Orthotropic Shoots Research Articles

Architecture of a clonal population ofMuehlenbeckia astoniiPetrie (Polygonaceae), a divaricating shrub endemic to New Zealand

Abstract Muehlenbeckia astonii Petrie is a compact, divaricating shrub. It produces both orthotopic and plagiotropic shoots but after a period of time the orthotopic shoots revert to a plagiotropic form. Orthotropic shoots differ from plagiotropic ones in that the internodes are longer, the shoots more erect and much straighter for the first 10-15 intemodes. A clonal population of two-year-old cuttings, taken from a female plant, was grown outdoors in pots. Those cuttings supplied with a balanced nutrient solution were more vigorous and produced more second-order orthotropic shoots than those not provided with nutrient. However, nutrient level did not affect the ultimate divaricating nature of the shoots. The vigour of the shoots varied. Generally, a shoot grew vigorously for the first season producing many other shoots of higher orders; then extension of the second-order axis ceased and further growth was restricted to the higher-order laterals. Most of the growth was carried out by shoots initiated in t...

Leaf Development and Primary Vascular Organization in Shoots of Anisophyllea disticha

Anisophyllea disticha is characterized by strong shoot dimorphism. Orthotropic shoots with helically arranged scale leaves produce tiers of plagiotropic shoots, while plagiotropic shoots are anisophyllous and bear dorsal scale and ventral foliage leaves arranged in a unique tetrastichous system. In this study we compare the patterns of leaf development and primary vascular organization in the two types of shoots. Orthotropic shoots have an open vascular system with five sympodia. Expansion of orthotropic shoot scale leaves occurs from P1 to P10–12, and leaf tissues mature precociously. Plagiotropic shoots have a closed vascular system with six sympodia. Leaves in ventral and dorsal orthostichies do not differ significantly in size until ca. P15, but ventral leaves are distinct histologically from the second node in an orthostichy, P4–6. Ventral foliage leaves have a diffuse plate meristem, and leaf expansion continues until ca. P30. Differentiation of ventral and dorsal leaf trace procambium parallels the divergent patterns of leaf expansion. These observations demonstrate the strong correlation among shoot symmetry, leaf development, and vascular differentiation within dimorphic shoots of one species.

LEAF DEVELOPMENT AND PRIMARY VASCULAR ORGANIZATION IN SHOOTS OF ANISOPHYLLEA DISTICH A

Anisophyllea disticha is characterized by strong shoot dimorphism. Orthotropic shoots with helically arranged scale leaves produce tiers of plagiotropic shoots, while plagiotropic shoots are anisophyllous and bear dorsal scale and ventral foliage leaves arranged in a unique tetrastichous system. In this study we compare the patterns of leaf development and primary vascular organization in the two types of shoots. Orthotropic shoots have an open vascular system with five sympodia. Expansion of orthotropic shoot scale leaves occurs from P1 to P10–12, and leaf tissues mature precociously. Plagiotropic shoots have a closed vascular system with six sympodia. Leaves in ventral and dorsal orthostichies do not differ significantly in size until ca. P15, but ventral leaves are distinct histologically from the second node in an orthostichy, P4–6. Ventral foliage leaves have a diffuse plate meristem, and leaf expansion continues until ca. P30. Differentiation of ventral and dorsal leaf trace procambium parallels the divergent patterns of leaf expansion. These observations demonstrate the strong correlation among shoot symmetry, leaf development, and vascular differentiation within dimorphic shoots of one species.

Comparative study of growth and carbon uptake inFagus sylvatica L. trees growing under different light conditions

Growth, carbon uptake and carbon utilization in leaves of various growing phase shoots (GPS) on beech trees(Fagus sylvatica L.) growing under different light conditions were compared. The values of photosynthetic capacity (maximum daily net photosynthetic rate, Pn max) were used as comparable parameters. Daily time and irradiance (I, PhAR), when PN max was attained, were investigated similarly. Statistically significant differences were found in growth, Pn max and SLM (specific leaf mass) between different GPS and within the same stand, as well as within the same GPS and different stands. Pn max and SLM increased in the leaves of GPS I (spring - plagiotropic shoots) on trees from a sun stand from May till September. At the end of the growing season, the spring leaves exhibited, in comparison with the summer ones, intensive senescence, but leaves of the GPS II and III (summer -orthotropic shoots) evidently attained higher values of Px max and SLM at higher I (PhAR). The correlation of growth, PN max and SLM in relation to environmental conditions, as well as the importance of transport, distribution and utilization of assimilates for annual carbon gain and biomass production are discussed in detail.

Propagation of Abiesfraseri by cuttings: orthotropic shoot production from hedged stock plants

Fraser fir (Abiesfraseri (Pursh) Poir.) stock plants grown as transplants (4 years old) or sheared Christmas trees (14 years old) were subjected to independent combinations of hedging and chemical treatments to induce orthotropic shoot production. Decapitation treatments that removed the most top growth produced the greatest number of orthotropic shoots in each age-class after one growing season. Sprays of dikegulac at 1000 and 3000 ppm did not stimulate orthotropic shoot formation. Orthotropic shoots induced on maturing Christmas trees rooted in lower percentages than plagiotropic cuttings from similar nondecapitated trees. Since rooting and survival of the severed shoots were largely or totally unaffected by hedging treatments, decapitation treatments that produced the most shoots the 1st year continued to exhibit the most rooted cuttings at the end of the following season. At that time, superior treatments on 4- and 14-year-old plants had produced less than three and five rooted orthotropic shoots per stock plant, respectively. The stock plants received no additional hedging and were evaluated for shoot production after a second season. No treatment differences occurred within the older plants, but superior treatments from the 1st year tended to be retained within the transplants. In a separate study, orthotropic shoot production by severe decapitation was enhanced by maintaining low fertility.

Gibberellic acid and the inhibition of aerial tuberisation in Solanum tuberosum L.

The sensitivity of aerial and subterranean tuberisation to photoperiod was studied in potato (Solanum tuberosum cv. Aracy). Although photoperiodic sensitivity varied with the position along the stem, all buds could be induced to develop tubers under SD. Gibberellic acid (GA3) applied to induced (30 short days) cuttings inhibited the photoperiodic effect. No tubers were formed and orthotropic shoots developed instead. The GA3 caused a reduction in starch content in induced buds, lowering it to the same level as found in long-day treated plants. However, α-amylase activity of buds of induced plants was not affected by GA3, suggesting that GA3 does not inhibit tuberisation by promotion of starch hydrolysis.

Inducing Orthotropic Shoots in Coffee with the Morphactin Chlorflurenolmethylester

SUMMARYThe auxin-transport-inhibiting morphactin chlorflurenolmethylester (CFM; Methyl 2-chloro-9-hydroxyfluorene-9-carboxylate) breaks the dormancy of axillary buds in young coffee plants and produces orthotropic shoots. A concentration of CFM as low as 50 mg/litre induced an average of 24 orthotropic shoots per 6-month-old seedling. This approach could provide a fast and inexpensive method of vegetative propagation for raising disease-resistant cultivars if adult clones respond similarly to the seedlings used here and the treatment does not adversely affect the propagation of induced shoots.

Bijugate phyllotaxis in Rhizophoreae (Rhizophoraceae)

Phyllotaxis in the mangrove genera of Rhizophoraceae is shown to be bijugate, the angle between orthostichies always less than 90d and in some species close to one half the Fibonacci angle (68.8d). The same leaf arrangement occurs in both orthotropic shoots with extended internodes and in the crowded terminal rosettes of those branches which develop plagiotropy by apposition growth, and can be interpreted as an adaptive architectural feature in relation to mutual leaf shading.

Effects of gibberellin A-3 on the dimorphic branch system of Theobroma cacao

The influence of gibberellin A-3 (GA 3) on the orthotropic and plagiotropic shoots of T. cacao was studied in order to determined if and how the morphogenesis of this unusual branch system is affected. Elongation of both types of shoots was promoted but elongation of the plagiotropic shoots, which exhibit marked growth/dormancy cycles, was promoted only after the dormancy of the terminal bud was broken. Elongation of the orthotropic shoots was inhibited by (2-chloroethyl)trimethylammonium chloride (CCC), an inhibitor of gibberellin biosynthesis. There was no effect on phyllotaxis or no geotropic orientation of the shoots.

THE INTERACTION BETWEEN GROWTH PROMOTERS IN APICAL DOMINANCE

SummaryPreliminary experiments with one‐node cuttings of Solanum andigena in sterile culture indicated that residual root effects, possibly due to stored cytokinins, could obscure the effects of exogenous growth promoters on lateral bud growth in rootless cuttings. Therefore two‐node cuttings, obtained from apical cuttings that had been maintained without roots for a number of days, were used in all subsequent investigations. Application of cytokinin or gibberellin to the base of rootless, two‐node cuttings promoted the growth of lateral buds as leafy, orthotropic shoots, or diageotropic stolons, respectively; simultaneous application of both hormones completely inhibited lateral bud growth. The effects of roots, 6‐benzylammopurine (BAP) and zeatin on lateral shoot growth were similar in leading to the formation of vigorous, orthotropic, leafy shoots.Indole‐3‐acetic acid (IAA) completely inhibited lateral bud growth in rootless cuttings for at least 7 days, even when BAP was included in the nutrient medium. By using [α‐14C BAP it was demonstrated that cytokinin accumulates in the lateral buds of cuttings not treated with IAA, prior to their growth as leafy shoots; evidence of a causal relationship between cytokinin accumulation and lateral shoot growth was provided by a parallel experiment using [8‐14C]‐adenine. IAA did not appear to reduce BAP or BAP‐riboside accumulation in lateral buds by diverting these cytokinins to the point of IAA application, but did promote the formation of an unknown metabolite of BAP which accumulated in stem tissue.

The role of roots, cytokinins and apical dominance in the control of lateral shoot form in Solanum andigena

The lateral bud of Solanum andigena has the potentiality to develop as a stolon or as a leafy, orthotropic shoot. Natural stolons are normally only produced from underground nodes, but aerial stolons can be induced to form by the application of a combination of indole-3-acetic acid and gibberellic acid (IAA/GA3) paste to the cut surface; under some conditions both natural or induced stolons are converted to upright, leafy shoots. The presence of roots was found to be necessary for the conversion of a natural stolon to a leafy shoot, but this root effect could be replaced by the synthetic cytokinin, 6-benzylaminopurine (BAP). By using α-(14)C-BAP it was demonstrated that cytokinin accumulates in the tip of an induced stolon, prior to its conversion to a leafy shoot caused by withdrawal of the IAA/GA3 paste. The application of IAA/GA3 to decapitated plants was shown to influence both the distribution and metabolism of the cytokinin. The possibility that the role of auxin in apical dominance, at least in part, is to control the distribution and metabolism of cytokinins is discussed.

Air layering in nutmeg (Myristica fragrans Houtt.)

Nutmeg is an important perennial spice crop, which is dioecious in nature. Vegetative propagation is the norm in commercial propagation of the tree. The existing practice of propagation is grafting and budding which needs good skill and expertise for reasonable success. As an alternative to these two methods, air layering was attempted in matured trees for the first time in the country. Air layering was successful in plagiotropic and orthotropic shoots with 100 per cent survival. This method is cost effective and is easy for adoption.

STRUCTURE AND DEVELOPMENT OF THE DIMORPHIC BRANCH SYSTEM OF THEOBROMA CACAO

The vegetative morphology of Theobroma cacao, the cacao tree, was studied in order to provide a foundation for further investigations on the morphogenesis of the cacao dimorphic shoot system. The seedling of cacao has a determinate orthotropic shoot with a (2+3) phyllotaxis. Branch dimorphism is initiated after 1 to 2 years of growth at which time the apical meristem of the orthotropic shoot aborts and a pseudowhorl of plagiotropic branches is initiated from axillary positions in the shoot tip. The plagiotropic branches are characterized by a distichous phyllotaxis and indeterminate growth. Subsequently an axillary bud below the pseudowhorl develops into a new orthotropic shoot. The apical meristem of this shoot eventually aborts and another pseudowhorl is formed. The apical anatomy of the two types of shoots is similar. The developmental potentiality of the orthotropic shoot axillary buds to form one or the other type of shoot was investigated. The phyllotaxis of the axillary buds of the orthotropic shoot is spiral and that of the axillary buds of the plagiotropic branch is distichous. Pruning and apical puncture experiments showed that the axillary buds of a plagiotropic branch, and of an orthotropic seedling shoot which has not yet formed a pseudowhorl, always give rise to the parent type of shoot. However, the axillary buds of an orthotropic shoot which already bears a pseudowhorl give rise to either type of shoot for several nodes below the point of origin of the pseudowhorl. The type of shoot has no influence on the form of branch which develops from an axillary bud grafted to it. This evidence supports the hypothesis that the axillary buds are initiated as one or the other type of shoot, i.e., once initiated they are predestined.