Dynamics of the Elongation of Internodes in Maize (Zea mays L.): Analysis of Phases of Elongation and their Relationships to Phytomer Development

The kinetics of elongation of individual internodes of maizestems were studied under field conditions. Thermal time coursesof internode length were recorded using non-destructive methods,based on direct measurement of X-ray photographs or on indirectestimates using heights of leaf collars. These data were complementedby serial dissections of maize stems, and by precise observationof the process of sheath emergence, to specify its role in thekinetics of internode elongation. The kinetics of elongationwere found to be composed of four phases. The rate of elongationrises exponentially during phase I, and then increases sharplyduring a short period (phase II), which is followed by a majorperiod of constant growth rate (phase III) and a shorter periodin which the rate declines (phase IV). During phase I, elongationappears to be integrated at the level of the whole apical cone.From phase II onwards, elongation becomes determined at thelevel of the phytomer. The emergence of the sheath attachedto the internode appears to be a possible trigger for the transitionbetween phase I and phase II, and it may also be involved invariation in final length among phytomers. Copyright 2000 Annalsof Botany Company Zea mays L., internode, elongation, modelling, dynamics, X-rays, collar, phytomer, stem, thermal time, phasic development     

Stem Elongation Response to Neighbour Shade in Sprawling and Upright Polygonum Species

Shading by neighbouring plants, which reduces energy for photosynthesisand lowers the ratio of red:far red light, can trigger a stemelongation or ‘overtopping’ response in herbaceousplants. We compared the stem elongation response of two Polygonumspecies in a greenhouse experiment. P. sagittatum, a sprawling,vine-like annual, and P. hydropiperoides, an upright perennial,were grown from seeds at three levels of neighbour shade producedby crowding a cohort of real neighbour plants or adult-sizedfake neighbour plants that provided shade and reduced the red:far-redratio. We hypothesized that the annual would show a more pronouncedelongation response to developing or adult neighbour shade becausevine-like plants are less mechanically constrained to remainupright and self-supporting. Internodes on stems of bothP. sagittatumand P. hydropiperoides increased in length as the amount ofshading by real or fake neighbours increased. P. sagittatumclimbed on adjacent plants, and had longer stems with more nodesthan those of P. hydropiperoides. Although both P. sagittatumand P. hydropiperoides tended to elongate with crowding, thegreater elongation response to both real and fake neighboursshown by the sprawling annual reflects its ability to extendupward into a canopy beyond self-supporting height. Self-supportingP. hydropiperoides can extend upward with, or overtop, cohortneighbours, but might less readily elongate into an extant canopy.In dense stands, P. sagittatum can become structurally dependenton close P. hydropiperoides neighbours. Our results suggestthat the elongation response of P. sagittatum to neighbourscan contribute to structural dependence and could facilitatecoexistence of these species.Copyright 2000 Annals of BotanyCompany Neighbour effects, light variation, red:far-red, plant growth strategy, Polygonum sagittatum, Polygonum hydropiperoides, smartweeds     

Photomodulation of Stem Extension in Light-Grown Plants: Evidence for Two Reactions

Internode elongation was measured in plants of Phaseolus vulgarisand Glycine max grown under 8 h photoperiods at 25 W m^–2in white fluorescent light, followed by light-extensions varyingin quality, irradiance and duration. Two distinct responsesto light were observed under these conditions. A reduction in P_FR/P increased elongation, but elongation wasalso modified by a second reaction in which internode lengthincreased with increase in the duration and irradiance of theday-extension. This light-promoted response occurred in bothred and blue light. In the P_FR-inhibition response, light acteddirectly on the expanding internode. The light-promoted response,in contrast, required irradiation of the leaf. The response to a short end-of-day exposure to far-red lightprogressively diminished as successive internodes expanded underthe treatment, whereas the light-promoted response increased.The two processes appeared to interact and, in the later-expandinginternodes, the effect of a reduction in P_FR was greater underlong day-extensions with mixed red and far-red light than inthe end-of-day treatments. ¹ Present address: British Telecom, Brunel House, 2 FitzalanRoad, Cardiff, U.K.     

Costs versus risks: Architectural changes with changing light quantity and quality in saplings of temperate rainforest trees of different shade tolerance

Light requirements and functional strategies of plants to cope with light heterogeneity in the field have a strong influence on community structure and dynamics. Shade intolerant plants often show a shade avoidance strategy involving a phytochrome‐mediated stem elongation in response to changes in red : far red ratio, while shade‐tolerant plants typically harvest light very efficiently. We measured plant size, stem diameter, internode and leaf lengths in randomly chosen saplings of 11 woody species differing in their shade tolerance in both a secondary forest and an old‐growth temperate evergreen rainforest in southern Chile. We also recorded the irradiance spectrum and the diffuse and direct light availabilities at each sampling point. Significant differences were found for the mean light environment of the saplings of each species, which also differed in basal stem diameter, internode length and leaf length, but not in plant height. Both plant slenderness (plant height/stem diameter) and mean internode length increased with increasing light availability, but no relationship was found between any of these two traits and red : far red ratio. The change in plant slenderness with light availability was of lesser magnitude with increasing shade tolerance of the species, while internode change with light availability increased with increasing shade tolerance of the species. Shade tolerators afford higher costs (thicker stems and plants), which render more biomechanically robust plants, and respond more to the light environment in a trait strongly influencing light interception (internode length) than shade intolerant species. By contrast, less shade‐tolerant plants afforded higher risks with a plastic response to escape from the understorey by making thinner plants that were biomechanically weaker and poorer light interceptors. Thus, species differing in their shade tolerances do differ in their plastic responses to light. Our results contribute to explain plant coexistence in heterogeneous light environments by improving our mechanistic understanding of species responses to light.     

Day/night temperature environment affects cell elongation but not division in Lilium longiflorum Thunb

Lilium tongiflorum Thunb. cv. ‘Nellie White’ plantswere grown in different day/night temperature (DT/NT) environmentsto determine the anatomical basis for differential responsesof stem elongation to DT and NT. Lilium plants were forced in1986 and 1987 under 25 and 12 different DT/NT environments,respectively, with temperatures ranging from 14 to 30 °C.Parenchyma and epidermal cell length and width were measuredin stem tissue (1987) and epidermal cell length and width weremeasured in leaf tissue (1986). Total cell number per internodeand vertical cell number per internode were calculated. Stemparenchyma and stem and leaf epidermal cell length increasedlinearly as the difference (DIF) between DT and NT increased(DIF = DT —- NT), i.e. as DT increased relative to NT.DIF had no effect on stem parenchyma width, stem and leaf epidermalcell width, or cell number per internode. Data suggested thatstem elongation responses to DIF are elicited primarily througheffects on cell elongation and not division. Key words: Thermoperiodism, thermomorphogenesis, stem elongation, DIF, cell division, cell elongation, leaf expansion     

Uncoupling light quality from light irradiance effects in Helianthus annuus shoots: putative roles for plant hormones in leaf and internode growth

An attempt has been made to uncouple the effects of the two primary components of shade light, a reduced red to far-red (R/FR) ratio and low photosynthetically active radiation (PAR), on the elongation of the youngest internode of sunflower (Helianthus annuus) seedlings. Maximal internode growth (length and biomass) was induced by a shade light having a reduced R/FR ratio (0.85) under the low PAR of 157 micromol m(-2) s(-1). Reducing the R/FR ratio under normal PAR (421 micromol m(-2) s(-1)) gave similar growth trends, albeit with a reduced magnitude of the response. Leaf area growth showed a rather different pattern, with maximal growth occurring at the higher (normal) PAR of 421 micromol m(-2) s(-1)), but with variable effects being seen with changes in light quality. Reducing the R/FR ratio (by enrichment with FR) gave significant increases in gibberellin A(1) (GA(1)) and indole-3-acetic acid (IAA) contents in both internodes and leaves. By contrast, a lower PAR irradiance had no significant effect on GA(1) and IAA levels in internodes or leaves, but did increase the levels of other GAs, including two precursors of GA(1). Interestingly, both leaf and internode hormone content (GAs, IAA) are positively and significantly correlated with growth of the internode, as are leaf levels of abscisic acid (ABA). However, changes in these three hormones bear little relationship to leaf growth. By implication, then, the leaf may be the major source of GAs and IAA, at least, for the rapidly elongating internode. Several other hormones were also assessed in leaves for plants grown under varying R/FR ratios and PARs. Leaf ethylene production was not influenced by changes in R/FR ratio, but was significantly reduced under the normal (higher) PAR, the irradiance treatment which increased leaf growth. Levels of the growth-active free base and riboside cytokinins were significantly increased in leaves under a reduced R/FR ratio, but only at the higher (normal) PAR irradiance; other light quality treatments evoked no significant changes. Taken in toto, these results indicate that both components of shade light can influence the levels of a wide range of endogenous hormones in internodes and leaves while evoking increased internode elongation and biomass accumulation. However, it is light quality changes (FR enrichment) which are most closely tied to increased hormone content, and especially with increased GA and IAA levels. Finally, the increases seen in internode and leaf GA content with a reduced R/FR ratio are consistent with FR enrichment inducing an overall increase in sunflower seedling GA biosynthesis.     

Light Effects on Apical Dominance

Reducing light intensity from 18·0 klx to 5·4klx promoted main-stem growth in Phaseolus vulgaris but leftlateral extension unaffected. Shading individual laterals orapices of main stems promoted elongation of the shaded portion.Increasing day length from 8 to 16 or 24 h did not greatly affectplant growth if full-intensity and full-spectrum light was used.If, however, the additional light was supplied by incandescenttubes containing a high proportion of infra-red light, growthof main stems but not laterals was induced in proportion tothe length of the additional light period. It is suggested thatthe increased growth of the main stem in response to infra-redlight prevented the equivalent response of the laterals becauseof the enhanced ability of the main stem to suppress lateralelongation.     

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.     

Correlative Growth in Young Terminalia superba in a Controlled Environment: Effect of the Leaves on Internode Elongation

Young Terminalia superba plants were cultivated in a controlledenvironment at the Phytotron. Effects of the excision of a youngleaf at definite elongation stages and at two given levels ofthe main axis were studied on the elongation of internodes inthese plants. Effects of the leaf did not seem to depend onits nodal position on the main axis but predominantly occurredon the immediate surrounding internodes. The excision of a youngleaf enhanced the growth rate of the internode located belowit and markedly decreased the elongation of the internode aboveit but slightly affected internode growth duration. This excisionenhanced the final length of the internode located below theleaf and decreased the final length of the internode locatedabove the removed leaf. Significant linear regressions werefound between the length of the excised leaf and the internodefinal lengths. Microscopic examination of epidermal cells ofcontrol and disrupted internodes revealed that the decreasedelongation after leaf excision could be attributed to reductionof cell divisions. The increased elongation after leaf excisioncould be attributed both to slight increase in the length ofcells (significant negative correlation was found with the lengthof the removed leaf) and to increase of cell divisions. Terminalia superba, leaf excision, cell division, internode elongation, correlative growth     

Changes in Endogenous Gibberellin and Auxin Activities during First Internode Elongation in Tulip Flower Stalk

Dark treatment during the most active period of tulip shootgrowth induced rapid elongation of the first internode. Endogenousfree-form gibberellin and diffusible auxin in the first internodeincreased while bound-form gibberellin decreased after the darktreatment. Alternating dark and light treatments at 24-h intervalscaused increases in elongation of the first internode and theamounts of free-form gibberellin and diffusible auxin in thedark but their decreases in the light. TIBA treatment at thefirst node inhibited both the elongation and the increase indiffusible auxin, but did not affect the gibberellin amount.Ancymidol application prior to the dark treatment inhibitedthe increase in both free-form gibberellin and diffusible auxin.Application of gibberellin A₃ increased both elongation of thefirst internode and the amount of diffusible auxin. It alsocaused recovery from ancymidol-mediated reduction in elongationand diffusible auxin content. Dark-induced elongation of thefirst internode was inhibited when all organs above the firstinternode were excised, but endogenous free-form gibberellinincreased and bound-form gibberellin decreased. After excision,elongation of the first internode occurred only when both GA₃and IAA were applied exogenously, or when IAA was applied withdark treatment. These results indicate that dark-induced elongationof the first internode of tulip is promoted by auxin, whichis transported from the upper organs into the first internodedue to stimulation from the dark-induced increase in free-formgibberellin. Free- and bound-form gibberellins changed complementarilywith the dark and light treatments. An interconversion systembetween the two forms in the first internode and its dependenceon light conditions are also discussed. (Received June 23, 1984; Accepted March 5, 1985)     

Distribution of Glycosidases and Acid Invertase Activities in Relation to Elongation Growth in Pearl Millet Internode

The mean cell length along a differentiating internode and alliedchanges in the activities of ß-glucosidase, - andß-galactosidase. -mannosidase and acid invertase,together with the contents of reducing and non-reducing sugars,were examined in pearl millet (Pennisetum americanum L. Leekecv. BJ-104). The specific activities of cytoplasmic -mannosidase,wall ß-glucosidase, and cytoplasmic and wall acidinvertase showed close relationships with the rate of cell elongation.The linear regressions of the rate of cell elongation, and thespecific activities of wall ß-glucosidase and cytoplasmicand wall invertase showed significant positive correlations(P<0·05), whereas cytoplasmic -mannosidase was negativelycorrelated (P<0·01). The results are discussed in the light of cell wall looseningand the provision of carbon substrates for cell elongation. Key words: Glycosidases, acid invertase, sugars, cell elongation, Pennisetum americanum L., Leeke     

Growth and Physiology of One-year old Poplar (Populus) Under Elevated Atmospheric CO2 Levels

The effects of elevated atmospheric CO₂ concentrations on theecophysiological responses (gas exchange, chlorophyll a fluorescence,Rubisco activity, leaf area development) as well as on the growthand biomass production of two poplar clones (i.e. Populus trichocarpax P. deltoides clone Beaupré and P. x euramericana cloneRobusta) were examined under open top chamber conditions. Theelevated CO₂ treatment (ambient + 350 µmol mol^-1) stimulatedabove-ground biomass of clones Robusta and Beaupré afterthe first growing season by 55 and 38%, respectively. This increasedbiomass production under elevated CO₂ was associated with asignificant increase in plant height, the latter being the resultof enhanced internode elongation rather than an increased productionof leaves or internodes. Both an increased leaf area index (LAI)and a stimulated net photosynthesis per unit leaf contributedto a significantly higher stem biomass per unit leaf area, andthus to the increased above-ground biomass production underthe elevated CO₂ concentrations in both clones. The larger LAIwas caused by a larger individual leaf size and leaf growthrate; the number of leaves was not altered by the elevated CO₂treatment. The higher net leaf photosynthesis was the resultof an increase in the photochemical (maximal chlorophyll fluorescenceFm and photochemical efficiency Fv/Fm) as well as in the biochemical(increased Rubisco activity) process capacities. No significantdifferences were found in dark respiration rate, neither betweenclones nor between treatments, but specific leaf area significantlydecreased under elevated CO₂ conditions.Copyright 1995, 1999Academic Press Biomass, chlorophyll a fluorescence, elevated CO₂, growth, Populus, poplar, photosynthesis, respiration, Rubisco     

An Ecophysiological Comparison of Measurements of the Diurnal Rhythm of the Leaf Elongation and Changes of the Leaf Thickness of Salt-resistant Dicotyledonae and Monocotyledonae

Rozema, J., Arp, W., van Diggelen, J., Kok, E. and Letschert,J. 1987. An ecophysiological comparison of measurements of thediurnal rhythm of the leaf elongation and changes of the leafthickness of salt-resistant Dicotyledonae and Monocotyledonae.—J.exp. Bot. 38: 442–453. The continuous measurement of leaf elongation and leaf thicknesswith the use of a rotation potentiometer set up revealed a rapidand sensitive reaction of halophytic plants to conditions affectingthe plant's water relations. At increased salinity (450 molm^–3 NaCl) the rate of leaf elongation decreased both inAster tripolium and in Sparlina anghca. Increased shrinkageduring the day and a long period for recovery swelling at nightin leaves of Aster iripolium at increased salinity illustratesthat water shortage is part of the cause of salinity-inducedgrowth reduction. All dicotyledonous species analysed (Aster tripolium, A triplexhastata, A. littoralis, Suaeda maritima and Beta vulgaris) showeda day/night ratio of the leaf elongation rate lower than 1,while this ratio was higher than or equal to 1 in Monocotyledons(Spartina anglica, Juncus gerardii, J. maritimus, Festuca rubrassp. litoralis, Elymus pycnanthus). With the exception of Triglochinmaritima none of the monocotyledonous halophytes tested (Sparlinaanglica, Juncus gerardii, J. maritimus, Festuca rubra ssp. litoralis,Elymus pycnanthus) exhibited a diurnal rhythm of leaf thicknesschanges, such as was observed for all dicotyledonous speciesstudied (Aster tripolium, Atriplex hastata, A. littoralis, Salicorniabrachyslachya, Suaeda maritima, Glaux maritima, Odontites vernassp. serotina). The diurnal pattern of the leaf elongation rateand the leaf thickness changes can be explained by variationof photosynthetic rate and transpiration water losses by stomatalclosure in the dark and opening in the light such as shown forthe dicotyledon species Glaux maritima. This difference betweendicot and monocot species in diurnal variation of the leaf elongationrate and leaf thickness may partly be explained in terms ofthe different position of the growth zone and possibly by adifference in elasticity of the tissue of halophytic monocotyledonsand dicotyledons. The consequences of these differences arediscussed. Key words: Leaf elongation rate, leaf thickness, water relations, salt resistance, Dicotyledonae, Monocotyledonae     

Invertase Activity, Carbohydrate Metabolism and Cell Expansion in the Stem of Phaseolus vulgaris L.

In the stem of Phaseolus vulgaris L. the specific activity ofacid invertase was highest in the most rapidly elongating internode.Activity of the enzyme was very low in internodes which hadcompleted their elongation, in young internodes before the onsetof rapid elongation, and in the apical bud. From shortly afterits emergence from the apical bud the elongation of internode3 was attributable mainly to cell expansion. Total and specificactivities of acid invertase in this internode rose to a maximumat the time of most rapid elongation and then declined. Transferof plants to complete darkness, or treatment of plants withgibberellic acid (GA₃), increased the rate of internode elongationand final internode length by stimulating cell expansion. Bothtreatments rapidly increased the total and specific activitiesof acid invertase in the responding internodes; peak activitiesof the enzyme occurred at the time of most rapid cell expansion. In light-grown plants, including those treated with GA₃, rapidcell and internode elongation and high specific activities ofacid invertase were associated with high concentrations of hexosesugar and low concentrations of sucrose. As cell growth ratesand invertase activities declined, the concentration of hexosefell and that of sucrose rose. In plants transferred to darkness,stimulated cell elongation was accompanied by a rapid decreasein hexose concentration and the disappearance of sucrose, indicatingrapid utilization of hexose. No sucrose was detected in theapical tissues of light-grown plants. The results are discussed in relation to the role of acid invertasein the provision of carbon substrates for cell growth. Key words: Cell expansion, Acid invertase, Hexose, Sucrose, Phaseolus     

A Quantitative Study of Shoot Development in Vicia faba: II. The Elongation of Internode and Petiole

The elongation of the internodes and petioles of Vicia fabahas been studied in the plumules of normal seedlings, in seedlingsfrom which part or all of the cotyledonary reserve has beenremoved, and in axillary shoots developed on seedlings of variousages. The curves obtained by plotting the lengths of the internodesagainst their plastochrone ages reveal constant differencesin behaviour between plumules and axillary branches. As thegrowth of any shoot progresses a greater contribution to thetotal elongation rate cornea to be made by the internodes fartherremoved from the apex. The length of each internode depends throughout its developmenton its position in the stem as well as on the length of theinternode below. The extent to which the elongation of an internodelags behind that of the one below increases upwards, a relationshipsimilar to that previously shown to exist in respect of thevascularization of the internodes. In plumules the length of petiole corresponding to any givenlength of internode undergoes a decrease followed by an increaseas the plumule is traversed from base to apex, a relationshipexactly oppsite to that previously demonstrated between thevascularization of a leaf-trace bundle and that of the internodein which it runs. The effects of age and of removal of cotyledonary reserves aredescribed, and it is concluded that it is unlikely that thecharacteristic difference in internode length within the limitsof a single shoot are wholly due to changes in the availabiltyof reserve substances.     

Effects of shading and plant density on leaf growth of Viciafaba

Faba beans (Viciafaba cv. Maris Bead) were grown in the field at densities of 20 and 60 plants m^-2 and under zero, 34 and 56% reduction in incoming solar radiation. Measurements of the area of individual leaves were made every two days. Rates of leaf appearance and the duration of expansion of a leaf were virtually unaffected by the experimental treatments. Leaves required approximately 200 ^oC days (above 1 ^oC) from appearance to full expansion. Shading consistently increased specific leaf area but decreased leaf weight only at the greater shading level. At low density leaves were largest under 34% shade and smallest under 56% shade, but at high density there were no significant differences in leaf size.     

The Effects of Dwarfing Genes Rht1 and Rht2 on Cellular Dimensions and Rate of Leaf Elongation in Wheat

The gibberellin insensitivity genes, Rht1 and Rht2, reducedepidermal cell lengths in leaves of isogenic lines of field-and laboratory-grown wheat (Triticum aestivum L.). Rht dosagesof zero (wild type), two (semi-dwarf) and four alleles (doubledwarf) had a linear negative effect on cell length in flag leavesof field-grown plants, and in the sheaths and blades of leafnumber 1 in laboratory grown plants. Decrease in cell length,rather than reduced cell number, accounted for most to all ofthe reduction in blade and sheath length. In sheaths, cell widthincreased with Rht dosage, but not sufficiently to compensatefor decreased length in determining average projected surfacearea. Rates of extension of leaf number 1 in laboratory-grownplants were negatively and linearly correlated with Rht dosage.Maximal growth rate was maintained longer in wild type thanin double dwarf, but the total duration of measurable extensionin leaf number 1 was not affected by Rht dosage. Cell size, elongation, Rht, wheat, Triticum aestivum L     

Day length affects the dynamics of leaf expansion and cellular development in Arabidopsis thaliana partially through floral transition timing

Background and Aims: Plant aerial development is well known to be affected by daylength in terms of the timing and developmental stage of floraltransition. Arabidopsis thaliana is a ‘long day’plant in which the time to flower is delayed by short days andleaf number is increased. The aim of the work presented herewas to determine the effects of different day lengths on individualleaf area expansion. The effect of flower emergence per se onthe regulation of leaf expansion was also tested in this study. Methods: Care was taken to ensure that day length was the only sourceof micro-meteorological variation. The dynamics of individualleaf expansion were analysed in Ler and Col-0 plants grown underfive day lengths in five independent experiments. Responsesat cellular level were analysed in Ler plants grown under variousday lengths and treatments to alter the onset of flowering. Key Results: When the same leaf position was compared, the final leaf areaand both the relative and absolute rates of leaf expansion weredecreased by short days, whereas the duration of leaf expansionwas increased. Epidermal cell number and cell area were alsoaltered by day-length treatments and some of these responsescould be mimicked by manipulating the date of flowering. Conclusions: Both the dynamics and cellular bases of leaf development arealtered by differences in day length even when visible phenotypesare absent. To some extent, cell area and its response to daylength are controlled by whole plant control mechanisms associatedwith the onset of flowering.