A model of seed dormancy

Amen, Ralph D.

doi:10.1007/bf02858619

Cited by 241 publications

(92 citation statements)

References 80 publications

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“…When the endosperm is surgically removed or punctured, germination is promoted [4] [5] [6] [7] suggesting that the endosperm acts as a mechanical restraint [8] [9]. Light microscopy studies on lettuce have observed that the endosperm surrounding the radicle tip undergoes structural changes prior to rupture [10] [11] [12] [13].…”

Section: Introductionmentioning

confidence: 99%

Carboxymethylcellulase Activity in Lettuce Seeds Prior to Germination

Pavlišta¹

2017

AJPS

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Does the endosperm pose a mechanical resistance on embryonic axis (radicle) growth for lettuce seed (achene) germination? To aid answering this question, the cell wall degrading enzyme, carboxymethylcellulase (CMCase) was extracted and assayed from lettuce seeds imbibed for 0 to 12 h, prior to germination. Measuring the loss of viscosity of carboxymethylcellulose, CMCase activity was high in dry seeds, low after 6 h of imbibition, high after 9 and 10 h, and then reduced again after 12 h. Fractions from Sephadex columns showed CMCase activity in three peaks labeled E1, E2, E3. The greatest change in CMCase activity during imbibition was with E3 (molecular weight of about 40,000 Daltons) and some reduction in E2 (molecular weight about 280,000). The RNA synthesis inhibitor, 6-methyl purine, eliminated CMCase activity when present from 4.5 to 7 h of imbibition and the protein synthesis inhibitor, cycloheximide, eliminated CMCase activity when present between 5.5 and 9 h. Imbibition in darkness lowered CMCase activity while 15 min of light at 3.5 h restored it and 30 min of far-red light at 3 h eliminated it. Increasing the imbibition temperature to 35˚C under light reduced activity while under darkness, activity was eliminated under 24˚C and 35˚C. CMCase activity was localized in the endosperm surrounding the embryonic axis (micropylar end) of 9 h imbibed seeds. These observations showed that CMCase was active in degrading the cell wall in the endosperm surrounding the radicle, weakening it, prior to radicle protrusion so that the radicle remains undamaged.

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Section: Introductionmentioning

confidence: 99%

Carboxymethylcellulase Activity in Lettuce Seeds Prior to Germination

Pavlišta¹

2017

AJPS

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“…In isolated aleurone layers of barley and wild oat, gibberellins stimulate synthesis of amylases (12,15,14,11) and protease (9). It has been stated that gibberellic acid promotes seed germination by enhancement of hydrolase synthesis (1,8). However, when the time course of amylase development was followed in the whole grains, it was found that the increase of amylase activity occurred 1 or 2 days after root protrusion, an accepted criterion for seed germination.…”

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confidence: 99%

Respiration and Protein Synthesis in Dormant and After-ripened Seeds of Avena fatua

Chen

Varner

1970

Plant Physiol.

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Measurement of Oxygen Uptake. The uptake of 02 was measured by means of a Gilson differential respirometer. Sterile precautions were taken as described previously (4). Each flask contained 10 seeds. Two flasks were included in each treatment.Incorporation of 1'C-Leucine into Protein. Lots of 10 seeds were husked, pricked at the dorsal side of the endosperm (a measure which facilitates entry of the applied compounds without affecting germination), sterilized in 1 % NaOCI for 2 min, washed, placed in a 25-mi Erlenmeyer flask with 2 ml of water, shaken at 21 -:-1 C for a period of time, then transferred to 1 ml of 1 mM leucine with 2.5 ,uc of uniformly labeled '4C-leucine (specific radioactivity 290 mc/mmole, New England Nuclear Corp.), and further shaken for 2 hr. The seeds were then washed in ice-cold, nonradioactive leucine solution, homogenized, extracted in 4 ml of 0.2 M NaCl plus 0.1 mm leucine, and centrifuged at 12,000g for 15 min. The pellet was suspended in 4 ml of the salt solution and recentrifuged. One twentieth of the pooled 12,000g supernatant fraction was precipitated with an equal volume of 15% trichloroacetic acid, and the precipitate (soluble protein) was collected on a Millipore filter. The filter was dried and the radioactivity was determined in a Nuclear Chicago gas flow detector with a counting efficiency of 40% for carbon-14. The pellet was suspended in water and precipitated in the same way as above. Approximately 80% of the radioactivity associated with the acid-insoluble material could be released by pronase, a potent proteolytic enzyme of bacterial source. Thus, this material is considered as insoluble protein.Microautoradiography of Seeds Exposed to 3H-Leucine. To locate the sites of protein synthesis, the seeds were exposed to L-leucine-4, 5-3H (specific radioactivity 6.0 c/mmole, Schwarz BioResearch), then washed in nonradioactive leucine, fixed, dehydrated and infiltrated with paraffin according to the technique of Feder and O'Brien (7). Sections 5 to 8 ,u thick were placed on a slide, dewaxed, coated with Kodak nuclear track emulsion type NTB 3, exposed, stained with toluidine blue-acid fuchsin, mounted, and examined under the microscope (10). RESULTSRespiratory Intensity. The rate of respiration (02 uptake) in dormant seeds was low as compared to that of nondormant seeds; the difference could be detected from the early hours of soaking (Fig. 1). In both kinds of seeds, the rate increased with time. However

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“…The progressive acidification of the reserve proteins of the bean cotyledons (Pusztai, unpublished) appears to be a general feature of legume seed germination (Catsimpoolas, Campbell and Mayer, 1968;Daussant, Neucere and Conkerton, 1969;Shutov and Vaintraub, 1973). Thus, the general hydrolysis of the reserve proteins, located in either the protein storage organelles or in other compartments of the cells as an early event in the protein metabolism of seed germination (Amen, 1968) is open to serious doubts.…”

Section: Discussionmentioning

confidence: 99%

COMPARTMENTALIZATION IN THE COTYLEDONARY CELLS OF PHASEOLUS VULGARIS L. SEEDS: A DIFFERENTIAL SEDIMENTATION STUDY

Pusztai¹,

Croy

Grant³

et al. 1977

New Phytologist

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SUMMARYThe appearance and the yield of sedimentable organelles from the cotyledons of Phaseolus vulgaris L. were measured with respect to the influence of the method of homogenization, the choice of dry or imbibed seeds, and the composition and the concentration of the homogenization medium. Sucrose, (0.2-0.8 M), the addition of Mg^"" (2 X 10~^M) or EDTA (3 X 10~^M) or the replacement of sucrose with mannitol made little difference to the average size distribution or the amount recovered of the 21 000 ^^v ^ 10 min pelleted organelles, the main protein body-containing fraction of the homogenate. Slicing the imbibed seeds with a razor blade or by a mechanical rotary cutter combined with a short extraction was the gentlest and the most efficient method for the production of organelles. Cell homogenates were fractionated on the basis of size by differential sedimentation into several subcellular fractions. These included a residue, starch particles (300 ^ X 10 min), a main protein body fraction (21 000 ^^v X 10 min), 38 000 ^av^ 60 min pellets, 78 000 ^av X 240 min pellets and a final supernatant. The activity in these fractions of several catabolic enzymes was measured. Most of the activity of the acidic nucleases, amylases, the BAPA-ase and a substantial part of the acidic phosphatase and the cathepsin A-type enzyme(s) were found in the supernatant, while no specific DNA-ase was found in these seeds. Protein bodies contained some of the trypsin inhibitors and most (if not all) of the lectins and Glycoprotein II. Most of the endopeptidase (azoproteinase) activity of the cotyledons appeared to be tightly bound to the cell walls or to other insoluble structural elements. Protein bodies and other intracellular organelles had very little autolytic activity and, thus, the main storage proteins of the seed were not degraded during the first 4 days of germination.

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A model of seed dormancy

Cited by 241 publications

References 80 publications

Carboxymethylcellulase Activity in Lettuce Seeds Prior to Germination

Carboxymethylcellulase Activity in Lettuce Seeds Prior to Germination

Respiration and Protein Synthesis in Dormant and After-ripened Seeds of Avena fatua

COMPARTMENTALIZATION IN THE COTYLEDONARY CELLS OF PHASEOLUS VULGARIS L. SEEDS: A DIFFERENTIAL SEDIMENTATION STUDY

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