Modification of growth habit of Majestic potato by growth regulators applied at different times

The effect of gibberellic acid, CCC (2-chloroethyltrimethylammonium chloride) and B 9 (N-dimethylaminosuccinamic acid) was studied on growth of potato plants in pots. Growth was analysed on four occasions and changes in habit defined in terms of internode lengths, leaf areas and growth of lateral branches. Soaking seed pieces for 1 hr. in GA solution caused six internodes to elongate greatly, an effect not prevented by CCC applied when the shoot emerged from the soil. The effects on internode extension were determined by the length of the interval between GA treatment and CCC treatment. Treatment at emergence with CCC shortened all internodes and more CCC applied 4 weeks later had no effect. Late application of CCC or B9 shortened the top two lateral branches, usually very long in untreated plants. The regulators affected leaf growth differently from internode growth: usually growth regulators had less effect on leaf growth. Effects on growth depended on when the regulators were applied. Treatment with GA alone inhibited bud development at higher nodes than in untreated plants; when followed by late treatment with CCC, lateral growth at higher nodes was also less. CCC retarded development of lateral branches especially when applied early. B9 had a similar effect to CCC applied late. When regulators retarded growth of lower laterals, upper laterals often grew more than in untreated plants. Treatments did not affect the number of leaves on the main stem at first but later GA hastened senescence. GA increased the number of leaves on lateral stems, and the effect was enhanced by CCC. CCC alone increased the number of first- and second-order lateral leaves. GA lengthened and CCC shortened stolons. The effect of CCC persisted throughout the life of the plant. CCC or B 9 shortened stolons whenever applied. CCC hastened tuber initiation but slowed tuber growth. CCC at first retarded formation of lateral tubers but had no effect on the ultimate numbers of lateral and terminal tubers. The value of E (net assimilation rate) did not alter with time. CCC applied at emergence increased E, probably because it hastened tuber initiation and temporarily increased sink capacity. Although tubers formed earlier with CCC, their growth was slower and their demand for carbohydrate was also less. The increase in second-order laterals in CCC-treated plants indicates that they utilize carbohydrate that would normally go to tubers. This experiment also demonstrates that crowding leaves by shortening stems did not diminish E, possibly because another over-riding process (bigger sinks) offsets the effect of shading.     

Nicotine synthesis in Nicotiana tabacum L. induced by mechanical wounding is regulated by auxin

The effects of different kinds of mechanical wounding on nicotine production in tobacco plants were compared, with sand or hydroponics culture under controlled conditions. Both removal of the shoot apex and damage of the youngest unfolded leaves nos 1 and 2 by a comb-like brusher with 720 punctures caused an increase in nicotine concentration in whole plants at day 3, and reached its highest level at day 6. The nicotine concentration induced by excision of the shoot apex was much higher than that induced by leaf wounding. Both treatments also caused an increase in jasmonic acid (JA) concentration within 90 min in the shoot, followed by an increase in the roots (210 min), in which the JA concentration induced by leaf wounding was significantly higher than that induced by excision of the shoot apex. The increase in nicotine concentration occurred throughout the whole plant, especially in the shoot, while the increase in JA concentration in the shoot was restricted to the damaged tissues, and was not observed in the adjacent tissues. Removal of the lateral buds that emerged after excision of the shoot apex caused a further increase in nicotine concentrations in the plant tissues. Removal of mature leaves, however, did not cause any changes in nicotine concentration in the plant, even though the degree of wounding in this case was comparable with that occurring with apex removal. The results suggest that the nicotine production in tobacco plants was not correlated with the degree of wounding (cut-surface or punctures), but was highly dependent on the removal of apical meristems and hence on the major sources of auxin in the plant. Furthermore, immediate application of 1-naphthylacetic acid (NAA) on the cut surface after removing the shoot apex completely inhibited the increase both in nicotine in whole plants and in JA in the damaged stem segment and roots. Application of an auxin transport inhibitor around the stem directly under the shoot apex of intact plants also caused an increase in nicotine concentration in the whole plant. The results strongly suggest that auxin serves as a negative signal to regulate nicotine synthesis in roots of tobacco plants.     

Interrelationships of Cotyledonary Shoots in Pisum sativum

Unequal two shoot systems of tall and dwarf varieties of Pisum sativum L. ev, Improved Pilot and Meteor, respectively, were used in experiments where manipulative treatments involving the removal of one or other or both of the shoot apices were carried out. These were combined with GA treatments. Twenty four hours after treatment, ¹⁴CO₂ was applied to the lowest expanded leaf on the larger shoot, and the distribution of radioactivity was determined after a further 24 hours. Removal ot the apex of the larger shoot reduced the level of translocation from the treated leaf, the effect being enhanced by the additional removal of the other apex. This (Heel was more marked in the tall than in the dwarf variety. In untreated control plants of both varieties there was very little transfer ot labelled material from the larger (dominant) shoot to the smaller (weaker) shoot. This pattern was not affected by the removal of the apex from the weaker shoot. In Improved Pilot, removal of the apex from the stronger shoot led to considerable transfer of radioactive material to the weaker shoot, GA treatment having little effect. However, in Meteor, transfer of radioactivity from the stronger to the weaker shoot. after removal of the apex from the stronger shoot, only occurred after the application of GA. Removal of both shoot apices again resulted in low levels of transfer of labelled material to the weaker shoot in both varieties. These results are consistent with the hypothesis that there is competition between the two shoots for photosynthates produced by the leaves and that treatments reducing the competitive ability of one shoot, reduce the level of nutrients received by that shoot and can result in transfer of materials from it to the other shoot. Continuation of such a situation will result in increased inequality and perhaps ultimately in the death of the weaker shoot.     

Interference Between Two Strains of Bean Common Mosaic Virus is Accompanied by Suppression of Symptoms Without Affecting Replication of the Challenging Virus

An unusual type of interference between two strains of bean common mosaic virus, viz. NY15 and NL3, infecting bean plants, was investigatred. Wdhen a primary leaf was inoculated with NY15 as inducer and 1–8 days later, the opposite leaf with NL3 as challenger, the plant did not develop symptoms characteristic of NL3, i.e. systemic necrosis in the top, stem and wilting and withering of the youngest trifoloclate leaves. A7-h interval between the inoculations with inducer and challenger already sufficed to reduce the number of plants showing NL3 symptoms. Surprisingly, the amount of NL3 in the challenge-inoculated leaf was always than that in the singly infected control, Furthermore, NY15 could not be detected in the opposite leaf until 8 days post-inoculation and appered enen later in that leaf when challenge-inoculated. Histological studies showed that NL3 appered later in the xylem of bothe the petiole and stem between primary leaves and first trifoliolate leaf, as compared with the singly inoculated control.
The results suggest that suppression of Nl3 symptoms by Ny15 is not caused by impeding its multiplication, but by delaying the transport of NL3 to the xylem of petiole and stem.     

Distribution of labelled assimilates within a young apple tree after supplying14CO2to a leaf or shoot

Labelled carbon dioxide was supplied for 22 hrs to a leaf of the leader or to the lateral shoot in two-year-old apple seedlings. The distribution of radioactive assimilates within the plant following this treatment was investigated by using radioautography. The transport of labelled assimilates from the young leaf of the leader was very meagre and affected only parts of the stem and the leaves situated in the close vicinity of the treated leaf. The¹⁴C-labelled assimilates from the mature leaf of the leader were transported in a considerable amount to the apex and to the other leaves of the leader. They were also found in an appreciable amount in the stem and the roots, as well as in some lateral shoots. After supplying¹⁴CO₂ to the lateral shoot remarkable transport of labelled assimilates was observed. Radioactivity was detected in the tip and in the youngest leaves of the leader, as well as in the roots. Their path in the stem was studied by dissecting the plant and examining the cross section from each internode. This method revealed that the assimilates from the treated leaf or shoot were transported downward only on one side of the stem in a helical pattern. The lateral shoots situated on the radioactive side of the stem were also labelled, whereas those situated on the opposite (non-radioactive) side were not labelled.     

Correlative inhibition of lateral bud growth in Phaseolus vulgaris L. timing of bud growth following decapitation

Summary On intact, 3-week-old plants of Phaseolus the larger bud in the axils of the primary leaves shows slow, continuous elongation growth. Release from correlative inhibition can be detected within 30 min following decapitation. When 0.1% indoleacetic acid in lanolin is applied to the decapitated stem stump, the lateral bud shows slow growth during the first 7 h, then stops completely for a further 15 h but after 2 days a further gradual increase in length is observed.The movement of ¹⁴C-labelled assimilates from the subtending primary leaf into the lateral bud increases following removal of the shoot apex. When indole acetic acid is applied to decapitated plants the ability of the buds to import ¹⁴C increases for 5–7 h and then declines to a negligible amount. Little or no radioactivity from tritiated indoleacetic acid is transported into the lateral buds of decapitated plants during the first 48 h following removal of the apex and it appears that rapid metabolism of the compound occurs in the stem tissues.     

Jasmonic acid treatment to part of the root system is consistent with simulated leaf herbivory, diverting recently assimilated carbon towards untreated roots within an hour

It is known that shoot application of jasmonic acid (JA) leads to an increased carbon export from leaves to stem and roots, and that root treatment with JA inhibits root growth. Using the radioisotope ¹¹C, we measured JA effects on carbon partitioning in sterile, split-root, barley plants. JA applied to one root half reduced carbon partitioning to the JA-treated tissue within minutes, whereas the untreated side showed a corresponding – but slower – increase. This response was not observed when instead of applying JA, the sink strength of one root half was reduced by cooling it: there was no enhanced partitioning to the untreated roots. The slower response in the JA-untreated roots, and the difference between the effect of JA and temperature, suggest that root JA treatment caused transduction of a signal from the treated roots to the shoot, leading to an increase in carbon allocation from the leaves to the untreated root tissue, as was indeed observed 10 min after the shoot application of JA. This supports the hypothesis that the response of some plant species to both leaf and root herbivores may be the diversion of resources to safer locations.     

Uptake and translocation of paclobutrazol by shoots of M.26 apple rootstock

When ¹⁴C-paclobutrazol, a gibberellin synthesis inhibitor, was applied to different parts of actively-growing M.26 apple rootstock shoots it was translocated acropetally when applied to the young stem and, to a lesser extent, from the youngest unrolled leaf. Paclobutrazol was not translocated out of leaf laminae, shoot tips or from one-year-old wood but translocation occurred out of a treated petiole into the attached leaf. No basipetal translocation was detected. This translocation pattern suggested movement through the xylem.Localised application of paclobutrazol caused a reduction in shoot extension and leaf production when the young stem or shoot tip were treated; the effect decreased as older parts of the stem were treated. Treatment of laminae or petioles had only a slight effect on shoot extension and treatment of one-year-old wood was ineffective. Combined treatment of the shoot tip plus young stem was similar in effect to treatment of the complete shoot.It is suggested that paclobutrazol exerts its effects on shoot growth by inhibiting gibberellin biosynthesis in the shoot tip and the expanding leaves.The findings contribute to an understanding of the requirements for efficient orchard application of foliar sprays of paclobutrazol.     

Transgenic tobacco over-expressing a homeobox gene shows a developmental interaction between leaf morphogenesis and phyllotaxy.

The tobacco gene, NTH1, encodes a polypeptide of 326 amino acids and is a member of the class1 KN1-type family of homeobox genes. Expression of NTH1 has mainly been observed in vegetative and reproductive shoot apices, not observed in roots or expanded leaves. Over-expression of NTH1 in transgenic plants caused abnormal leaf morphology, consisting of wrinkling and curvature. Interestingly, the direction of leaf curvature tended to be conserved among almost all of the leaves in any given transformant. In transgenic plants exhibiting clockwise or anticlockwise phyllotaxy, leaves curved to the right or left, respectively, when looking from the shoot apex toward the base. Micro-surgical experiments demonstrated that the presence of the shoot apex is necessary for the development of leaf curvature, indicating that the order of formation of leaves on the stem (the generative spiral) affects leaf development. We found a correlation between the severity of leaf curvature and the value of the plastochron ratio, a parameter of phyllotaxy. Transformants with more severe phenotypes had larger plastochron ratios. From these findings, we discuss the possibility that an increase in the plastochron ratio, caused by over-expression of NTH1 in the shoot apex, may be involved in leaf curvature.     

Gibberellins are not essential for photoperiodic flower induction of Pharbitis nil

The influence on photoperiodic flowering of (2-chloroethyl)trimethylmmonium chloride (CCC), an inhibitor of gibberellin (GA) biosynthesis, was studied in the short-day plant Pharbitis nil cv. Violet. The cotyledons contained high levels of endogenous bioactive gibberellins, whereas in the plumules and first leaves the levels were low or undetectable. The first leaf responded to a single'dark treatment by inducing flowering when it was 10 mm or wider. Similar seedlings, but without cotyledons, were used as the assay plants to study the effect of CCC on photoperiodic flowering. Treatment with CCC had no effect on flowering of seedlings without cotyledons, although stem elongation was inhibited. By contrast. CCC inhibited flowering of the intact seedlings with cotyledons. Gibberellic acid applied to the shoot apex or to the first leaf promoted flowering in the CCC-treated seedlings without cotyledons. The results indicate thai gibberellins are not essential for the flower induction process in leaves, but that they promote flower initiation and/or later processes in the shoot apices.     

Long-day induction of flowering in Lolium temulentum involves sequential increases in specific gibberellins at the shoot apex

One challenge for plant biology has been to identify floral stimuli at the shoot apex. Using sensitive and specific gas chromatography-mass spectrometry techniques, we have followed changes in gibberellins (GAs) at the shoot apex during long day (LD)-regulated induction of flowering in the grass Lolium temulentum. Two separate roles of GAs in flowering are indicated. First, within 8 h of an inductive LD, i.e. at the time of floral evocation, the GA(5) content of the shoot apex doubled to about 120 ng g(-1) dry weight. The concentration of applied GA(5) required for floral induction of excised apices (R.W. King, C. Blundell, L.T. Evans [1993] Aust J Plant Physiol 20: 337-348) was similar to that in the shoot apex. Leaf-applied [(2)H(4)] GA(5) was transported intact from the leaf to the shoot apex, flowering being proportional to the amount of GA(5) imported. Thus, GA(5) could be part of the LD stimulus for floral evocation of L. temulentum or, alternatively, its increase at the shoot apex could follow import of a primary floral stimulus. Later, during inflorescence differentiation and especially after exposure to additional LD, a second GA action was apparent. The content of GA(1) and GA(4) in the apex increased greatly, whereas GA(5) decreased by up to 75%. GA(4) applied during inflorescence differentiation strongly promoted flowering and stem elongation, whereas it was ineffective for earlier floral evocation although it caused stem growth at all times of application. Thus, we conclude that GA(1) and GA(4) are secondary, late-acting LD stimuli for inflorescence differentiation in L. temulentum.     

Nicotine concentration in leaves of flue-cured tobacco plants as affected by removal of the shoot apex and lateral buds

It is believed that the nicotine concentration in tobacco is closely correlated with the amount of nitrogen (N) supplied.On the other hand,N uptake mainly occurs at the early growth stage,whereas nicotine concentration increases at the late growth stage,especially after removing the shoot apex.To identify the causes of the increased nicotine concentration in tobacco plants,and to compare the effects of different ways of mechanical wounding on nicotine concentration,field experiments were carried out in Fuzhou,Fujian Province in 2003 and 2004.Excision of the shoot apex had almost no influence on N content in the plant;however,it caused dramatic increases in nicotine concentration in leaves,especially in the middle and upper leaves.An additional increase of the nicotine concentration was obtained by removal of axillary buds.The wounding caused by routine leaf harvests,however,did not change the leaf nicotine concentration,and neither did reducing leaf harvest times.The present results revealed no direct relationship between N supply and nicotine concentration in tobacco leaves,and indicate that not all kinds of mechanical wounding were capable of stimulating nicotine synthesis in tobacco plants.Since nicotine production is highly dependent on the removal of apical meristems and hence on the major sources of auxin in the plant,and application of 1-naphthylacetic acid onto the cut surface of the stem after removing the shoot apex markedly decreased the nicotine concentration in different leaves and the total nicotine content in the plant,the results suggest that decreased auxin supply caused by removal of the shoot apex as a kind of mechanical wounding might regulate nicotine synthesis in the roots of tobacco plants.     

Effects of Ethylene on Photosynthesis and Partitioning in Tomato, Lycopersicon esculentum Mill

The extended period of ethylene release from ethephon (2-chloroethylphosphonicacid) after application to intact tomato plants has provideda model system in which the effects of ethylene on photosyntheticmetabolism and carbon partitioning has been studied. Ethylenerelease from leaf tissue after ethephon treatment was 10 timesgreater than that from untreated control leaves. The specificactivity of 14C2H4 released from [14C] ethephon remained constantover several days demonstrating that the ethylene was derivedfrom the applied ethephon. The ethephon-treated plants exhibitedextreme epinasty of the leaves and 24 h after application theflower buds in the first visible cluster had abscised, leafexpansion at the apex had ceased and developing adventitiousroots were visible on the lower stem. Rates of steady-state photosynthesis, respiration, photorespirationand transpiration were the same in treated and control leaves24 h after ethephon application. Both treated and control leavespartitioned similar proportions of newly-fixed 14C from 14CO²into neutral (46.4%), acidic (14.0%), basic (5.0%) and insoluble(34.0%) leaf fractions under steady-state conditions. The speedof 11C-assimilate movement in the stems of control plants (3.62±0.42cm min-1 towards the apex and 4.03±0.15 cm min-1 towardsthe roots) was more rapid than in the ethephon-treated plants(2.90±0.31 cm min-1 upwards and 2.59±0.22 cm min-1downwards). Furthermore, in the control plants 20.0±5.4%of the 14C exported to the plant from the source leaf was transportedtowards the developing flower cluster and young leaves. Twenty-fourhours after ethephon application only 6.5 ±1.7% of theexported 14C was translocated towards the shoot. Contrary tosome reports ethylene did not affect steady-state gas exchangeprocesses while carbon partitioning was significantly alteredindicating that ethylene effects on photosynthetic carbon metabolismare indirect and not due to direct effects on photosyntheticprocesses per se. Key words: Ethylene, photosynthesis, partitioning     

Expression of a gibberellin 2-oxidase gene around the shoot apex is related to phase transition in rice

A major catabolic pathway for gibberellin (GA) is initiated by 2beta-hydroxylation, a reaction catalyzed by GA 2-oxidase. We have isolated and characterized a cDNA, designated Oryza sativa GA 2-oxidase 1 (OsGA2ox1) from rice (Oryza sativa L. cv Nipponbare) that encodes a GA 2-oxidase. The encoded protein, produced by heterologous expression in Escherichia coli, converted GA(1), GA(4), GA(9), GA(20), and GA(44) to the corresponding 2beta-hydroxylated products GA(8), GA(34), GA(51), GA(29), and GA(98), respectively. Ectopic expression of the OsGA2ox1 cDNA in transgenic rice inhibited stem elongation and the development of reproductive organs. These transgenic plants were deficient in endogenous GA(1). These results indicate that OsGA2ox1 encodes a GA 2-oxidase, which is functional not only in vitro but also in vivo. OsGA2ox1 was expressed in shoot apex and roots but not in leaves and stems. In situ hybridization analysis revealed that OsGA2ox1 mRNA was localized in a ring at the basal region of leaf primordia and young leaves. This ring-shaped expression around the shoot apex was drastically decreased after the phase transition from vegetative to reproductive growth. It was absent in the floral meristem, but it was still present in the lateral meristem that remained in the vegetative phase. These observations suggest that OsGA2ox1 controls the level of bioactive GAs in the shoot apical meristem; therefore, reduction in its expression may contribute to the early development of the inflorescence meristem.     

Autoinhibition of indoleacetic acid transport in the shoots of two-branched pea (Pisum sativum) plants and its relationship to correlative dominance

Two-branched pea plants ( Pisum sativum L. cv. Lisa ZS) with different dominance degrees, obtained by removing the epicotyl shortly after germination, were used to study the interaction between the polar transport of indoleacetic acid (IAA) in both branches of the plants and its relationship to correlative dominance. The dominant shoot had higher transport capacity for 3H-IAA, exported more IAA out of its apex and possessed more endogenous IAA in apex and the first internode than the dominated one. Decapitation of the dominant shoot resulted in a rapid resumption of growth in the dominated shoot, accompanied by a considerable increase in its capacity to export endogenous IAA and to transport 3H-IAA. Parallel experiments with intact two-branched plants and Y-formed explants showed that the 3H-IAA transport on one side was inhibited by the other branch apex or by pre-application of 12C-IAA to the cut stump of the decapitated side. The higher the concentration of 12C-IAA applied to the cut stump of one side of the Y-form explant was used, the stronger the 3H-IAA transport was inhibited and the more the transported IAA was conjugated above the junction on the other side. The results of these experiments support the autoinhibition hypothesis at junctions. The relationship between elongation growth and IAA export/transport in the two-branch pea plants is considered.     

Carbon balance of a whole tomato plant and the contribution of source leaves to sink growth using the 14CO2 steady-state feeding method

To clarify the entire carbon balance of a young tomato plant and the contribution of each leaf to sink growth, the carbon balance of each leaf was quantitatively measured using the 14CO₂ steady-state feeding method to quantitatively measure the photosynthesis, translocation, distribution and respiration of newly fixed 14C. The entire carbon balance of the whole plant was calculated by adding the data of each leaf. The total amount of carbon fixed by all source leaves was 70.2 mg. Of this amount, in a 24-h period, 29% was accumulated in the sinks, 28% remained in the source leaves and 42% was respired. Of the total amount of carbon accumulated in the sinks, the proportion accumulated in the shoot apex, stem and roots were 27, 40 and 29%, respectively. The third and fourth leaves contributed about 30–40% of the total growth of the main sinks. The distribution pattern of each leaf to the shoot apex of the plant was greatest in the first leaf and decreased with decreasing leaf age, whereas it showed an opposite trend in the roots.     

The nature of floral signals in Arabidopsis. II. Roles for FLOWERING LOCUS T (FT) and gibberellin

Signals produced in leaves are transported to the shoot apex where they cause flowering. Protein of the gene FLOWERING LOCUS T (FT) is probably a long day (LD) signal in Arabidopsis. In the companion paper, rapid LD increases in FT expression associated with flowering driven photosynthetically in red light were documented. In a far red (FR)-rich LD, along with FT there was a potential role for gibberellin (GA). Here, with the GA biosynthesis dwarf mutant ga1-3, GA(4)-treated plants flowered after 26 d in short days (SD) but untreated plants were still vegetative after 6 months. Not only was FT expression low in SD but applied GA bypassed some of the block to flowering in ft-1. On transfer to LD, ga1-3 only flowered when treated simultaneously with GA, and FT expression increased rapidly (<19.5 h) and dramatically (15-fold). In contrast, in the wild type in LD there was little requirement for GA for FT increase and flowering so its endogenous GA content was near to saturating. Despite this permissive role for endogenous GA in Columbia, RNA interference (RNAi) silencing of the GA biosynthesis gene, GA 20-OXIDASE2, revealed an additional, direct role for GA in LD. Flowering took twice as long after silencing the LD-regulated gene, GA 20-OXIDASE2. Such independent LD input by FT and GA reflects their non-sympatric expression (FT in the leaf blade and GA 20-OXIDASE2 in the petiole). Overall, FT acts as the main LD floral signal in Columbia and GA acts on flowering both via and independently of FT.     

Restoration of gibberellin biosynthesis by 2,6-diisopropylphenoxyacetic acid in uniconazole-treated rice plants

2,6-Diisopropylphenoxyacetic acid (DIPA), a promoter of growth and flowering of Sagittaria species, was found to improve the shoot growth of rice plants treated with uniconazole, an inhibitor of gibberellin (GA) biosynthesis. In a modified micro-drop bioassay using semi-dwarf rice, Oryza sativa L. cv. Tan-ginbozu, in which uniconazole had been incorporated into the agar medium, a significant recovery from growth inhibition was observed for both the 3rd and the 4th leaf sheaths but not for the 2nd sheath. In greenhouse experiments, uniconazole-treated rice plants partially recovered from growth inhibition when DIPA was applied after uniconazole treatment, whereas DIPA applied with, or before, uniconazole treatment did not improve growth. The levels of GA₁ and GA₂₀ in the rice plants treated with uniconazole plus DIPA were almost equal to those of the untreated controls, indicating that the observed growth recovery is attributable to the restoration of GA biosynthesis by DIPA.     

Growth of the Stem of Agropyron repens (L.) Beauv

The growth rate of the stem of Agropyron repens (L.) Beauv.begins to decline when the sixth foliage leaf has expanded butthe relative growth rate declines throughout the period betweenthe production of one and ten mature leaves. On an absolutetime scale there is a progressive decline in growth rate ofsuccessively formed stem (node-internode) units. On a plastochronscale the relative growth rate of successive stem units declineswithin the apical region but increases behind the apex. Thedecline in the apical region is related to a decrease in therate of cell division and in the later formed stem units thereis no significant increase in cell number from the time of theirformation by the apex until the internode is initiated duringtheir fourth plastochron. These changes are related to concurrentchanges in the size of the shoot apex and in rates of leaf growth.     

Bud induction inSesamum indicum by splitting shoot apices followed by treatment with Amo-1618

Couples of buds were induced at the eccentric sites in the axial of the cotyledon inSesamum indicum by treating the embryo with a growth retardant Amo-1618 after the embyro shoot apex was split in the intercotyledonary plane, or incised between the primordia of the first opposite leaves. They appeared at first to have been transformed from the primordia of the first leaves. Developmental studies of the buds, however, revealed that they did not arise from the primordia, but from their adjacent area which is the presumptive stem tissue situated between the primordia and the cotyledon. Buds could occur only when the original shoot apex of the embryo as well as the first leaf primordia were degenerated. From experimental and circumstantial evidences, they were interpreted as axially buds induced at an unusual site.