Gibberellins and Stem Growth as Related to Photoperiod in Silene armeria L

Stem growth and flowering in the long-day plant Silene armeria L. are induced by exposure to a minimum of 3 to 6 long days (LD). Stem growth continues in subsequent short days (SD), albeit at a reduced rate. The growth retardant tetcyclacis inhibited stem elongation induced by LD, but had no effect on flowering. This indicates that photoperiodic control of stem growth in Silene is mediated by gibberellins (GA). The objective of this study was to analyze the effects of photoperiod on the levels and distribution of endogenous GAs in Silene and to determine the nature of the photoperiodic after-effect on stem growth in this plant. The GAs identified in extracts from Silene by full-scan combined gas chromatography-mass spectrometry (GC-MS), GA₁₂, GA₅₃, GA₄₄, GA₁₇, GA₁₉, GA₂₀, GA₁, GA₂₉, and GA₈, are members of the early 13-hydroxylation pathway. All of these GAs were present in plants under SD as well as under LD conditions. The GA₅₃ level was highest in plants in SD, and decreased in plants transferred to LD conditions. By contrast, GA₁₉, GA₂₀, and GA₁ initially increased in plants transferred to LD, and then declined. Likewise, when Silene plants were returned from LD to SD, there was an increase in GA₅₃, and a decrease in GA₁₉, GA₂₀, and GA₁ which ultimately reached levels similar to those found in plants kept in SD. Thus, measurements of GA levels in whole shoots of Silene as well as in individual parts of the plant suggest that the photoperiod modulates GA metabolism mainly through the rate of conversion of GA₅₃. As a result of LD induction, GA₁ accumulates at its highest level in shoot tips which, in turn, results in stem elongation. In addition, LD also appear to increase the sensitivity of the tissue to GA, and this effect is presumably responsible for the photoperiodic after-effect on stem elongation in Silene.     

Stem growth,flower formation,and endogenous gibberellins in a normal and a dwarf strain of Silene armeria

The physiological basis of dwarfism in a single-gene, recessive mutant of Silene armeria L. was investigated through comparison with a normal strain. Exposure of the normal strain to long days led to stem growth and flower formation while similar exposure of the dwarf strain led only to flowering, with very little stem growth. Application of gibberellin A₃ or A₄₊₇ in short days promoted stem elongation in the normal strain, but had a much lesser effect in the dwarf strain. Upon extraction and chromatographic fractionation of the endogenous gibberellins (GAs) in the normal strain of S. armeria, three zones of GA activity were found. An increase in one zone of activity was found in both strains after 1 long day. Neither the quality nor the quantity of the extractable GAs differed greatly between the dwarf and the normal strain. Vegetative dwarf scions, grafted onto fully induced, normal stocks formed flowers, but their growth habit was not changed. Thus, the lack of stem growth in response to long days in the dwarf strain appears to result from a lack of GA sensitivity in the stem tissue of these plants. However, during flower formation dwarf plants did exhibit elongation of the peduncles. This response was suppressed by the growth retardant 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine-carboxylate methyl chloride (AMO-1618), and applied GA₃ could partially overcome this inhibition. Thus, peduncle elongation in the dwarf strain appears to be regulated by endogenous GAs.Abbreviations AMO-1618 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine-carboxylate methyl chloride - GA(s) gibberellin(s) - LD long day(s) - SD short day(s)     

Influence of changes in daylength and carbon dioxide on the growth of potato

Potatoes (Solanum tuberosum L.) are highly productive in mid- to high-latitude areas where photoperiods change significantly throughout the growing season. To study the effects of changes in photoperiod on growth and tuber development of potato cv. Denali, plants were grown for 112 d with 400 micromol m-2 s-1 photosynthetic photon flux (PPF) under a 12-h photoperiod (short days, SD), a 24-h photoperiod (long days, LD), and combinations where plants were moved between the two photoperiods 28, 56, or 84 d after planting. Plants given LD throughout growth received the greatest total daily PPF and produced the greatest tuber yields. At similar levels of total PPF, plants given SD followed by LD yielded greater tuber dry mass (DM) than plants given LD followed by SD. Stem DM per plant, leaf DM, and total plant DM all increased with an increasing proportion of LD and increasing daily PPF, regardless of the daylength sequence. When studies were repeated, but at an enriched (1000 micromol mol-1) CO2 concentration, overall growth trends were similar, with high CO2 resulting in greater stem length, stem DM, leaf DM, and total plant DM; but high CO2 did not increase tuber DM.     

Gibberellins in Relation to Flowering and Stem Elongation in the Long Day Plant Silene armeria

Two long days induced some flowering and 4 or more long days caused 100% flowering in Silene armeria. On long days microscopically detectable flower primordia were first seen after 6 days, which is at least 1 day before the start of stem elongation. Both gibberellin A₃ and A₇ caused flowering on short days, but the results were variable and flowering was never 100%. Three different gibberellins were detected in Silene extracts. The pattern of gibberellins extracted from plants on short and long days was qualitatively the same, but on long days gibberellin content was up to 100% higher than on short days. Only small amounts of diffusible gibberellins were obtained from Silene shoot tips (including very young leaves) on short days. However, on long days the diffusible gibberellins increased by as much as 10-fold after 4 to 6 long days but then declined somewhat after 10 long days. The gibberellins extracted from the shoot tips at the completion of the diffusion period also increased under long days, although the increase was not as large as for the diffusible gibberellins. An A₅-like gibberellin present in extracts was not detected in diffusates.     

Chemical composition and antifungal activity of essential oil and various extract of Silene armeria L

The aims of this study were to examine the chemical composition of the essential oil isolated from the floral parts of Silene armeria L. by hydrodistillation, and to test the efficacy of essential oil and various leaf extracts (n-hexane, chloroform, ethyl acetate and methanol) as an antifungal potential. The GC-MS analysis determined that 28 compounds, which represented 89.03% of total oil, were present in the oil containing mainly 1-butene, methylcyclopropane, 2-butene and caryophyllene oxide. The oil (1000ppm/disc) and the leaf extracts (1500ppm/disc) revealed remarkable antifungal effect against Fusarium oxysporum, Fusarium solani, Phytophthora capsici, Colletotrichum capsici, Sclerotinia sclerotiorum, Botrytis cinerea and Rhizoctonia solani, in the growth inhibition range of 39.6-67.6% and 9.3-61.3%, respectively, along with their respective MIC values ranging from 62.5 to 1000mug/ml and 125 to 2000mug/ml. The essential oil had also a strong detrimental effect on spore germination of all the tested plant pathogens along with concentration as well as time-dependent kinetic inhibition of B. cinerea. Thus, the results obtained in this study demonstrate that S. armeria essential oil and various organic extracts possess a wide range spectrum of fungicidal activity and could become an alternative to synthetic fungicides for controlling certain important plant fungal diseases.     

Cellular changes induced by exogenous and endogenous gibberellins in shoot tips of the long-day plant Silene armeria

Stem elongation and flowering are two processes induced by long-day (LD) treatment in Silene armeria L. Whereas photoperiodic control of stem growth is mediated by gibberellins (GAs), the flowering response cannot be obtained by GA applications. Microscopic observations on early cellular changes in the shoot meristem following LD induction or GA treatment in short days (SD) were combined with GA analyses of stem sections at various distances below the shoot apex. The earliest effects of both LD and GA induction on the subapical meristem were an increase in the number of cells per cell file and a reduction of cell length in the meristematic tissue approx. 1.0–3.0 mm below the shoot apex. Within 8 d after the beginning of LD induction or after GA application, the cells in the subapical meristem were oriented in long files. In induced tips, cellulose deposition occurred mostly in longitudinal walls, indicating that many transverse cell divisions had taken place which, in turn, increased the length of the stem. In contrast to LD induction, GA treatments did not promote the transition from the vegetative to the floral stage. Endogenous GAs were analyzed by selected ion monitoring (SIM), using labeled internal standards, in extracts from transverse sections of the tip at various distances below the apical meristem. In control plants, the levels of the six 13-hydroxy GAs studied (GA₅₃, GA₄₄, GA₁₉, GA₂₀, GA₁, and GA₈) decreased as the distance from the apical meristem increased. Except for GA₅₃, GA levels were higher in tips of LD-induced plants, particularly in the meristematic zone approx. 0.5–1.5 mm below the apical meristem. In comparison with SD, the highest increase observed was for GA₁, the content of which increased 30-fold in the zone 0.5–3.5 mm below the shoot apex. These data indicate a spatial correlation between the accumulation of GA₁ and its precursors, and the enhanced mitotic activity which occurs in the subapical meristem of elongating Silene apices.Abbreviations GA_n gibberellin A_n - LD long day(s) - SD short day(s) We thank Dr. L.N. Mander, Australian National University, Canberra, for providing [²H]- gibberellins, Dr. B.O. Phinney, University of California, Los Angeles, USA, for [¹³C]GA₈, Dr. D.A. Gage, MSU-NIH Mass Spectrometry Facility, for advice with mass spectrometry, and Mr. M. Chassagne, I.N.R.A. C.R. Bordeaux, for the photography. This work was supported, in part, by a fellowship from the Spanish Ministry of Agriculture (Instituto Nacional de Investigaciones Agrarias) to M.T., by the U.S. Department of Energy under contract DE-ACO2-76ERO-1338, and by the U.S. Department of Agriculture grant No. 88-37261-3434 to J.A.D.Z.     

Different mechanisms account for enhanced copper resistance in Silene armeria ecotypes from mine spoil and serpentine sites

The resistance to excess Cu was evaluated in solution culture in three ecotypes of Silene armeria from different origin, a garden soil (Cadriano), a serpentine site (Prinzera) and a Cu mine spoil (Vigonzano). Root elongation and viability staining of root tip cells were used as indicators for Cu resistance. The Cu resistance increased in the order Cadriano <Prinzera<Vigonzano. Renewal of the root cap in Prinzera and enhanced border cell production in Vigonzano in response to excess Cu provided a more efficient protection of the root tip meristem than in Cu sensitive Cadriano. The enhanced Cu resistance in Prinzeracould not be attributed to high soil Cu acting as a natural selection factor at the serpentine site. In PrinzeraCu exclusion from roots and shoots probably was a consequence of root impermeabilization causing reduced radial water and ion flux in roots. In contrast, the high Cu resistance in the mine spoil ecotype, Vigonzano, was due to both reduced Cu uptake and higher tissue tolerance of Cu.     

Photoperiod and gibberellic acid – control of the cell cycle in the meristem of Silene armeria and its effects on flowering

Plants of Silene armeria L., strain S_2.1, a quantitative long-day (LD) species which is known to react to GA₃ by flowering after attaining, the'intermediate stage', were induced by two LD or by two GA₃ applications. Changes in the mitotic index and DNA content (microdensitometric estimation) of cells in the axial zone, lateral zone and rib meristem of the shoot apex were observed during the first 48 h of each treatment. Similar mitotic activation occurred in response to LD or GA₃ after a 6-8 h lag period. This was preceded by a decrease in the proportion of nuclei with a 2C DNA content, indicating that in this species the control point for the shortening of the cell cycle was essentially in G₁. A second mitotic peak was observed 16 h later in photoinduced meristems, resulting in more pronounced cellular synchronization. These further events were not seen in GA₃-treated plants where only the meristematic activity was slightly, but reproducibly higher than in the control. Thus, two successive synchronizations of cell division are a typical feature of LD induction. The data are discussed with regard to the competence of shoot apical cells to be reactivated. The essential changes for the transition to flowering depend on these differential patterns of cell reactivation.     

Cellular basis of the effects of gibberellin and the pro gene on stem growth in tomato

Tomato (Lycopersicon esculentum Mill.) plants homozygous for the mutant pro gene, exhibiting the distinctive procera phenotype, appeared virtually identical to gibberellic acid (GA₃)-treated isogenic normal plants. The pro gene and GA₃ caused analogous increases in internode length, and in the length and number of cells in the outer cell layers of each internode. Internode number was also increased by pro and GA₃ over the period of the experiment. Despite their greater length, the internodes of GA₃-treated and pro plants reached their final size within a time period similar to that of internodes of untreated normal plants. The pro mutant itself was responsive to GA₃, especially in the seedling stage, but the proportional increase in height seen in the later stages of growth was less than that of normal plants.Abbreviations GA gibberellin - GA₃ gibberellic acid - LSD least significant difference     

Inhibition of stem growth and gibberellin production in Agrostemma githago L. by the growth retardant tetcyclacis

The effects of the new growth retardant tetcyclacis (TCY) on stem growth and endogenous gibberellin (GA) levels were investigated in the long-day rosette plant Agrostemma githago. Application of TCY (10 ml of a 5·10^-5M solution daily) to the soil suppressed stem elongation in Agrostemma grown under long-day conditions. A total of 10 g GA₁ (1 g applied on alternate days) per plant overcame the growth retardation caused by TCY.Control plants and plants treated with TCY were analyzed for endogenous GAs after exposure to nine long days. The acidic extracts were fractionated by high-performance liquid chromatography. Part of each fraction was tested in the d-5 maize bioassay, while the remainder was analyzed by combined gas chromatography-selected ion monitoring. The bioassay results indicated that the GA content of plants treated with TCY was much lower than that of untreated plants. The data obtained by gas chromatography-selected ion monitoring confirmed that the levels of seven GAs present in Agrostemma were much reduced in TCY-treated plants when compared with the levels in control plants: GA₅₃ (13%), GA₄₄ (0%), GA₁₉ (1%), GA₁₇ (33%), GA₂₀ (15%), GA₁ (4%), and epi-GA₁ (13%). These results provide evidence that TCY inhibits stem growth in Agrostemma by blocking GA biosynthesis and thus lowering the levels of endogenous GAs.Abbreviations AMO-1618 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine-carboxylate methyl chloride - GA(s) gibberellin(s) - HPLC high-performance liquid chromatography - TCY Tetcyclacis (5-[4-chlorophenyl]-3,4,5,9,10-pentaaza-tetracyclo-5,4,1,0^2,6,0^8,11-dodeca-3,9-diene)     

Seed effects on gibberellin metabolism in pea pericarp

Pea fruit (Pisum sativum L.) is a model system for studying the effect of seeds on fruit growth in order to understand coordination of organ development. The metabolism of ¹⁴C-labeled gibberellin A₁₂ (GA₁₂) by pea pericarp was followed using a method that allows access to the seeds while maintaining pericarp growth in situ. Identification and quantitation of GAs in pea pericarp was accomplished by combined gas chromatography-mass spectrometry following extensive purification of the putative GAs. Here we report for the first time that the metabolism of [¹⁴C]GA₁₂ to [¹⁴C]GA₁₉ and [¹⁴C]GA₂₀ occurs in pericarp of seeded pea fruit. Removal of seeds from the pericarp inhibited the conversion of radiolabeled GA₁₉ to GA₂₀ and caused the accumulation of radiolabeled and endogenous GA₁₉. Deseeded pericarp contained no detectable GA₂₀, GA₁, or GA₈, whereas pericarp with seeds contained endogenous and radiolabeled GA₂₀ and endogenous GA₁. These data strongly suggest that seeds are required for normal GA biosynthesis in the pericarp, specifically the conversion of GA₁₉ to GA₂₀.     

Photoperiodic control of gibberellin metabolism in spinach

[(3)H]GA(20) applied to spinach plants (Spinacia oleracea L.) was metabolized to several products. Two of these were identified by combined gasliquid chromatography-radio counting as [(3)H]GA(29) and [(3)H]3-epi-GA(1). Inasmuch as both GA(20) and GA(29) are endogenous gibberellins in spinach (Metzger, Zeevaart 1980 Plant Physiol 65: 623-626), it was concluded that the conversion of GA(20) to GA(29) is a natural process. However, 3-epi-GA(1) was not detected in extracts of spinach shoots analyzed by combined gas chromatography-mass spectrometry. This indicates that the conversion of exogenous [(3)H]GA(20) to [(3)H]3-epi-GA(1) may be an artifact.Long-day pretreatment of spinach shoots caused a 2-fold increase in the rate of [(3)H]GA(20) metabolism over the rate of metabolism in plants maintained under short-day conditions. Furthermore, [(3)H]GA(29) accumulated more rapidly under long than under short days, whereas photoperiodic treatment had no effect on the accumulation of [(3)H]3-epi-GA(1). Thus, the long-day-induced increase in the level of endogenous GA(29) in spinach shoots (Metzger, Zeevaart 1980 Plant Physiol 66: 844-846) appears to be the result of an increased capability to convert GA(20) to GA(29).     

Influence of the Ca/Mg ratio on Cu resistance in three Silene armeria ecotypes adapted to calcareous soil or to different, Ni- or Cu-enriched, serpentine sites

This hydroponic study addresses the influence of low (0.3) and high (4.0) Ca/Mg molar ratios on Cu resistance of Silene armeria ecotypes from different habitats: a calcareous soil (ecotype Cadriano), a Ni-rich serpentine site (ecotype Prinzera), and an acid Cu-mine spoil soil containing serpentinite (ecotype Vigonzano). Under control conditions, without excess Cu, only Cadriano was negatively affected by the low Ca/Mg ratio. Under both low and high Ca/Mg ratios Cu resistance followed the order Vigonzano > Prinzera > Cadriano. More efficient Cu exclusion accounted for enhanced Cu resistance in Prinzera. The low Ca/Mg ratio increased Cu uptake in Prinzera but did not worsen toxicity effects; i.e. the plants had higher internal Cu effect concentrations. In Vigonzano Cu resistance was enhanced by the low Ca/Mg ratio. This was due only in part to better Cu exclusion. Magnesium-induced tolerance to higher Cu tissue concentrations appears to be in ecotypes from serpentine and acid mine spoils, but not in plants from calcareous soil, the exposure to low Ca/Mg ratio favours internal detoxification of Cu by means of more efficient chelation and compartmentation.     

Stem elongation and changes in the levels of gibberellins in shoot tips induced by differential photoperiodic treatments in the long-day plant Silene armeria

The effects of differential photoperiodic treatments applied to shoot tips and mature leaves of the long-day (LD) plant Silene armeria L. on growth and flowering responses, and on the levels of endogenous gibberellins (GAs), were investigated. Gibberellins were analyzed by gaschromatography-mass spectrometry and the use of internal standards. Exposure of mature leaves to LD, regardless of the photoperiodic conditions of the shoot tips, short days (SD), LD, or darkness, promoted elongation of the stems and of the immature leaves. Long-day treatment of the mature leaves modified the levels of endogenous GAs in shoot tips kept under LD, SD, or darkness. In shoot tips kept in LD or darkness the levels of GA₅₃ were reduced, whereas the levels of GA₁₉ and GA₂₀ were increased. The contents of GA₁ were increased in all three types of shoots: SD twofold, LD fivefold, and darkness eightfold. Dark treatment of the shoot tips on plants of which the mature leaves were grown in SD promoted elongation of the immature etiolated leaves and increased the GA₁ content of the shoot tips threefold. However, this treatment did not cause stem elongation. The different photoperiodic treatments applied to the shoot tips did not change the levels of GAs in mature leaves. These results indicate that both LD and dark treatments result in an increase in GA₁ in shoot tips. In addition, it is proposed that LD treatment induces the formation of a signal that is transmitted from mature leaves to shoot tips where it enhances the effect of GA on stem elongation.Abbreviations GA_n gibberellin A_n - LD long day(s) - SD short day(s) We thank Dr. L.N. Mander, Australian National University, Canberra, for providing [²H]-gibberellins and Dr. D.A. Gage, MSU-NIH Mass Spectrometry Facility, East Lansing, for advice with mass spectrometry. This work was supported, in part, by a fellowship from the Spanish Ministry of Agriculture (Instituto Nacional de Investigaciones Agrarias) to M.T., by the U.S. Department of Energy grant No. DE-FG02-91ER20021, and by the U.S. Department of Agriculture grant No. 88-37261-3434 to J.A.D.Z.     

Photocontrol of gibberellin metabolism in situ in maize

Two forms of spinach acyl carrier protein (ACP-I and ACP-II) have recently been characterized and found to be expressed in a tissue-specific manner (JB Ohlrogge, TM Kuo, 1985 J Biol Chem 260: 8032). To examine possible different functions for these ACP isoforms, we have tested purified preparations of spinach leaf ACP-I and ACP-II and Escherichia coli ACP in several in vitro reactions of fatty acid metabolism. Total de novo fatty acid synthesis and malonyl-CoA:ACP transacylase do not appear to discriminate between acyl carrier protein isoforms. In contrast, the K_m of oleoyl-ACP thioesterase for oleoyl-ACP-II is 10-fold higher than for oleoyl-ACP-I, whereas the K_m of acyl-ACP glycerol-3-phosphate acyl transferase is 5-fold higher for oleoyl-ACP-I than for oleoyl-ACP-II. A characterization of these reactions and a possible role for ACP isoforms in regulation of fatty acid metabolism in plants are described.     

Phytochrome controlled gibberellin metabolism in etioplast envelopes

Summary Disruption of preparations of intact etioplasts isolated from wheat (Triticum aestivum L.) leaves in the dark leads to an increase in the level of extractable gibberellin-like (GA-like) activity. Irradiation of disrupted preparations with red light causes an alteration in the Rf of part of the GA-like activity. A study of sub-etioplast fractions prepared by gradient centrifugation indicates that the phytochrome and the GA-like substances are associated principally with the etioplast envelope.Abbreviations GA gibberellin - MOPS N-morpholino-3-propanesulphonic acid - EDTA ethylene diamine tetra-acetic acid - ATP adenosine triphosphate - R red light     

Genetic manipulation of gibberellin metabolism in transgenic rice

The 'green revolution' was fueled by the introduction of the semi-dwarf trait into cereal crop cultivars. The semi-dwarf cultivars--which respond abnormally to the plant growth hormone gibberellin (GA)--are more resistant to wind and rain damage and thus yield more grain when fertilized. To generate dwarf rice plants using a biotechnological approach, we modified the level of GA by overproduction of a GA catabolic enzyme, GA 2-oxidase. When the gene encoding GA 2-oxidase, OsGA2ox1, was constitutively expressed by the actin promoter, transgenic rice showed severe dwarfism but failed to set grain because GA is involved in both shoot elongation and reproductive development. In contrast, OsGA2ox1 ectopic expression at the site of bioactive GA synthesis in shoots under the control of the promoter of a GA biosynthesis gene, OsGA3ox2 (D18), resulted in a semi-dwarf phenotype that is normal in flowering and grain development. The stability and inheritance of these traits shows the feasibility of genetic improvement of cereal crops by modulation of GA catabolism and bioactive GA content.