Gibberellin Metabolism and Transport During Germination and Young Seedling Growth of Pea (<Emphasis Type="Italic">Pisum sativum</Emphasis> L.)

The role of gibberellins (GAs) during germination and early seedling growth is examined by following the metabolism and transport of radiolabeled GAs in cotyledon, shoot, and root tissues of pea (Pisum sativum L.) using an aseptic culture system. Mature pea seeds have significant endogenous GA₂₀ levels that fall during germination and early seedling growth, a period when the seedling develops the capacity to transport GA₂₀ from the cotyledon to the shoot and root of the seedling. Even though cotyledons at 0–2 days after imbibition have appreciable amounts of GA₂₀, the cotyledons retain the ability to metabolize labeled GA₁₉ to GA₂₀ and express significant levels of PsGA20ox2 message (which encodes a GA biosynthesis enzyme, GA 20-oxidase). The large pool of cotyledonary GA₂₀ likely provides substrate for GA₁ synthesis in the cotyledons during germination, as well as for shoots and roots during early seedling growth. The shoots and roots express GA metabolism genes (PsGA3ox genes which encode GA 3-oxidases for synthesis of bioactive GA₁, and PsGA2ox genes which encode GA 2-oxidases for deactivation of GAs to GA₂₉ and GA₈), and they develop the capacity to metabolize GAs as necessary for seedling establishment. Auxins also show an interesting pattern during early seedling growth, with higher levels of 4-chloro-indole-3-acetic acid (4-Cl-IAA) in mature seeds and higher levels of indole-3-acetic acid (IAA) in young root and shoot tissues. This suggests a changing role for auxins during early seedling development.     

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     

The Effect of Gibberellic Acid and Guanosine Monophosphates on Extension Growth, Leaf Production and Flowering of Impatiens balsamina

Gibberellic acid (GA₃) increases the height of Impatiens balsamina under both 8- and 24-h photoperiods. The height also increases with all guanosine monophosphates (GMPs) under 8-h photoperiods but only with 5′-GMP under 24-h photoperiods. GA₃ as well as GMPs increase the number of leaves under 8-h but not under 24-h photoperiods. GA₃ as well as GMPs induce floral buds under strictly non-inductive photoperiods and increase the number of floral buds under 8-h photoperiods. The floral bud initiation occurs earlier when cGMP is used in combination with 100 mg/l GA₃.     

A gibberellin-regulated protein phosphorylated by a putative Ca2+-dependent protein kinase is G-protein mediated in rice root

The GA-signal transduction pathways downstream to the Gα protein in rice seedling root were investigated using in-gel kinase assay and in vitro protein phosphorylation techniques with a Gα protein defective mutant, d1. A 50-kDa protein kinase was detected downstream to Gα protein in the membrane fraction of rice seedling roots using an in-gel kinase assay with histone III-S as a substrate. The activity of a 50-kDa protein kinase increased in the wild-type rice by gibberellin (GA₃) treatment, but did not change in the d1 mutant. This protein kinase activity was inhibited by the Ca²⁺ chelator ethyleneglycol-bis-(beta-aminoethylether)-N,N,N ¹,N ¹-tetraacetic acid (EGTA), protein kinase inhibitors, staurosporine and H7, and calmodulin antagonist, trifluoperazine, suggesting that the 50-kDa protein kinase is a putative plant Ca²⁺-dependent protein kinase (CDPK). The activity of the 50-kDa putative CDPK reached its highest level at 3 h after GA₃ treatment and then gradually declined with time. In order to identify the endogenous substrate for 50-kDa putative CDPK, two-dimensional polyacrylamide gel electrophoresis followed by in vitro protein phosphorylation was carried out. The phosphorylation activity of an endogenous protein PP30, identified as an unknown protein having molecular weight 30 kDa and isoelectric point 5.8 was increased in the wild-type rice by GA₃ treatment, compared with the d1 mutant. The addition of GA₃ treated membrane fraction, which predominantly represent a 50-kDa putative CDPK further increased the phosphorylation of PP30. Almost similar to GA₃ treatment, phosphorylation activity of PP30 was also increased by the treatment with cholera toxin in the wild-type rice but not in d1 mutant. These results suggest that the 50-kDa putative CDPK and an unknown protein, PP30 promoted by GA₃ treatment are G-protein mediated in rice seedling roots.     

盐胁迫下赤霉素对黄瓜种子萌发及幼苗生长的影响

研究外源GA₃对盐胁迫下黄瓜种子萌发和幼苗生长的影响。结果表明,添加不同质量浓度GA₃的各处理,其发芽率、发芽势和发芽指数均显著高于NaCl胁迫处理,其中以100 mg/L GA₃处理的发芽势、发芽率和发芽指数最高,幼苗的叶面积、根长、根冠比也最大,同时叶片中叶绿素含量最高,幼苗叶片的光合速率(P_n)、气孔导度(G_s)、胞间CO₂摩尔分数(C_i)及蒸腾速率(T_r)等均达到最大;而当赤霉素的质量浓度为50 mg/L时,叶片中的POD活性为2 005 U/(g·min）,达最大值。     

外源GA3对紫斑牡丹幼苗叶片解剖结构与光合特性及内源激素含量的影响

以1年生紫斑牡丹幼苗为试验材料,采用不同浓度(0、100、300、500 mg/L)赤霉素(GA_3)喷施叶片处理,通过透射电镜、扫描电镜、光学显微镜观察幼苗叶片解剖结构,光合仪测定幼苗光合参数并以酶联免疫吸附法测叶片内源激素含量,探究外源GA_3对紫斑牡丹幼苗叶片解剖结构、光合特性和内源激素水平的影响。结果表明:(1)低浓度GA_3处理的紫斑牡丹叶肉细胞增大,栅栏组织外层细胞中叶绿体数量增加,高浓度GA_3处理则与之相反;GA_3处理叶片的栅栏组织/海绵组织比值(P/S)、组织结构紧密度(CTR)均下降,而其组织结构疏松度(SR)增加;GA_3处理的幼苗叶片的叶肉细胞内各叶绿体大小显著大于对照,随着GA_3处理浓度增加,紫斑牡丹叶肉细胞内叶绿体的体积趋于增大,类囊体垛叠凝聚逐渐松散,叶绿体上淀粉颗粒在300 mg/L GA_3处理中较明显;叶片气孔长度、宽度、气孔器大小、气孔开度和气孔密度随着GA_3浓度升高先升高后下降,同时叶片上表皮角质层厚度随GA_3浓度的升高而增加。(2)紫斑牡丹叶片净光合速率(P_n)、气孔导度(Cond)、蒸腾速率(T_r)、水分利用率(WUE)在100和300 mg/L GA_3处理下大都显著高于对照,且300 mg/L GA_3处理显著高于其余处理,而其在500 mg/L GA_3处理下显著低于对照。(3)紫斑牡丹叶片脱落酸(ABA)和吲哚乙酸(IAA)含量均在500 mg/L GA_3下显著高于对照,而在其余浓度处理下不同程度低于对照,叶片内源玉米素核苷(ZR)和GA_3含量均在300 mg/L GA_3处理下显著高于其余处理和对照,而其余处理相比对照均无显著变化;叶片的ZR/ABA、ZR/IAA、ZR/GA_3和(IAA+GA_3+ZR)/ABA比值都在300 mg/L GA_3处理下显著高于其他处理,叶片的IAA/ABA和ABA/GA_3比值均在500 mg/L GA_3处理下显著高于其他处理。研究发现,适宜浓度外源GA_3处理,能显著提高紫斑牡丹幼苗叶片光合速率、水分利用效率及蒸腾速率,调节植物体内源激素的含量及平衡,从而使叶片能合成较多有机物,促进幼苗生长。     

Exogenous GA3 Application Can Compensate the Morphogenetic Effects of the GA-Responsive Dwarfing Gene Rht12 in Bread Wheat

The most common dwarfing genes in wheat, Rht-B1b and Rht-D1b, classified as gibberellin-insensitive (GAI) dwarfing genes due to their reduced response to exogenous GA, have been verified as encoding negative regulators of gibberellin signaling. In contrast, the response of gibberellin-responsive (GAR) dwarfing genes, such as Rht12, to exogenous GA is still unclear and the role of them, if any, in GA biosynthesis or signaling is unknown. The responses of Rht12 to exogenous GA₃ were investigated on seedling vigour, spike phenological development, plant height and other agronomic traits, using F_2∶3 and F_3∶4 lines derived from a cross between Ningchun45 and Karcagi-12 in three experiments. The application of exogenous GA₃ significantly increased coleoptile length and seedling leaf 1 length and area. While there was no significant difference between the dwarf and the tall lines at the seedling stage in the responsiveness to GA₃, plant height was significantly increased, by 41 cm (53%) averaged across the three experiments, in the GA₃-treated Rht12 dwarf lines. Plant height of the tall lines was not affected significantly by GA₃ treatment (<10 cm increased). Plant biomass and seed size of the GA₃-treated dwarf lines was significantly increased compared with untreated dwarf plants while there was no such difference in the tall lines. GA₃-treated Rht12 dwarf plants with the dominant Vrn-B1 developed faster than untreated plants and reached double ridge stage 57 days, 11 days and 50 days earlier and finally flowered earlier by almost 7 days while the GA₃-treated tall lines flowering only 1–2 days earlier than the untreated tall lines. Thus, it is clear that exogenous GA₃ can break the masking effect of Rht12 on Vrn-B1 and also restore other characters of Rht12 to normal. It suggested that Rht12 mutants may be deficient in GA biosynthesis rather than in GA signal transduction like the GA-insensitive dwarfs.     

ABA and GA3 affect the growth and pigment composition in Andrographis paniculata Wall.ex Nees., an important folk herb

In this study, 5 μmol·L⁻¹ abscisic acid (ABA) and gibberellic acid (GA₃) were used to study the effect of both growth regulators on the morphological parameters and pigment composition of Andrographis paniculata. The growth regulators were applied by means of foliar spray during morning hours. ABA treatment inhibited the growth of the stem and internodal length when compared with control, whereas GA₃ treatment increased the plant height and internodal length. The total number of leaves per plant decreased in the ABA-treated plants, but GA₃ treatment increased the total number of leaves when compared with the control. Both growth regulators (ABA and GA₃) showed increased leaf area. ABA and GA₃ treatments slightly decreased the total root growth at all the stages of growth. The growth regulator treatments increased the whole plant fresh and dry weight at all stages of growth. ABA enhanced the fresh and dry weight to a larger extent when compared with GA₃. An increase in the total chlorophyll content was recorded in ABA and GA₃ treatments. The chlorophyll-a, chlorophyll-b, and carotenoids were increased by ABA and GA₃ treatments when compared with the control plants. The xanthophylls and anthocyanin content were increased with ABA and GA₃ treatments in A. paniculata plants.     

GA3 induced flowering in Podophyllum hexandrum Royle: A rare alpine medicinal herb

Podophyllum hexandrum Royle, an important alpine herb, is the source of highly valued podophyllotoxin. The effect of some plant growth substances (GA₃, BAP & ABA), uniconazole (an inhibitor of GA biosynthesis), and a combination of GA₃ and uniconazole were examined in respect to influence on sprouting in rhizomes of P. hexandrum and on induction of flowering at a lower altitude. Amongst the various chemicals tested, GA₃ had a marked effect resulting in uniform sprouting and also induced flowering in about half of the treated rhizomes. While BAP also promoted early sprouting, delayed sprouting was seen in rhizomes treated with ABA. Uniconazole treatment, either alone or with GA₃ was found to inhibit flowering and also resulted in reduced plant height. GA₃ treatment of rhizomes from plants that was maintained for up to 30 months at a lower altitude also induced flowering thus replacing the normal chilling requirement of plants. These results suggest that treatment of GA₃ could be effectively used for inducing uniform sprouting and flowering in rhizomes of P. hexandrum grown at lower altitudes.     

Growth Responses and Allocation of Assimilates of Rice Seedlings by Paclobutrazol and Gibberellin Treatment

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)methyl-4,4-dimethyl-2-(1h-1,2,4-trizol-1-yl)penten-3-ol] effectively decreased vegetative growth of rice (Oryza sativa L.) seedlings and increased the chlorophyll content. The number of veins in a leaf, the calculated number of stomata per leaf, and the length of guard cells were not altered by the paclobutrazol treatment, suggesting an effect on cell elongation. The allocation pattern of carbohydrates was changed by either gibberellin (GA) or paclobutrazol treatment. GA₃ induced more shoot growth and less accumulation of starch than the control and paclobutrazol-treated seedlings. Photosynthetic ability was not affected by either paclobutrazol or GA₃ treatment. Paclobutrazol-treated plants allocated a smaller amount of photosynthates for vegetative shoot growth and stored more as starch in the crowns than the control and GA₃-treated plants. The same starch degrading activity in the crown tissue of paclobutrazol-treated seedlings as in control plants suggests that the accumulated starch is utilized in a normal activity for growth including leaf emergence, tiller formation, and root production, resulting in improved seedling quality. Received May 30, 1996; accepted December 10, 1996     

Physiological characteristics and related gene expression of after‐ripening on seed dormancy release in rice

After‐ripening is a common method used for dormancy release in rice. In this study, the rice variety Jiucaiqing (Oryza sativa L. subsp. japonica) was used to determine dormancy release following different after‐ripening times (1, 2 and 3 months). Germination speed, germination percentage and seedling emergence increased with after‐ripening; more than 95% germination and 85% seedling emergence were observed following 1 month of after‐ripening within 10 days of imbibition, compared with <45% germination and 20% seedling emergence in freshly harvested seed. Hence, 3 months of after‐ripening could be considered a suitable treatment period for rice dormancy release. Dormancy release by after‐ripening is mainly correlated with a rapid decline in ABA content and increase in IAA content during imbibition. Subsequently, GA₁/ABA, GA₇/ABA, GA₁₂/ABA, GA₂₀/ABA and IAA/ABA ratios significantly increased, while GA₃/ABA, GA₄/ABA and GAs/IAA ratio significantly decreased in imbibed seeds following 3 months of after‐ripening, thereby altering α‐amylase activity during seed germination. Peak α‐amylase activity occurred at an earlier germination stage in after‐ripened seeds than in freshly harvested seeds. Expression of ABA, GA and IAA metabolism genes and dormancy‐related genes was regulated by after‐ripening time upon imbibition. Expression of OsCYP707A5, OsGA2ox1, OsGA2ox2, OsGA2ox3, OsILR1, OsGH3‐2, qLTG3‐1 and OsVP1 increased, while expression of Sdr4 decreased in imbibed seeds following 3 months of after‐ripening. Dormancy release through after‐ripening might be involved in weakening tissues covering the embryo via qLTG3‐1 and decreased ABA signalling and sensitivity via Sdr4 and OsVP1.     

Gibberellin structure-activity effects on flower initiation in mature trees and on shoot growth in mature and juvenile Prunus avium

When applied to spurs of mature Prunus avium before floral initiation, gibberellins GA₁, GA₄ and GA₃ inhibited floral initiation by 9–17%, GA₇ by 43%, GA₃ by 65–71% and 2,2-dimethyl GA₄ by 78%. GA₉ and GA₂₀ were inactive. Thus activity only of the GAs with a C-3 hydroxyl was increased markedly by a double bond in the C-1,2 or C-2,3 position, and activity increased with increasing hydroxylation. None of the GAs affected the total number of buds (vegetative and floral) surviving in the spur. Measured by the threshold dose required for activity, seedling shoot growth responses to GA₃, GA₇, GA₁ or GA₄ resembled those of floral initiation, but di-methylation of GA₄ at C-2 had no effect, and GA₉ was as active as GA₇. Mature shoots, including those on rooted cuttings, were less responsive to GA treatment than were juvenile shoots, with terminal shoots on mature trees more responsive than spur shoots. Spur shoot growth on mature trees responded to GA₃ and to a lesser extent GA₇, but not to GA₁ or GA₄. However, all these GAs promoted the growth of terminal shoots on mature trees to similar extents, whereas 2,2-dimethyl GA₄ was less active than GA₄ The differences between juvenile and mature shoot growth in sensitivity to a C-1,2 or C-2,3 double bond, and between mature shoot growth and floral initiation in GA-structure requirements, indicate that phase change alters the GA complement and/or GA receptor/transduction mechanisms of P. avium. The difference in sensitivity to 2,2-dimethyl GA₄ indicates that floral initiation and growth have different requirements for GA transport and/or action.     

Changing root and shoot architecture with the rolA gene from Agrobacterium rhizogenes: Interactions with gibberellic acid and polyamine metabolism

The effects of rolA on root and shoot architecture have been ascribed to a deficiency in gibberellic acid (GA₃) and to changes in polyamine metabolism. Using tobacco, we examined interactions among GA₃, a polyamine accumulation inhibitor (α-DL-difluoromethylornithine or DFMO) and the rolA gene controlled by the 35S CaMV promoter. We measured the effects of these three agents on architecture and polyamine accumulation in excised roots and whole plants grown in vitro. Previous work showed that DFMO or genetic transformation with the rolA gene from Agrobacterium rhizogenes, controlled by the 35S promoter (P_35S-rolA), caused excised tobacco roots to grow faster with altered root system architecture. We show that gibberellic acid (GA₃) reversed the effects of DFMO on the architecture of excised root systems, but neither reversed the effects of DFMO on growth, nor the changes in growth and architecture associated with P_35S-rolA. GA₃ treatment alone resulted in increased agmatine levels, suggesting that the inhibition of the effects of DFMO on architecture was through a stimulation of the arginine decarboxylase (ADC) pathway, GA₃ alone also inhibited the accumulation of putrescine and tyramine conjugates in excised roots. In tobacco plants growing in vitro DFMO and P_35S-rolA were associated with reduced shoot height, which was partially restored by GA₃ treatment; however, GA₃ also stimulated shoot height in the controls. GA₃ did not lessen the leaf wrinkling associated with P_35S-rolA. P_35S-rolA increased root number in young seedlings in vitro, and increased root system length in seedlings grown in soil. As in excised roots, the developmental changes linked to DFMO and P_35S-rolA were accompanied by reductions in putrescine titers. GA₃ treatment stimulated putrescine accumulation in stems and leaves, and partially reversed the negative effects of DFMO and P_35S-rolA on putrescine accumulation in roots, stems and leaves. Again, the restoration of putrescine pools appeared to be through a stimulation of the ADC pathway, since agmatine accumulated in plants exposed to GA₃. In general, the effects of DFMO and P_35S-rolA on phenotype and polyamine metabolism were coordinated, and in many cases these effects were similarly modulated by GA₃, reinforcing the previous conclusion that the phenotypic effects of rolA in roots and shoots occur through interference with polyamine metabolism and that the putrescine conjugates are particularly important in regulating root system growth and architecture. We were unable, however, to discem consistent evidence for a direct role for GA₃ in establishing the RolA phenotype.     

Micronucleus frequency and lipid peroxidation in <Emphasis Type="Italic">Allium sativum</Emphasis> root tip cells treated with gibberellic acid and cadmium

Gibberellic acid (GA₃) is a very potent hormone whose natural occurrence in plants controls their development. Cadmium is a particularly dangerous pollutant due to its high toxicity and great solubility in water. In this study, the effect of GA₃ on Allium sativum root tip cells was investigated in the presence of cadmium. A. sativum root tip cells were exposed to CdNO₃ (50, 100, 200 μM), GA₃ (10-3 M), both CdNO₃ and GA₃. Cytogenetic analyses were performed as micronucleus (MN) assay and mitotic index (MI). Lipid peroxidation analysis was also performed in A. sativum root tip cells for determination of membrane damage. MN exhibited a dose-dependent increase in Cd treatments in A. sativum. GA₃ significantly reduced the effect of Cd on the MN frequency. MN was observed in GA₃ and GA₃ + 50 μm Cd treatments at very low frequency. MI slightly decreased in GA₃ and GA₃ + Cd treatments. MI decreased more in high concentrations of Cd than combined GA₃ + Cd treatments. The high concentrations of cadmium induce MN, lipid peroxidation and lead to genotoxicity in A. sativum. Current work reveals that the effect of Cd on genotoxicity can be partially restored with GA₃ application.     

Differential effects of camptothecin and interactions with plant hormones on seed germination and seedling growth

Effects of camptothecin, a naturally occurring alkaloid, on seed germination varied from promotive to inhibitory, depending on the species used. It markedly inhibited seedling root growth but its inhibition of hypocotyl growth varied among species. Camptothecin inhibited GA₃-induced dark germination of lettuce (Lactuca sativa L.) seeds and hypocotyl elongation of seedlings. In contrast to ABA, the camptothecin inhibition of GA₃-induced germination could not be overcome by cytokinin. When seeds were germinated at 29C with a 0.5 h light treatment, little or no germination occurred in the camptothecin treatment, but addition of cytokinin overcame this inhibition.     

Biological activity of some synthetic gibberellin glucosyl esters

Four gibberellin (GA₁, GA₃, GA₄ and GA₃₇) glucosyl esters were synthesized and found to be as active as their respective free acids in the rice seedling bioassay. The rapid hydrolysis of the glucosyl esters in rice seedlings was demonstrated by feeding experiments with glucosyl esters of [³H]GA₁ and [³H]GA₄.     

GA3浸种处理对五种晚花杜鹃种子萌发的影响

晚花杜鹃(late flower Rhododendron)是一类花期较晚的杜鹃品种,具有较高的观赏价值,被广泛应用于庭院种植和园林绿化。随着旅游以及经济发展的需要,开发和利用晚花杜鹃资源显得非常迫切。自然条件下晚花杜鹃萌发率相对较低,因此为提高晚花杜鹃萌发率,探究不同浓度赤霉素(GA_3)处理对五种杜鹃种子萌发的影响,该文以五种晚花杜鹃(小白杜鹃、大白杜鹃、桃叶杜鹃、长蕊杜鹃和九龙山杜鹃)为实验材料,通过不同浓度(0、300、400、500、600、700 mg·L~(-1))的GA_3对五种晚花杜鹃种子进行24 h浸种处理,测定其发芽指数、发芽势、发芽率以及成苗率等指标,分别确定五种杜鹃种子萌发的最适GA_3浓度,并对相同处理下五种杜鹃种子的萌发率和成苗率进行比较。结果表明:(1) GA_3浸种对五种晚花杜鹃种子萌发具有促进作用,在适当GA_3浓度下五种杜鹃种子的发芽指数、发芽势和发芽率均显著高于对照组,萌发时滞、萌发高峰期和持续萌发时间均较对照组浓度相对缩短。(2)大白杜鹃、桃叶杜鹃和九龙山杜鹃种子在GA_3浓度为600 mg·L~(-1)处理时各项萌发指标相对较好;长蕊杜鹃以GA_3浓度为700 mg·L~(-1)浸种处理萌发效果相对较好;小白杜鹃以GA_3浓度为400和700 mg·L~(-1)处理最好。因此,在杜鹃的栽培中,可以采用赤霉素GA_3处理法提高种子发芽率,缩短萌发时间。     

植物激素和接种方式对广西金线莲壮苗生根的影响

该文以广西野生金线莲无菌播种离体茎段为材料,采用单因素对比试验,研究了植物激素(NAA、IBA、6-BA、GA_3、KT、ZT、TDZ、2-IP)以及接种方式(竖直接种和水平接种)对壮苗生根培养的影响。结果表明:与对照相比,生长素有利于壮苗生根,NAA的效果优于IBA;细胞分裂素对壮苗生根的效果依次为6-BATDZKT=ZT 2-IPCK,其中6-BA诱导平均株高8.4 cm,3.6条根,茎粗为2.84 mm,植株生长健壮,诱导效果最好;赤霉素GA_3诱导出的植株高且直,但植株细弱,且抑制根系生长,不利于壮苗生根培养;在激素组合6-BA 0.5 mg·L~(-1)、NAA1.0 mg·L~(-1)处理中,组培苗生长健壮且根数量较多,效果最佳;水平接种能诱导出更多的根系,且便于接种操作,可以节省接种时间。因此,确定广西金线莲最适宜的壮苗生根培养基配方为1/2MS+6-BA 0.5 mg·L~(-1)+NAA 1.0 mg·L~(-1)+香蕉汁100 g·L~(-1)+AC(活性炭) 1.0 g·L~(-1)+蔗糖20 g·L~(-1),最佳接种方式为水平接种。     

Non-Reversibility of Gibberellin-Induced Inhibition of Regeneration in Begonia Leaves

With applied to the petioles of detached Begonia x cheimantha leaves before planting, Gibberellic acid (GA₃) inhibited the formation of adventitious buds and roots ill an apparently irreversible manner. Bud formation was entirely suppressed by 10^?6M and higher concentrations and a significant inhibition was still present at 10^?9M the lowest concentration tested. Root formation was not affected by GA₃ below 10^?7M and was possible even at 10^?4 M GA₃. Petiole elongation was stimulated by GA₃ with an optimum at 10^?5M. GA₃ also blocked the action of 6-benzyiamino-purine (BAP) and 1-naphthaleneacetic acid (NAA), compounds which are potent stimulators of bud and root formation, respectively. When applied simultaneously with GA₃ they were, at their optimal concentrations, devoid of any effect in counteracting or reversing the gibberellin-induced inhibitions. Abscisic acid and the growth retardants CCC and Phosfon also were unable to restore bud and root formation. In leaves initially treated with water or 10^?5M BAP, endogenous bud and root formation as well as BAP-induced bud formation were entirety suppressed when 10^?5M GA₃ was applied 8 days after the initial treatments. Even when delayed for 14 days GA₃ treatment inhibited BAP-induced bud formation, while treatment after 21 days bad little effect on bud and root formation. Development of pre-existing, visible bud primordia was not inhibited by GA₃. BAP and NAA competitively inhibited the action of GA₃ in petiole extension growth. The results are discussed in relation to results obtained in other plant systems. It is suggested that GA₃ acts by blocking of the organized cell divisions initiating the formation of bud and root primordia.