Cotyledon Expansion as a Bioassay for Cytokinins

Esashi, Yohji; Leopold, A. C.

doi:10.1104/pp.44.4.618

Cited by 31 publications

(12 citation statements)

References 10 publications

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“…As with TU, BA was effective in stimulating the extension growth in both the axial and cotyledonary segments, in conjunction with an increased C2H4 production regardless of their dormancy status (Table III). The BA stimulation of growth was particularly profound in the cotyledons, such a BA-stimulated cotyledon expansion having been reported previously by Esashi and Leopold (9). Also, the BA-stimulated C2H4 production was previously reported (1).…”

Section: Resultssupporting

confidence: 74%

Dormancy and Impotency of Cocklebur Seeds

1977

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Germination of nondormant but impotent small cocklebur seeds (Xanthium pennsylvanicum Walr.) was promoted profoundly with thiourea or benzyladenine, and slightly with gibbereUlic acid. GibbereUic acid was ineffective in causing the germination of dormant cocklebur seeds, although thiourea and benzyladenine were effective. Experiments with excised seed pieces showed that the promotive effects of thiourea, benzyladenine, and gibbereUlic acid on cocklebur seed germination were associated with the enhancement of growth of seed parts; thiourea stimulated predominantly the axial growth, whereas benzyladenine stimulated predominantly the cotyledonary growth.Potassium nitrate or indoleacetic acid had little effect on the initial growth of either axes or cotyledons. Except for gibberellic acid, all of the compounds employed enhanced ethylene production, but in general, the ethylene production seemed more likely to be a consequence of growth rather than a cause of it. We conduded that the chemical regulation of seed germination may be a consequence of the alteration of growth capabilities in either the axes or cotyledons, or both.In a previous paper (10), we observed that cocklebur seeds respond in different manners to various germination stimulators: seeds treated with TU' or CO2 exhibited normal germination, but 02 enrichment caused germination in which the seed coat was mostly broken at the cotyledonary side rather than at the axial end. On the other hand, the seeds germinated with BA, C2H4, and GA3 exhibited an intermediate pattern in which approximately half of the germinations were normal. Granting that seed germination in dicot plants is a phenomenon occurring when the axis and the cotyledons generate enough thrust to overcome the restraint by the seed coat (8), these diverse response patterns might result from the differential growth responsiveness of the axis and cotyledon: for example, TU could preferentially enhance growth of the embryonic axis proper, whereas BA could more greatly enhance growth of the cotyledons and hence the abnormal lateral breaking of the seed coat. We have previously presented some evidence that C2H4, unlike CO2, strongly stimulates both the axial and cotyledonary growth (7).These findings caused us to examine the relative effectiveness of various known germination stimulators (15), such as TU, KNO3, BA, GA3, and IAA, in stimulating the growth of axial and cotyledonary seed pieces. Experiments were also directed toward a comparison between the dormant and nondormant seeds in response to these stimulators.' Abbreviation: TU: thiourea. MATERIALS AND METHODSSeeds of cocklebur (Xanthium pennsylvanicum Wallr.) were used in this experiment. For germination tests, dormant small seeds newly harvested in 1973, and the nondormant but impotent small seeds fully after-ripened since 1972 were exposed to various drugs on two filter paper discs in 5-cm Petri dishes with 2 ml water. For growth tests, the embryonic axis and cotyledon segments were excised from large seeds according to the procedur...

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Section: Resultssupporting

confidence: 74%

Dormancy and Impotency of Cocklebur Seeds

1977

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“…Benzyladenine (BA) Cytokinins promote the expansion of cotyledons in several plant species (7,17,19). The effect on growth is associated, at least in some cases, with an accelerated mobilization of starch reserves (1, 9, 10).…”

Section: Introductionmentioning

confidence: 99%

Effect of Benzyladenine on Some Enzymes of Mitochondria and Microbodies in Excised Sunflower Cotyledons

Servettaz¹,

Cortesi²,

Longo³

1976

Plant Physiol.

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Benzyladenine (BA) Cytokinins promote the expansion of cotyledons in several plant species (7,17,19). The effect on growth is associated, at least in some cases, with an accelerated mobilization of starch reserves (1, 9, 10). We have recently observed that BA also accelerates the disappearance of reserve fat in excised sunflower cotyledons (O. Servettaz and C. P. Longo, unpublished data). Since mitochondria and glyoxysomes collaborate in the utilization of fat reserves during germination, we have investigated whether the treatment with BA raises the level of some representative glyoxysomal and mitochondrial enzymes. Our results show that BA stimulates the development of several enzymes of mitochondria and microbodies and that its effect on microbody enzymes is very similar to that of white light. MATERIALS AND METHODSSunflower (Helianthus annuus L.) seeds of the oil-rich Rumanian strain H.S. 52 were selected for uniform size. After removal of the seed coat, the embryos were soaked for 24 hr between two layers of moist filter paper at 27 C in the dark. The cotyledons were then excised from the embryonic axis and cultured in darkness at 27 C in Petri dishes on two discs of filter paper saturated with distilled H20 or with a 0.1 mm BA solution. The time of excision of the cotyledons was taken as day zero. The cotyledons increased in fresh weight for at least 6 days after excision. No signs of contamination with bacteria or fungi were detected during this time span.

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“…In light-sensitive lettuce seeds, cytokinins increase the growth rate of cotyledons (5), while red light primarily enhances elongation of radicle cells (20). Cotyledons from numerous other dicots also grow faster in the presence of exogenous cytokinins (2,4,9,10,16,19), and this phenomenon has been developed as a cytokinin bioassay by Esashi and Leopold (2), Letham (9,10), and Narain and Laloraya (16 ing wall plasticity, while red light-enhanced lettuce seed germination seems to arise from an osmotic effect due to more rapid degradation of some macromolecule (15). We are not aware of data indicating that either red light or cytokinins increase wall plasticity, and our studies were to determine whether increased cell expansion (10) of excised radish cotyledons by cytokinins could be due to water uptake resulting from osmotic effects of enhanced solute accumulation.…”

mentioning

confidence: 99%

mentioning

confidence: 99%

Promotion of Radish Cotyledon Enlargement and Reducing Sugar Content by Zeatin and Red Light

Huff¹,

Ross²

1975

Plant Physiol.

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Effects of zeatin on amino acid and sugar contents of detached radish (Raphanus saivus L) cotyledons were investigated to determine if accumulation of these solutes contributes to cytokinin-enhanced growth. Protein (14,18,21), and certain portions of grass leaves expand faster after treatment with either of these stimuli, as evidenced by leaf unrolling (11,23). In light-sensitive lettuce seeds, cytokinins increase the growth rate of cotyledons (5), while red light primarily enhances elongation of radicle cells (20). Cotyledons from numerous other dicots also grow faster in the presence of exogenous cytokinins (2,4,9,10,16,19), and this phenomenon has been developed as a cytokinin bioassay by Esashi and Leopold (2), Letham (9,10), and Narain and Laloraya (16). ing wall plasticity, while red light-enhanced lettuce seed germination seems to arise from an osmotic effect due to more rapid degradation of some macromolecule (15). We are not aware of data indicating that either red light or cytokinins increase wall plasticity, and our studies were to determine whether increased cell expansion (10) of excised radish cotyledons by cytokinins could be due to water uptake resulting from osmotic effects of enhanced solute accumulation. We found that both cytokinins (in the presence of light) and red light increased the reducing sugar contents of the cotyledons, and these increases were highly correlated with cotyledon growth. MATRIAILS AND METHODSRadish seeds (Raphanus sativus L. var. Early Scarlet Globe) were surface sterilized with 10% (v/v) Clorox and, after thoroughly rinsing, were germinated in darkness for 48 hr on wet paper. The smaller cotyledon cut from each selected seedling was used in all studies. Usually five cotyledons (20-35 mg fresh weight) were randomly selected for each sample, blotted gently, weighed as a group, and placed adaxial side down on Whatman No. 1 filter paper covering the bottom of a 5.5-cm Petri dish. The filter paper was previously wetted with 1 ml of 2 mm potassium phosphate buffer (pH 6.4) containing designated additives. The Petri dishes were placed on wet paper towels in glass trays covered with clear plastic film, and cotyledons were incubated at 25 C. The trays were also covered with aluminum foil for incubation in darkness. After incubation, cotyledons were blotted and reweighed.Immediately after obtaining final weights, cotyledons in each sample to be analyzed for protein and amino acids were placed in 10 ml of hot 80% (v/v) ethanol and boiled until volumes were reduced to about 2 ml. An additional 10 ml of 80% ethanol was then added, and samples were homogenized with a Brinkmann Polytron and centrifuged for 15 min at 17,300g at 4 C. Supernatant volumes were adjusted to 20 ml, and a-amino nitrogen was determined on 1-ml aliquots, as described by Yemm and Cocking (24), using glutamine as a standard. Residues from centrifugation were prepared for protein analysis by twice dissolving in 0.1 N KOH and precipitating with 10% (w/v) trichloroacetic acid. The final precipitates were...

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Cotyledon Expansion as a Bioassay for Cytokinins

Cited by 31 publications

References 10 publications

Dormancy and Impotency of Cocklebur Seeds

Dormancy and Impotency of Cocklebur Seeds

Effect of Benzyladenine on Some Enzymes of Mitochondria and Microbodies in Excised Sunflower Cotyledons

Promotion of Radish Cotyledon Enlargement and Reducing Sugar Content by Zeatin and Red Light

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