Interaction with gravitropism,reversibility and lateral movements of phototropically stimulated potato shoots

Phototropic (PT) and gravitropic (GT) bending are the two major tropic movements that determine the spatial position of potato shoots. We studied PT bending of potato plantlets grown under long-day photoperiods in several prearranged position setups providing different interactions with the GT response. Starting with the standard PT stimulation setup composed of unilateral irradiation of vertically positioned shoots, experiments were also done in antagonistic and synergistic setups and in treatments with horizontal displacement of the light source. In the standard setup, PT bending suppressed the GT bending, which could occur only if the PT stimulation was cancelled. The antagonistic position, with phototropism and gravitropism attempting to bend shoots in opposite directions, showed phototropism and gravitropism as independent bending events with the outcome varying throughout the day reflecting diurnal changes in the competence of individual tropic components. Whilst gravitropism was constant, phototropism had a marked daily fluctuation of its magnitude with a prominent morning maximum starting an hour after the dawn in the growth room and lasting for the next 6 h. When phototropism and gravitropism were aligned in a synergistic position, stimulating shoot bending in the same direction, there was little quantitative addition of their individual effects. The long period of morning PT bending maximum enabled multiple PT bending events to be conducted in succession, each one preceded by a separate lag phase. Studies of secondary PT events showed that potato plantlets can follow and adjust their shoot position in response to both vertical and horizontal movements of a light source. PT bending was reversible, since the 180° horizontal change of a blue light (BL) source position resulted in reversal of bending direction after a 20-min-long lag phase.     

Organogenesis from shoot segments and via callus of endangered <Emphasis Type="Italic">Kosteletzkya pentacarpos</Emphasis> (L.) Ledeb.

Efficient plant regeneration systems both from shoot segments and via callus organogenesis were developed for Kosteletzkya pentacarpos (L.) Ledeb., a rare and endangered Eurasian species. In the experiments with existing meristems, factors affecting shoot proliferation, including explant type, i.e. decapitated and intact shoots, and plant growth regulators, indole-3-acetic acid or kinetin, were investigated. Shoot proliferation was significantly affected by the type of explant, the hormones and their interaction. The highest shoot multiplication rate was obtained from decapitated shoots. Increasing kinetin concentration promoted shoot elongation regardless of explant type. In intact shoots, shoot length was also affected by increasing auxin concentration, although this effect tends to decrease with higher concentration. Decapitated shoots were not responsive to the addition of auxin. Micropropagation through organogenesis from callus was also investigated. Calli were obtained from leaf, stem internode and root explants. Only the leaf-derived calli produced shoots and indole-3-acetic acid favoured increased numbers of shoots. A number of experiments were conducted for rooting of in vitro produced shoots. All of them induced high rooting frequency, the number and the length of roots being dependent on the strength of the basal medium. The use of 1–2 mg l⁻¹ indole-3-butyric acid resulted in refining the optimal concentration for root elongation. The regenerated plants (70%) survived and flowered in their first vegetative period.     

Micropropagation of juvenile and adult Sorbus domestica L.

Successful propagation of seedlings and mature trees of Sorbus domestica L. has been achieved by in vitro methods. Multiple shoot formation was obtained by placing shoot apices or nodal segments on a modified Schenck and Hildebrandt medium containing benzyladenine. Regenerated shoots were excised and induced to root on media with auxin. In the best treatments 75–85% of shoots from juvenile material rooted. Rooting capacity of shoots from mature explants was lower (30%) and was not improved by dipping the base of shoots in concentration solutions of indolebutyric or naphthaleneacetic acids. Plantlets were ultimately established in soil.Abbreviations BA benzyladenine - IAA indoleacetic acid - IBA indolebutyric acid - NAA naphthaleneacetic acid     

Species differences in ligand specificity of auxin-controlled elongation and auxin transport: comparing Zea and Vigna

The plant hormone auxin affects cell elongation in both roots and shoots. In roots, the predominant action of auxin is to inhibit cell elongation while in shoots auxin, at normal physiological levels, stimulates elongation. The question of whether the primary receptor for auxin is the same in roots and shoots has not been resolved. In addition to its action on cell elongation in roots and shoots, auxin is transported in a polar fashion in both organs. Although auxin transport is well characterized in both roots and shoots, there is relatively little information on the connection, if any, between auxin transport and its action on elongation. In particular, it is not clear whether the protein mediating polar auxin movement is separate from the protein mediating auxin action on cell elongation or whether these two processes might be mediated by one and the same receptor. We examined the identity of the auxin growth receptor in roots and shoots by comparing the response of roots and shoots of the grass Zea mays L. and the legume Vigna mungo L. to indole-3-acetic acid, 2-naphthoxyacetic acid, 4,6-dichloroindoleacetic acid, and 4,7-dichloroindoleacetic acid. We also studied whether or not a single protein might mediate both auxin transport and auxin action by comparing the polar transport of indole-3-acetic acid and 2-naphthoxyacetic acid through segments from Vigna hypocotyls and maize coleoptiles. For all of the assays performed (root elongation, shoot elongation, and polar transport) the action and transport of the auxin derivatives was much greater in the dicots than in the grass species. The preservation of ligand specificity between roots and shoots and the parallels in ligand specificity between auxin transport and auxin action on growth are consistent with the hypothesis that the auxin receptor is the same in roots and shoots and that this protein may mediate auxin efflux as well as auxin action in both organ types.     

Triiodobenzoic acid, an auxin polar transport inhibitor, suppresses somatic embryo formation and postembryonic shoot/root development in Eleutherococcus senticosus

The effect of auxin polar transport inhibitor on somatic embryo development and postembryonic growth in Siberian ginseng (Eleutherococcus senticosus) was examined. In the presence of 2,3,5-triiodobenzoic acid (TIBA), an auxin polar transport inhibitor, embryo formation from embryogenic cells was suppressed, while cell division was not affected. When globular embryos at different stages were transferred onto medium containing TIBA, development of axial and bilateral polarity was suppressed in a stagespecific manner. In abnormal embryos induced by TIBA, further development of shoot and root apical meristems and vascular differentiation was also suppressed. Thus, abnormal development of embryos induced by inhibition of auxin polar transport resulted in plantlets without shoots and roots.     

The Effect of Coumarin on Young's Modulus in Sunflower Stems and Maize Roots and on Water Permeability in Potato Parenchyma

By means of the resonance frequency method Young's, modulus has been determined after coumarin treatment of growing segments of etiolated sunflower hypocotyl segments and in maize roots. Coumarin caused a decrease in Young's modulus in both shoot and root tissue. The response was very rapid; in sunflower hypocotyls the decrease in elastic modulus appeared 3 min after application of coumarin. The effects produced by coumarin were similar to those found by auxin. Coumarin increased the rate of water efflux out of potato parenchyma by about 20%. The increase in water permeability was evident within 3 min.     

AXR1 acts after lateral bud formation to inhibit lateral bud growth in Arabidopsis

The AXR1 gene of Arabidopsis is required for many auxin responses. The highly branched shoot phenotype of mature axr1 mutant plants has been taken as genetic evidence for a role of auxin in the control of shoot branching. We compared the development of lateral shoots in wild-type Columbia and axr1-12 plants. In the wild type, the pattern of lateral shoot development depends on the developmental stage of the plant. During prolonged vegetative growth, axillary shoots arise and develop in a basal-apical sequence. After floral transition, axillary shoots arise rapidly along the primary shoot axis and grow out to form lateral inflorescences in an apical-basal sequence. For both patterns, the axr1 mutation does not affect the timing of axillary meristem formation; however, subsequent lateral shoot development proceeds more rapidly in axr1 plants. The outgrowth of lateral inflorescences from excised cauline nodes of wild-type plants is inhibited by apical auxin. axr1-12 nodes are resistant to this inhibition. These results provide evidence for common control of axillary growth in both patterns, and suggest a role for auxin during the late stages of axillary shoot development following the formation of the axillary bud and several axillary leaf primordia.     

Photo- and Gravitropic Bending of Potato Plantlets Obtained In Vitro from Single-Node Explants

Etiolated and light-grown plantlets obtained from potato shoot cultures were shown to perform vigorous tropic movements. Unilateral blue irradiation actively induced phototropic curvature of the shoots toward the light source, although etiolated plantlets required ten times longer stimulation than the light-grown plantlets to achieve a 90° angle. The fluence requirements for induction of second positive phototropism (PT) of light-grown plantlets spanned almost five orders of magnitude (~30–1.7?×?10⁵ μmol/m²). Upon responding to unilateral blue light by curving, plantlets entered the process of straightening after irradiation ended. Straightening also occurred in plantlets placed on a clinostat but it was of lower magnitude. Compared to early-morning and day-time hours, plantlets exhibited a significantly lower PT response in the late afternoon (5 p.m.) and gravitropic (GT) response at the end of the day (11 p.m.), suggesting that these responses may be under the control of circadian rhythms. GT was also recorded for both light-grown and etiolated plantlets. Ninety-degree stimulation, used to induce GT in etiolated plantlets, needed to be 50?% longer than stimulation used for light-grown plantlets to induce a similar response. Straightening was also recorded for the shoots that exhibited GT but was smaller when plantlets were placed on a clinostat compared to straightening exhibited by those plantlets left standing in an upright position for 2?h.     

Micropropagation of Plumbago rosea Linn.

Multiple shoot formation from the medicinal plant Plumbago rosea Linn. was induced on callus from stem segments on Murashige & Skoog media containing auxin and cytokinin. 2,4-D (2.5 mg l^-1) and kinetin (1.5 mg l^-1) added to the media gave best callus production, while BAP (2 mg l^-1) plus NAA (1.0 mg l^-1) induced shoot formation from that callus. Numerous shoots with roots could be produced by transferring shoots to media containing IBA (1.5 mg l^-1). Regenerated plantlets were transferred to pots and 60% survived.     

生长素介导OsRGP1和0sSuS参与水稻地上部基部向重性弯曲生长

在水稻幼苗被放平后,地上部重力响应部位（地上部基部）的上半部生长比下半部生长慢,从而导致地上部基部发生向上弯曲．发生不对称生长的向重性反应。通过抑制差减杂交（SSH）实验发现．水稻地上部基部向重性弯曲生长过程中,反复糖基化多肽OsRGP1和蔗糖合成酶OsSuS在基部上下部有不对称表达。我们还采用Realtime PCR开展进一步研究。实验结果显示OsRGP1和0sSMS的表达受到IAA的调控。通过生物信息学分析也发现OsRGPl和OsSuS的启动子上存在着生长素的调控元件．生长素极性运输抑制剂TIBA处理能够消除OsRGP1和OsSuS在向重性过程中的不对称表达．这进一步说明向重性过程中不对称分布的生长素介导了OsRGP1和OsSuS基因的不对称表达。另外．向重性反应过程中,检测到基部下半部的己糖浓度增加。因此,OsRGP1的不对称表达可能有助于下半部细胞壁多糖的积累,进而促进了下半部细胞壁的扩张。OsSuS不对称表达也有可能会引起己糖在上下半部的不对称分布。己糖和细胞壁多糖在下半部的积累可能在下部细胞扩张从而导致向重性弯曲生长中起一定的作用。     

The Influence of Shoots, Roots, and Hormones on Sucrose Distribution

The effects of hormones on sucrose distribution were studiedin relation to the control of the relative growth of the shootand the root. The roots and the shoots above the cotyledonsof bean seedlings were removed and the remaining explants allowedto regenerate so that they consisted of growing buds, a segmentof the hypocotyl, and short growing roots. [¹⁴C]Sucrose wasapplied to the middle of the hypocotyl and its distributionwas measured in relation to the presence of the shoots and rootsand to their replacement by auxin and a cytokinin. It was foundthat radioactivity moved towards both the shoot and the root,and that removing one growing region greatly reduced the transportin its direction and increased the relative transport in theopposite direction. Both hormones restored a large part of themovement of radioactive sucrose when they replaced any one ofthe growing regions. However, there was some preferential actionof benzyladenine when it replaced the buds and of auxin whenit replaced the roots. The results indicate that in the intactplant the development of the shoot and the root is correlatedby a positive feedback involving auxin and cytokinins, and themovement of sucrose is controlled indirectly by the sink activityof these growing regions. This control of the movement of sucrose,and presumably other metabolites, accounts for the short-termcompetitive relations between the shoot and the root.     

Induction of adventitious shoots in vitro in Campanula carpatica

Efficient protocols have been developed to induce adventitious shoots in different types of explants of Campanula carpatica Jacq. More than five shoots per explant developed on hypocotyls of 5-week-old seedlings after 2 weeks of culture. Hypocotyls produced twice as many shoots as the cotyledons. TDZ proved to be about 6 times more efficient than BA. NAA had to be added to the regeneration medium to obtain the optimal balance of auxin and cytokinin to induce shoot regeneration. Significant differences were noted between different growth regulator concentrations in their effects on shoot organogenesis. BA induced double the number of callus clumps as TDZ. Incubation of explants in the dark produced about 6 shoots per explant while those in the light produced about 2 shoots per explant. Explants derived from 5-week-old seedlings were five times more regenerative compared to those derived from 15-week-old seedlings. Explants from cv. White Uniform were more organogenic than those from cv. Blue Clip. Root segments were also found to form shoots when treated with CPPU.     

The gravity-regulated growth of axillary buds is mediated by a mechanism different from decapitation-induced release

When the upper part of the main shoot of the Japanese morning glory (Pharbitis nil or Ipomoea nil) is bent down, the axillary bud situated on the uppermost node of the bending region is released from apical dominance and elongates. Here, we demonstrate that this release of axillary buds from apical dominance is gravity regulated. We utilized two agravitropic mutants of morning glory defective in gravisensing cell differentiation, weeping (we) and weeping2 (we2). Bending the main shoots of either we or we2 plants resulted in minimal elongation of their axillary buds. This aberration was genetically linked to the agravitropism phenotype of the mutants, which implied that shoot bending-induced release from apical dominance required gravisensing cells. Previous studies have shown that basipetal translocation of auxin from the apical bud inhibits axillary bud growth, whereas cytokinin promotes axillary bud outgrowth. We therefore compared the roles of auxin and cytokinin in bending- or decapitation-induced axillary bud growth. In the wild-type and we plants, decapitation increased cytokinin levels and reduced auxin response. In contrast, shoot bending did not cause significant changes in either cytokinin level or auxin response, suggesting that the mechanisms underlying gravity- and decapitation-regulated release from apical dominance are distinct and unique.     

Thidiazuron-induced Shoot Multiplication and Plant Regeneration in Bamboo (Dendrocalamus strictus Nees)

Thidiazuron (TDZ) stimulated shoot proliferation from different seedling explants (i.e., shoot, basal node, node and apical segment) of bamboo (Dendrocalamus strictus) when incorporated in half-strength Murashige and Skoog (MS) medium having 2% (w/v) sucrose. All the concentrations of TDZ (0.01 to 1.0 mg l^?1) tried were effective in shoot proliferation. Maximum shoots (14.8 ± 1.0) were obtained from the shoot explants cultured in 0.5 mg l^?1 TDZ supplemented halfstrength MS liquid medium for 21 days and subsequently transferred to the same medium devoid of TDZ. The longer culture period (i.e. 28 and 35 days) in TDZ medium caused reduction in shoot proliferation. The shoots regenerated with lower concentrations of TDZ treatment (i.e. 0.01 to 0.1 mg l^?1) rooted in half-strength MS liquid medium. The shoots formed with 0.5 mg l^?1 TDZ treatment did not root in basal medium and required auxin supplementation in the medium for rooting and about 55% shoots produced roots in 1.0 mg l^?1 IBA supplemented medium. The shoots formed with 1.0 mg l^?1 TDZ did not root even after auxin treatment. The well rooted shoots transplanted to plastic pots filled with sand and garden soil (1:1) mixture showed 98% establishment.     

Micropropagation ofPenstemon serrulatus and iridoid formation in regenerated plants

A method for the micropropagation ofPenstemon serrulatus Menz. from shoot tips or nodal segments was developed. Multiple microshoot cultures (up to 20 shoots from a single explant) were obtained by maintenance of shoot tip explants on Schenk & Hildebrandt medium (SH) supplemented with 4.4 µM benzyladenine (BA) or 8.9 µM BA and 0.57 µM indole-3-acetic acid (IAA). Microshoots developed into numerous, normal shoots when explants were transferred to SH medium containing 2.9 µM IAA or 2.5 µM indole-3-butyric acid (IBA). Shoot cultures were also established from nodal segments (max. 6.8 shoots per segment) when they were placed on SH medium with 0.49 µM IBA and 2.2 µM BA. Rooting of shoots was better on SH medium containing auxin (IBA, NAA or IAA) than on SH medium without growth regulators. The plantlets were then transferred to pots and grown in the greenhouse. Four-month-old regenerated plants demonstrated similar iridoid content (leaves contained 3.83% dry wt. penstemide and 1.8% dry wt. serrulatoloside) as the original plants.     

Plants as competing populations of redundant organs

At any given time, a vascular or land plant may be a colony of functional sectors, each consisting of a shoot and its associated roots. In most plants, however, the activity of the cambium can change the relative vascular contacts of neighbouring shoots. Vascular tissues can even differentiate along new orientations, forming contacts that change the sectorial structure of the plant. Such reoriented differentiation is induced by the same auxin from developing leaves as are other types of vascular differentiation. The occurrence of vascular reorientation is determined by two criteria: the presence of an auxin flow that exceeds the transport capacity of the tissues that follow the previous, established orientation and the availability of nearby channels that are not fully occupied, not‘protected’ by their own flow of auxin. These controls of vascular orientation suggest that neighbouring shoots (and neighbouring roots) compete with one another, by means of signals indicating their state and their environment, for vascular contacts with the rest of the plant. Such internal competition between genetically equivalent shoots is an adaptation to heterogeneous environments: it is the shoots in the best conditions available to the plant that receive the support of a greater part of the root system. The potential for changes of vascular contacts points to open problems and to neglected aspects of the role of the cambium in plant organization.     

Are xylem radial development and hydraulic conductivity in downwardly-growing grapevine shoots influenced by perturbed auxin metabolism?

Downwardly-growing grapevine shoots have smaller and more frequent vessels than upwardly-growing ones and, as a consequence, a lower hydraulic conductivity. Here, grapevine (Vitis vinifera L.) shoot growth orientation was manipulated to test whether downward shoot orientation negatively affects vessel growth in the apex via a shortage of water and nutrients. The orientation of the central vine shoot portion was inverted by two consecutive 135 degrees bends, resulting in double-bent N-shaped vines; the central downward shoot portion was of different lengths in the experimental treatments to induce increasing reductions of shoot conductivity. These treatments reduced shoot conductivity and water flow, but had no effects on vessel development and frequency in the apex. In a second experiment, auxin concentration was assessed in shoots of upwardly- and downwardly-growing plants. IAA concentration at the apical internodes was higher in downwardly-oriented shoots than in shoots growing upwards. In addition, a higher density and a lower vessel diameter were observed in the lower, than the upper side, of the downwardly-oriented shoot, suggesting increased accumulation of auxin in the lower side. These results suggest that the downward orientation induces accumulation of auxin in the apex, which in turn affects the density and the size of the xylem vessels, causing reduction of hydraulic conductivity.     

Enhanced bud regeneration in aspen (Populus tremula L.) roots cultured in liquid media

 The regeneration potential of excised aspen (Populus tremula L.) roots cultivated in liquid medium, as affected by plant growth regulators and by the position of the isolated root explant on the main root, was investigated. The effect of various levels of benzyladenine (BA) and thidiazuron (TDZ) on bud regeneration in root explants was studied. TDZ in the medium had a marked effect on bud development as compared with BA, inducing a tenfold increase in the number of buds regenerated from various root explants. TDZ enhanced both root and root-borne shoot biomass production but reduced further shoot development and elongation. The position of the isolated root sections on the main root affected regeneration, the proximal sections further away from the root tip producing the highest number of buds per explant in both BA and TDZ treatments. Buds regenerated in close proximity to the site of lateral roots in BA-treated roots, while in TDZ-treated root sections, the buds formed all over the root regardless of the presence of lateral roots. The buds developed from inner cortical and sub-epidermal cell layers, disrupting the epidermis and the inner layers. Root biomass production and growth was greatly enhanced in well-aerated bioreactor culture in the presence of 4.5×10^–2 μM TDZ. A high number of the root-borne shoots could be rooted and converted to plantlets. However, while shoots regenerated in a medium with BA rooted well in a growth regulator-free medium, shoots formed in a medium with TDZ required auxin for rooting. Roots cultured in the presence of ancymidol, a gibberellin biosynthesis inhibitor, regenerated non-hyperhydric bud clusters and hyperhydric shoots. These were separated mechanically, subcultured to growth and rooting medium and transplanted ex vitro resulting in phenotypically true-to-type plantlets. The potential of liquid cultures for aspen shoot biomass production from roots is discussed. Received: 24 January 2000 / Revision received: 6 March 2000 / Accepted: 7 March 2000