Inhibition Of Stem Elongation Research Articles

Light regulation of gibberellin A1 content and expression of genes coding for GA 20-oxidase and GA 3β -hydroxylase in etiolated pea seedlings

White light (WL) inhibited the stem elongation of etiolated pea (Pisum sativum L.) seedlings and the inhibition was partially reversed by the application of gibberellin A1 (GA1), the active GA in shoot growth. The amount of GA1 in the apical shoot was reduced to about 25% after 2 h of WL, and to a trace level after 4 h. The effect of light on GA1 content was reversed when the plants were transferred again to the dark after 6 h of WL. The effect of light on the expression of GA 20-oxidase and GA 3β-hydroxylase genes, coding for the last steps of GA1 biosynthesis, was also investigated. Contrary to expectations, the amounts of GA 20-oxidase and GA 3β-hydroxylase transcripts increased in the entire apical shoot of WL-irradiated seedlings, and this increase was negated in seedlings treated with GA1 before WL irradiation, probably as a result of negative feed-back regulation. The effect of WL on GA 20-oxidase transcripts was mainly localized in the apex (hook) whereas the effect on GA 3β-hydroxylase transcripts was mainly localized in the subapical tissues. Red and far-red light also enhanced the GA 20-oxidase transcript level, but not that of GA 3β-hydroxylase, suggesting that different photoreceptors are involved in the regulation of these genes by WL. The results presented indicate that the inhibition of stem elongation by light is due, at least partially, to a decrease of GA1 content by a still unknown mechanism. The increase of GA8 upon WL irradiation raises the possibility that an inactivation activity may be involved in the control of the content of GA1 by light.

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When cabbage plug seedlings were stored under a modified atmosphere packaging (MAP) at 15°C in the dark for 2 weeks, a passive MAP did not create an environment to inhibit stem elongation of seedling in the 0.1mm thick polyethylene (PE) film pouch. An active MAP by adjusting N2 rich air with 2% O2 did not successfully retard elongation either. In the active MAP where the internal atmosphere was replaced with N2 enriched air (2.5% O2) with elevated CO2, the elongation was delayed as CO2 concentration increased. When 16% CO2 was introduced to the 0.08mm thick nylon/PE film pouch, the inhibit of stem elongation was most successful. Analysis of plant weight, total number of leaves, green color intensity, ascorbic acid content in the leaf blade and head weight of harvested cabbage revealed that the elevated CO2 active MAP is a favorable storage condition for cabbage plug seedlings. The elevated CO2 active MAP, however, caused CO2 injury when CO2 concentration exceeded 24%.

Effects of D-ring modified gibberellins on flowering and growth in lolium temulentum

Abstract The modified gibberellins, 16-methyl-16,17-dihydro-GA 5 , 16,17-methano-16,17-dihydro-GA 5 , 16,17-methano-16,17-dihydro-GA 3 and several halogenated derivatives of 16,17-methano-16,17-dihydro-GA 3 and GA 5 were prepared and tested for bioregulating properties in Lolium temulentum . The effects ranged from the promotion of both stem elongation and flowering, the promotion of flowering but not elongation, and vice versa , the inhibition of stem elongation combined with the promotion of flowering, and the inhibition of both.

Growth and Branching Responses of Portulaca grandiflora to Foliar Applications of Chemical Growth Regulators

During container production of portulaca, growth of long, prostrate, sparsely branched stems makes handling of plants difficult, and reduces their commercial appeal. Growers prefer to minimize shoot elongation while increasing branching to provide a full, compact plant. The objectives of this study were to evaluate growth regulators for promotion of branching and inhibition of stem elongation. Container-grown plants ≈21 cm in diameter were treated with sprays of ProShear (benzylaminopurine) at 62.4, 125, and 250 ppm; Promalin (benzyaminopurine + gibberellins 4+7) at 125, 250, and 500 ppm; Atrimmec (dikegulac) at 250, 500, and 750 ppm; and Florel (ethephon) at 250, 500, and 750 ppm. These treatments were compared with untreated controls in a randomized complete-block design. Main shoot lengths were measured at 16, 31, and 51 days after treatment (DAT). Numbers of new shoot breaks were counted 16 DAT. The growth habit, that is, tendency to grow upright or prostrate, was also evaluated 16 DAT. The most-effective material for retarding primary shoot elongation and for stimulating secondary shoot development was ProShear. At 16 DAT, 250 ppm ProShear reduced shoot elongation by 25% compared to control plants. This treatment also increased the number of secondary shoot breaks by 143%. Promalin increased the number of new shoot breaks, but it also increased the lengths of all shoots. High rates of Florel and Promalin caused shoots to grow predominantly upright rather then prostrate. ProShear, however, caused more prostrate growth as rate increased.

Identification of Endogenous Gibberellins and Their Role in Rosetted Seedlings of Eustoma grandiflorum.

Endogenous gibberellins (GAs) were extracted from shoots with floral buds of Eustoma grandiflorum and analyzed by full scan gas chromatography/mass spectrometry (GC/MS). Consequently, five C13-hydroxylated GAs, GA1, GA19, GA20, GA44, and GA53, were identified. The presence of these GAs suggests that one major GA biosynthetic pathway, the early C13-hydroxylation pathway, is operating in these shoots. Stem elongation of resetted plants was promoted by applications of GA1, GA4, GA9, and GA20. C13-hydroxylated GAs, GA1, and GA20, were more active in stem elongation than were the non-C13-hydroxylated GAs, GA4, and GA9. Inhibition of stem elongation on Uniconazole-P (UCZ) and Prohexadione-calcium (PCa)-treated plants was wholly reversed by application of GA1, where the inhibition by PCa was partially overcome by GA20. These results suggest that the activation steps of precursory GAs, such as 3β-hydroxylation steps from GA20 to GA1 and from GA9 to GA4, are functioning in the rosetted plants and that the endogenous GA1 is physiologically important in regulating stem elongation of E. grandiflorum.

Irradiance-induced alterations of growth and cytokinins in Phaseolus vulgaris seedlings

Light is a major environmental factor affecting plant growth and development. The cytokinins have many similar effects on these processes and may be involved in photomorphogenesis. In order to study the correlation between light and endogenous cytokinins, we have examined growth parameters and endogenous cytokinins in stems, leaves and other organs of Phaseolus vulgaris, cultivated for 10 days under a range of irradiances (25, 110, 350 and 500 µmol m−2 s−1). The nucleotides isopentenyladenosine-5′-monophosphate and zeatin riboside-5′-monophosphate were the dominant cytokinins, whereas both free bases and ribosides were below the detection level (0.5 pmol g−1). Plants grown at the highest irradiance had in their stems, leaves, petioles and roots significantly higher levels of cytokinins than had plants grown at the lowest irradiance. As expected, increased light influx increased the dry weight of the root, petiole and leaf, and increased the leaf area, with concomitant increases in the cytokinins in these plant parts. However, the stem showed a different and more complex relationship with irradiance. Stem cytokinin levels increased drastically between 350 and 500 µmol m−2 s−1, but this was not correlated with any change in stem length; the light inhibition of stem elongation was mainly seen when irradiance was increased to 110 µmol m−2 s−1. Taken as a whole, the results are consistent with an effect of irradiance and cytokinins on the processes favouring biomass production.

γ-aminobutyric acid promotes stem elongation in stellaria longipes : the role of ethylene

The response of stems to GABA was biphasic in that lower concentrations of GABA (upto 500 µM) promoted stem elongation, but higher concentrations of GABA inhibited stem elongation. An optimal GABA concentration of 250 µM produced maximum stem elongation. The higher GABA concentrations also stimulated 1-aminocyclopropane-1-carboxylate (ACC) synthase (EC 4.4.1.14) mRNA accumulation and ethylene production. Results suggest that the inhibitory effect of higher GABA concentrations on stem elongation is partly mediated by ethylene.

Effect of Gibberellin A4 and GA Biosynthesis Inhibitors on Growth and Flowering of Stock (Matthiola incana (L.) R. Br.).

Effects of gibberellin A4 (GA4) and three GA biosynthesis inhibitors, uniconazole (UCZ), prohexadione-calcium (PCa), and trinexapac-ethyl (TNE) on growth and flowering of Matthiola incana (L.) R. Br. were investigated. In an early flowering 'Sourei', UCZ inhibited stem elongation and flowering. GA4, PCa and TNE promoted flowering at 20°/15°C and 25°/20°C (day/night) under 12-hr photoperiod as compared to the control. However, only PCa and TNE induced flowering of a late flowering 'Banrei' at 20°/15°C. Flowering was not induced in any treatment at 25°/20°C and 30°/25°C but stem elongation of both cultivars was promoted by GA4 and PCa at all temperatures. Under green house conditions in the winter, PCa promoted flowering of 'Banrei'. Although GA4 and PCa promoted stem elongation, they did not induce flowering in the summer. These results indicate that biosynthesis of GA4 and its deactivation are important factors that control stem elongation and flowering.

Persistence of Triazole Growth Retardants on Stem Elongation of Rhododendron and Kalmia

Triazole growth retardant chemicals may inhibit stem elongation of woody ornamental species for several years after application. Potted plants of large-leaf Rhododendron catawbiense and Kalmia latifolia were treated with a single spray application of paclobutrazol or uniconazole in the 2nd year from propagation. They were transplanted into the field the next spring. The elongation of stems was measured in the year of application and in the next 2–4 years. Treatments with a wide range of doses were applied in 1991, 1992, or 1995. For all except the most dilute applications, stem elongation was retarded in the year after application. At the highest doses, stem growth was inhibited for 2 years after application. The results were fit to a model of growth regulator action which assumed that stem elongation was inversely related to the amount of growth regulator applied. For paclobutrazol, the dose per plant that inhibited stem elongation half as much as a saturating dose was tenfold that for uniconazole, about 0.5 and 0.05 mg, respectively. For both chemicals, the dose-response coefficient decreased exponentially with time after application, with an exponential time constant of about 2 year−1. A dose of growth regulator which reduced stem elongation by half immediately after application would only inhibit 12% of stem elongation the next year. However, a tenfold greater dose would result in less than half the stem elongation of untreated plants in the next year.

Analysis of Horticultural Performance of Ethylene-insensitive Petunias and Tomatoes

We are studying the horticultural performance of two model plant systems that carry a mutant gene that confers ethylene-insensitivity: Never Ripe tomatoes and petunia plants transformed with the mutant etr1-1 gene isolated from Arabidopsis thaliana. Having two model systems to compare side-by-side allows us to determine with greater certainty ethylene's role at different developmental stages. Presence of the mutant etr1-1 gene in transgenic petunias was determined using three techniques: PCR analysis, the seedling triple response assay (inhibition of stem elongation, radial swelling of stem and roots, and an exaggerated apical hook when grown in the dark and in the presence of ethylene), and the flower wilting response to pollination, which is known to be induced by ethylene. Flowers from ethylene-insensitive petunias took almost four times as long to wilt after pollination as wild-type plants. It is well known that fruit ripening in Never Ripe tomato is inhibited, and a similar delayed fruit ripening phenotype is observed in petunia plants transformed with etr1-1. In an effort to maintain ethylene-insensitive petunia plants by vegetative propagation, we observed that the rate of adventitious root formation was much lower with transgenic plants than in wild-type plants. In subsequent experiments on adventitious root formation in Never Ripe tomato, we observed the same result. Therefore, while ethylene-insensitive tomato and petunia plants appear phenotypically normal for many characters, other factors are altered by the presence of this mutation. The fact that these changes are present in two model systems helps to define the role of ethylene perception in plant growth and reproduction.

Long-term Effects of Triazol Growth Regulators on Stem Elongation of Rhododendron and Kalmia

The persistence of effects of paclobutrazol or uniconazol on stem elongation was determined for several years after large-leaf Rhododendron and Kalmia latifolia were treated with a single-spray application of these triazol growth-regulator chemicals. Potted plants were treated in the second year from propagation, and transplanted into the field in the following spring. The elongation of stems was measured in the year of application and in the following 2 to 4 years. Treatments with a wide range of doses were applied in 1991, 1992, or 1995. For all except the most-dilute applications, stem elongation was retarded in the year following application. At the highest doses, stem growth was inhibited 2 years following application. The results could be explained by a model of growth regulator action that assumed stem elongation was inversely related to amount of growth regulator applied. The dose response coefficient for paclobutrazol was less than that for uniconazol. The dose that inhibited stem elongation one-half as much as a saturating dose was about 0.5 and 0.05 mg/plant, for paclobutrazol and uniconazol, respectively. The dose response coefficient decreased exponentially with time after application, with an exponential time constant of about 2/year. The model predicted a dose of growth regulator that inhibited 0.9 of stem elongation immediately after application would continue to inhibit 0.5 of stem elongation in the following year.

Growth‐promoting activity of gibberellins on shoot elongation in Salix pentandra is reduced by 16,17‐dihydro derivatisation

The metabolism of GA10 is thought to be under photoperiodic control in the woody plant Salix pentandra. However, in a recent study using 16,17‐[3H2]GA19 as a mimic of Ga10, no effect of photoperiod was found on its metabolism to 16,17‐dihydro‐GA20 and 16,17‐dihydro‐GA1. To investigate if this was due to differential action of exogenous 16,17‐dihydro‐GAs and GAs, the effects of the 16,17‐dihydro‐derivatives of the gibberellins GA19, GA1, and GA1 as compared with their parent GAs, on shoot elongation in seedlings of S. pentandra were studied. 16,17‐Dihydro‐GA19, and ‐GA20 were both almost inactive, while 16,17‐dihydro‐GA1 induced some shoot elongation in seedlings treated with ancymidol as well as under short days. GA19, GA20 and GA1 were all able to counteract the inhibitory effect of ancymidol under continuous light, while inhibition induced by a 12‐h photoperiod was antagonised only by GA20 and GA1. Thus, the growth‐stimulating activity of the tested GAs is significantly reduced by 16,17‐dihydro derivatisation, but the derivatives do not inhibit stem elongation in S, pentandra, as has been found in monocotyledons.

Effects of uniconazole and GA3 on cold-induced stem elongation and flowering of Raphanus sativus L.

The effects of gibberellin (GA) on cold-induced stem elongation and flowering of Japanese radish (Raphanus sativus L.) were investigated using application of GA3 and a GA-biosynthesis inhibitor, uniconazole (UCZ). UCZ very strongly inhibited stem elongation and delayed flowering, and the inhibition and delay were completely reversed by GA3 application. These results suggest that GA is necessary not only in the stem elongation but also in the flowering. When cold treatment (CT) was conducted on the plants whose GA level was lowered by UCZ, GA3 applied after CT completely reversed the delay of flowering. Thus low GA level probably did not retard cold induction. Microscopic observation of apical meristem showed that UCZ delayed flowering by delaying the shift from vegetative to dome-shaped meristem. This result suggested that low GA level delayed floral evocation. Consequently it was suggested that low GA level retarded physiological process involved in long day induction or in floral evocation, resulting in delay of floral evocation.

Cell number and organ size in developing sunflower hypocotyls

Hypocotyl elongation in etiolated sunflower seedlings ( Helianthus annuus L.) is inhibited by white light (WL). It has been suggested that this response is largely due to an inhibition of cell elongation with little effect on cell numbers. During growth in darkness, a positive correlation between the increase in hypocotyl length and cell numbers per organ was observed. In WL, stem elongation and the increment in the number of cells were both inhibited to the same extent (correlation coefficients r>0.98 for both etiolated and irradiated seedlings). We conclude that WL inhibits stem elongation via two separate effects: retardation of cell expansion and a concomitant suppression of cell division in the meristematic region of the hypocotyl.

Solar Ultraviolet-B Radiation Affects Seedling Emergence, DNA Integrity, Plant Morphology, Growth Rate, and Attractiveness to Herbivore Insects in Datura ferox.

To study functional relationships between the effects of solar ultraviolet-B radiation (UV-B) on different aspects of the physiology of a wild plant, we carried out exclusion experiments in the field with the summer annual Datura ferox L. Solar UV-B incident over Buenos Aires reduced daytime seedling emergence, inhibited stem elongation and leaf expansion, and tended to reduce biomass accumulation during early growth. However, UV-B had no effect on calculated net assimilation rate. Using a monoclonal antibody specific to the cyclobutane-pyrimidine dimer (CPD), we found that plants receiving full sunlight had more CPDs per unit of DNA than plants shielded from solar UV-B, but the positive correlation between UV-B and CPD burden tended to level off at high (near solar) UV-B levels. At our field site, Datura plants were consumed by leaf beetles (Coleoptera), and the proportion of plants attacked by insects declined with the amount of UV-B received during growth. Field experiments showed that plant exposure to solar UV-B reduced the likelihood of leaf beetle attack by one-half. Our results highlight the complexities associated with scaling plant responses to solar UV-B, because they show: (a) a lack of correspondence between UV-B effects on net assimilation rate and whole-plant growth rate, (b) nonlinear UV-B dose-response curves, and (c) UV-B effects of plant attractiveness to natural herbivores.

Methoxylation modifies the activity of 1,2-benzisoxazole-3-acetic acid: 6,7-dimethoxy-1,2-benzisoxazole-3-acetic acid is an auxin antagonist in cytokinin mediated processes

The insertion of a methoxy group in different positions of the aromatic ring modifies the activity of 1,2-benzisoxazole-3-acetic acid (BOAA), a specific morphogenetic compound with no activity on cell elongation or root growth. Monomethoxylation in the 4- and 7-position is critical in determining the kind of activity: 4-OMeBOAA induces stem elongation, inhibits root growth and does not improve shoot production; 7-OMeBOAA inhibits stem elongation and shoot production and is unable to induce root growth. 6,7-OMeBOAA, inactive on stem elongation and root growth, is unable to induce the expression of Pg5-GUS gene in the presence of BAP and inhibits the expression of this gene when induced by BAP plus IAA. Furthermore, 6,7-OMeBOAA inhibits completely shoot production and can therefore be regarded as an auxin antagonist in these cytokinin-mediated processes.

Anaerobic promotion of stem extension in Potamogeton pectinatus. Roles for carbon dioxide, acidification and hormones

Dark‐grown shoots of tubers of the aquatic monocot Potamogön pectinatus L. elongated more strongly in anaerobic than aerobic solutions over 5 days. The response was located in the stem rather than the leaf. Anaerobic carbon dioxide (CO2) production was similar to that in aerobic conditions. Approximately half the anaerobic stem extension was attributed to acidification of the submerging medium by respiratory CO2. Sparging with an anaerobic gas mixture of nitrogen and hydrogen to remove dissolved CO2 inhibited stem elongation and prevented acidification of the medium. Similarly, supplying CO2 anaerobically promoted stem elongation while acidifying the medium. Carbon dioxide was also active on aerobic shoots. The effect of CO2 on anaerobic stem extension could be mimicked with an acidic buffer. Anaerobic stem extension was inhibited by exogenous abscisic acid (ABA), while gibberellic acid and the gibberellin‐biosynthesis inhibitor paclobutrazol proved inactive. Exogenous indole‐3‐acetic acid promoted stem extension in the absence of oxygen. A strong gravitropic response by anaerobic stems of P. pectinatus was inhibited by the auxin‐efflux inhibitor naphthylphthalamic acid.

Photomorphogenic Effects of UV-B Radiation on Plants: Consequences for Light Competition

A combination of field and labotatory studies were conducted to explore the nature of photomorphogenic effects of ultraviolet-B radiation (UV-B; 280–320 nm) on plant morphology and to evaluate the ecological consequences of these alterations in morphology for interspecific competition. Under laboratory conditions, seedlings of cucumber (Cucumis sativus L.) and tomato (Lycopersicon esculentum Mill.) exhibited appreciable (ca. 50%) and rapid (< 3h) inhibition in hypocotyl elongation in response to UV-B exposure. In cucumber, this inhibition was reversible, occurred without any associated changes in dry matter production and was caused by UV-B incident on the cotyledons and not the stem or growing tip. Inhibition of stem elongation in etiolated tomato seedlings occurred at least 3 h prior to the onset of accumulation of UV-absorbing pigments and monochromatic UV supplied against a background of visible radiation tevealed maximum effectiveness in inhibition around 300 nm. Collectively, these findings suggest that a specific, but yet unidentified, UV-B photoreceptor is involved in mediating certain morphological responses to UV-B. For mixtures of wheat (Triticum aestivum L.) and wild oat (Avena fatua L.), a common weedy competitor, supplemental UV-B irradiation in the field differentially altered shoot morphology which resulted in changes in canopy structure, light interception and calculated stand photosynthesis. It is argued that, because of its asymmetrical nature, competition for light can potentially amplify the effects of UV-B on shoot morphology and may, therefore, be an important mechanism by which changes in the solar UV-B spectrum associated with stratospheric ozone reduction could alter the composition and character of terrestrial vegetation.

New lv Mutants of Pea Are Deficient in Phytochrome B.

The lv-1 mutant of pea (Pisum sativum L.) is deficient in responses regulated by phytochrome B (phyB) in other species but has normal levels of spectrally active phyB. We have characterized three further lv mutants (lv-2, lv-3, and lv-4), which are all elongated under red (R) and white light but are indistinguishable from wild type under far-red light. The phyB apoprotein present in the lv-1 mutant was undetectable in all three new lv mutants. The identification of allelic mutants with and without phyB apoprotein suggests that Lv may be a structural gene for a B-type phytochrome. Furthermore, it indicates that the lv-1 mutation results specifically in the loss of normal biological activity of this phytochrome. Red-light-pulse and fluence-rate-response experiments suggest that lv plants are deficient in the low-fluence response (LFR) but retain a normal very-low-fluence-rate-dependent response for leaflet expansion and inhibition of stem elongation. Comparison of lv alleles of differing severity indicates that the LFR for stem elongation can be mediated by a lower level of phyB than the LFR for leaflet expansion. The retention of a strong response to continuous low-fluence-rate R in all four lv mutants suggests that there may be an additional phytochrome controlling responses to R in pea. The kinetics of phytochrome destruction and reaccumulation in the lv mutant indicate that phyB may be involved in the light regulation of phyA levels.

Ethylene biosynthesis and action: a case of conservation.

Ethylene is one of the simplest organic molecules with biological activity. At concentrations as low as 0.1 ppm in air, it has been shown to have dramatic effects on plant growth and development [1]. Neljubov [78] was the first to show that ethylene has three major effects in etiolated pea seedlings called the triple response: (1) diageotropic growth, (2) thickening of stem and inhibition of stem elongation, and (3) exaggeration of apical hook curvature. Since then, numerous ethylene effects have been described in light-grown plants such as sex determination in curcurbits, fruit ripening in climacteric fruits, epinastic curvature, flower senescence, and root initiation [1]. Interestingly, ethylene has also been shown to have opposite effects in some plants; for instance, it inhibits stem elongation in most dicots, whereas in some aquatic dicots and rice, it stimulates growth [1, 45, 72].