The Role of Glucose on Flower Bud Formation in Thin-Layer Tissue 12Nicotiana tabacum L.

The effect of glucose on flower bud formation was studied inthin-layer tissue cultures of epidermal strips from flower stalksof Nicotiana tabacum L. cv. Samsun. A minimum concentration of 30 mol m^–3 glucose in the MS-mediumcontaining 1.0 mmol m^–3 of both NAA and BA was necessaryfor flower bud formation. With 150 mol m^–3 glucose a minimumstay of 10 d was required for optimal flower bud formation. Withholding glucose for a limited period at different time intervalsafter the onset of culture caused a delay in flower bud formationand did not affect previous development on glucose. The resultsindicated that competence for flower bud initiation is not restrictedto the early stage of culture. The process may start at anytime later at the appropriate glucose concentration. However,for both optimal initiation and further development of flowerbuds the presence of a metabolizable sugar is required. Incubationof the tissue on glucose is associated with higher respirationrate. Key words: Flower formation, Glucose, mannitol, Nicotiana tabacum, Respiration, tissue culture     

Tissue 11In vitro Bud Formation on Explants from the Inflorescence of Nicotiana tabacum L.

Croes, A. F., Creemers-Molenaar, T., van den Ende, G., Kemp,A. and Barendse, G. W. M. 1985. Tissue age as an endogenousfactor controlling in vitro bud formation on explants from theinflorescence of Nicotiana tabacum L.—J. exp. Bot. 36:1771–1779. The in vitro formation of generative buds was studied on explantsfrom flower and fruit stalks and from internodes of the floralramifications of tobacco. A floral gradient was found to existalong the axis of the branch. The gradient concerns the numberof flower buds formed in vitro and is present in both typesof tissues. The number of flower buds is greater on tissuesfrom the apical than from the basal portion of the branch. Thecapacity to generate these buds is largely determined by tissueage at the moment of the excision. Consequently, the gradientmoves along the axis during the outgrowth of the inflorescence. The alternative possibility that some apex-derived stimuluspredetermines the morphogenetic capacity of the tissue priorto excision is excluded by the observation that the gradientremains virtually unaltered if the apex is removed one weekbefore the onset of culturing. Auxin affects the floral gradient Increasing the auxin concentrationin internode tissue culture causes a steeper gradient of flowerbud generation by almost completely abolishing bud formationon older tissues. Key words: Auxin, flower buds, gradient, tissue culture, tobacco     

Experimentally Synthesized Plant Chimeras I. In vitro Recovery of Nicotiana tabacum L. Chimeras from Mixed Callus Cultures

Experiments were conducted to develop techniques for synthesizingchimeras between plants of known genotype by utilizing in vitrotechniques Chimeral calli composed of green and albino tobaccocells were obtained by initiating callus tissue from mixturesof albino and green cotyledons, hypocotyls, callus culturesand cell suspensions The most effective mixing of genotypesoccurred when callus was derived from mixed filtered cell suspensionsUpon shoot regeneration, chimeral calli yielded 1317 non-chimeraland four chimeral plants Chimeras may have arisen as a resultof experimental procedures or possibly from spontaneous chromosomalabnormalities since leaves of some albino control plants occasionallyproduced small green islands of cells Explanations for the recoveryof a high percentage of non-chimeral shoots are presented Tobacco, callus cultures, cell suspensions, tissue culture, shoot apical meristems, somatic-crossing over     

硝酸银对离体培养烟草叶片愈伤组织形成和芽再生及其脯氨酸和丙二醛含量的影响(简报)

培养基中添加不同浓度硝酸银离体培养烟草叶片的结果表明,1～5mg·L-1硝酸银可提高烟草愈伤组织的芽分化率,5 mg·L-1硝酸银对芽再生的促进作用最佳,而高于10mg·L-1的硝酸银抑制愈伤组织的形成和芽再生.在愈伤组织和再生芽中,脯氨酸和丙二醛含量均随硝酸银浓度的增加而增加.     

Steryl Glycoside Formation in Seedlings of Nicotiana tabacum L

Particulate enzyme preparations from tobacco seedlings (Nicotiana tabacum L.) were used in the synthesis of steryl glycoside. The data obtained by measuring cholesterol-4-¹⁴C incorporation generally agree with results obtained with UDP-glucose-¹⁴C. The in vitro reaction was linear for the first 10 minutes and had a pH optimum of 7.0 to 7.4. Addition of ATP activated while UDP-glucose inhibited slightly the reaction. In short term experiments, the percentage disappearance of endogenous and added sterol was about the same.     

Role of Ethylene in Abscisic Acid-induced Callus Formation in Citrus Bud Cultures

The induction of callus formation in cultured buds of Shamouti orange (Citrus sinensis [L.] Osbeck) by abscisic acid (ABA) is a multiphasic process. (Altman, and Goren 1974 Physiol Plant 32: 55.) A study of the mediation by ethylene on this effect of ABA was undertaken. It was found that: (a) ethylene and (2-chloroethyl) phosphonic acid, as well as ABA, induced callus formation; (b) callus induction is best attained when explants are exposed to ethylene during the 1st day after excision; and (c) ABA-induced callus formation is inhibited by rhizobitoxine analog, an inhibitor of ethylene biosynthesis. It is concluded that the effect of ABA on callus formation is mediated via ethylene.     

Rapid flowering Nicotiana tabacum L.

 Selected Nicotiana tabacum Tobacco Introductions from the Nicotiana Germplasm Collection were crossed, back-crossed, and then selfed. When compared to parents, the new genotypes produce smaller plants with a shortened life-cycle that go from seed to seed in under 11 weeks. Received: 11 December 1998 / Revision accepted: 8 January 1999     

Sperm dimorphism in Nicotiana tabacum L.

Sperm cells of tobacco have been intensively studied as examples of isomorphic gametes in which major cellular and organellar parameters remain statistically indistinguishable in the two sperm cells. An examination of sperm cells late in maturation, however, displays that the sperm cell associated with the vegetative nucleus becomes statistically significantly smaller than the other sperm cell in tobacco. If late divergence occurs in the two sperms of other angiosperms, sperm dimorphism may be more prevalent than has previously been assumed and dimorphism may have a major influence on the pattern of double fertilization. Received: 15 December 2000 / Accepted: 4 May 2001     

Tryptophan Biosynthesis in Cell Cultures of Nicotiana tabacum

Some of the general features of the pathway for l-tryptophan biosynthesis in cell cultures of Nicotiana tabccum var. Wisc. 38 have been investigated. The results of both isotope competition and direct-labeling experiments show that shikimic acid, anthranilic acid, indoleglycerol phosphate, and indole can serve as precursors to l-tryptophan in these cells, indicating that, in terms of its biochemical intermediates, the pathway is similar to that described for the bacteria and fungi.     

Feruloylputrescine and Caffeoylputrescine Are Not Involved in Growth and Floral Bud Formation of Stem Explants from Nicotiana tabacum L. var Xanthi nc

The role of feruloylputrescine (FP) and of caffeoylputrescine (CP) was investigated in an explant system of stem explants from day-neutral Nicotiana tabacum L. var Xanthi nc. Previously, a correlation between cortical callus formation and increase in FP content, as well as between in vitro flower formation and increase in CP content had been shown. During the explant growth in vitro, the increase of both FP and CP was inhibited by 4-fluor-(1-amino-2-phenylethyl)phosphonic acid and 2-amino-indene-2-phosphonic acid, both inhibitors of phenylalanine ammonia-lyase (EC 4.3.1.5). dl-α-difluoromethylarginine, an inhibitor of arginine decarboxylase (ADC, EC 4.1.1.19), prevented only the increase in FP, while dl-α-difluoromethylornithine, an inhibitor of ornithine decarboxylase (EC 4.1.1.17), reduced only that of CP. Increase in dry weight and the formation of cortical callus and of floral buds of explants were not affected by any of the inhibitors. We conclude, in contrast to earlier hypotheses, that FP and CP do not trigger growth and differentiation in the explants. It seems more likely that FP and CP increase in response to auxin and cytokinin in the media.     

Amino-acid-transport mutant of Nicotiana tabacum L.

The structure of spinach ribulose 1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) has been investigated by tilted-view electron microscopy of negatively stained monolayer crystals and image processing. The structure determined consists of a cylinder of octagonal cross-section with a large central hole. Based on this and other available evidence a model for the arrangement of the large and small subunits is suggested with the eight small subunits arranged equatorially around the core of eight large subunits.Abbreviations LS large subunit - Rubisco ribulose 1,5-bisphosphate carboxylase/oxygenase - SS small subunit     

Anther cultures of Nicotiana tabacum L. mutants

Summary The theoretically expected and experimentally observed phenotypic ratios have been compared in populations of haploids derived from chlorophyll mutants of Nicotiana tabacum L. with a known genotypic constitution. The frequencies of mutant genotypes were significantly lower than the expected values, proving the existence of selection in a system of haploid embryoids developing in the anther.The anthers from M₁ plants of a diploidized Nicotiana tabacum haploid cv. Samsun, treated with various concentrations of N-nitroso-N-methylurea and n-butylmethane sulphonate, were cultivated in vitro. The number of anthers which gave rise to haploids (embryogenic anthers) was stimulated by lower concentrations of both the mutagens. The stimulation at the level of M₁ sporophyte is explained by internal genetic heterogeneity induced by adequate mutagen concentration. The average number of haploids per embryogenic anther decreased in all the treatments. The frequency of haploid plants of the mutant phenotypes increased with increasing mutagen concentration.     

Variation of Alkaloid Production in Nicotiana rustica Callus Cultures

Callus cultures have been established from the seed, root and leaf of Nicotiana rustica L. var. brasilia in a synthetic medium containing 1 μM 2,4-D and μM kinetin. These callus tissues behaved similarly not only in growth and organogenesis but also in nicotine production. The nicotine contents of callus cultures, which were in the order of 0.25–0.58% of dry weight during a few passages subsequent to callus induction, rapidly decreased to trace amounts in succeeding subcultures in association with the decline of the root-regenerating activity. On the other hand, free cells prepared from a callus tissue in the third passage developed into individual clones showing wide differences in growth and nicotine production. One of these clones gave rise to a relatively stable strain which is capable of producing nicotine at a high rate (0.29% of dry weight) in the absence of organization. The significance of these findings is discussed in connection with some results which have been reported for other callus cultures of Nicotiana species.     

Biological effects of ion beams in Nicotiana tabacum L.

The biological effects of ion beams on Nicotiana tabacum L., particularly the induction of chromosome aberrations, were investigated. Dry seeds were exposed to ¹²C⁵⁺, ⁴He²⁺ and ¹H⁺ beams with linear energy transfer (LET) ranging from 1 to 111 keV/μm and irradiated with gamma-rays. Ion beams were more effective in reducing germination and survival of the seeds than gamma-rays. The LD₅₀ for ¹²C⁵⁺ beams, ⁴He²⁺ beams and gamma-rays were 35, 60 and 500 Gy, respectively. The frequencies of mitotic cells with chromosome aberrations, such as chromosome bridges, acentric fragments and lagging chromosomes in the root tip cells of the exposed seeds, increased linearly with increasing doses. Relative biological effectiveness (RBE) values, based on the doses that induced a survival inhibition of 50% and a 10% frequency of aberrant cells, were 14.3–17.5 for the ¹²C⁵⁺ beams, 7.0–8.3 for the ⁴He²⁺ beams and 7.8 for the ¹H⁺ beams. Furthermore, the relative ratios of the chromosome aberration types were significantly different between the ion beam and the gamma-ray regimes: chromosome fragments were more frequent in the former, and chromosome bridges in the latter. Based on these results, we concluded that the repair process of initial lesions induced by ion beams may be different from that induced by low- LET radiation. Received: 29 October 1998 / Accepted in revised form: 25 March 1999     

Developmental physiology of floral initiation in Nicotiana tabacum L.

The central process in the making of a multicellular organismis the fating of cells and tissues for their terminal phenotypes.The formation of a flower from a shoot apical meristem completesa sequence of fating processes initiated in embryogenesis. Thefating of a vegetative meristem of Nicotiana tabacum L. to initiatea flower involves at least two signals and two developmentalstates. A signal from the roots maintains vegetative growth,or prevents flowering, in the young seedling. As the plant grows,the vegetative meristem gains greater competence to respondto the floral stimulus from the leaves until it is evoked, byfloral stimulus, into a florally determined state. The florallydetermined state is then expressed. These developmental processesnot only establish the time of floral initiation, but also regulateplant size as measured by the number of nodes produced. Key words: Plant size, floral stimulus, competence, floral determination, induction     

Embryoid Formation in Pollen Grains of Nicotiana tabacum

Anthers of Nicotiana tabacum (n = 24) were cultured on nutrientagar and examined at intervals for pollen embryoids. Embryoidswere formed in anthers of varying developmental stage, the youngestof which coincided with the liberation of free microspores fromtetrads, and the oldest with the formation of bicellular grains.This period in the development of the anther occupied 4–5days. Older anthers within this range were more successful thanyounger anthers. The first mitosis of the pollen was typicallyasymmetric and resulted in the formation of unequal generativeand vegetative cells. Some of the grains then went into a lagphase for at least 5–6 days, after which the mitotic conditionwas restored. Embryoids were formed by repeated division ofthe vegetative cell. If the generative cell divided, it didso only once or twice. Occasionally the first mitosis was symmetricand gave rise to equal cells, and in these instances both cellsprobably participated in embryoid formation. The youngest anthersexamined were probably less successful because fewer grainssurvived to enter mitosis. The number of embryoids produced varied considerably from oneanther to another both within the same bud and between differentbuds: values ranging from less than 400 to 10 000 per antherwere encountered. Most of these degenerated after the firstfew divisions, partly because they burst prematurely from thepollen grain wall. Embryoids which continued to develop formedplantlets and/or callus. The largest number of plantlets obtainedfrom one anther was 32. Haploid plantlets were also regeneratedfrom callus by transferring it to a low-sugar medium withoutauxin. The behaviour of grains not forming embryoids was also noted.