Root influence on shoot development in tea (Camellia sinensis (L.) O. Kuntze) following shoot pruning

The physiological interaction between the factors controlling the development of new shoots in pruned tea plants was investigated in an experiment using a widely cultivated TRI clone growing at low elevation in Sri Lanka. The functional importance during new shoot growth of root reserves, feeder roots and leaves and buds on unpruned branches (lung-shoots) is critically evaluated. A scheme for their interaction is presented, which highlights the need to maintain feeder roots alive during new shoot development, for which a large proportion of both reserve and current assimilates seem to be utilized. Mature leaves on lung-shoots, besides supplementing carbohydrate supply by current photosynthesis, may also serve to maintain the flow of metabolites from feeder roots to developing shoots and also function as ‘sinks’ for excess, toxic levels of root metabolites. Removing all mature leaves, as is done during ‘clean pruning’, leads to the depletion of reserves below the critical level for feeder root survival, resulting in death of feeder roots and failure of new buds to form shoots.     

Changes in root morphology accompanying mycorrhizal alleviation of phosphorus deficiency in micropropagated Annona cherimola Mill. plants

The effect of the mycorrhizal inoculation on survival rate, growth, nutrient uptake and root morphology during the acclimatization period and plant establishment of micropropagated juvenile or adult cherimoya plants (Annona cherimola Mill.) was determined. Although mycorrhizal colonization did not improve the survival rate of plants, which was already high in non-inoculated plants, it had a positive effect on plant development (shoot length, leaf number, leaf area and fresh and dry weights). Mycorrhizal juvenile plants tripled the macronutrients and increased by four the micronutrient uptake, and mycorrhizal adult plants increased by two phosphorus and all micronutrients, with copper uptake increased five times. Moreover, mycorrhizal colonization changed the root morphology of adult plants increasing three-fold the total number of roots, doubling the number of first-order laterals and increasing second-order laterals by four. Total root length was also increased three-fold, adventitious root length was almost doubled, first-order laterals tripled and second-order roots length increased four-fold. The effect of mycorrhizal colonization seems to be stronger or different in juvenile than in adult plants, suggesting that ontogenic stage is an important factor determining mycorrhizal effect and the plant performance during the acclimatization period.     

Changes in the competence of Quercus robur ‘Fastigiata’ to grow in vitro as affected by seedling rootstocks and differential pruning

Three physiologically distinct forms of the same genotype of Quercus robur ‘Fastigiata’, all derived from adult budwood, were identified following the growth of severely-pruned hedge plants grafted onto juvenile seedling rootstocks. Only explants from the form displaying the juvenile-like characteristic of over-winter leaf retention were capable of establishing sustainable cultures in vitro, although growth was not as rapid as those from a two year old seedling source. Pruning to release correlative inhibition of buds low on the scion framework produced vigorous shoot growth, but explants from these failed to show sustained growth in vitro. Withholding light from stockplants reduced excessive phenolic oxidation in explants taken from flushing unripe shoots, however, despite a beneficial effect on culture initiation, later growth was dependent upon the juvenile- or adult-like physiology of the original explant. A new medium was devised for this subject, which in addition to promoting growth generally, also stimulated the flushing of shoot apices. The relevance to in vitro culture of expression of juvenile habit in the stockplant is discussed.     

应用~(32)P研究核桃原位枝接中接芽的作用

利用32P示踪技术研究了核桃(JuglansregiaL.)原位枝接愈合过程中接芽的作用。新梢中32P动态变化曲线表明,接芽对接合部位的愈合有一定影响。接芽个数和接芽距接合部位的距离对早期愈合及新梢生长都有影响。双芽枝上检测到32P的时间最早,其次是上芽枝和下芽枝,这表明最早的砧穗间物质运输发生在双芽枝上。尽管无芽枝形成嫁接愈合体,但其上没有检测到32P的出现。双芽枝上所抽生的两个新梢的生长情况并不相同。     

Cytokinins in citrus. I. Fluctuations in the leaves during seasonal and developmental changes

Leaves of Citrus sinensis (L.) Osbeck, cultivar ‘Valencia’, were analysed for cytokinin activity on a seasonal and developmental basis. In spring, high levels of polar and low levels of non-polar cytokinins were detected in the mature leaves. This situation was reversed in early summer, when the polar cytokinins in these leaves became almost undetectable and the non-polar cytokinins, which co-chromatographed with zeatin and ribosylzeatin, increased. This apparent interconversion was followed by a decrease in the overall cytokinin content of the mature leaves, so that low levels were detected from mid-summer until late autumn. In developing leaves, particularly those expanding rapidly, low levels of cytokinin activity that co-chromatographed with zeatin and ribosylzeatin were detected. Once leaves were fully expanded, the activity associated with these cytokinins, as well as the polar derivatives, increased markedly. It is suggested that cytokinins are utilised during periods of active shoot growth, particularly when rapid leaf-expansion is taking place. In this respect, the mature leaves may play an important role in evergreen citrus. Cytokinin remobilisation and utilisation or export to the new shoot may occur from mature leaves following quiescent periods.     

The influence of rootstock lateral buds on bench-chip-budded ‘Mirandy’ field roses

A positive correlation existed between the development of shoot and root systems of ‘Mirandy’ roses. Scions bench-chip-budded below rootstock lateral shoots were inhibited by apical dominance. Inhibition of scion apices was overcome by pruning the top of each rootstock above the graft. Rootstock axillary buds were necessary for adequate initial root-system establishment, but should be eliminated early in the growth cycle to maximize scion development of rose bushes and reduce field production time.     

桃幼胚下胚轴高频植株离体再生

以桃品种京艳和晚蜜不同发育阶段合子胚下胚轴为外植体进行离体培养,用6-BA、CPPU和TDZ等细胞分裂素诱导下胚轴直接再生不定芽试验。结果表明,花后70d下胚轴为诱导的最佳材料,供试细胞分裂素中,诱导活性为TDZ>CPPU>6-BA,苯脲类细胞分裂素TDZ5mg/L与NAA0.01mg/L配合对下胚轴再生具有极强的诱导作用,京艳诱导再生率高达95.2%,平均不定芽数达每外植体25.3个。京艳的诱导率显著高于晚蜜。IBA 0.5mg/L适于诱导再生幼茎的生根,生根率和移栽成活率分别达到92.6%和65.5%。组织学观察表明不定芽起源于皮层薄壁细胞,属直接再生方式。     

Endogenous cytokinin distribution patterns at budburst in Granny Smith and Braeburn apple shoots in relation to bud growth

The possible relationship of branching habit to cytokinin content of apple shoots (Malus×domestica Borkh.) was investigated. One-year old apple shoots are acrotonic (distal branching), more strongly so in Granny Smith than in Braeburn. In the first trial, long, 1-year old Granny Smith and Braeburn apple shoots were sprayed on 29 August 1995 to break rest with dinitro-o-cresol (DNOC) oil (5%). The cytokinin contents of the xylem sap, the combined bark and buds, and the wood were determined in distal and proximal shoot halves over the next 6 weeks. Budburst (terminal and lateral buds) was first visible (green tip) in both cultivars on 20 September 1995. A greater increase in cytokinin content of distal xylem sap, coupled with elevated cytokinin in the distal wood, reflect the overall acrotony of both cultivars. The strong acrotony of Granny Smith is reflected in the higher cytokinin concentration in distal portion 1 week before the proximal portion of the shoot. The differential distribution of cytokinin reflects the pattern of budburst and may be correlated with growth habit. In a subsequent trial, Granny Smith shoots chilled and forced in the absence of roots showed an increase in cytokinin content of the bark and buds, and the wood as growth resumed. This was roughly comparable in magnitude to the increase observed under field conditions. The cytokinin increase in rootless shoots and differential distribution of cytokinin prior to sprouting, support the hypothesis that shoot-derived, rather than root-derived, cytokinins act to trigger spring budburst.     

Chilling response of ‘Granny Smith’ apple lateral buds inhibited by distal shoot tissues

Apple (Malus×domestica Borkh.) shoots were decapitated before or after chilling and then forced to budburst to determine the influence of distal inhibition (paradormancy) on the chilling response of lateral buds. Shoots were chilled and forced with the presence or absence of an inhibitory distal disbudded shoot piece. Endogenous cytokinins were determined from distal and proximal segments of shoots segmented before and after chilling and/or forcing. The isolation of lateral buds from distal inhibition by decapitation before chilling resulted in a dramatic increase in growth rate. This increase is greater than that observed in terminal buds during the normal development of acrotony on intact shoots. Distal shoot tissues appear to inhibit the chilling response of lateral buds. On intact shoots cytokinin increased more in the distal shoot tissues, but in decapitated shoots cytokinin increased more in the proximal shoot tissues. Increased cytokinin in the proximal stem segment following decapitation is possibly associated with an increased lateral bud growth rate.     

不同栽培方式下‘巧玲’芍药花蕾败育研究

 芍药生长发育的各个时期都存在花蕾败育现象,降低了成花率。以芍药品种‘巧玲’为材料,研究温室促成盆栽、室外盆栽和大田地栽方式下的花蕾败育情况,结果表明：不同栽培方式下芍药花蕾败育率明显不同,与各生长发育阶段蕾径大小相关。蕾径2 ~ 4 mm败育蕾发生率呈现温室促成栽培（67.9% ~ 86.6%）> 室外盆栽（44.9%）> 大田地栽（16.3%）的规律,此类败育蕾是由萌芽初期芽分化速度晚于同期正常芽的芽体发育而引起,蕾径达2 mm的败育蕾的雄蕊、雌蕊原基分化已完成;蕾径4 ~ 8 mm的败育蕾发生率呈现室外盆栽（29.6%）> 温室促成栽培（9.2% ~ 25.6%）> 大田地栽（11.8%）的规律,蕾径达5 mm的败育蕾处于胚珠原基分化阶段;蕾径8 ~ 17 mm的败育蕾在温室促成栽培条件下发生率为0 ~ 4.8%,但在室外盆栽及大田地栽环境中均没有发生,蕾径达10 mm的败育蕾其胚珠的珠心和珠柄已形成;蕾径17 ~ 27 mm的败育蕾在室外盆栽环境中发生率最高,为19.9%,其次为大田地栽,为9.2%,温室促成栽培最低,为0 ~ 1.4%,蕾径达18 mm的败育蕾可见胚珠的珠心、珠被、珠孔。3种栽培方式下败蕾率最高均出现在茎伸长期,即主要发生在2 ~ 4 mm大的花蕾,温室促成栽培中控制该阶段花蕾败育是降低败蕾率的关键,可以通过肥水管理,适当延长低温处理时间及保持后期栽培温度稳定来减少其发生,提高成花率。     

‘红丽’海棠早实植株发育过程中内源激素变化

 以童期不同的海棠（Malus sp.）植株为试材,使用酶联免疫法（ELISA）测定花芽分化期间 短枝顶芽、幼叶、细根中内源激素含量的变化,以探讨内源激素对花芽分化的影响,为缩短果树童期、 开发利用早实海棠资源奠定基础。结果显示,早实植株与成熟嫁接植株的内源激素含量变化趋势相似。 花芽分化的前期阶段,芽和根中IAA 含量均逐渐减少,到9 月初开始上升,成熟植株含量整体低于未成 熟植株;成熟植株叶中内源IAA 含量高于未成熟植株。芽中GAs 先上升后下降再上升,成熟植株8 月份 达到最低,而未成熟植株9 月份处于最低水平;叶中GAs 含量在成熟植株均保持较低水平;根中GAs 变 化与芽相反。内源ZR 含量在不同器官均有大幅增加,成熟植株均高于未成熟植株,实生早实植株中的变 化幅度最大。成熟植株芽中ABA 含量在160 ~ 170 ng · g^-1FW 上下波动,未成熟植株始终低于160 ng · g^-1FW;叶和根中的ABA 含量变化趋势一致,即先升高后逐渐下降,9 月之后回升。成熟植株较未成 熟植株在芽与叶中均表现为高比值的ABA/GAs 与ZR/GAs,而根中与此相反。     

Grundlagen der Reaktion von Apfelbäumen auf Wurzelschnitt – eine Übersicht

Root pruning in order to reduce shoot growth is characterized by inconsistent results and has unavoidable side effects. The theoretical basis for reliable predictions of apple tree's responses to root pruning is still largely missing. Here it is proposed that root pruning primarily interferes with the plant's mechanism of growth control: Reduced provision of cytokinins by the roots → reduced activity of shoot gibberellins → limited shoot growth and reduced auxin formation by the shoots → less inhibition of root growth and less shoot competition for carbohydrates → renewed root formation, cytokinin supply by the roots and shoot gibberellin activity → probably renewed shoot growth. Obviously, the initially reduced activity of gibberellins is crucial for the reduction of shoot growth and the various side-effects of root pruning. It depends – next to the extent and timing of root pruning – on the endogenous and external growing conditions. If these are optimal, the effect of root pruning is very limited as renewed root formation and vigorous root growth subsequently soon abolish the reduction of gibberellin activity. For a general recommendation of root pruning as part of a strategy of growth control, the prerequisites are missing.     

Observations on the Winter Dormancy of tea (Camellia Sinensis L.) in Malawi

In Malawi, over 80 % of the tea yield is harvested during the five months of the hot, wet, tropical summer. Characteristics of shoot growth were examined to define the nature of the fall in yield during the subsequent winter months of May to August. Slower shoot extension and more apical bud dormancy reduced the rate at which shoots reached harvestable size in winter. No changes were observed in other characteristics of shoot growth such as individual shoot weight, shoot death or dormancy of the axillary buds in their initial state. During the winter there was a stimulation of root growth and the low yield was possibly related in part to a redistribution of assimilate. Altering the photoperiod had little effect on yield but maintenance of warm night temperatures (20°C) during parts of the cold season accelerated the rate of shoot growth to a level as high as that of the hot, wet season.     

Castanea sativa plantlets proliferated from axillary buds cultivated in vitro

Chestnut plants were proliferated in vitro from axillary buds of juvenile shoots. N6-Benzyl-aminopurine (BAP) at 0.1?0.5 mg l^?1 was optimal for shoot multiplication. The important role played by the macronutrient formula on shoot multiplication, and especially on the rooting-stage, is emphasized. The MS ($\text{1}\text{2}$ NO₃) macronutrients gave the best rooting percentage as well as the highest number of roots per rooted shoot. In these experiments, shoots remained in the 3 mg l^?1 indole-3-butyric acid (IBA) medium for 12 days, after which they were transferred to an auxin-free medium where roots developed fully. Optimum rooting was achieved by immersing the 1 cm basal end of shoots in concentrated IBA solutions (0.5?1 mg ml^?1) for periods ranging from 2 to 15 min.     

Nutritional and cultural factors affecting rooting of papaya (Carica papaya L.) in vitro

Summary

Experiments were conducted to optimize nutritional and cultural requirements for initiation and growth of roots on papaya in vitro. Axillary shoots were obtained from plants which had been sub-cultured monthly for two years. Root initiation was enhanced when 1 to 2 mm of stem base was removed and shoots were growing actively before transfer to the rooting medium. Decreasing daylength during incubation from 24 h to 12 h promoted root initiation. Within the day temperature range of 22 to 29°C, optimum rooting occurred at 27°C and higher temperatures produced higher mean root weights per shoot. High concentrations of growth factors and the absence of sucrose in the medium both reduced root initiation, however, varying the concentration of sucrose and removing growth factors affected mean root weight per shoot. All media contained a modified de Fossard et al. (1974) basal medium plus 10 μM IBA.     

De novo differentiation of shoot buds from leaf-callus of Dianthus caryophyllus L. and control of hyperhydricity

A method is described for producing de novo shoots from leaf derived callus of carnation (Dianthus caryophyllus L.). Plants were regenerated in four steps, viz. callus induction, shoot regeneration, removal of hyperhydricity from regenerated shoots and root development. Callus induction medium contained 2,4-D and BAP. Shoot buds were formed when the callus was further subcultured on 2,4-D- and BAP-containing medium, or MS medium without any growth regulators. The shoots so formed were hyperhydric, bushy in appearance with reduced stem length and watery leaves. The normal conformation of shoots was restored by culturing the hyperhydric shoots onto medium supplemented with GA₃ and bactopeptone. The recovered shoots were rooted on MS medium added with NAA (1 mg/l) or IBA (2 mg/l). Regenerated plants with well-developed root and shoot systems were successfully transferred to field conditions after initial acclimation.     

Growth in horizontal apple shoots: Effects of stem orientation and bud position

In horizontal apple stems extension shoots were usually produced only from buds on the upper side of the stem, while buds on the lower side remained dormant or grew into spurs, and the same tendency was shown in inclined stems bent so that the “upper” and “under” sides became reversed.

On horizontal stems lateral shoots showed a gradient of vigour, the longest shoots being produced by proximal buds. Xylem of horizontal branches was epitrophic. These responses appear to be due to effects of gravity on the distribution of endogenous growth regulating factors within stems. In trees grown horizontally and rotated, shoots and spurs grew from all sides of the stem and xylem developed concentrically.

In studies of lateral shoots of partly disbudded horizontal stems, including cincturing treatments, it was found that the vigour of basal lateral shoots was a function of bud position in relation to the apex rather than in relation to the roots.

A model for lateral shoot growth in horizontal branches is proposed, in which shoot vigour is related to the position of buds along a postulated inhibitory gradient.     

The effect of rootstock shoot growth on the level of bud-grafting success in apple

Poor stands of ‘Queen Cox’ apple bud-grafted in summer onto M.9 rootstock were shown to be due to the scion bud not growing, or growing too late to produce a worthwhile ‘maiden’ tree, despite virtually all scion graft-chips forming unions with the rootstock. This problem was caused by raising the budding height to 30 cm above ground, as a method of increasing the height of lateral branches. The key element in higher budding which depressed subsequent scion bud growth was the complete removal of all rootstock shoots to a height of 35 cm to give a traditional ‘clean leg’ during the budding year. Removing rootstock shoots only at the budding position gave good stands of high quality trees. This appears to be a general effect, with the benefits of retaining rootstock shoots applying also to Malus tschonoskii when budded at 30 cm on M.9 rootstock. For both ‘Queen Cox’ and M. tschonoskii, failure of scion buds to grow vigorously often resulted in the development of ‘papery bark canker’ on the M.9 rootstock. The main benefit of root- stock shoots retained in the budding year was to ensure that scion buds grew early in the following ‘maiden’ year, whereas allowing these and new rootstock shoots to remain for the first two months of ‘maiden’ growth reduced the number of secondary scion buds which developed, and raised the height of laterals by delaying their emergence.     

In vitro propagation of Gladiolus by precocious axillary shoot formation

Axillary buds excised from corms of 3 cultivars of hybrid Gladiolus were cultured on nutrient medium containing various levels of 6-benzylaminopurine (BAP). BAP prevented dormancy, promoted shoot growth and inhibited root development. These effects were accompanied by precocious outgrowth of axillary shoots which developed into detachable, independent in vitro plantlets which could be serially sub-cultured for further proliferation. The level of BAP required to promote a steady rate of axillary branching was inversely related to its natural propagation rate. Plantlets not sub-cultured on to fresh medium eventually became dormant with the formation of small corms which could be planted in compost.     

Root induction in three species of bamboo with different rooting abilities

Rooting of in vitro axillary shoots from adult field culms of Bambusa atra, Dendrocalamus giganteus and D. hookeri and of juvenile seedling shoots of D. giganteus were investigated. B. atra rooted spontaneously without exogenous auxin during axillary shoot proliferation, while both Dendrocalamus species rooted only on transfer to rooting media with indole-3-butyric acid (IBA). D. giganteus required coumarin, an auxin protector, in addition to IBA. Rooting in adult shoots of D. giganteus was lower (45.6%) than that in the juvenile shoots (96.7%) but adult shoots of D. hookeri rooted well (88.9%). A pretreatment with thidiazuron (TDZ: N-phenyl-N-[(1,2,3-thidiazol-5-yl)urea]) induced development of axillary buds and subsequently 95% rooting in adult D. giganteus shoots but had no significant effect on rooting in juvenile shoots of D. giganteus or D. hookeri. Pretreatment with tri iodobenzoic acid (TIBA) arrested shoot and bud development leading to very low or no rooting in all three species.