course patterns of leaf and internode elongation were studied in bean plants. Each leaf started its main elongation period when the leaf below reached half of its final length. The onset of leaf unfolding was nearly synchronous with the initiation of the elongation of the subjacent internode. Excision of young leaves increased the rate of stem elongation as a result of an earlier unfolding of the next upper leaves and the concomitant advancement in the elongation of their subjacent internodes. IAA or NAA (1% in lanolin) suppressed the enhancement effects of leaf excision on leaf and internode elongation. The excision of a young leaf increased the final length of internodes located below it, and at the same time decreased the final length of the internodes located above the excised leaf. The reduction was greater the younger the internode. Differences in internode elongation after leaf excision were related to changes during internode ontogenesis in their relative response to the availability of assimilates on the one hand, and on the other hand to hormonal factors transported acropetally from the young leaves to the growing internodes.