Cytokinins in citrus. II. Fluctuations during growth in juvenile and adult plants

Juvenile and adult plants of ‘Pickstone Valencia’ orange (Citrus sinensis (L.) Osbeck) were compared for differences in shoot and root growth and for endogenous cytokinins in a synchronized growth flush. Dry-mass accumulation in both shoots and roots of juvenile-budded plants was significantly greater than in adult plants. Cytokinins extracted from leaves and roots of plants removed from the dormancy-induction environment, and subsequently during active growth, were mostly of the non-polar type. Buds of juvenile scions appeared to accumulate higher levels of polar cytokinins during dormancy than adult scion buds. In both plant categories, the level of polar cytokinins decreased once growth was stimulated by higher temperatures. However, cytokinin levels in buds were markedly higher than in new shoot, leaf or root material. Polar cytokinins were present in particularly low concentrations in the developing new shoots, and non-polar cytokinins only increased after the extent of shoot enlargement reached a maximum at about 50 days after warm-temperature incubation.The possible involvement of cytokinins in growth differences between adult and juvenile plants seems to be at the stage of bud activation, prior to breaking of dormancy. At this stage, polar cytokinins reached a much higher level of activity in juvenile buds, and this may have resulted in the greater scion growth of juvenile plants.     

Studies on the relationship between leaf number and area and fruit development in mango (Mangifera indica L.)

The optimum leaf number: fruit ratio in various mango cuitivars was sought by isolating individual fruits with known numbers of supporting leaves by shoot girdling. ¹⁴CO₂ feeding experiments showed a higher rate of carbon fixation in the leaves of girdled shoots than of control shoots but the translocation of ¹⁴C assimilates to the developing fruits on the girdled and control shoots was comparable. Starch accumulation in the leaves was reduced by shoot girdling. The stomatal resistance of the leaves of girdled shoots was comparable to that of leaves on control shoots. In all the cuitivars studied it was observed that 30 leaves, the maximum available on a shoot, could not support the growth of a single fruit to normal size. The results also show that fruit development depends not only on the current assimilates but also to a great extent on reserves. The utilization of reserve metabolites from vegetative organs during the ‘on’ year could be a contributing factor towards biennial and erratic bearing.     

High efficiency shoot regeneration from calluses of strawberry (Fragaria X ananassa Duch.) stipules of in vitro shoot cultures

A highly efficient method of shoot regeneration was developed from calluses of four culti- vars of strawberries (Fragaria x ananassa Duch.), ‘Addie’, ‘Dana’, ‘Gea’ and ‘Santana’, grown in vitro. Optimum shoot regeneration (84-96% of the explants), with four to eight shoots was obtained from calluses developed from stipules near the internal zone between petiole and stipule, on Murashige and Skoog (1962) or Gamborg et al. (1968) media, supplemented with 3% (w/v) glucose, 10 [iM BAP and 2.5 IBA and 0.8% agar. The calluses continued to produce shoots for at least six subsequent subcultures. This has been reported, up to now, only in juvenile explants. Microscopic observation showed no preformed buds or meristematic groups of cells in the connecting zone of petiole and stipule prior to culture. However, there were several layers of cells in this area containing higher amounts of starch, which were not observed in the cells of the bottom or in the external side of the stipule. Regeneration from stipules occurred five to six days earlier in whole leaves (stipule + petiole + lamina) than in leaves without laminae, but the final percentage was the same in the cases of all explants. The percentage of regenerating calli from the other explant sources (leaf lamina, petiole and root) was low and dependent on cultivar. Cv. Gea, which showed the highest regeneration capacity, regenerated 32% from leaf laminae, 16% from petiole and root calluses, followed by cv. Addie with 12% from leaf laminae only; the others failed to regenerate from calluses derived from these tissues. The regenerated shoots were successfully rooted and hardened for further observations on eventual somaclonal variation.     

Effects of pruning intensity on the biochemical status of shoot buds in three mango (Mangifera indica L.) cultivars planted at high density

Summary

Mango (Mangifera indica L.) trees grown at high density show a decline in flowering and fruiting after good fruiting years as a result of various factors. Annual pruning can restore production and productivity in such trees. Chlorophyll, total sugars (TS), total phenolics (TP), and proline contents as well as polyphenol oxidase (PPO) activities, were measured in the 2005–2006 and 2006–2007 seasons in shoot buds with a few leaves in three mango cultivars (‘Amrapali’, ‘Mallika’, and ‘Dashehari’). Trees were grown at high density in an orchard and the aforesaid parameters were measured 1 month after different degrees of pruning (Stage I) and after subsequent fruit bud differentiation (FBD; Stage II). Severely-pruned mango trees had the highest contents of chlorophyll a, while chlorophyll b and total chlorophyll contents were found to be highest in moderately-pruned trees. Lightly-pruned trees had the highest contents of reducing sugars (RS), whereas TS contents were highest in severely-pruned trees. The contents of RS and TS increased in shoot buds during the FBD stage. A moderate intensity of pruning significantly increased TP contents, while the lowest TP contents were recorded in non-pruned trees. ‘Off’-year shoots had higher TP contents than ‘on’-year shoots. Irrespective of pruning intensity, shoot buds of ‘Mallika’ trees had the highest PPO activities, with lower levels in ‘Amrapali’ and ‘Dashehari’ shoot buds. PPO activities were reduced at the FBD stage in ‘on’-year shoots. Severely-pruned trees had the highest PPO activities, while the lowest PPO activities were recorded in lightly-pruned trees. Shoot bud proline contents were found to be highest in non-pruned trees, and decreased with increasing pruning intensity. Thus moderate pruning can be adopted in high density orchards to obtain sustainable production with improved maintenance of canopy architecture.     

The Incorporation of Growth Hormones in Seed Dressings

Summary

The consequences of using ex vitro, single-node explants from different topophysical positions in chrysanthemum (Chrysanthemum grandiflorum /Ramat./ Kitam) were determined. In particular, how explant topophysis affected the rate of propagation, which is important for the successful micropropagation of chrysanthemum. Uniform shoots of five cultivars of chrysanthemum, cultured in vitro, were each divided into three equal zones: distal, central, and proximal. Two single-node explants were isolated from each zone and cultured on MS medium without any added growth regulators. After 10 weeks of culture, 50% of the shoots that had developed from axillary buds on each single-node explant were excised and measurements were taken in order to compare those shoots that had developed from explants from the different topophysical zones. The remaining shoots were sub-cultured on rooting medium. After 4 weeks, the numbers of roots per plantlet, and the total fresh weight (FW) of roots were recorded. The cultivars fell into two groups. ‘Lady Amber’, ‘Lady Orange’, and ‘Lady Vitroflora’ explants were topophysis-dependent, while ‘Lady Bronze’ and ‘Lady Rosy’ explants were topophysis-independent. For the three topophysis-dependent cultivars, the propagation rate, growth rate, shoot length, internode length, single leaf weight, and total plantlet FW values were highest for those shoots derived from the central and proximal zones. Topophysis failed to affect the number of leaves per shoot or the number of days between the appearance of two successive leaves. The effects of topophysis on the number of roots per plantlet and on root FW were inconsistent. The unequal growth of chrysanthemum plantlets during in vitro micropropagation can be an effect of topophysis, and this phenomenon is cultivar-specific in chrysanthemum.     

Effect of Leaf Number and Area on the Fruit Growth of Regular and Biennial Bearing Mango (Mangifera indica L.) Grown Under North Indian Conditions

Abstract

The optimum leaf number required for normal fruit growth in the regular bearing mango cultivar ‘Amrapali’ and the biennial bearing cultivars ‘Chausa’, ‘Dashehari’ and ‘Langra’ were studied by isolating individual fruits with known numbers of supporting leaves by shoot girdling at the time of fruit set. There were significant differences in the leaf area (249.01-1817.10 cm2), fresh weight (7.0-77.0 g) and dry weight (3.7-50.0 g) of leaves on shoots having 30, 20, 10 and 5 leaves as compared with control in different cultivars. In both types of cultivars, there was a progressive reduction in fruit size in terms of total fruit, pulp, peel, and seed weight with decreasing numbers of supporting leaves, however, a minimum reduction (2.4%) in fruit growth in ‘Amrapali’ was noticed with 30 supporting leaves. A nonsignificant difference in photosynthetic rate with varying number of leaves was found but its efficiency in leaves was higher in ‘Amrapali’ as compared with biennial bearing cultivars. Starch accumulation in the leaves was reduced by shoot girdling. The stomatal resistance of the leaves of girdled shoots was comparable with that of leaves on control shoots. In all the cultivars except ‘Amrapali’ it was observed that 30 leaves, the maximum retained on a shoot, could not support the growth of a single fruit to normal size. The data on rate of photosynthesis in different pool size of leaves and fruit growth in girdled and nongirdled shoots clearly show that fruit development depends not only on the current assimilates but also to a great extent on reserves. A 14CO2 feeding experiment showed a higher rate of carbon fixation in the leaves of girdled shoots than in the control shoots, but the translocation of 14C assimilated to the developing fruits on the girdled and control shoots was comparable. The results also indicated that developing fruits are major sinks for current photosynthates as more than 60 percent of the 14C exported from the treated leaf was found in the fruit in all instances.     

Influence of shoot age on floral development and early fruit set in avocado (Persea americana Mill.) cv. Hass

Floral bud development, early fruit set, bud size, leaf nitrogen and shoot starch content were recorded in spring, summer and autumn shoots of ‘Hass’ avocado (Persea americana Mill.). Floral initiation occurred in late autumn, but only in buds on terminal shoots (the last-formed shoot module on a terminal or axillary growth axis). In branching systems with three growth flushes, more flowers were produced and more fruit set on autumn and summer, than on spring flush terminal shoots. Floral development and leaf nitrogen accumulation occurred later in autumn than in summer shoots, but leaf numbers, dry and fresh weights, starch content of wood, mean floral status at anthesis and anthesis date were similar. The results suggest that nitrogen and starch were present in excess during floral development, and that shoot age did not influence the ability of a shoot to flower and set fruit, provided the shoot had sufficient vigour to produce new shoot growth in spring.     

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.     

An efficient adventitious shoot regeneration system on excised leaves of micropropagated lingonberry (Vaccinium vitis-idaea L.)

Summary

An efficient system to regenerate shoots in vitro on excised leaves of lingonberry (Vaccinium vitis-idaea L.) was developed. Leaf explants from shoot-proliferating cultures produced multiple shoots without an intermediary callus phase on zeatin (ZN)-containing shoot induction media within 3–4 weeks of culture initiation. Cultivars Regal and Splendor, and one clone from a natural stand in Estonia (ECL1), were used in the first experiment. Young expanding leaves with the adaxial side touching the culture medium, and maintained for 7 d in darkness, produced the best results. There were significant genotypic differences in adventitious shoot formation. A second experiment studied the effects of ten concentrations of three cytokinins: ZN at 5, 10, 20, 30 and 40 μM; 1-phenyl-3-(1,2,3-thiadiazol-5-yl) urea (thidiazuron, TDZ) at 0.1, 1, 5 and 10 μm; and 6-(γ-γ-dimethylallylamino) purine (2ip) at 25 μM were compared with leaf segments of different polarity in ‘ECL1’. Zeatin was found to be more effective than TDZ or 2iP as an inductive signal for regenerating many vigorous shoots. Zeatin induced multiple shoot formation at all concentrations tested, but maximum morphogenic response was observed at 20 to 30 μM. The media containing TDZ generally promoted more callus formation and suppresed shoot elongation. In a third experiment with the lingonberry cultivar Erntedank and the clone ‘ECL1’, a new medium developed for lingonberry shoot culture proved more effective than the modified Murashige and Skoog medium for regenerating shoots on leaf explants. Elongated shoots were excised and rooted directly on a 2 peat:1 perlite (v/v) medium after dipping in 0.8% indole-3-butyric acid. Rooted plantlets were acclimatized under greenhouse conditions to evaluate somaclonal variation.     

Factors affecting shoot development in apically dominant Acer cultivars in vitro.

Summary

Axillary shoot cultures of both Acer saccharinum L. ‘Pyramidale’ and A. platanoides L. ‘Crimson King’ displayed strong apical dominance and prolific basal callus in vitro, which was not conducive to rapid multiplication and rooting. Basal callus was reduced in ‘Pyramidale’ by replacing 6-benzylaminopurine (BAP-5μM) with zeatin (5μM), but this also reduced axillary shoot growth. The addition of 2,3,5-triiodobenzoic acid (1-20 μM) altered callus development and promoted a concentration-dependent increase in axillary shoot growth. Supplementing medium with thidiazuron (0.005 and 0.05 μM) in addition to BAP (1 μM) enhanced shoot growth, especially with nodal shoot sections, and increased subsequent rooting. Although thidiazuron also increased basal callus, this correlated with better shoot growth in ‘Crimson King’. Selection of apical buds from ‘Crimsom King’ stockplants was essential for the establishment of sustainable cultures; axillary bud-derived expiants quickly died. Once shoots of ‘Pyramidale’ and ‘Crimson King’ had elongated, they could be readily rooted in vitro, and plantlets were successfully weaned under high humidity ‘dry fog’.     

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.     

水分胁迫对荔枝幼树根系与梢生长的影响

以盆栽沙培1年生荔枝空中压条苗为试材,研究了水分胁迫对荔枝幼树根系和梢生长的影响以及二者的相互关系。3个处理为:沙体积含水量为7.5%(严重缺水),15.0%(一般缺水),22.5%(充分供水)。结果表明:水分胁迫严重抑制荔枝幼树地上部分和各级侧根的生长,使地上部枝梢生长严重受阻,叶片数量、平均叶面积、叶片厚度均显著变小;根总干重、侧根长度、根表面积显著减少。水分胁迫下促进须根的生长,须根的长度、根表面积比水分充足时显著增加。水分胁迫时叶片淀粉含量下降,而根系积累更多的淀粉。比较不同处理的根梢比发现,干旱对根系生长的抑制作用比枝梢更显著。     

Root and shoot growth of newly-transplanted apple trees as affected by rootstock cultivar,defoliation and time after transplanting

Summary

An experiment with Malus demonstrated that a large proportion of the transplanted root system was lost through death and decomposition soon after transplanting in the open ground. Mortality of the roots was not influenced by the rootstock cultivars or by defoliation but increased significantly with time. In the first month, shoots of maiden trees of Malus transplanted in June when in-leaf grew, but roots did not. Subsequently, most of the new roots on the rootstock M.9 regenerated from the rootstock stem, whereas with MM.106 the old coarse roots (>2.0 mm diameter) initially present at planting were most important. Root growth occurred in concert with shoot growth such that a functional balance was maintained as shown by the existence of a constant root length:leaf area ratio over a large part of the growing season. Following transplanting, the trees appear to re-establish their optimal ‘functional’ ratio by way of a co-ordinating pattern of growth tending to correct any disturbance to the ratio resulting from transplanting. Defoliation in the early establishment phase caused only a temporary initial reduction in the root growth, but reduced all the shoot growth variables measured and increased the root length:leaf area ratio throughout the growing season.     

The Influence of Shoot Competition on Fruit Retention and Cropping of Apple Trees

Fruit set was increased by removing all shoots 5 days after full bloom and at weekly intervals thereafter from trees of Sunset and Laxton’s Fortune, but removing shoots from Fortune trees 25 days after full bloom produced no beneficial effect on fruit retention. All treatments resulted in a heavier rate of fruit shedding during the ‘June drop’ period than occurred from control trees, and at harvest the trees without shoots had fewer fruits, and lower yields, than the controls. In a comparison of shoot removal and shoot tip removal starting 15 days after full bloom on Fortune trees, both treatments improved set, but whereas shoot removal caused a heavier ‘June drop’ compared with untreated trees, shoot tip removal increased the number of fruits retained to harvest and produced a yield increase. The difference between the two treatments in their influence on fruit retention, during and after the ‘June drop’, is accounted for by the beneficial effect of a relatively small number of leaves on each tipped shoot. Studies on the pattern of distribution of photosynthates, using ¹⁴CO₂ and autoradiography, produced results supporting the concept of competition between fruits and shoots and also showed changes in the pattern of assimilate movement brought about by shoot tip removal. It is concluded that competition between fruits and shoots, occurring during blossoming and the following 2–3 weeks, may limit fruit set, but the presence of shoot leaves is beneficial to fruit retention in the later part of the season, particularly during the ‘June drop’ period.     

Direct shoot organogenesis on shoot apex from seedling explants of Capsicum annuum L.

In vitro direct multiple shoot formation from seedling explants of Indian high pungent varieties of Capsicum annuum cv. Arka Abhir (AA) and Arka Lohit (AL) was successfully obtained. We were able to induce regeneration potency in these varieties by inverting the explant. Aseptically grown seedling explants with decapitated roots, apical meristem and cotyledonary leaves were inoculated in an inverted position in bud induction medium comprising of Murashige and Skoog's basal medium supplemented with 2-(N-morpholine) ethanesulphonic acid (MES) buffer along with 26.63 μM benzyl adenine (BA), 2.28 μM indole-3-acetic acid (IAA) and 10 μM silver nitrate. Profuse shoot bud induction with 20–25 shoot buds per explant was obtained. Supplementation of phloroglucinol in the bud induction medium resulted in 17 and 18% enhancement in bud induction response in Arka Abhir and Arka Lohit variety, respectively on the inverted hypocotyls. Auxin transport inhibitor tri-iodo benzoic acid (TIBA) in the bud induction medium resulted in induction of buds in a shorter period of 40–45 days when compared to bud induction (BI) medium which takes 55–65 days for bud induction. These buds were transferred to MS medium containing 2.8 μM gibberellic acid and 10 μM silver nitrate resulting in elongation of shoot buds. Transfer of shoots to MS basal medium induced rooting to produce plantlets. This protocol can be efficiently used for mass propagation and presumably also for regeneration of genetically transformed C. annuum tissues.     

In vitro propagation of spathiphyllum

An in vitro method for propagation of Spathiphyllum cultivar ‘Clevelandii’ is described as an alternative vegetative-propagation method.Leaves, inflorescences, peduncles, buds and stem pieces were tried as explants. Initiation and development of shoots did not occur when leaves and peduncles were used. In a few cases, it was possible to induce shoots from pieces of inflorescence explants. Buds and especially stem pieces were very suitable as explants, with shoots developing on the basal medium both with or without a cytokinin.Further multiplication of the shoots was optimal on the basal medium supplemented with 2 mg/l PBA. On this medium, the basal part of the old shoots became swollen and callus-like, and new shoots emerged from the callused area.Shoots developed roots very easily on the basal medium without hormone additives.     

苹果幼树铜、镉分布特征与累积规律研究

 以3年生盆栽苹果(红富士/平邑甜茶) 为试材, 土壤施入重金属铜(Cu) 和镉(Cd) 后,于生长季不同时期检测根、枝、叶内铜、镉的含量变化。结果表明, 苹果根系、新梢和叶片中Cu和Cd累积量都随着土壤Cu和Cd施入量的增加而增大。从春梢展叶开始, 根系和新梢Cu、Cd含量逐渐增加, 到春梢停长时达到最高, 之后下降; 叶片Cu、Cd含量变化比根系和新梢滞后, 到秋梢生长期才达到最高。Cu、Cd在不同器官的累积量由高到低为: 根系>枝干>新梢>叶片; 苹果根系吸收和积累Cu的能力大于Cd, 但Cd向地上部的迁移能力大于Cu。     

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.     

In vitro propagation of garlic by shoot proliferation

Shoot buds (5–8 mm long), excised from dormant cloves of the New Zealand commercial garlic (Allium sativum L.) and a virus-free French cultivar ‘Rose-de-Kakylis’, proliferated both axillary and adventitious shoots on B-5 basal medium supplemented with 0.5 mg l^?1 isopentenyladenine (2-ip) and 0.1 mg l^?1 naphthaleneacetic acid (NAA). An 8-fold increase in shoot number occurred every 6 weeks. Shoots were readily rooted in B-5 + 0.01 mg l^?1 2-ip + 0.2 mg l^?1 NAA and transferred to pots, where about 70% of the shoots formed established plants. The plants raised by this shoot-proliferation method retained the diploid condition of the parents.     

黄花梨茎段培养及植株再生

以黄花梨的顶芽和带芽茎段为外植体,研究了不同生长调节剂组合对其丛生芽诱导及生根的影响。结果表明:顶芽和带芽茎段以0.1%的HgCl2分别处理10、13min为宜;适宜的增殖培养基是MS+1mg/L 6-BA+0.5mg/L IAA;适宜的生根培养基是MS+2.0mg/L IBA+0.5mg/L NAA。