In vitro shoot growth of Brugmansia × candida Pers

The objective of this study was to improve the growth of in vitro shoot cultures of Brugmansia × candida ‘Creamsickle’. Several mineral nutrient experiments were conducted to determine the effect of NH₄⁺, NO₃⁻, K⁺, FeSO₄/EDTA, ZnSO₄, MnSO₄, and CuSO₄ on quality, leaf width and length, size and weight of shoot mass, and shoot number. The experiment to determine the levels of NH₄⁺, NO₃⁻, and K⁺, was conducted as a 2-component NH₄⁺: K⁺ mixture crossed by [NO₃⁻] and resulted in an experimental design free of ion confounding and capable of separating the effects of proportion and concentration. The results of the NH₄⁺-K⁺-NO₃⁻ experiment revealed a region in the design space where growth was significantly improved; the region generally had lower total nitrogen and lower NH₄⁺:K⁺ ratios than MS medium. The experiments to determine the appropriate levels of Fe, Zn, Mn, and Cu were conducted at six log levels ranging from 0 to 1 mM. Of the four metal salts tested, MnSO₄ had the least effect on in vitro shoot growth and its concentration was reduced from 0.1 mM (MS level) to 0.001 mM. CuSO₄ had large effects on in vitro shoot growth and was increased from 0.0001 mM to 0.001 mM. A 2-level factorial of NH₄⁺-K⁺-NO₃⁻, FeSO₄/EDTA, and ZnSO₄ was conducted and several formulations identified for their improvements of quality and growth. In addition to the changes to MnSO₄ and CuSO₄, these formulations were characterized by lower levels of NH₄⁺, K⁺, NO₃⁻ and Zn, and higher levels of FeSO₄/EDTA. Overall, several nutrient formulations were identified as superior to MS medium for growth of in vitro shoot cultures of B. ‘Creamsickle’.     

Root–shoot growth responses during interspecific competition quantified using allometric modelling

Background and Aims

Plant competition studies are restricted by the difficulty of quantifying root systems of competitors. Analyses are usually limited to above-ground traits. Here, a new approach to address this issue is reported.

Methods

Root system weights of competing plants can be estimated from: shoot weights of competitors; combined root weights of competitors; and slopes (scaling exponents, α) and intercepts (allometric coefficients, β) of ln-regressions of root weight on shoot weight of isolated plants. If competition induces no change in root : shoot growth, α and β values of competing and isolated plants will be equal. Measured combined root weight of competitors will equal that estimated allometrically from measured shoot weights of each competing plant. Combined root weights can be partitioned directly among competitors. If, as will be more usual, competition changes relative root and shoot growth, the competitors'' combined root weight will not equal that estimated allometrically and cannot be partitioned directly. However, if the isolated-plant α and β values are adjusted until the estimated combined root weight of competitors matches the measured combined root weight, the latter can be partitioned among competitors using their new α and β values. The approach is illustrated using two herbaceous species, Dactylis glomerata and Plantago lanceolata.

Key Results

Allometric modelling revealed a large and continuous increase in the root : shoot ratio by Dactylis, but not Plantago, during competition. This was associated with a superior whole-plant dry weight increase in Dactylis, which was ultimately 2·5-fold greater than that of Plantago. Whole-plant growth dominance of Dactylis over Plantago, as deduced from allometric modelling, occurred 14–24 d earlier than suggested by shoot data alone.

Conclusion

Given reasonable assumptions, allometric modelling can analyse competitive interactions in any species mixture, and overcomes a long-standing problem in studies of competition.     

How does spittlebug oviposition affect shoot growth and bud production in two willow species?

We measured the effects of oviposition by the spittlebug Aphrophora pectoralis on shoot growth and bud production in two willow species, Salix miyabeana and Salix sachalinensis. In autumn, adult females of A.pectoralis insert their ovipositor into the apical region of 1-year-old shoots, resulting in the death of most shoot tips within 1week. Consequently, an increase in the number of dead buds and a decrease in the number of vegetative buds on 1-year-old shoots was recorded. In the following spring, the growth of current-year shoots was greatly increased on 1-year-old shoots damaged by spittlebug oviposition. Furthermore, spittlebug oviposition increased the production rate of vegetative buds in both S.miyabeana and S.sachalinensis. However, no impact on the production rate of reproductive buds was detected in either willow. We conclude that the compensatory growth of current-year shoots and an increase in vegetative buds in the two willow species was caused by oviposition of A.pectoralis.     

Soil compaction. A role for ethylene in regulating leaf expansion and shoot growth in tomato?

The role of ethylene in regulating growth in tomato (Lycopersicon esculentum Mill.) during compaction stress was examined using wild-type (cv Ailsa Craig) and transgenic (ACO1_AS) genotypes; the latter has a reduced capacity to produce ethylene. Ethephon or silver ions were applied to increase ethylene production or block its action. Shoot growth in both genotypes was comparable in uncompacted (1.1 g cm⁻³) and uniformly compacted soil (1.5 g cm⁻³). However, a 1.1/1.5-g cm⁻³ split-pot treatment invoked marked genotypic differences: growth was reduced in cv Ailsa Craig but was comparable to uncompacted control plants in ACO1_AS. As xylem sap abscisic acid levels were similar, abscisic acid was not responsible for inhibiting growth in cv Ailsa Craig. These genotypic differences in growth were accompanied by increased ethylene evolution in cv Ailsa Craig, suggesting that the ability of ACO1_AS to maintain growth in the split-pot treatment reflected its lower ethylene levels, a view supported by the observation that excising the roots in the compacted compartment reduced ethylene evolution and restored shoot growth in cv Ailsa Craig. Treatment with silver restored shoot growth in cv Ailsa Craig, whereas treatment with ethephon reduced growth in ACO1_AS. Thus, ethylene apparently has a key role in determining growth when tomato plants encounter differential soil compaction.     

A filter paper-based liquid culture system for citrus shoot organogenesis—a mixture-amount plant growth regulator experiment

This study determined the effects of a static liquid culture system on shoot regeneration from citrus epicotyl explants. A mixture-amount experiment was used to determine the effects of zeatin riboside (ZR), 6-benzylaminopurine (BA), and indole-3-acetic acid (IAA) on two citrus types—citrange (Citrus sinensis ‘Washington’ L. Osbeck. × Poncirus trifoliata L. Raf var. Carrizo) and sweet orange (Citrus sinensis L. Osbeck var. ‘Ridge Pineapple’). A liquid culture system comprising a Petri dish, cellulose filter paper, and liquid culture medium was used. Shoot regeneration experiments were conducted over 6 wk that included 2 wk in the dark followed by 4 wk in the light. Three responses were measured: (1) number of explants forming buds and/or shoots, (2) number of explants with shoots >?2 mm, and (3) overall explant and shoot quality. The effects of paper disc number, liquid medium volume, and explant size on shoot regeneration were determined. High-quality shoots were produced from explants cultured in 5.25 to 12 mL medium volume and explant sizes ranging from 2 to 15 mm. The effects of the plant growth regulators were similar for the two citrus types and were as follows: (1) use of ZR or BA resulted in high-quality shoot production; (2) ZR and BA were not synergistic; (3) culture in 20 μM ZR resulted in the highest shoot production; (4) BA and IAA were strongly synergistic, with the greatest production with BA when IAA was included in the mixture; and (5) ZR and IAA were antagonistic, particularly with Ridge Pineapple.     

Do compensatory shoot growth and mycorrhizal symbionts act as competing above- and below-ground sinks after simulated grazing?

Since mycorrhizal symbionts are dependent on host carbon availability, shading and grazing of the host plant often decrease mycorrhizal colonization in host roots. We conducted field experiments on an intensively mycorrhizal host, Autumn gentian, Gentianella amarella to investigate the effects of neighbor removal and simulated grazing on host growth and reproduction as well as mycorrhizal colonization. In the neighbor removal experiment, we manually removed the above-ground parts of companion plants of gentians. Reduced competition tended to improve the performance of both the host and the symbionts. Total fungal as well as arbuscular, hyphal, and coiled hyphal colonizations were higher in gentians with neighbors removed. Simulated grazing (clipping off 50% of shoot height) reduced host shoot and seed biomass, whereas the responses of the root symbionts were most often positive or neutral. In the first experiment (with late-flowering plants), clipping increased arbuscular, hyphal, and total colonizations but decreased dark septate endophyte colonization. In the second experiment (with both early- and late-flowering plants), clipping did not affect total mycorrhizal colonization. Higher arbuscular, hyphal, and total colonizations were found in late-flowering gentians compared to early-flowering ones. Early-flowering plants, on the other hand, tolerated simulated grazing better compared to late-flowering plants, which may indicate a higher cost of the symbionts for the late-flowering plants. Above-ground herbivory tends to increase carbon limitation, and under these conditions, regrowing shoots and the fungal symbionts may appear as alternative, competing sinks for the host’s limited carbon reserves.     

Do rhizome severing and shoot defoliation affect clonal growth of Leymus chinensis at ramet population level?

Leymus chinensis (Trin.) Tzvel. is a perennial species of Gramineae, usually subject to defoliation from grazing and mowing. We examined whether shoot defoliation and rhizome severing affected rhizome and ramet growth, and vegetative bud outgrowth of L. chinensis ramet populations. We also tested the hypothesis that clonal growth of the ramets subject to defoliation would benefit from clonal integration between interconnected ramets besides from possible compensatory growth. To 48 experimental plots, we applied six treatments resulting from interactions between two rhizome connection states (unsevered/severed) and three defoliation regimes (non-defoliated, mildly-defoliated and heavily-defoliated). Defoliation affected rhizome growth and bud outgrowth, but had little effect on shoot growth. Mild and heavy defoliation exerted similar effects on rhizome growth. Only heavy defoliation significantly reduced bud outgrowth while mild defoliation did not. The fact that shoot growth did not change after defoliation and that the bud numbers remained unchanged after mild defoliation suggest that the compensatory response enable the species to tolerate grazing to some extent. Neither rhizome severing nor the interaction of rhizome severing and defoliation had effect on any tested variables. Lack of the effect of rhizome severing falsified the first half of our hypothesis, that is, clonal integration was unimportant in our experiment. The probable reasons were suspected to be the short duration of the experiment and/or the buffer effect of carbohydrate reserves in rhizomes for shoot growth and bud production in time of defoliation.     

In vitro morphogenesis patterns from shoot apices of sugar cane are determined by light and type of growth regulator

The regeneration patterns of shoot apices derived from in vitro plants of four varieties of sugar cane in response to different growth regulators and light were evaluated. The cellular origin of the regeneration processes was also investigated. Explants cultivated on medium supplemented with NAA and incubated under light showed direct bud regeneration from cells of external layers of the ground parenchyma of the stem. Explants cultivated in the dark on medium supplemented with low concentrations of picloram (PIC) or 2,4D (4.0 and 4.5 μM, respectively) showed callus formation derived from the ground parenchyma of stem and development of preembryogenic masses derived from bundle sheath cells facing the phloem tissue of immature leaves. Somatic embryos at further developmental stages were visible following transfer to medium devoid of growth regulators and incubation under light. When incubated under light since the begining of the experiment, explants cultivated in the presence of higher PIC or 2,4D concentrations (40 and 22.6 μM, respectively) first displayed direct organogenesis from external layers of the ground parenchyma of the stem, followed by the development of organogenic calluses. Preembryogenic masses were also observed from bundle sheath cells of immature leaves. However, in contrast to the cultures pre-incubated in darkness for 30 days, the subsequent stages of embryo development were not detected. The regeneration efficiency of calluses induced by 2,4D and PIC was generally increased following desiccation in laminar flow or incubation on medium solidified with phytagel.     

Growth-active gibberellins overcome the very slow shoot growth of Hancornia speciosa, an important fruit tree from the Brazilian “Cerrado”

Shoot elongation of Hancornia speciosa, an endangered tree from the Brazilian savannah “Cerrado”, is very slow, thus limiting nursery production of plants. Gibberellins (GAs) A₁, A₃, and A₅, and two inhibitors of GA biosynthesis, trinexapac-ethyl and ancymidol were applied to shoots of Hancornia seedlings. GA₁ and GA₃ significantly stimulated shoot elongation, while GA₅ had no significant effect. Trinexapac-ethyl and ancymidol, both at 100 μg per seedling, inhibited shoot elongation up to 45 days after treatment, though the effect was statistically significant only for ancymidol. Somewhat surprisingly, exogenous GA₃ more effectively stimulated shoot elongation in SD-grown plants, than in LD-grown plants. The results from exogenous application of GAs and inhibitors of GA biosynthesis imply that Hancornia shoot growth is controlled by GAs, and that level of endogenous growth-active GAs is likely to be the limiting factor for shoot elongation in Hancornia. Application of GAs thus offer a practical method for nursery production of Hancornia seedlings for outplanting into the field.     

Influences of medium consistency and shoot density on in vitro shoot proliferation of Populus alba × P. grandidentata

The in vitro shoot proliferation of Populus alba × P. grandidentata was affected by the medium consistency and shoot density, but not by three sizes of vessels. After 4 weeks of culture, the fresh weight and number of shoots per explant on liquid medium were significantly greater than those on agar-solidified medium. In particular, 3.2 shoots, 7 mm or longer per explant, were produced on liquid medium compared with 1.6 shoots per explant or agar-solidified medium. The fresh weight per explant after 4 weeks of culture on liquid medium and agar-solidified medium were 0.68 and 0.25 g, respectively. Increasing the number of shoots per vessel slowed the growth of the explants as measured by fresh weight and the number of shoots produced. There was little difference in the number of shoots produced between vessels with 1 or 2 shoots per vessel, but there were many fewer shoots produced when 3 shoots were placed in each vessel.Journal Paper No. J-11977 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project 2210.     

High-frequency adventitious shoot bud induction and shoot elongation of Chile pepper (Capsicúm annuum L.)

Summary In vitro plantlet regeneration was obtained from cultured cotyledon and young leaf explants of five Indian chile pepper cultivars (Capsicum annuum L. evs. Gujarat-1, Gujarat-2, Guntur-4, Selection-49, and Jwala). Adventitious shoot buds (ASB) were regenerated directly from cotyledon and young leaf explants in all the five cultivars on media containing benzyladenine (BA) alone or in combination with 1-naphthaleneacetic acid (NAA). Regeneration frequency was highly influenced by cultivar explant type, media combination and their interactions, except the interaction between cultivar and explant, for number of ASB per explant. Percent contribution of individual source suggested that selection of explant type followed by medium combination and cultivars was essential for obtaining high-frequency ASB induction. Across different cultivars the young leaf explant was found to be the most responsive explant, while Murashige and Skoog (MS) medium containing BA alone (17.8, 26.6, and 35.5 μM) was found to be the best medium for the production of maximum number of ASB. Between the two explants, shoot elongation was observed with ASB obtained from young leaf explants on MS medium containing BA (2.2 and 4.4 μM) and gibberellie acid (GA₃) (1.4, 2.9, 4.3 and 5.8 μM). The MS medium fortified with 4.4 μM BA+2.9μM GA₃ was optimum for shoot elongation. Elongated shoots were rooted on liquid MS medium supplemented with 2.9 μM indole-3-acetic acid (IAA) and successfully established ex vitro.     

Is the shoot a root with a view?

Recently, it has been shown that the same sets of genes act in both root and shoot to regulate cell fate and patterning. One gene cassette regulates epidermal cell fate, another cassette regulates ground tissue derived cell fate and organization. Ectopic expression and laser ablation have been used to probe the mechanisms by which these genes perform their tissue and organ-specific functions.     

Does water availability regulate biomass partitioning between trunk and branches?

• The extent to which a vertical trunk is differentiated from its branches is a key trait for the architecture of trees and may affect interspecific relationships.
• In this study, we analysed the effect of soil water availability on biomass partitioning for Nothofagus pumilio by means of a nursery experiment. Juvenile trees were subject to three irrigation conditions: no irrigation, intermediate irrigation and high irrigation. Irrigation conditions emulated the mean precipitation of the most representative environments inhabited by N. pumilio.
• Changes in soil water availability modified the biomass partitioning patterns of trees. In comparison to the other two conditions, high irrigation caused: (i) a higher ratio of biomass partitioning to stems than roots; (ii) more trunk growth in relation to its branches; and (iii) more photosynthetic organs relative to the aboveground biomass. Trunk size relative to that of its most recent branches was not increased by water availability.
• Water availability may play a significant role in the capacity of N. pumilio for space occupation due to the effects on axis differentiation.

     

Is optimal gene order impossible?

Recent evidence suggests that yeast genes encoding proteins that are present in the same protein complex tend to be linked and to be co-expressed. More generally, we found that genes that are close to each other in the protein interaction network tend to be linked more often than expected and are often co-expressed. Unexpectedly, we found that linked genes in network proximity have unusually high recombination rates. Because high recombination rates are associated with high rates of genome re-organization, our findings might explain why the clustering of genes in proximity in the network is such a weak effect: there could be a co-evolutionary cycle of physical linkage for co-expression, upwards modification of the recombination rate and concomitant break-up of a cluster. Under such a model an "optimal" gene order is never stable.     

Auxin–cytokinin interactions in the control of shoot branching

In many plant species, the intact main shoot apex grows predominantly and axillary bud outgrowth is inhibited. This phenomenon is called apical dominance, and has been analyzed for over 70 years. Decapitation of the shoot apex releases the axillary buds from their dormancy and they begin to grow out. Auxin derived from an intact shoot apex suppresses axillary bud outgrowth, whereas cytokinin induced by decapitation of the shoot apex stimulates axillary bud outgrowth. Here we describe the molecular mechanisms of the interactions between auxin and cytokinin in the control of shoot branching.     

Effects of NO3– and BAP on organogenesis in tissue-cultured shoot primordia induced from shoot apices of Utricularia praelonga St. Hil.

The effects of NO₃ ^– and BAP on organogenesis in shoot primordia of Utricularia praelonga subcultured in B5 liquid medium were studied. In B5 liquid basal medium supplemented with 24.73 mM KNO₃ and 2.0 mg/l BAP the subcultured shoot primordia continuously multiplied into numerous small, globular masses, while with dilution of the KNO₃ to 3 mM organogenesis was promoted. Pulse treatment of the shoot primordia with 3 mM KNO₃ in B5 liquid medium for 72 h and then transplantation to the B5 basal liquid-medium induced meristemoids in this tissue. When the shoot primordia regenerated meristemoids, they never reverted back into the proliferation cycle. The addition of BAP in the B5 liquid medium with 3 mM KNO₃ regulated the differentiation rate of the stems and leaves in the meristemoids induced in the masses of shoot primordia. The control produced 3 parts stems to 1 part leaves; medium with 0.02 mg/l BAP regenerated approximately 2 parts stems and 1 part leaves; that of 0.20 mg/l BAP 1 part stems and 2 parts leaves; and medium with 2.00 mg/l BAP regenerated leaves only. Received: 17 September 1997 / Revision received: 30 October 1997 / Accepted: 18 November 1997     

Does shoot water status limit leaf expansion of nitrogen-deprived barley?

The role of shoot water status in mediating the decline in leaf elongation rate of nitrogen (N)-deprived barley plants was assessed. Plants were grown at two levels of N supply, with or without the application of pneumatic pressure to the roots. Applying enough pressure (balancing pressure) to keep xylem sap continuously bleeding from the cut surface of a leaf allowed the plants to remain at full turgor throughout the experiments. Plants from which N was withheld required a greater balancing pressure during both day and night. This difference in balancing pressure was greater at high (2.0 kPa) than low (1.2 kPa) atmospheric vapour pressure deficit (VPD). Pressurizing the roots did not prevent the decline in leaf elongation rate induced by withholding N at either high or low VPD. Thus low shoot water status did not limit leaf growth of N-deprived plants.