Root Initiation in Cuttings of Pinus radiata Seedlings: I. DEVELOPMENTAL SEQUENCE

Adventitious root initiation in hypocotyls of Pinus radiataD. Don consists of three distinct phases. In the pre-initiativephase, following selection of the cuttings, no histologicalchanges are observed. The initiative phase begins with swellingof a single parenchymatous cell, the meristematic locus. Distinctcytoplasmic changes within the meristematic locus are followedby cytoplasmic migration and asymmetric division in the surroundingcortical or peripheral cells. The third, or post-initiative,phase includes continued division of derivatives of the peripheralcells to form meristemoids which subsequently differentiateinto root primordia.     

Starch Accumulation Is Associated with Adventitious Root Formation in Hypocotyl Cuttings of Pinus radiata

apd: 15 September 2000     

Root Regeneration and Plant Water Status of Pinus radiata D. Don Seedlings Transplanted to Different Soil Temperatures

The regeneration and configuration of new roots on transplanted8 month old Pinus radiata D. Don seedlings were measured inrelation to soil temperature and time after transplanting. Theeffects of root wrenching and nutrition on root regenerationwere compared. Low soil temperature adversely affected the initiationand elongation of new roots. The branching and morphology ofthe new roots were also influenced by soil temperature. Theprocesses of initiation and elongation are greatly retardedbelow a critical root temperature between 11 and 14 ?C. Wrenchingand fertilization stimulated new root growth at low temperatures.There is a close interrelationship between the constituent partsof the network which forms the new root system. The first-orderlaterals on transplants are critical as a basic framework forextension and production of second-order laterals which formthe major part of the regenerating root system. Needle water potential was closely related to the new root growth.The water stress experienced by the transplants for severalweeks after planting was due primarily to the suppressive effectof low soil temperature on root regeneration. Wrenched plantswere less water-stressed than unwrenched plants. Field measurements confirmed the finding from controlled experimentsthat, in southern Australia, the low soil temperature in theplanting season imposes a major restriction on early root regenerationwhich in turn inflicts water stress in transplants. This needsto be considered during the planning of planting and fertilization.     

The Anatomy of Root Initiation in Cuttings of Griselinia littoralis and Griselinia lucida

The initiation of root primordia in Griselinia littoralis andG. lucida occurred a few millimeters above the cut base. Inall cases the first cellular event was the activation of specificregions of the cambium which were associated with traces fromleaves which themselves were particularly vigorous root-formersif detached. In cuttings from seedlings, the first cells cutoff continued to divide and gave rise to root primordia in situ,whereas those from mature plants produced files of six to 22rows of cells and it was only when the cells first cut off hadbeen displaced outwards towards the fibre caps that the cambiumstopped dividing. Primordium development may then occur at theadvancing front, possibly as a result of a stimulus originatingfrom damaged cells. Thus the same cells were involved in organizedprimordium formation both in seedling and mature cutting, butthe location differed. The reduced rooting and the long lag phase in cuttings frommature plants of G. lucida may be due to the presence of a completering of fibres. This does not seem to present a mechanical barrierto emergence - since elongating primordia can force throughthe ring - nor can it affect the receipt of any root-inducingstimulus by the target cells since it is considered that thisarrives via the vascular tissues. However, evidence suggeststhat it is the initial phase of cambial activation which isprevented in cuttings from mature plants. This suggested eitherthat the initial stimulus was less effective or that the targetcells were less responsive than those of seedlings, which havevery few fibres, or of mature G. littoralis, which only hasfibm associated with the vascular bundles. Griselinia littoralis Raoul Choix, Griselinia licida Forst. f. Prodr., adventitious roots, cuttings, primordium initiation and location     

The Movement of Zinc through Excised Stems of Seedlings of Pinus radiata D. Don.

Radioactive Zn solns were drawn through 10 cm stem sectionsexcised from seedlings of P. radiata to determine the locationand quantity of ⁶⁵Zn remaining in the stems and the concn of⁶⁵Zn in the exudate. Zinc was removed from solns passing through the excised stemsby processes which appeared to be non-metabolic because coolingthe inflow solns did not decrease the proportion of Zn removedand non-specific because Ca competed with Zn for ‘exchangesites’. The formation of anionic or uncharged complexes between Zn andEDTA, or citrate resulted in more Zn passing through the excisedstems. Consistent with the greater stability of Zn-EDTA complexesmore Zn passed through stems treated with EDTA than with citrate.Decreasing the pH of solns containing Zn, Ca and potassium citrateincreased the amount of Zn deposited in the basal (inflow) endof the stems, probably by decreasing the amount of Zn boundto citrate. Increasing the conen of Zn in test solns containingZn, Ca and potassium citrate did not change the distributionof ⁶⁵Zn in the stems as the capacity of the stems to removeZn from soln was large enough to remove all the free Zn in allthe solns Pinus radiata D. Don, pine, zinc, movement, stems     

Involvement of the Cotyledon in Adventitious Root Initiation in Impatiens balsamina L. Seedlings

Adventitious root primordia are found in the pre-hypocotyl tissueof developing seeds of Impatiens balsamina L. by the third weekafter petal drop, and are present in the mature seed. Aftergermination, the adventitious roots emerge from a collet swellingon the hypocotyl of the young seedlings. Removal of the colletduring the first five days results in the formation of anotherat the base of the remaining hypocotyl. Older seedlings respondto the excision of the collet by producing one or more rootsnear the cut end, unless the cut is made close to the cotyledon,when, even in nine-day seedlings, a reduced collet is formedassociated with four or fewer roots. The influence of the cotyledonon collet/root regeneration diminishes in older seedlings andin these is manifested only in hypocotyl tissue adjacent tothat organ. Impatiens balsamina, balsam, cotyledon, adventitious roots, collet     

Root Formation in Pea Cuttings III.

Cuttings were either decapitated or both decapitated and disbudded at different time intervals. Cytokinin, at different concentrations, was applied to the cuttings in lanoline. Higher concentrations of cytokinin inhibited root initiation during the early stage. However, the inhibitory effect of cytokinin disappeared during the later stage of root initiation. Lower concentrations of cytokinin promoted the root initiation during the early stage. This effect was observed on cuttings which were only decapitated. These results seem to indicate that the influence of cytokinin changes with the stage of development. There seems to be an interaction between cytokinin and one or more other growth factors. A possible reason for this may be that cytokinin, in higher concentrations, produces inhibitory effects during the early part of root initiation by blocking the activity of auxin. The loss of the inhibitory effect of cytokinin during the later part of the initiation phase suggests that, at this stage, developing root primordia are capable of controlling the level of active cytokinin and thus do not react to the exogenous application of cytokinin.     

Soil Temperature Influences on Root Resistance of Pinus contorta Seedlings

The influence of low temperature in the root zone on water uptake in lodgepole pine (Pinus contorta Dougl. ex Loud.) was studied under laboratory conditions. To remove soil hydraulic influences, two-year-old seedlings were transferred to solution cultures and maintained in temperature controlled water baths. Short term measurements of leaf conductance, leaf water potential and tritiated water movement were taken at root temperatures from 22 C down to 0 C. Root resistance was calculated to be 67% of total plant resistance at 7 C and 93% at 0 C. In addition an Arrhenius break was found in a plant resistance versus temperature plot, suggesting a significant change with temperature in the membrane pathway in the root water uptake system.     

The Role of Auxin Metabolism in Root Meristem Regeneration by Pinus lambertiana Embryo Cuttings

Since the existence of root promoting substances that consist of a complex between auxin and another molecule has been suggested, we have examined the role of auxin conversion products in root regeneration by Pinus lambertiana embryo cuttings. Auxin conversion products were detected using radioactive forms of the auxins IAA (indoIe-3-acetic acid), NAA (a-napthaleneacetic acid) and 2,4-D (2,4-dichlorophenoxyacetic acid). 10^?7M NAA was more effective than 10^?6M IAA at promoting rooting, yet it formed conversion products much less rapidly. Also continuous exposure to IAA was necessary for optimum root formation. Based on these and other findings, we conclude that free auxin, and not the conversion products we detected, is essential to root meristem formation.     

Polyamines and Root Formation in Mung Bean Hypocotyl Cuttings : II. Incorporation of Precursors into Polyamines

The incorporation of [¹⁴C]arginine and [¹⁴C]ornithine into various polyamines was studied in mung bean (Vigna radiata [L.] Wilczek) hypocotyl cuttings with respect to the effect of indole-3-butyric acid on adventitious root formation.

Both [¹⁴C]arginine and [¹⁴C]ornithine are rapidly incorporated into putrescine, spermidine, and spermine, with similar kinetics, during 5- to 24-hour incubation periods. The incorporation of arginine into putrescine is generally higher than that of ornithine. The biosynthesis of putrescine and spermidine from the precursors, in the hypocotyls, is closely related to the pattern of root formation: a first peak at 0 to 24 hours corresponding to the period of root primordia development, and a second peak of putrescine biosynthesis at 48 to 72 hours corresponding to root growth and elongation. Indole-3-butyric acid considerably enhances putrescine biosynthesis in both phases, resulting in an increase of the putrescine/spermidine ratio.

It is concluded that the promotive effect of indole-3-butyric acid on putrescine biosynthesis, from both arginine and ornithine, supports the hypothesis that auxin-induced root formation may require the promotion of polyamine biosynthesis.

     

Anatomical Changes Which Occur in Cuttings of Agathis australis (D. Don) Lindl 2. The Initiation of Root Primordia and Early Root Development

Cuttings of Agathis australis undergo complex anatomical changesin the sub-base and base. These changes include wound responsesin addition to the processes leading to adventitious root production.Although the root pnmordia form in the mid cortex the firstevents are associated with divisions in the interfasicular regiona few millimetres above the base of the Cutting. This is followedby differentiation into tracheids and phloem which then areoutwards and downwards into the mid cortex. When the inducedvascular strand is only a few cells wide, conditions at theadvancing front are most favourable for primordium formation.If sheets of vascular tissue occur, there is neither the spacenor the focal point for primordia to initiate. In cuttings fromolder material there are abundant resin canals, sclerenchymaand branch traces. These may reduce the amount of parenchymatissue to such a low level that potential primordial sites areno longer present and root formation is prevented. Organization is not observed until over 1500 cells are presentand at about this stage the beginning of organized cell arrangementcan be seen at the site of the apex of the primordium. Untilthis time the progress towards a primordium could not be saidto be ‘determined’. Although the lag phase before any morphological or anatomicalchanges are observed is variable in duration, the time takenfor the period of tracheid development and then for primordiumorganization and outgrowth is fairly constant, taking about2 weeks for each of the two phases. Evidence suggests that thevariation between species is probably in the duration of thelag phase and in the precise site of origin and pattern of theearly events. Once the primordium has formed the events leadingto root formation are probably similar for most species bothfor adventitious and lateral roots. Agathis australis (D. Don) Lindl, kauri, cuttings, wound responses, vascular connections, root primordia, root anatomy     

The Anatomical Relationship Between Cambial Regeneration and Root Initiation in Wounded Winter Cuttings of the Apple Rootstock M.26

Root primordia differentiate remote from the existing vasculartissue of split- or incision- wounded winter cuttings. Thisis preceded by heavy callusing of the wounds and basal cut surface.Most of the callus is cortical in origin but callus is alsoformed as a result of damage to the cambium. In the incisiontreatment a new cambium differentiates within the cambial callusfrom the undamaged cambium on either side so as to form an outward-pointingsalient enclosing randomly orientated xylem. Two such salientsare formed in the split base treatment since each resultanthalf behaves like a separate cutting. The salients are subdividedhorizontally into finger-like projections due to the dispositionof the rays at the edges of the wound. Once a root primordiumforms, differentiation of procambium-like tissue between itand one or more projections proceeds rapidly, followed by outgrowthof the root. Roots emerge from the basal callus and in verticalfiles from the wound callus. The split base treatment increases16-fold the number of rooted cuttings over controls, while incisionwounds increase rooting four-fold; this is associated with thefact that more rhizogenic (salient-forming) sites are formedby splitting the base. The physical and anatomical factors involvedin cambial regeneration are discussed. Anatomy, apple, callus, cambium, cambial regeneration, M.26 rootstock, Malus pumila L., rooting, root initiation, wound response     

The Control of Lateral Root Development in Cultured Pea Seedlings. II. Root Fasciation Induced by Auxin Inhibitors

Lateral root development in cultured seedlings of Pisum sativum (cv. Alaska) was modified by the application of auxin transport inhibitors or antagonists. When applied either to replace the root tip or beneath the cotyledonary node, two auxin transport inhibitors, 2,3,5-triiodobenzoic acid (TIBA) and 3,3a-dihydro-2-(p-methoxyphenyl)-8H-pyrazolo[5,1-α]isoindol-8-one (DPX-1840), increased cell division activity opposite the protoxylem poles. This resulted in the formation of masses of cells, which we are calling root primordial masses (RPMs), 2 to 3 days after treatment. RPMs differed from lateral root primordia in that they lacked apical organization. Some roots however developed both RPMs and lateral roots indicating that both structures were similar in terms of the timing and location of cell division in the pericycle and endodermis leading to their initiation. Removal of the auxin transport inhibitors allowed many of the RPMs to organize later into lateral root primordia and to emerge in clusters. When the auxin, indoleacetic acid (IAA) was added to the growth medium along with DPX-1840, 3 ranks of RPMs now in the form of fasciated lateral roots emerged from the primary root. The auxin antagonist, p-chlorophenoxy-isobutyric acid (PCIB), also induced RPM formation. In contrast to DPX-1840 treatment, the addition of IAA during PCIB treatment caused normal lateral root development.     

苹果幼苗侧根形成与内源多胺关系的通径分析(英文)

本文采用偏回归和通径分析研究苹果幼苗侧根形成与内源多胺含量之间的关系。多胺对苹果幼苗侧根形成有重要的调节作用,内源多胺的水平高低与侧根数量之间有显著的线性相关。腐胺、亚精胺和精胺对侧根形成的影响不同,它们对侧根数量的直接通径系数分别是0.0756,0.1558和0.8023。因而表明精胺在增加侧根数量中的作用最大,而亚精胺和腐胺几乎没有直接的作用。不过,亚精胶和腐胺通过影响精胺水平,对侧根形成有很大的间接作用。     

Auxin Transport Inhibitors and the Rooting of Hypocotyl Cuttings from Etiolated Mung-bean Vigna radiata (L.) Wilczek Seedlings

The auxin transport inhibitors 2, 3, 5-triiodobenzoic acid (TIBA)and naphthylphthalamic acid (NPA) inhibited adventitious rootformation (ARF) induced by indol-3-butyric acid (IBA) on cuttingsfrom etiolated mung-bean seedlings floated on solutions of thegrowth regulators. The concentrations of TIBA and NPA requiredfor a 25 per cent reduction in ARF with 10 µM IBA wereestimated by linear interpolation to be 11.3 µm and 0.42µM respectively. NPA is a particularly potent inhibitorof IBA-induced ARF. The inhibitory effect of either compoundwas reversible by higher concentrations of IBA. NPA had no effectwhen applied after the auxin treatment. The inhibitory effects of TIBA or NPA could not be explainedby effects on the uptake or metabolism of [2-^14C]IAA. Consideringthis and other evidence, it is suggested that NPA and possiblyTIBA are acting as specific antagonists of auxin in the inductionof ARF. Vigna radiata (L.), mung-bean, root induction, hypocotyl cuttings, auxin inhibitors, indol-3-butyric acid, 2,3,5-triiodobenzoic acid, naphthylphthalamic acid, auxin uptake, auxin metabolism, adventitious roots     

Competitive processes in a monoculture of Pinus radiata D. Don

Summary The changes between 9 and 40 years of age of the frequency distribution of tree diameters were studied in an experiment in a plantation of Pinus radiata D. Don in South Australia in which the spacing between trees at planting varied. Empirical functions were developed to relate tree diameter to growth rate in diameter, variance of growth rate in diameter and mortality rate. These functions were used in solving a forward diffusion equation to predict future diameter distributions. The contributions from each of the terms in the diffusion equation were examined and it was found that the drift (growth rate in diameter) term made the greatest contribution to the solution, whilst the diffusion (variance in growth rate) term had neglible effect. This implied that competition between individual trees for light was the dominant competitive process operating in this plantation, rather than below ground competition for soil resources. The ramifications of this finding to forest growth modelling are discussed.     

Changes in the Root System of Wheat Seedlings Following Root Anaerobiosis II. Morphology and Anatomy of Evolution Forms

Morphological and anatomical parameters which are variable underroot anaerobiosis in Triticum aestivum were checked on fivetaxa of primitive and modern wheats (and the related genus Aegilops).The plants were grown in nutrient solution which was eitheraerated or flushed with nitrogen. When the plants were flushedwith nitrogen a general retardation in longitudinal root growthoccurred in all of them, but only Triticum aestivum showed aclear promotion of growth of later appearing roots enablingit to maintain the same root/shoot ratio even under stress conditions.There was an increase in the volume of intercellular space inthe root cortex of nearly all the plants investigated. The diameterand the lignin content of the roots and the form of their corticalcells also varied. All these changes were expressed in the primitivewheats to a lesser extent than in the advanced Triticum aestivumindicating that there is a clear increase in the adaptive responsein the latter. Triticum species, Aegilops species, wheat, roots, anatomy, anaerobiosis, stress, intercellular space, selection     

Pinus radiata D. Don in Chile. Fertilization trials with copper

Summary YoungPinus radiata D. Don were fertilized with copper oxychloride and copper sulfate on a random block basis with four replicates. Roots, needles, stems and shoot apices were analyzed separately for Cu, Fe, Mn and Zn contents at different times from fertilization. The results showed a rapid plant copper absorption, no effects being found on the Fe, Mn and Zn content. The dynamic internal distribution of copper among different plant parts is shown. The treatments applied did not cause any phenotypical alteration nor phytotoxicity in the plants, and no significant effect of the fertilizer chemicals on each other.     

The Roles of the Cotyledons and Auxin in the Adventitious Root Formation of Hypocotyl Cuttings of Light-Grown Cucumber Seedlings

Adventitious root formation in encumber hypocotyl cuttings was studied. Root formation was quantitatively related to the amount of the cotyledons attached to the hypocotyl. Complete removal of the cotyledons diminished root formation entirely. Hut the removal of the apical bud had no effect. Treatment of the hypocotyl with triiodobenzoic acid resulted in the inhibition of root formation. On t he other hand, IAA promoted root formation. Promoting concentration of IAA was 1 mg/1 for the cuttings with intact cotyledons and 10 mg/1 for those with l/8th of the cotyledons. The first two or three days of treatment was most effective. The presence of auxin (IAA-like. substance) in cucumber seedlings was demonstrated by paper chromatography and the pea straight test. It is concluded that the cotyledon is necessary for root formation in cucumber hypocotyl cuttings and that auxin is at least one of the factors supplied from the cotyledons.