Shoot Bending Research Articles

AN EXPERIMENTAL TEST OF THE ADAPTIVE EVOLUTION OF PHOTOTROPINS: BLUE-LIGHT PHOTORECEPTORS CONTROLLING PHOTOTROPISM IN ARABIDOPSIS THALIANA

Phototropins are blue-light photoreceptor molecules mediating the capacity for phototropism or bending toward or away from directional light. Like the red-light sensing phytochromes that control shade avoidance, phototropins modulate developmental plasticity in plant architecture. Yet, unlike phytochromes, the adaptive significance of phototropins has been largely a topic of conjecture. In Arabidopsis thaliana, phototropism of seedling and plant stems is under the control of two paralogous genes, PHOT1 and PHOT2, that encode different phototropins with partially redundant light response qualities. The PHOT1 gene product interacts with the NPH3 gene product to cause phototropic bending over a broad range of light intensity, from very weak light in the soil to stronger light in the aerial environment. The PHOT2 gene product modulates shoot bending in response to light of higher intensity only. We compared the fitness of wild-type, phot1, phot2, and nph3 genotypes over a range of light conditions in the field. Seeds were sown in the field on the soil surface and left bare or covered with either gravel or bark mulch chips. Plantings were made under full sun and dense canopy cover. Rates of seedling emergence, survival to flowering, and total seed set were measured. All mutant genotypes had significantly reduced lifetime fitness compared to wild-type. Consistent with their different fluence rate sensitivities, phot1 and phot2 signaling pathways affected fitness at discrete life-cycle stages. Fitness costs of phot1 and nph3 were expressed mainly during seedling emergence from the soil whereas that of phot2 was expressed solely after emergence. Surprisingly, the only significant genotype-by-environment interaction for fitness occurred during emergence: genotypes blind to dim blue light (phot1 and nph3) had poor emergence in the open, but not in the shade. Possibly, the loss of negative phototropism in seedling roots of mutant genotypes reduced establishment success in open (dry soil) conditions. Results show that phototropin-modulated pathways are adaptive and that their evolution has involved functional specialization. However, mechanism(s) of selection on these pathways remain a mystery.

Inhibition of the gravitropic bending response of flowering shoots by salicylic acid

The upward gravitropic bending of cut snapdragon, lupinus and anemone flowering shoots was inhibited by salicylic acid (SA) applied at 0.5 mM and above. This effect was probably not due to acidification of the cytoplasm, since other weak acids did not inhibit bending of snapdragon shoots. In order to study its mode of inhibitory action, we have examined in cut snapdragon shoots the effect of SA on three processes of the gravity-signaling pathway, including: amyloplast sedimentation, formation of ethylene gradient across the stem, and differential growth response. The results show that 1 mM SA inhibited differential ethylene production rates across the horizontal stem and the gravity-induced growth, without significantly inhibiting vertical growth or amyloplast sedimentation following horizontal placement. However, 5 mM SA inhibited all three gravity-induced processes, as well as the growth of vertical shoots, while increasing flower wilting. It may, therefore, be concluded that SA inhibits bending of various cut flowering shoots in a concentration-dependent manner. Thus, at a low concentration SA exerts its effect in snapdragon shoots by inhibiting processes operating downstream to stimulus sensing exerted by amyloplast sedimentation. At a higher concentration SA inhibits bending probably by exerting general negative effects on various cellular processes.

Characterization of the asymmetric growth of gravistimulated snapdragon spikes by stem and cell dimension analyses

Growth patterns of detached spikes of gravistimulated snapdragon (Antirrhinum majus L.) were analyzed in detail. The length increment of 5-mm marked subsections in the upper and lower flanks of the stem-bending zone was measured during gravistimulation using time-lapse photographs. At the onset of bending, a negative relative growth rate of the upper flank was detected, followed by increased relative growth rate in both lower and upper flanks. Consequently, a differential stem growth pattern was obtained during gravistimulation, which was significantly and specifically abolished by calcium antagonists reported previously to inhibit stem curvature of snapdragon. The differential growth patterns resulted from dynamic modifications of the cell dimensions in the epidermal and cortical stem layers. Bending started with both shrinking and widening of the epidermal cells and a parallel decrease in length and height of cortical cells at the upper stem flank. These changes were accompanied with a concomitant increase in length and height of the cortical cells on the lower stem flank, followed by a growth increase of epidermal cells. Our results suggest that both the epidermal and cortical cells play an important role in gravitropic shoot bending of snapdragon.

Crown development of a clone of Populus tremuloides exhibiting "crooked" architecture and a comparison with wild-type trees

Populus tremuloides Michx. (trembling aspen) is a tree species native to much of North America and is normally ascribed to the architectural model of Rauh, characterized by an excurrent crown structure with a central main stem and orthotropic branches. A mutant clone of trembling aspen is located near Hafford, Saskatchewan, exhibiting an architecture with crooked and twisted tree trunks. It was the objective of the present study to determine how the architectural development of the crooked clone differed from the wild type. In a study conducted over a 5-year period, four mutant trees were compared with four young wild-type aspen in the Winnipeg, Manitoba, area. Based on detailed quantitative data, it was determined that the architecture of the crooked clone of aspen differs greatly from the wild type. The trees are built by the continuous superposition of vigorous relay shoots with a mixed orientation, that is, shoots that take over the main growth of the tree, and have a more or less upright basal part and a horizontal to pendulous distal part. The development of the crookedness starts with the bending of the relay shoots, mostly in relation to the gravitational direction, which is followed in the subsequent years by various gravimorphic responses. In particular, the longest lateral shoots on a parent relay shoot occur in the middle regions, and the tip of the parent relay shoot generally loses vigour over time. The parent shoot may die back to the junction with a daughter relay shoot, causing a sharp bend at that point. Moreover, the divergence angles of relay shoots with the parent shoots were shown to be greater than in wild-type aspen, and this appears to exacerbate the crookedness. The new relay shoot may actually grow back towards the centre of the crown, opposite to the direction of growth of the parent. The results of this study demonstrate how a quantitative change in one architectural character can set in motion a series of developmental processes that result in a vastly different crown structure from the wild type.Key words: Populus tremuloides, trembling aspen, architecture, crooked clone.

The role of actin filaments in the gravitropic response of snapdragon flowering shoots.

The involvement of the actin and the microtubule cytoskeleton networks in the gravitropic response of snapdragon ( Antirrhinum majus L.) flowering shoots was studied using various specific cytoskeleton modulators. The microtubule-depolymerizing drugs tested had no effect on gravitropic bending. In contrast, the actin-modulating drugs, cytochalasin D (CD), cytochalasin B (CB) and latrunculin B (Lat B) significantly inhibited the gravitropic response. CB completely inhibited shoot bending via inhibiting general growth, whereas CD completely inhibited bending via specific inhibition of the differential flank growth in the shoot bending zone. Surprisingly, Lat B had only a partial inhibitory effect on shoot bending as compared to CD. This probably resulted from the different effects of these two drugs on the actin cytoskeleton, as was seen in cortical cells. CD caused fragmentation of the actin cytoskeleton and delayed amyloplast displacement following gravistimulation. In contrast, Lat B caused a complete depolymerization of the actin filaments in the shoot bending zone, but only slightly reduced the amyloplast sedimentation rate following gravistimulation. Taken together, our results suggest that the actin cytoskeleton is involved in the gravitropic response of snapdragon shoots. The actin cytoskeleton within the shoot cells is necessary for normal amyloplast displacement upon gravistimulation, which leads to the gravitropic bending.

Effets de quelques pratiques horticoles de conduite des plantes sur la production de roses coupées

Four different plant management treatments, corresponding with different existing growing practices, were compared for flower production of Rosa hybrida L. cv. Meiqualis plants grown for 1 year in a greenhouse in the south of France. Two of them used shoot bending during plant formation and subsequent production management. The harvest level practiced on the thickest stems differentiated these two treatments. Two other treatments consisted in using shoot removal and pruning during plant formation. In the first one, during production management, unmarketable shoots were removed by pinching, whereas they were bent and left on the plant in the second one. This last treatment resulted in the highest yield of marketable stems and stem quality after 1 year, although the treatment using shoot bending during plant formation and production associated with a high harvest level on the thickest stems produced the largest quantity during autumn and winter. The results are discussed with reference to different yield components determined by the different plant management treatments applied, such as inter-flush cycle time, bud sprouting, occurrence of certain types of unmarketable stems (blind shoots and bowed peduncled stems), and development of new bottom breaks.Key words: shoot bending, bottom breaks, blind shoots, bowed stems, production, Rosa hybrida L.

The effect of shoot-bending on the amount of diffusible indole-3-acetic acid and its transport in shoots of Japanese pear

The amount of diffusible indole-3-acetic acid (IAA) in shoots ofJapanese pear (Pyrus pyrifolia) decreased when vertical shootswere bent at an angle of 45°. A significant decrease of diffusibleIAA was observed one day after shoot bending (DAB), and the degree ofthis decrease was larger in the apical region of the shoot than in thebasal region. The decrease caused by the shoot bending increased withthe duration of the treatment. The IAA amounts in the bent shoot in theapical, central, and basal segments on 1 DAB were58.2±6.4%, 92.6±7.6%, and79.1±7.1% of the control, while 43.7±4.1%,30.8±2.9%, and 39.4±2.5% on 14 DAB.Radiolabelled IAA transport velocity was also examined, but it was notinfluenced by the shoot angle in the apical region of the shoot.However, the IAA transport velocity in the basal region decreased. Itdropped first on 1 DAB, but it recovered to the control level 3 DAB,then it decreased again on 14 DAB. A large increase in ethyleneproduction was observed in the bent shoot, but it seemed transient anddid not continue for 14 days. These results suggest that the decrease ofdiffusible IAA amounts may be induced not by the decrease of IAAtransport velocity but by the production/supply of IAA in the apicalregion.

Bending Shoots Stimulates Flowering and Influences Hormone Levels in Lateral Buds of Japanese Pear

Flower development of the lateral buds was accelerated in Japanese pear [Pyrus pyrifolia (Burm.) Nak.] when vertical shoots were bent at a 45° angle in late June. The indole-3-acetic acid (IAA) concentration in lateral buds on vertical (control) shoots increased in mid-July, while remaining nearly constant in bent shoots. The abscisic acid (ABA) concentration of buds in bent shoots rose between 4 July and 15 Aug., whereas control shoots exhibited an increase in concentration followed by a decline. Gibberellin4+7 (GA4+7) concentration was high on 16 June, and then declined by 4 July, with the decline being greatest in bent shoots. Gibberellin4+7 concentration was higher in the buds on vertical shoots than in those on bent shoots for much of July. The concentrations of zeatin-type cytokinins (CKs) in lateral buds were higher in bent shoots than in vertical shoots. Bending of pear shoots may weaken competition between buds and other organs through altering hormone levels in lateral buds, resulting in acceleration of flower development.

Shoot orientation affects vessel size, shoot hydraulic conductivity and shoot growth rate in Vitis vinifera L.

Vitis vinifera L. plants were grown in containers and each plant's single shoot was orientated upwards or downwards. Some plants were trained first upwards, then downwards, then again upwards (N-shaped plants). Vegetative growth was reduced in plants trained downwards compared to that in upward and N-shaped plants. Shoot growth rate slowed in downward shoot portions, but only after the apex had grown downwards for at least 10 internodes. Shoot hydraulic conductivity kh, measured after elimination of xylem embolisms, was lower in downward than in upward plants. In N-shaped plants kh was higher in the upward-growing shoot portions, and lower in the central, downward-growing portion. Shoot- and leaf-specific conductivities were also lower in downward than in upward shoot portions. Xylem cross-sectional area and xylem structure (number of wedges, number of vessels per unit xylem area) differed little in the three orientations. In contrast, vessel diameter and the sum of vessel cross-sectional areas were significantly smaller in downward than in upward shoot portions. These differences could explain the reduction in conductivity observed in the downward-orientated shoot portions. The measurements taken on N-shaped plants showed that the decreases in kh and in vessel size were a result of shoot orientation, not shoot bending.

ニホンナシの花芽形成, 栄養成分並びに内生生長調節物質に及ぼす SADH 及び新梢誘引の影響

In order to clarify the mechanism of flower bud formation in Japanese pear (Pyrus serotina Rehd.), the effects of SADH application and bending of shoots on nutrient elements and endogenous growth regulators in shoot tips and axillary buds were studied in relation to the differentiation and development of flower buds.1. SADH application or bending of each shoot in ‘Shinsui’ was carried out on June 10; after application of SADH shoot growth stopped one month earlier than in controls, and after bending, shoot growth stopped twenty days earlier than in controls.2. In both treatments there was a rapid increase in the number of nodes (scales and bracts) in axillary buds ten days after treatment. On June 30, twelve scales were formed, after which the first visible signs of flower initiation were found. Thereafter the flower buds differentiated and developed in both treatments. The final percentage of flower bud formation was about 60%.3. On the other hand in controls the number of nodes in axillary buds increased slowly, so that only a few of the first visible signs of flower initiation were found on July 30, which was one month later than in both treatments. Thereafter differentiation and development did not occur, so that the final percentage of flower bud formation was 15.2%.4. Both treatments led to a marked decrease in sorbitol and amino acid contents in the shoot tips, but to increases in axillary buds.5. Both treatments caused a decrease in IAA and cytokinin contents in shoot tips, but caused rapid increases in axillary buds.6. Both treatments markedly decreased the gibberellin content of shoot tips and axillary buds.From these results, it was suggested that flower initiation in Japanese pear is determined by the active state of buds, giving an increase in the number of nodes followed by formation of twelve scale. Endogenous growth regulators are closely involved in these processes, particularly gibberellin and cytokinin, which play a major role in flower bud formation.

Correlative Effects Modifying the Course of Bud Dormancy in Woody Plants

Summary Spring and summer treatments like pruning, defoliation, disbudding and shoot bending greatly affect the depth and the development of bud dormancy in the following winter period. Correlations between plant parts are thus among the factors that control onset and course of dormancy and through which the behaviour of the plant in given winter climates could be modified.

Influence of the seagrass, Zostera marina L., on current flow

A salt-water flume was used to describe the mechanics of current flow around an articial Zostera marina meadow. Shear velocity and roughness height were positively correlated with seagrass surface area, and were positively/negatively correlated with current velocity. Current velocity intrusion into the meadow before diminution and maximum reduction (both at the 2 cm height line) proceed by factors of 1·25 and 2·07 cm into the meadow per cm s −1 of current velocity, respectively. Froude number was correlated with mean bending angle of the canopy as a whole. Maximum bending had occurred with Froude = 1, but most bending had taken place by Froude = 0·4, a velocity of 40–50 cm s −1 in this experiment. The meadow edge is the most dynamic zone of a seagrass meadow in regard to current flow. Bending of the shoot canopy is a mechanism for re-direction of current flow and in-canopy reduction of current velocity. Meadow dimensions may be regulated by scouring processes in different hydraulic regimes. Shoot bending and subsequent in-meadow current velocity reduction are mechanisms that affect self-shading and photosynthetic capabilities as well as providing habitat stability.

Ethylene Evolution from Apple Shoots and Spur Buds1

Abstract An effective and simple system for studying ethylene evolution from apple (Malus domestica Borkh.) shoots was devised and used to follow seasonal patterns of ethylene evolution, as well as changes in ethylene evolution following ethephon and shoot bending treatments. Field studies using intact two year wood of spur and non-spur strains of ‘Delicious’ and ‘McIntosh’ showed similarly high levels of ethylene early in the season which subsequently declined. The large differences in ethylene evolution between sampling dates may have been caused by climatic differences at the time of sampling. No differences in ethylene evolution were detected among strains or cultivars although differences in flowering were observed in the following season.

Diplodia pinea . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Diplodia pinea . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Pinus species. Also on Abies excelsa, Araucaria cunninghamii, Chamaecyparis lawsoniana, Cupressus macrocarpa, Cupressus lusitanica, Cupressus sempervirens, Picea abies, Pseudotusga menziesii, P. taxifolia and Thuja orientalis [Platycladus orientalis] . DISEASES: Tip and twig blight, stag-head, red top, bud-wilt and seedling collar rot of conifers. Causes stunting of new growth, browning of needles, bending or curling of young shoots and discoloration and death of parts of the crown. Also affecting germination of Pinus seed and causing blight and dieback of coniferous seedlings in the nursery. Frequently found as a wound parasite of injured or weak trees causing bark cankers and dieback of branches and as a saprophyte causing blue-stain of sap-wood of fallen or freshly cut timbers (17: 150; 36: 436; 41: 339). GEOGRAPHICAL DISTRIBUTION: Africa (Kenya, Malawi, Mauritius, Mozambique, Rhodesia, S. Africa, Tanzania, Uganda); Asia (Japan, Malaysia, Thailand); Australasia & Oceania (Australia, New Zealand); Europe (Austria, Belgium, France, Germany, Italy, Portugal, Rumania, Spain, Sweden, U.K.); North America (Canada, U.S.A.); Central America & West Indies (Jamaica), South America (Argentina, Brazil, Chile, Paraguay). (CMI Map 459, 1969). TRANSMISSION: The pathogen is disseminated as spores by wind, rain and in fluid secreted by the pine spittle-bug, Aphrophora parallela and as mycelium on seed of Pinus (16: 219; 21: 398). Infection may take place through natural infection courts such as leaf traces or cones and cone-stalks (5: 708; 48, 3187) as well as through living tissues following wounding (31: 1; 44, 889; 48, 3187) or damage from hail (8: 535; 16: 219; 20: 150), frost (21: 398; 40: 388) or insects (pine spittle-bug, 21: 398; bark beetles, Myelophilus piniperda [Tomicus piniperda] , 14: 727) or attack by rust, Cronartiurn ribicola , causing progressive wilt in Pinus halepensis (25: 493) or by drought (14: 65) or other unfavourable growing conditions (13: 426, 553; 16: 148). Gilmour found that the amount of infection in P. radiata appeared to be correlated with trunk wounding and varied with the type of pruning tool used: secateurs, 12%; axe, 48%, slasher, 68% (44, 889). The pathogen may persist in infected tissues up to 400 days (48, 3187) and is commonly saprophytic on forest debris which provides a source of abundant spores during periods of rain (41: 339).

Effects of shoot bending of apple trees on accumulation and translocation of14C-labelled assimilates

The translocation of14C-labelled assimilates from a single leaf in bent and intact apple shoots was studied in varying stages of shoot development. In actively growing shoots14C-labelled assimilates translocated from the treated leaf and accumulated mainly in the shoot apex. In moderately growing apple shoots radioactive assimilates were translocated from the treated leaf in both directions towards and down the shoot. In apple shoots showing only slight growth activity the14C-labelled assimilates were transported from the treated leaf mainly to the base of the shoot, stem and roots. Bending shoots changed the pattern of distribution of radioactive assimilates. Bending actively and moderately growing shoots resulted in higher concentration of 14-carbon in the shoot apex than in controls. In slowly growing and non-growing apple shoots bending caused a higher accumulation of radioactive assimilates in the bent section than in an equal section of control shoots.

Synthetic strogenic Compounds

SPEAKING at a discussion on hormones at a meeting of Section B (Chemistry) of the British Association on September 8, Prof. F. Kogl foreshadowed the importance of a paper to be read by a subsequent speaker on the significance of synthetic cestrogenic compounds. Prof. Kogl was referring to the oat shoot bending test for auxin. He stated that until comparatively recently this test was regarded as specific for this compound; but he now felt less positive concerning this in view of the picking of the oestrus lock with a skeleton key.