Gibberellin-induced elongation and osmoregulation in internodes of floating rice

Internodal elongation in floating rice ( Oryza sativa L. cv. Habiganj Aman II) is known to be enhanced by treatment with ethylene or gibberellic acid (GA₃) at high relative humidity (RH). However, ethylene-induced internodal elongation is inhibited at low RH. while GA₃-induced internodal elongation is hardly affected by humidity. We examined the possible involvement of osmoregulation in the stimulation by GA₃ of the elongation of internodes at low RH. Submergence and treatment with ethylene or GA3₃ at 100% RH increased the osmotic potential in internodes of excised stem segments, while GA₃ at 20% RH maintained the osmotic potential at a low level. In internodes of stem segments that had been treated with GA₃ at 20% RH, the activity of invertase and the level of soluble sugars were almost 2- and 1.5-fold higher, respectively, than those in internodes that had been treated with GA₃ at 100% RH. These results indicate that one of the possible mechanisms by which GA₃ promotes elongation of internodes at low RH involves the osmoregulation that is achieved by promotion of the synthesis of invertase.     

Effect of gibberellic acid on growth and carbohydrate metabolism of developing tubers of potato (Solanum tuberosum)

Potato plants (Solanum tuberosum L. cv. Ostara) were grown in aerated water culture in a controlled environment. When the tubers had reached a diameter of 1–3 cm. ¹⁴C-labelled or unlabelled gibberellic acid (GA₃) was applied to the surface of the stolons at points approximately 1 crn from the developing tubers, and treatment continued for 10 days. - Significant quantities of GA₃ moved into tuber tissue within 2–4 days of hormone application. This influx of GA₃ was accompanied by a marked reduction in both the activity of ADPG-pyrophospharylase and the ratio ADPG-pyrophosphorylase/starch phosphorylase and an increase in the activity of UDPG-pyrophosphorylase. Starch phosphorylase activity initially increased slightly but then fell, whereas the activity of starch synthase remained constant throughout the experiment. The soluble sugar composition of the tubers changed qualitatively towards a pattern characteristic of growing stolon tips prior to tuber initiation, but there was no clear evidence of net starch degradation. Changes in the activities of the enzymes were observed prior to noticeable effects of the hormone on tuber growth rate or the development of new stolons at the tuber eyes. - GA₃- treated tubers imported more ¹⁴C from labelled photosynthate than expected on the basis of growth rate. However, the capacity to convert solub#e-¹⁴C to ethaTiol-insoluble-¹⁴C (predominantly starch) was reduced in comparison with non-treated tubers. - The observed changes in carbohydrate composition and enzyme activities indicate that GA₃ induces a drastic change in potato tuber metabolism towards a pattern characteristic for the termination of the storage process.     

Distribution of [14C]-labeled photosynthates within intensively cultured Populus clones during the establishment year

Seasonal patterns of [¹⁴C]-labeled photosynthate distribution within two intensively cultured Populus clones with contrasting phenology ( P. tristis × P. balsamifera cv. 'Tristis no. 1'; P. × euramericana cv. Eugenei) were investigated during the establishment year. During active shoot elongation upper mature leaves exported ¹⁴C acropetally to the expanding leaves and elongating internodes, and basipetally to the stem. Little ¹⁴C was exported to lower mature leaves or lateral branches. At budset the ¹⁴C export pattern shifted dramatically in the basipetal direction, i.e., to the lower stem, hardwood cutting, and roots. The timing of budset was the primary factor determining the differences between the clones, except that in all cases Tristis exported more ¹⁴C to the roots than Eugenei. After budset lower mature leaves had a similar export pattern to upper leaves, but the quantity of ¹⁴C exported to the roots was slightly higher. The results confirm the importance of autumn foliage for root growth in poplar. Clonal differences in seasonal patterns of photosynthate distribution offer potential for the poplar breeder seeking to match a clone's growth pattern with the specific growing season of the site.     

Gibberellic acid promotes growth and cell wall synthesis in Avena internodes regardless of the orientation of cell expansion

Segments cut from the next-to-last (peduncular-1) internode of Avena sativa L. cv. Victory (oat) shoots elongate as much as 10-fold in response to gibberellic acid (GA₃). The objective of the present investigation was to differentiate the effects of GA₃ on growth from its effects on wall synthesis (measured gravimetrically and through the incorporation of [¹⁴C]-glucose) by using several cell wall synthesis inhibitors with widely varying mechanisms of action. Four compounds, viz. monensin, cycloheximide, lanthanum, and galactose. caused (1) relatively little inhibition of either cell wall synthesis or elongation in segments without GA₃, (2) roughly proportionate, dose-dependent inhibition of elongation and wall synthesis in GA₃-treated segments and (3) generally greater inhibition of GA₃-promoted uptake of radioactivity than of wall incorporation or elongation. Two other compounds, colchicine and 2,6-dichlorobenzonitrile (DCB). (1) inhibited GA₃-induced elongation considerably more than cell wall synthesis and (2) caused swelling (radial expansion). especially of GA₃-treated segments. DCB-treated internodal cells apparently compensated for inhibited cellulose synthesis by greater synthesis of matrix polysaccharide (beginning between 3 and 6 h). While normal cellulose synthesis was not required for short-term (up to 6 h) GA₃-induced elongation or for long-term hormone-promoted radial expansion, it was required for sustained GA₃-induced elongation. These results indicate that GA₃-promoted cell wall loosening (manifested as radial expansion) and cell wall synthesis in Avena internodes occur at least partially independently of any hormonal effect on the orientation of microtubules and microfibrils.     

Temporal, spatial and hormonal regulation of the S-adenosylmethionine synthetase gene in petunia

Gibberellic acid (GA₃) promotes corolla elongation and pigmentation in petunia flowers. We have previously shown that G.A₃ induces pigmentation by activating specific genes of the anthocyanin biosynthetic pathway. The aim of the present work was to examine whether GA₃ induces also the expression of genes from other metabolic pathways in petunia corollas that may be associated with growth. Recently we reported the cloning of the petunia sam gene coding for S -adenosylmethionine synthetase (SAM-S). In the present work we show that sam expression is induced by GA₃ in both corollas and stems. The expression of the gene was correlated with corolla elongation. GA₃ and the cylokinin, N -6-benzyladenine (BA) promoted corolla growth and sam expression, whereas abscisic acid (ABA) inhibited corolla elongation and repressed sam mRNA accumulation. An analysis of sam expression in stems indicated a high level in young, elongating internodes and a very low level in the mature, non-elongating stem zone. The results of the present study show that the effect of GA₃ on gene expression in the corolla of petunia, is not restricted to the anthocyanin biosynthetic pathway, they also suggest a possible role for sam in GA₃-induced corolla and stem elongation.     

Stimulation of shoot elongation in Salix pentandra by gibberellin A9; activity appears to be dependent upon hydroxylation to GAl via GA20

Cessation of shoot elongation in seedlings of Salix pentandra L. is induced by short photoperiod. Gibbereliin A₉ (GA₉) applied either to the apical bud or injected into a mature leaf, induced shoot elongation under a short photoperiod of 12 h, and GA₉ could completely substitute for a transfer to a long photoperiod. When [³H]GA₉ or [²H₂]GA₉ was injected into a leaf, no [³H]GA₉ was detected in the elongating apex and only traces of [³H]GA₉ were found in the shoot above the treated leaf. By the use of gas chromatography-mass spectrometry (GC-MS), [²H₂]GA₂₀ was identified as the main metabolite of [²H₂]GA₉ in both the shoot and the treated leaf. In addition, [²H₂]GA₁ and [²H₂]GA₂₉ were also identified as metabolites of [²H₂]GA₉. These results are consistent with the hypothesis that exogenous GA, promotes shoot elongation in Salix through its metabolism to GA₂₀ and GA,.     

Internode length in Pisum. Estimation of GA1 levels in genotypes Le, le and led

The levels of GA₁, 3-epiGA₁ and GA₈ in genotypes Le, le and le^d of Pisum sativum L. were determined by gas chromatography-selected ion monitoring (GC-SIM) after feeds of [³H, ¹³C]-GA₂₀ to each genotype. The levels of endogenous and [¹³C]-labelled metabolites were determined by reverse isotope dilution with unlabelled GA₁, 3-epiGA₁ and GA₈. The results demonstrate a quantitative relationship between the level of GA₁ and the extent of elongation both on a per plant and a per g fresh weight basis. These results are consistent with previous findings in peas and other species possessing a predominant early 13-hydroxylation pathway for GA biosynthesis.
The levels of 3-epiGA₁ also decreased in the genotypic sequence Le, le, le^d although not as rapidly as for the level of GA₁. This may suggest that the alleles at the le locus also influence the formation of 3-epiGA₁.     

Hormone directed sucrose transport during fruit set induced by gibberellins in Pisum sativum

A new system has been developed to study hormone-directed transport in intact plants during parthenocarpic fruit set induced by gibberellins. Gibberellic acid (GA₃) and gibberellin A₁ (GA₁) applied to unpollinated ovaries of pea ( Pisum sativum L. cv. Alaska) promoted sucrose transport from the leaf to the site of hormone application. In vivo experiments showed an early (30 min) accumulation of [¹⁴C]-sucrose in ovaries of pea stimulated by gibberellins. This activation of sucrose transport appears to be mediated by gibberellins (GA₁, GA₃), increasing both loading of phloem with sucrose in the leaf (source) and sucrose unloading in the ovary (sink). The ability of pea tissue segments to take up sucrose in vitro was not affected by the hormonal treatment.     

Translocation of photoassimilate from leaves of two popyploid genotypes of tall fescue differing in photosynthetic rates

The photosynthetic rate of a decaploid genotype (1-16-2) of tall fescue ( Festuca arundinacea Schreb.) is about twice that of a common hexaploid genotype (V6-802) (Plant Physiol. 72: 16–21, 1983). Translocation of photosynthate out of the leaves is a possible means of regulating carbon assimilation. To evaluate this possibility, we have examined a) translocation velocity, b) time course of translocation from leaves, c) photoassimilate partitioning pattern into whole plants in pulse and chase experiments, and d) interveinal distances between two ploidy genotypes. Most of the ¹⁴C accumulated in sucrose, and the labelled carbon moved down the leaf blades at similar velocities (6 to 10 cm h⁻¹) in both genotypes. Recent ¹⁴C assimilate was rapidly translocated from the fed area of the leaf blade. For example, the decaploid and the common hexaploid had translocated 40 and 26% of the ¹⁴C, respectively, at 6 h, and 79 and 49% of the ¹⁴C, respectively, at 24 h. Partitioning of ¹⁴C among plant organs was considerably different between the genotypes after a 24 h chase. For example, out of the total ¹⁴C recovered from the whole plant, the decaploid had retained 40% in the labelled leaf with 10, 33 and 29% in other leaves, stem bases and roots, respectively; whereas the hexaploid had retained 91% in the labelled leaf with 4, 3 and 2% in other leaves, stem bases and roots, respectively. However, the higher rate of translocation was correlated with greater interveinal distances in the decaploid genotype. These results suggested that the higher translocation percentage in the decaploid than the hexaploid genotype was due to greater sink activity.     

Analysis of [14C] indole-3-acetic acid metabolites from the primary roots of Zea mays seedlings using reverse-phase high-performance liquid chromatography

Methanolic extracts of Zea mays L. cv. Fronica root segments which had been incubated in [¹⁴C] indole-3-acetie acid were analysed by reverse-phase high-performance liquid chromatography. Metabolism of indole-3-acetic acid was found to be rapid and extensive with at least 11 products apparent after a 2 h incubation. A comparison of metabolites of [1-¹⁴C]– and [2-¹⁴C] IAA, calculations of ¹⁴CO₂ evolution, and data on the polarity of products indicated that decarboxylation had not occurred. An average of 34% of the radioactivity remained associated with the indole-3-acetic acid peak.     

Further evidence for dolichyl phosphate-mediated glycosyl translocation through membranes

Abstract Mannosyl residues from GDP-[¹⁴C]Man are transferred into liposomes and onto internal GDP if the liposomal membranes contain dolichyl phosphate and the enzyme GDP-Man: Dol-P mannosyl transferase. Experiments using a mixture of GDP-[¹⁴C]Man and [³H]GDP-Man excluded the possibility that the transmembrane translocation of [¹⁴C]mannose is due to a GDP-[¹⁴C]Man_outside ag GDP_inside exchange reaction.     

Gibberellic acid-stimulated and auxin-stimulated cell growth in relation to RNA synthesis, protein synthesis and development in the wheat coleoptile

Young excised coleoptiles from dark grown wheat have their cell growth promoted by gibberellic acid (GA₃), while sections from older coleoptiles have their cell growth promoted by auxin. The GA₃ response has a much longer lag period than that of auxin. Neither GA₃ nor auxin has any effect on ¹⁴C-leucine and ¹⁴C-uridine incorporation and uptake after 1 h, indicating that the lag in growth stimulation following GA₃ application is not associated with changes in protein or RNA synthesis. Following a 6 h incubation there are small increases in ¹⁴C-leucine and ¹⁴C-uridine incorporation in response to both GA₃ and auxin, and in the case of auxin this is associated with increased uptake. Studies on protein and RNA turnover using pulse-chase experiments have shown that both GA₃ and auxin have no effect on protein and RNA stability. There are, however, developmental changes in RNA and protein synthesis that should be considered in any explanation of the mechanism of action of these hormones on cell growth. Young GA₃-sensitive tissue has high rates of RNA synthesis and low protein and RNA turnover, while auxin-sensitive tissue has low rates of RNA synthesis, slightly higher rates of RNA turnover and much higher rates of protein turnover. The evidence overall favours more effective utilisation by GA₃ and auxin of a basal control level of RNA and protein synthesis and turnover in coleoptile tissue.     

[14C]-Assimilate partitioning in photoperiodically induced seedlings of Pharbitis nil. The effect of benzyladenine

Partitioning of [¹⁴C]-labeled assimilates was studied in relation to photoperiodic floral induction and evocation in one-week-old Pharbitis nil Choisy cv. 'Violet' seedlings. In plants kept under 16 h photoperiods, one 15 h night induced 100% axillary flowering whereas a 24 h night induced both terminal and axillary flowering. A 15 min night break of red light given 8 h after the beginning of the dark period inhibited flowering. Total [¹⁴C]-assimilate distribution among major sinks (plumules + epicotyl and roots + hypocotyl) from a single source cotyledon was unchanged by one inductive night; however, import of [¹⁴C]-assimilates into shoot apices was increased in induced plants compared to vegegative controls. This increase was several-fold in plants subjected to a 24 h night. N⁶-Benzyladenine (BA) application to cotyledons or plumules under non-saturating night lengths increased the number of floral buds per plant without affecting the position of the first floral bud (i.e. the speed of induction). The same treatment caused increased label accumulation in induced apices, while it only slightly affected non-induced ones. The mode of action of BA on flowering through growth stimulation and resulting assimilate mobilization is discussed.     

Effect of zeatin on the growth and indolyl-3-acetic acid and abscisic acid levels in maize roots

Elongation, indolyl-3-acetic acid (IAA) and abscisic acid (ABA) levels, – gas chromatography-mass spectrometry quantification –, in the elongating zone were analysed for maize ( Zea mays L., Cv. LG11) roots immersed in buffer solution with or without zeatin (Z). The effect of Z depends on the initial extension rate of roots. The slower growing roots are more strongly inhibited by Z (10⁻⁷−10₋₅ M ) and they show a greater increase in IAA and ABA content. When compared to the rapidly growing roots, the larger reactivity of the 'slow'ones cannot be attributed to a higher Z uptake as shown when using [¹⁴C]-Z. It is suggested that Z could regulate root elongation by acting on the IAA and/or ABA level. The comparative action of these two hormones is discussed.     

A localised decrease of GA1 in shoot tips of Salix pentandra seedings precedes cessation of shoot elongation under short photoperiod

By application of a recently developed method allowing analysis of gibberellins (GAs) in mg amounts of tissue, the effect of photoperiod on levels of GAs in shoot tips of individual seedlings of the woody species Salix pentandra was studied. In elongating long day-grown seedlings, maximum levels of GA₁ were found 5–20 mm below the apex, approximately twice the levels in other segments. After exposure of plants to 5 or 15 short days, the levels of GA₁ were about 50% lower within this specific region of the stem, as compared with seedlings grown under long days. Short day-induced cessation of shoot elongation also correlated with overall declines in the levels of GA₅₃, GA₁₉, GA₂₀ and GA₈, Within each photoperiodic treatment the levels of these GAs were generally relatively similar throughout the upper 35 mm of stems. No differences in internode lengths or in lengths of pith or epidermal cells were found in plants grown under long days compared with those exposed to 5 short days. In both cases, cells in mitosis were observed in the subapical stem tissues of shoot tips. After 15 short days, stem elongation was completed, and dividing cells were generally not found in the subapical part of the stem. However, short day exposure did not prevent elongation of internodes and cells differentiated before the treatment was started. Thus, the localised decrease in level of GA₁ in shoot tips under short days precedes the morphological and anatomical changes connected with the short day-induced cessation of elongation growth. This supports the hypothesised role for GA₁ in photoperiodic control of shoot elongation in S. pentandra .     

Comparison of endogenous gibberellins in roots and shoots of elongating Salix pentandra seedlings

Gibberellins GA₁, GA₈. GA₁₉. GA₂₉. GA₂₀ and GA₅₆ (2-epi-GA₈). were identified by combined gas chromatography-mass spectrometry in root extracts of elongating Salix pentandra L. seedlings. The presence of GA₈ was also demonstrated for the first time in S. pentandra shoots. The levels of GA₁, GA₈, GA₁₉, GA₂₀ in shoot tissue and in roots were estimated by selected ion monitoring. While the amounts of GA₈ and GA₁₉ were similar in both plant parts. the levels of the biologically active GA₁ and its immediate precursor GA₂₀. were found to be much lower in roots than in shoots.     

The effect of water status and season on the incorporation of 14CO2 and [14C]-acetate into resin and rubber fractions in guayule

The effects of drought stress and season on both allocation of photosynthates to stems and leaves and potential for stem rubber synthesis were studied in guayule ( Parthenium argentatum Gray USDA line 11604). Two-year-old plants grown under field conditions in the Negev desert of Israel were subjected to different irrigation regimes, and water status was assessed by measuring the relative water content (RWC). Undetached plant tips were exposed to a 1 h pulse of ¹⁴CO₂, followed by a 24 h chase. ¹⁴C fixed and translocated to different plants parts and notably ¹⁴C incorporation into rubber and resin fractions was determined. The potential of detached branch slices to incorporate [¹⁴C]-acetate into rubber was also studied. A higher percentage of fixed ¹⁴C was translocated from shoot tips in winter (28–30%) than in summer (15–18%). The percentage of [¹⁴C]-acctate incorporated into the rubber fraction by stem slices was maximal in winter (20%) and minimal in summer (3–5%) in both cases in the absence of drought stress. In summer the translocation of photosynthates into stems was inversely related to plant RWC, dropping from 18% three days after irrigation to 3% 14 days later, and the potential of stems to synthesise rubber was high under drought conditions and low in well irrigated plants.     

Vanillic acid, a metabolite of 4-hydroxy-3-methoxyphenylglycol and 4-hydroxy-3-methoxymandelic acid in man

Abstract: 4-Hydroxy-3-methoxyphenylglycol (HMPG) labelled with ¹⁴C was used to study the metabolic fate of HMPG in six healthy volunteers. Besides conjugation and oxidation to 4-hydroxy-3-methoxymandelic acid (HMMA, VMA) a minor portion, 8.4 ± 1.1% (mean ± SEM) was excreted as ¹⁴C-labelled vantllic acid (VA). To study if VA was formed from HMPG or HMMA (VMA), deuterium-labelled HMPG ([²H₃]HMPG) and HMMA ([²H₆]HMMA) were simultaneously injected intravenously to seven healthy volunteers. The recovery of [²H₃]VA from [²H₃]HMPG was 8.3 ± 2.1% and the recovery of [²H₆]VA from [²H₆]HMMA was 9.0 ± 2.1%. The ²H-labelled VAs were probably formed by a decar boxylation reaction, in the case of HMPG after previous oxidation to HMMA.     

Growth and gibberellin relations of the extreme dwarf dx tomato mutant

The extreme dwarf d ^x tomato ( Lycopersicon esculentum Mill.) mutant has very short internodes which were found to contain shorter and fewer epidermal cells. The leaves are highly abnormal. The mutant showed a substantial stem growth response to GA₃, without approaching normal stature or morphology. The active gibberellin GA₁ and its precursors GA₁₉ and GA₂₀ were identified by coupled gas chromatography-mass spectrometry (GC/MS) in d ^x shoots. Quantitative GC/MS revealed that GA₂₀ accumulated to far higher levels than normal in stems and leaves of the mutant.