Nana gene--a regulator of cell division and elongation of stem cells in Arabidopsis thaliana (L.) Heynh

The dominant nana (na) mutation localized to the upper arm of Arabidopsis thaliana chromosome 1 blocks cell proliferation in apical meristem (AM) of the flower-bearing stem at its early development and suppresses the subsequent elongation of its internode cells. The na mutation reduces the sensitivity of cells of the flower-bearing stem to gibberellin (GA) and paclobutrazole (PBZ) and prevents resting and immature seeds from restoring the germinating ability in response to exogenous GA. On the other hand, exogenous GA and PBZ affects the onset of flowering, hypocotyl length, and leaf color; i.e., the na mutant displays a distortion of only several, rather than all, GA-dependent processes. Based on the results obtained, the product of the NA gene was assumed to play a role in the negative regulation of GA signaling and to act later than the products of the known GAI and SPY genes.     

Genetic regulation of gibberellin deactivation in Pisum

The regulation of gibberellin (GA) deactivation was examined using the sin (slender) mutation in the garden pea (Pisum sativum L.). This mutation blocks the deactivation of GA₂₀, the precursor of the bioactive GA₁. Firstly, crosses were made to combine sin with the GA biosynthesis mutations na, lhⁱ and le-3. The combination sin na produced a novel phenotype, with long (‘slender’) basal internodes and extremely short (‘nana’) upper internodes. In contrast, the double mutant sin lhⁱ was phenotypically dwarf. The mutation sin causes an accumulation of GA₂₀ in maturing seeds, and this was unaffected by na, since the na mutation is not expressed in seeds. In contrast, lhⁱ seeds did not accumulate GA₂₀, since lhⁱ imposes an early block on GA biosynthesis. Secondly, the effects of sin on several steps in GA deactivation were investigated. In maturing seeds, the mutation sin blocks two steps in GA₂₀ metabolism, namely, GA₂₀ to GA₂₉, and GA₂₉ to GA₂₉-catabolite. In the vegetative plant, on the other hand, sin blocked the step GA₂₀ to GA₂₉, but not GA₂₉ to GA₂₉-catabolite; the steps GA₂₀ to GA₈₁ and GA₂₀ to GA₁ were also not impaired in this mutant. It is clear that the effects of sin, like those of na, are strongly organ-specific. The presence of separate enzymes for the steps GA₂₀ to GA₂₉ and GA₂₉ to GA₂₉-catabolite was suggested by the observation that GA₈ inhibited the latter step, but not the former, and by the inability of GA₂₀ and GA₂₉ to inhibit each other's metabolism. It is suggested that the Sin gene may be a regulatory gene controlling the expression of two structural genes involved in GA deactivation.     

WOX14 promotes bioactive gibberellin synthesis and vascular cell differentiation in Arabidopsis

Procambial and cambial stem cells provide the initial cells that allow the formation of vascular tissues. WOX4 and WOX14 have been shown to act redundantly to promote procambial cell proliferation and differentiation. Gibberellins (GAs), which have an important role in wood formation, also stimulate cambial cell division. Here we show that the loss of WOX14 function phenocopies some traits of GA‐deficient mutants that can be complemented by exogenous GA application, whereas WOX14 overexpression stimulates the expression of GA3ox anabolism genes and represses GA2ox catabolism genes, promoting the accumulation of bioactive GA. More importantly, our data clearly indicate that WOX14 but not WOX4 promotes vascular cell differentiation and lignification in inflorescence stems of Arabidopsis.     

Antioxidant potential in <Emphasis Type="Italic">Stevia rebaudiana</Emphasis> callus in response to polyethylene glycol,paclobutrazol and gibberellin treatments

The study on Stevia callus has the potential to advance the knowledge of antioxidant mechanisms involved in unorganized cells response to drought stress. The effects of polyethylene glycol (PEG; 0 and 4% w/v) in combination with paclobutrazol (PBZ; 0 and 2 mg l^?1) and gibberellin (GA; 0 and 2 mg l^?1) were studied on Stevia rebaudiana callus. PEG treatment led to an oxidative stress, as indicated by increased H₂O₂ content whose accumulation was prevented with PBZ and GA treatments. All treatments of PEG, PBZ and GA increased the total antioxidant capacity, with the highest antioxidant power in PBZ and GA treatments without PEG. The activity of superoxide dismutase, catalase and ascorbate peroxidase significantly increased in PEG treatment alone or in combination with PBZ and GA. All treatments of PEG, PBZ and GA significantly increased proteins, amino acids and proline contents, with the highest increase in presence of PBZ in medium culture. In contrary to proline, the activity of pyrroline-5-carboxylate synthetase and proline dehydrogenase did not change in response to any of the treatments. Collectively, our results demonstrated that PBZ and GA increased reactive oxygen species scavenging and osmolytes in PEG-treated calli more than PEG treatment alone to alleviate negative effects of PEG on Stevia calli. These findings will enable us to design effective genetic engineering strategies in callus culture to generate some somaclonal variation that may be useful in enhancing drought resistance in Stevia.     

Physiological,biochemical, antioxidant and growth characterizations of gibberellin and paclobutrazol-treated sweet leaf (<Emphasis Type="Italic">Stevia rebaudiana</Emphasis> B.) herb

A greenhouse experiment was designed to study the responses of Stevia rebaudiana herb to paclobutrazol (PBZ) and gibberellin (GA) treatments. GA and PBZ treatments caused no significant impact on photosynthesis pigments while they increased carbohydrates, amino acids and protein metabolites. Stevia showed a potent antioxidant activity through scavenging DPPH, NO^·; O ₂ ^·? and OH^· radicals which was highlighted in GA and PBZ treatments. The enzymatic and non-enzymatic antioxidant system of Stevia plant showed a significant increase in response to PBZ and GA treatments. PBZ treatment decreased plant growth while GA treatment had no significant effect on it. Collectively, both GA and PBZ treatments effectively increased metabolites and antioxidant property of Stevia herb.     

Isolation and preliminary characterization of gas1-1, a mutation causing partial suppression of the phenotype conferred by the gibberellin-insensitive (gai) mutation in Arabidopsis thaliana (L.) Heyhn

The semi-dominant gai mutation of arabidopsis confers a dark-green dwarf phenotype resembling that of gibberellin (GA)-deficient mutants. In contrast to GA-deficient mutants, gai mutants do not respond to GA treatments and accumulate higher levels of bioactive GAs than are found in wild-type controls. The gai mutation thus alters the responses of plant cells to GA, indicating that the GAI (wild-type) gene product is involved in GA reception and/or signal transduction. Here we describe the isolation and preliminary characterization of a mutation, gas1-1, which is not linked to gai and which partially suppresses the effect of the gai mutation. Double mutant, gai gas1-1, homozygotes are less severely dwarfed and lighter green than gai GAS1 controls. However, comparisons of the effects of treatments with exogenous GA demonstrate that gas1-1 does not increase the GA responsiveness of the gai mutant. Thus the gas1-1 mutation appears to reduce the GA-dependency of plant growth, and identifies a gene (GAS1) whose product is a candidate GA signal-transduction component.Abbreviations GA gibberellin - GA₃ gibberellic acid We thank Maarten Koornneef (Wageningen Agricultural University, The Netherlands) for providing mutant seed stocks; Mark Aarts and Bernard Mulligan (University of Nottingham, UK) for performing the -irradiation. This work was made possible by AFRC/BBSRC PMB Grants PG208/520 and PG208/0600, and by a grant from the Gatsby Charitable Foundation. P.C. was supported by a Human Capital and Mobility Fellowship from the EC.     

The Roles of the NANA and LEPIDA Genes in Regulating the Stem Growth in Arabidopsis thaliana

Genetic, physiological, and morphological studies of dwarf mutants of Arabidopsis thaliana (L.) Heynh. from the collection of the Department of Genetics and Breeding, Moscow State University, showed that the NA and LE genes are involved in regulating elongation of internode cells and sensitivity to various hormones. The na mutation suppressed stem growth only in the presence of the active LE gene. The absence of the LE activity (in the lele homozygote) restored stem growth of the na mutant to the level characteristic of thele-2 mutant, and a decrease inLE activity (in LE/le heterozygote) almost completely suppressed the na phenotype. Phenotypic analysis of homozygous double mutants and heterozygotes obtained by crossing the na and le-2 mutants showed that the recessive le-2 allele has an epistatic effect on the semidominant na allele and that the genes possibly control consecutive steps of one biochemical pathway or one morphogenetic process. A hypothetical scheme was proposed for the interaction of the NA and LE gene products.     

Effect of Paclobutrazol Application on Plant Growth and Flower Quality in Herbaceous Peony

Herbaceous peony (Paeonia lactiflora Pall.) is an important ornamental plant worldwide. In its natural state, P. lactiflora often manifests traits like rapidly elongating internodal growth, loose plant types, and soft inflorescence stems. However, very little has been known about the measures for controlling these traits. This study investigated the effect of applying paclobutrazol (PBZ) on the plant growth and flower quality in P. lactiflora. The results indicated that PBZ application reduced the plant height (8.05%), plant crown width (14.72%), and leaf area (10.90%), but increased the leaf thickness (18.18%) and stem diameter (over 11%) in P. lactiflora. Meanwhile, PBZ application was also found to increase the chlorophyll (Chl) a (29.63%), Chl b (33.33%), Chl a+b (30.56%), SPAD (27.32%), relative water content (0.47%), soluble sugar (5.09%) and activities of three antioxidant enzymes (superoxide dismutase 169.66%, peroxidase 3.59%, catalase 319.30%), but decreased the relative electrical conductivity (18.52%). Additionally, the application of PBZ was found to affect the flowering quality of P. lactiflora, increasing the flower diameter and fresh weight only in the flower-bud stage. This initiates the bloom stage, where there was a decrease in the total content of the aromatic compounds except for the flower-bud stage, and faded the flower color by reducing the content of anthocyanin. These results demonstrated that the application of PBZ can regulate the P. lactiflora plant types with no significant decrease in its ornamental values. This might provide a theoretical basis for further applying PBZ in P. lactiflora for use in urban landscape spaces.     

Different inhibitors of the gibberellin biosynthesis pathway elicit varied responses during in vitro culture of aspen (<Emphasis Type="Italic">Populus tremula</Emphasis> L.)

Several synthetic plant growth regulators (PGRs), including prohexadione-calcium (ProCa), paclobutrazol (PBZ), and chlormequat chloride (CCC), known for their ability to inhibit gibberellin (GA) biosynthesis, were investigated for their influence on Populus tremula L. (aspen) shoots grown in vitro. Changes in plant growth induced by these inhibitors were compared to the effects of exogenous gibberellins (GA₃ and GA_4/7). All PGRs were added to the nutrient medium at concentrations of either 1 or 5 μM. Stem segments with and without apical buds were excised from in vitro-grown shoot culture, and these explants were incubated either in test tubes or Petri dishes. In the presence of 5 μM ProCa, shoot growth and rooting were inhibited when grown in test tubes, while shoots grown in Petri dishes exhibited strongly enhanced shoot and root growth. PBZ suppressed shoot development both in test tubes and Petri dishes, although 1 μM PBZ promoted adventitious root formation when shoots were grown in test tubes. Five micromolars CCC suppressed shoot and root development in test tubes, but promoted shoot growth in Petri dishes.     

Gibberellins and the procera mutant of tomato

The procera mutant of tomato (Lycopersicon esculentum L.) has a phenotype which is remarkably similar to that of normal tomatoes treated with exogenous gibberellin (GA), indicating that it might be a GA over-producer. However, analysis of endogenous GAs by gas chromatography-mass spectrometry showed that Procera actually has lower levels of GA₂₀ and GA₁ than normal. The reason for these anomalously low GA levels is not clear, as there was no difference between procera and normal plants in their ability to metabolize [³H]GA₂₀. The procera mutant responded to exogenous gibberellic acid with increased extension growth, but the proportional response for a given dose of GA was the same in procera and normal plants. It therefore appears that the procera mutation does not directly affect either the GA status of the plant, or its ability to respond to GA.Abbreviations GA gibberellin - GC-MS gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - MeTMSi methyl trimethylsilyl - SIM selected ion monitoring     

gid1, a gibberellin-insensitive dwarf mutant, shows altered regulation of probenazole-inducible protein (PBZ1) in response to cold stress and pathogen attack

A recessive gibberellin (GA)-insensitive dwarf mutant of rice, gibberellin-insensitive dwarf1 (gid1), has been identified, which shows a severe dwarf phenotype and contains high concentrations of endogenous GA. To elucidate the function of gid1, proteins regulated downstream of gid1 were analysed using a proteomic approach. Proteins extracted from suspension-cultured cells of gid1 and its wild type were separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Of a total of 962 proteins identified from the suspension-cultured cells, 16 were increased and 14 were decreased in gid1 compared with its wild type. Among the proteins hyper-accumulated in gid1 were osmotin, triosephosphate isomerase, probenazole inducible protein (PBZ1) and pathogenesis-related protein 10. Of these four genes, only the expression of PBZ1 was increased by exogenous GA3 application. Expression of this gene was also enhanced in shoots of the wild type by cold stress or by rice blast fungus infection. Under normal growth conditions, there was more PBZ1 protein in gid1 than in the wild type. In addition, gid1 showed increased tolerance to cold stress and resistance to blast fungus infection. The entcopalyl diphosphate synthase (OsCPS) genes, which encode enzymes at the branch point between GA and phytoalexin biosynthesis, were expressed differentially in gid1 relative to the wild type. Specifically, OsCPS1, which encodes an enzyme in the GA biosynthesis pathway, was down-regulated and OsCPS2 and OsCPS4, which encode enzymes in phytoalexin biosynthesis, were up-regulated in gid1. These results suggest that the expression of PBZ1 is regulated by GA signalling and stress stimuli, and that gid1 is involved in tolerance to cold stress and resistance to blast fungus.     

Flowering of Chrysanthemum under non-inductive long days by gibberellins and N6-benzyladenine

Summary The flowering and inflorescence development of Chrysanthemum morifolium cv. Pink Champagne under non-inductive long days was promoted by exogenous application of GA₅, GA₃, GA₄+GA₇ or GA₉ in combination with the cytokinin, BA. The combination of BA and GA₅ was highly effective, BA and GA₃ moderately effective. Applications of the GAs alone or BA alone also resulted in some flowering, with GA₃ and GA₅ being most effective. In general, the effects of GA and BA were synergistic, and the concentration of both growth substances was a limiting factor with regard to the number of plants flowering under long days. Only the concentration of GA was a limiting factor for inflorescence development, however. Simultaneous application of indole-3-acetic acid reduced inflorescence development in most treatments. Development to the stage of anthesis was in no case effected.Abbreviations BA N⁶-benzyladenine - GA gibberellin - IAA indole-3-acetic acid This research was supported by National Research Council of Canada Grant No. 2585.     

Paclobutrazol Improved the Reproductive Growth and the Quality of Seed Oil of Jatropha curcas

Jatropha curcas was treated by soil drench paclobutrazol (PBZ) (0, 2, and 3 g m^?1 of canopy diameter) and foliar spray PBZ (0, 500, 800, and 1,200 ppm). The results showed that PBZ treatments greatly retarded vegetative growth and improved reproductive growth. The lengths of new branches were greatly decreased, whereas the number of fruits per inflorescence, fruit-bearing branches per tree, and total fruit load per tree were increased. Only the 2-g soil drench and the 1,200-ppm foliar PBZ spray significantly increased fruit load. The 2-g soil drench PBZ treatment resulted in a decrease in seed S and Cu contents of J. curcas, whereas Mn and B were greatly or moderately increased. A higher dose (3-g soil drench PBZ) reversed the improvement in reproductive growth and alleviated the negative effects on element contents in seeds compared with the 2-g soil drench PBZ. Finally, soil drench PBZ treatments significantly improved seed oil content and oil quality by reducing the oil acid value, increasing stearic acid and oleic acid contents, and reducing palmitic acid and linoleic acid content. The optimum drench dose was below 2 g m^?1 of canopy diameter. The optimum foliar spray concentration of PBZ was not determined in this study but our results suggest that it is higher than 1,200 ppm.     

GA application induces alteration in sex ratio and cell death in <Emphasis Type="Italic">Jatropha curcas</Emphasis>

Jatropha curcas L. is a commercially important plant with biodiesel and medicinal potential. It is a monoecious plant with staminate and pistillate flowers in same inflorescence with number of staminate flowers being higher than pistillate ones resulting in very low fruit yield. Altering sex ratio to increase the number of female flowers would lead to better yield. Phytohormones are most important factors known to alter sex ratio in plants. The mechanism by which phytohormones alter sex ratio differs in different plant species. Among phytohormones, GA plays an important role in sex alteration. In this study, we report the effect of exogenous application of GA on sex modification in J. curcas. There was considerable increase in number of female flowers by application of GA. At lower concentrations (10 and 100 ppm), increase in number of female flowers and fruit yield was proportionate to the concentration of hormone used but at higher concentration (1,000 ppm) though there was an increase in number of female flowers, fruit yield decreased. This was due to an increased peduncle length and enhanced cell death as a consequence of endogenous release of hydrogen peroxide in response to increased GA, resulting in withering of fruits.     

A single nucleotide mutation in GID1c disrupts its interaction with DELLA1 and causes a GA‐insensitive dwarf phenotype in peach

Plant stature is one important factor that affects the productivity of peach orchards. However, little is known about the molecular mechanism(s) underlying the dwarf phenotype of peach tree. Here, we report a dwarfing mechanism in the peach cv. FenHuaShouXingTao (FHSXT). The dwarf phenotype of ‘FHSXT’ was caused by shorter cell length compared to the standard cv. QiuMiHong (QMH). ‘FHSXT’ contained higher endogenous GA levels than did ‘QMH’ and did not response to exogenous GA treatment (internode elongation). These results indicated that ‘FHSXT’ is a GA‐insensitive dwarf mutant. A dwarf phenotype‐related single nucleotide mutation in the gibberellic acid receptor GID1 was identified in ‘FHSXT’ (GID1c^S191F), which was also cosegregated with dwarf phenotype in 30 tested cultivars. GID1c^S191F was unable to interact with the growth‐repressor DELLA1 even in the presence of GA. ‘FHSXT’ accumulated a higher level of DELLA1, the degradation of which is normally induced by its interaction with GID1. The DELLA1 protein level was almost undetectable in ‘QMH’, but not reduced in ‘FHSXT’ after GA₃ treatment. Our results suggested that a nonsynonymous single nucleotide mutation in GID1c disrupts its interaction with DELLA1 resulting in a GA‐insensitive dwarf phenotype in peach.     

Changes in growth and photosynthetic characteristics of Ocimum sanctum under growth regulator treatments

A field experiment was conducted to investigate the effect of growth regulators on growth characteristics such as root length, shoot length, total leaf area, number of inflorescence per plant, number of flower per inflorescence, whole plant fresh weight and whole plant dry weight. Photosynthetic characteristics were also analyzed based on the same experiment. For this, various photosynthetic pigment contents such as chlorophyll, carotenoid, anthocyanin and xanthophyll content were calculated. The conventional growth regulator abscisic acid (ABA) and non-conventional growth regulator triazole compound paclobutrazol (PBZ) were used. Root length increased due to growth regulator treatment, but shoot length decreased. Leaf area was decreased due to growth regulator treatment. The number of inflorescence increased in ABA treated plants, but it was decreased in PBZ treated plants. In ABA treated plants, the number of flowers per inflorescence was increased. In PBZ treated plants the number of inflorescence was reduced. The whole plant fresh weight (FW) and dry weight (DW) were increased in ABA and PBZ treated plants. There was an increase in chlorophyll content in growth regulator treated plants compared to control, and it was more in PBZ treated plants. The carotenoid content was also increased in ABA and PBZ treated plants.     

Molecular and Functional Characterization of <Emphasis Type="Italic">ZmNF-YC14</Emphasis> in Transgenic Arabidopsis

The optimum transition stage from vegetative to reproductive development is important for flowering plants to obtain the desired plant architecture to maximize yield. In this study, we overexpressed the maize NUCLEAR FACTOR Y, SUBUNIT C 14 (ZmNF-YC14) gene in Arabidopsis to investigate its potential functions in the regulation of plant transition. Overexpression of ZmNF-YC14 in Arabidopsis inhibited plant flowering and retarded the duration of the branch-producing inflorescence phase 1 (I₁). These plants exhibited increased length of I₁ and higher ratio of inflorescence phase 1 to inflorescence phase (I) (I₁:I) under long-day conditions. As a consequence, these transgenic plants exhibited dramatic changes in their overall inflorescence morphology. In addition, the phenotypes of inflorescence morphology caused by ZmNF-YC14 overexpression were enhanced by exogenous gibberellin (GA) treatment, which obtained a significant increase in I₁:I, inflorescence phase 1 to inflorescence phase 2 (I₂) (I₁:I₂), and remarkable decrease in I₂ and I₂:I in transgenic plants compared to those under normal conditions. Taken together, the results of this study suggest that ZmNFYC14 negatively regulates flowering and controls flower formation under long-day conditions in Arabidopsis and may be involved in a GA regulation pathway.