Responses of Vegetable Seeds to Controlled Hydration

Leek, onion and carrot seeds were imbibed in water and in solutionsof polyethylene glycol (PEG) 6000 over the range –0.5to –4.0 MPa osmotic potential, for periods up to 28 dat 15 C. Seeds started to germinate after 7 and 14 d at –0.5MPa and –1.0 MPa PEG, respectively, but in the lattercase, germination did not exceed 5%. No germination occurredin solutions of lower (more negative) osmotic potential. Seedmoisture content increased with osmotic potential in all threespecies and the relationships were unaffected by the durationof imbibition in solutions of –1.0 to –4.0 MPa,though leek seeds had higher moisture contents than the otherspecies for any given osmotic potential. Linear relationships between response to priming (differencebetween mean germination times of primed and untreated seeds)and seed moisture content were obtained for each species, positiveresponses being obtained above 30–35% seed moisture contentwith optima at 46, 44.5 and 44% seed moisture contents in leek,onion and carrot, respectively. Priming had no effect on embryovolume or cell number per embryo in leek and onion. Carrot embryovolume increased by 43% and cell number per embryo doubled inprimed compared with untreated seeds, whereas seeds imbibedin water showed only a slight increase in cell number per embryoat the stage when radicles were beginning to penetrate the seedcoat. Allium cepa L. cv. Rijnsburger Robusta, onion, Allium porrum L. cv. Winterreuzen, leek, Daucus carota L. cv. Nantaise, carrot, germination, priming, polyethylene glycol, seed moisture, cell number, embryo volume     

Biochemical Changes During Osmopriming of Leek Seeds

Osmotic priming treatments reduced both the mean time to germinationand the spread of germination for two leek seed-lots of highviability but differing vigour. In addition the differencesin germination performance between these two seed-lots was abolishedby the priming treatments. In the unprimed seed-lots, differencesin germination performance were reflected in differences inrates of protein biosynthesis in leek embryo tissue during germination.Osmopriming treatments abolished these differences upon subsequentgermination of osmotically primed seed and furthermore inducedhigh levels of protein biosynthesis in embryo tissue. DNA synthesiswas detectable in leek embryos during the priming period inthe absence of any cell division and was followed by a five-foldincrease in the rate of DNA synthesis in embryo tissue upongermination following priming at which time the rates of DNAsynthesis in these leek embryos was significantly greater thanthat found at any time over the first 4 d of germination inembryos of unprimed leek seeds. The increases in rates of bothprotein and DNA synthesis observed upon germination of primedseed occurred only after a 6–12 h lag period during whichtime there is little increase in these rates above those foundat the end of priming Analysis of nucleotide and nucleotide sugar levels in leek embryosboth during and after priming showed that only traces of GTPand CTP and low levels of ATP and UTP were present in embryosduring priming. After a 6 h lag period following the end ofpriming these levels increased sharply, probably via de novosynthesis. A similar pattern was found for UDP glucose levelsduring priming and subsequent germination. These results indicatethat there is considerable biochemical activity during primingand that the significant benefits in germination performanceof primed leek seeds is accompanied by marked increases in protein,DNA and nucleotide biosynthesis after a lag period of 6–12h following the end of the priming period Allium porrum, leek, seed, osmopriming, germination, protein synthesis, nucleic acids, nucleotides, nucleotide sugars     

Resistance to Water Loss in the Mesophyll of Leek (Allium porruni)

Measurement of the rate of water loss and the gradient in water-vapourconcentration from the evaporating surface to the air enabledcalculation of the resistance to water loss from the leaf mesophyllof leek (Allium porruni) and from green blotting-paper. Theadditional resistance found in the case of mesophyll estimatesthe mesophyll cell-wall resistance (wall resistance). Wall resistancewas, however, small, less than 0.09 sec cm^–1 in turgidmesophyll and only 0.15 sec cm^–1 greater when the mesophyllwater deficit was 50 per cent. Results are discussed in relationto the evidence of other workers indicating greater resistancesto water loss in the mesophyll.     

Structure and Histochemistry of Embryo Envelope Tissues in the Mature Dry Seed and Early Germination of Phacelia tanacetifolia

The embryo envelope tissues in both mature dry seed and duringearly germination of Phacelia tanacetifolia were investigatedby bright-field and fluorescence light microscopy and scanningelectron microscopy. The ruminate seed had an irregularly reticulatesurface owing to the presence of polygonal areas, correspondingto the cells of the seed coat. The raised margins of these cellsjoined at the lobe tips, where radially arranged thickeningsoccurred. The unitegmic seed coat was made up of three distinctlayers: the frayed outer layer, the middle layer with portionsrising outwards to form the radial thickenings, and the innerlayer, the thickness of which was greatest in the micropylarzone. The endosperm tissue had two regions, the micropylar andthe lateral endosperm, which differed in polysaccharide composition,thickness and metachromasy intensity, and presence (in the lateralendosperm) or absence (in the micropylar endosperm) of birefringenceof the cell walls. Moreover, in the micropylar region, wherethe embryo suspensor remnant was found, Ca-oxalate crystalswere scarce or absent. The presence of a partially permeablecuticle covering the seed endosperm was observed. Incubationof seeds in Lucifer Yellow CH indicated that water was ableto penetrate quickly into the seed coat along the pathway formedby the radial thickenings, the raised margins of the polygonalcells and the middle layer. Afterwards, LY-CH readily infiltratedthe apical portions of the seed lobes and then the whole endosperm.Following imbibition, morphological changes were found in themicropylar endosperm, such as the initial digestion of proteinbodies. In addition, both in the seed coat and in the endosperm,a weaker fluorescence, probably due to leaching of polyphenolicsubstances, was observed. Once the seed coat was broken at themicropylar end of the seed, the endosperm cap surrounding theradicle tip had to be punctured by it so that complete germinationcould occur. Weakening and rupture of the micropylar endospermare briefly discussed. Copyright 2000 Annals of Botany Company Phacelia tanacetifolia, seed coat, micropylar endosperm, endosperm cap, early germination, structure, histochemistry     

Relationships between indices of seed maturity and carrot seed quality

Carrot seeds cvs Chantenay and Amsterdam were harvested on several occasions from crops grown in 1985 and 1986, from the time they had reached or were close to their maximum dry weight and were starting to turn brown. Maximum seed dry weight occurred approximately 40–45 days after flowering (DAF) in both cultivars. Maximum germination (International Seed Testing Association 14-day count) occurred 40 and 55 DAF in cvs Chantenay and Amsterdam, respectively, but the maximum 7-day count and the minimum coefficient of variation of embryo length did not occur until 60 DAF in cv. Chantenay and 55 to 65 DAF in cv. Amsterdam. Percentage germination was negatively and linearly related to seed moisture content, chlorophyll a + b content in the seed coat and seed distortion, measured on a modified tensile-testing machine, the relationships accounting for 77, 71 and 64% of the variance in the 7-day germination count, respectively. The corresponding values for the 14-day count were 63, 61 and 50%. A simple field test for monitoring seed maturity is proposed.     

Moisture Loss as a Prerequisite for Seedling Growth in Soybean Seeds (Glycine max L. Merr.)

Rosenberg, L. A. and Rinne, R. W. 1986. Moisture loss as a prerequisitefor seedling growth in soybeanseeds (Glycine max L. Merr.).—J.exp. Bot. 37: 1663–1674. As soybean seeds [Glycine max (L.) Merr.] develop, they undergoa change in seed moisture. When excised prematurely from thepod and planted, seeds do not exhibit seedling growth until63 d after flowering (DAF) when the seed moisture has fallenbelow 60%. In contrast, seed germination (radicle protrusion)can occur when seeds as young as 35 DAF (68–79% moisture)are excised, but this germination docs not lead to comparableseedling growth frequencies unless seeds are first given a moistureloss treatment to artificially reduce their moisture below 60%.A moisture loss treatment applied at 35 DAF thus enables seedto undergo the transition from germination (cell expansion)to seedling growth (cell division and expansion) to the extentthat treated immature seed have a vigour index comparable toseeds matured on the plant (100%). The pattern of protein synthesisin vivo was examined in 35 DAF seed using [³⁵S]-methionine incorporation.When moisture loss treatment was applied for 24 h to 35 DAFseeds, seeds synthesized several new polypeptides when comparedwith untreated seeds at the same developmental stage. The sameseed samples showed 0% seedling growth in the absence of moistureloss treatment and 80% seedling growth when the treatment hadbeen applied. Moisture loss from soybean seeds appears to bea prerequisite for the synthesis of new proteins which may bepart of the metabolic process or processes that allow the soybeanseed to undergo the transition from seed germination to seedlinggrowth. Key words: Moisture loss, germination/growth, soybean     

Transfer of a male-sterility-inducing cytoplasm from onion to leek ( Allium ampeloprasum)

Two interspecific triploid (AAC) hybrids (84/1-94 and 99/1-94) from crosses between onion [ Allium cepa (2 n=2 x=16, CC)] and leek [ A. ampeloprasum (2 n=4 x=32, AAAA)] were backcrossed to leek in order to transfer a male-sterility-inducing cytoplasm from onion that would enable the production of hybrid leek. GISH evaluations of meiosis in the interspecific hybrids revealed irregularities due to univalent onion chromosomes producing micronuclei from onion chromatin, whereas the pairing of the two sets of leek chromosomes was nearly normal. Attempts to use colchicine to double the chromosome number of the hybrids failed. Backcrosses of 84/1-94 to leek as the pollen parent were not successful. The first backcross of 99/1-94 to tetraploid leek produced 11 BC(1) plants with chromosome numbers between 38 and 41. Identification of parental chromosomes by GISH showed that all eight onion chromosomes and 30-33 leek chromosomes were transmitted to the backcross progenies due to unreduced egg cells. Onion chromosomes were eliminated during the second backcross. Southern hybridization confirmed the transfer of the T-cytoplasm like source of CMS from onion to the BC(2) progenies. After the third backcross to leek, 158 plants were obtained with varying numbers of onion chromosomes and some intergenomic recombinant chromosomes. Alloplasmic leek plants without onion chromatin were selected for further characterization of male sterility and quality traits.     

Seed Coat Dormancy in Two Species of Grevillea(Proteaceae)

The role played by the seed coat in seed dormancy of Grevillealinearifolia(Cav.) Druce and G. wilsonii(A. Cunn.) was testedby a series of manipulations in which the seed coat was dissectedand removed, dissected and returned to the decoated seed, ordissected, removed and given a heat shock, and returned to thedecoated seed. Germination of intact seeds of both species wasalso examined after exposure to heat shock, smoke, or heat shockand smoke combined. Water permeability of the seed coat wasinvestigated by examining imbibition. For intact seeds, virtuallyno germination occurred under any treatment (G. wilsonii), orgermination was increased by exposure to either heat or smoke(G. linearifolia). Removal of the seed coat led to germinationof all decoated seeds for G. linearifolia, or a proportion ofdecoated seeds for G. wilsonii. Inclusion of smoked water inthe incubation medium led to a higher proportion of decoatedseeds germinating for G. wilsonii. Returning the seed coat,either with or without heat shock to the seed coat, did notsignificantly affect germination in either species. Seed coatswere permeable to water in both species. For the two Grevilleaspecies, there were different dormancy mechanisms that werecontrolled by the seed coat (G. linearifolia) or by both theseed coat and embryo (G. wilsonii). Copyright 2000 Annals ofBotany Company Grevillea linearifolia, Grevillea wilsonii, dormancy, seed coat dormancy, seed coat permeability, smoke, heat shock, germination     

The Role of Maturation Drying in the Transition from Seed Development to Germination: III. INSOLUBLE PROTEIN SYNTHETIC PATTERN CHANGES WITHIN THE ENDOSPERM OF Ricinus communis L. SEEDS

Kermode, A. R., Gifford, D. J. and Bewley, J. D. 1985. The roleof maturation drying in the transition from seed developmentto germination. III. Insoluble protein synthetic pattern changeswithin the endosperm of Ricinus communis L. seeds.—J.exp. Bot. 36: 1928–1936. Immature seeds of Ricinus communisL. cv. Hale (castor bean) removed from the capsule at 30 or40 days after pollination (DAP) can be induced to germinateby being subjected to drying. This desiccation–inducedswitch from development to germination is mirrored by a change,upon subsequent rehydration, in the pattern of insoluble proteinsynthesis within the endosperm storage tissue. During normaldevelopment from 25–40 DAP there is rapid synthesis ofthe insoluble (11S) crystalloid storage protein. At later stagesof development (45 and 50 DAP), crystalloid protein synthesisdeclines markedly and synthesis of new insoluble proteins commences.Following premature drying at 30 or 40 DAP, the pattern of insolubleprotein synthesis upon rehydration is virtually identical tothat following imbibition of the mature seed. Proteins synthesizedduring normal late development (at 45 and 50 DAP) are producedup to 48 h after imbibition; a subsequent change in the patternof insoluble protein synthesis occurs between 48 and 72 h. Thus,in contrast to the rapid switch in the pattern of soluble proteinsynthesis induced by drying, insoluble protein syntheses withinthe endosperm are redirected towards those uniquely associatedwith a germination/growth programme only after a considerabledelay following mature seed imbibition, or following rehydrationof the prematurely dried seed. Nevertheless, these results supportour contention that drying plays a role in the suppression ofthe developmental metabolic programme and in the permanent inductionof a germination/growth programme. Key words: Desiccation, crystalloid storage proteins, castor bean, seed development, seed germination     

The C-S lyases of higher plants. Purification and characterization of homogeneous alliin lyase of leek (Allium porrum)

The characteristic odors of freshly macerated tissue of Allium species such as garlic and onion are due to the action of the enzyme alliin lyase (EC 4.4.1.4) on endogenous S-alkyl-I-cysteine sulfoxides which are present as secondary amino acids yielding volatile sulfur-containing products. Purification and characterization of the alliin lyase of leek ( Allium porrum L.) has been carried out for comparison with the analogous enzymes previously characterized from garlic and onion. The purification involved homogenization, followed by ammonium sulfate fractionation, elution from an hydroxylapatite column, concentration of the active fractions and passage through a concanavalin A-Sepharose 4B affinity column. The purified enzyme was found to be a glycoprotein with a pH optimum for activity of 8.0. Sodium dodecylsulfate-urea polyacrylamide gel electrophoresis gels of the homogeneous leek enzyme showed it consisted of 1 subunit with a molecular weight of 48000. By gel filtration, 2 stable forms of the native enzyme with molecular weights of 386000 and 580000 were found.     

Identification of a new bioregulator acting in ultralow doses in bulb onion (<Emphasis Type="Italic">Allium cepa</Emphasis> L.)

A bioregulator that has physicochemical and biological properties similar to a group of bioregulators isolated from various animal tissues has been found in the bulb onion (Allium cepa L.). It was determined that the biological action of the plant bioregulator is determined by a peptide with molecular weight of 4036 ± 2 Da whose 18-C-terminal amino acid sequence consisted of 18 residues. On models of seed germination of some vegetable cultures, the ability of the bioregulator isolated from supernatant of onion extract in ultralow doses (10⁻¹³ mg of protein/ml) to inhibit growth and development was demonstrated.     

Agrobacterium tumefaciens-mediated transformation of leek (Allium porrum) and garlic (Allium sativum)

Transgenic leek (Allium porrum) and garlic (Allium sativum) plants have been recovered by the selective culturing of immature leek and garlic embryos via Agrobacterium-mediated transformation using a method similar to that described by Eady et al. (Plant Cell Rep 19:376–381, 2000) for onion transformation. This method involved the use of a binary vector containing the m-gfp-ER reporter gene and nptII selectable marker, and followed the protocol developed previously for the transformation of onions with only minor modifications pertaining to the post-transformation selection procedure which was simplified to have just a single selection regime. Transgenic cultures were selected for their ability to express the m-gfp-ER reporter gene and grown in the presence of geneticin (20 mg/l). The presence of transgenes in the genome of the plants was confirmed using TAIL-PCR and Southern analysis. This is the first report of leek and true seed garlic transformation. It now makes possible the integration of useful agronomic and quality traits into these crops.     

THE ROLE OF THE ENDOSPERM IN THE GERMINATION OF LEGUMES: GALACTOMANNAN,NITROGEN, AND PHOSPHORUS CHANGES IN THE GERMINATION OF GUAR (CYAMOPSIS TETRAGONOLOBA; LEGUMINOSAE)

The endosperm of Cyamopsis tetragonoloba (“guar”) contains 41 % of the dry weight and 45 % of the acetone-insoluble-solids of the seed, but only 3–11 % of the nitrogen and phosphorus. At least 75 % of the acetone-insoluble-solids of the endosperm is galactomannan, only about 12% being accounted for as pentosan, pectin, protein, phytin, ash, and dilute-acid-insoluble residue. During a five-day germination period at 30 C, all of the galactomannan and all but 5 % of the dry weight of the endosperm disappeared, being translocated to the cotyledons. About ⅓ of the nitrogen and phosphorus of the endosperm plus seed coat were also translocated. After a 36-hr lag, the accumulation of the nitrogen and acetone-insoluble-solids in the seedling axis were linear, while the total dry weight and phosphorus showed a rapid increase followed by a slower accumulation during the five-day period. In the cotyledons, the dry weight temporarily increased, but the acetone-insoluble-solids, nitrogen and phosphorus showed only a net decrease after 84, 36 and 36 hr, respectively. Scanning election micrographs of dry-fractured and sectioned endosperm show that the bulk of the endosperm is a solid mass of galactomannan with essentially no cell lumina; a several-cell layer (“aleurone”) of thick-walled cells of similar structure is metabolically active.     

Primary dormancy in tomato (Lycopersicon esculentum cv. Moneymaker): studies with the sitiens mutant

Intact wild-type tomato (Lycopersicon esculentum cv. Moneymaker)seeds do not complete germination to the same percentage orat the same speed as intact ABA-deficient sitiens (sit^w) mutantseeds when seeds of both genotypes are imbibed on polyethyleneglycol (PEG) solutions of –0.3 to –1.5 MPa osmoticpotential. However, if the thicker testas of wild-type seedsare removed (stripped) from the micropyle without damaging theendosperm, both the percentage and speed of germination at lowexternal water potential are similar to that of sit^w mutantseeds. Removing the micropylar end of the testa from sit^w seedsdid not enhance either the speed or percentage of germinationon PEG solution. Despite similar germination percentage and speed between strippedwild-type seeds and either stripped or intact sit^w seeds underosmotic stress, some differences in seed metabolism are evidentbetween genotypes. The activity of endo-ß-mannanasewas greater in the endosperm of sit^w mutant seeds compared tothe endosperm of wild-type seeds when seeds were exposed toosmotic stress. Although     

Bulb Development in Onion (Allium cepa L.) II. The Influence of Red: Far-red Spectral Ratio and of Photon Flux Density

Bulb development was followed in four onion cultivars growingin controlled environments under 17 h days in factorial combinationsof photon-flux densities (PFD) of 111 and 333 µmol m^–2s^–1 with red: far-red spectral ratios (R : FR) of 2.88and 1.41. A PFD of 111with R : FR of 0.86 was used in a secondexperiment. The lower the R : FR or the higher the PFD the higherthe mean bulbing ratio and the ratio of bulb plus sheath toleaf blade dry weight and the earlier the bulb swelling. LowerR : FR accelerated scale initiation as did the higher PFD underR : FR 2.88 but not under R : FR 1.41. In high PFD bulb swellingoccurred before scale initiation because many sheaths of bladedleaves thickened, but in low PFD and low R : FR bulb swellingand scale initiation were concurrent. In the low PFD a low R: FR increased soluble carbohydrate concentrations in sheathsand scales compared to high R : FR. In high PFD, soluble carbohydrateconcentrations did not vary with R : FR and were higher thanunder low PFD. Onion, Allium cepa L., bulb, photon flux density, red: far-red ratio, light spectral quality, soluble carbohydrate     

Composition, Degradation and Utilization of Endosperm During Germination in the Oil Palm (Elaeis guineensis Jacq.)

The insoluble carbohydrate and lipid fractions, and -D-galactosidase,ß-D-mannosidase and isocitrate lyase activities werestudied in the various tissues of oil palm (Elaeis guineensisJacq.) kernels prior to and during germination. In ungerminatedkernels insoluble carbohydrate and lipid constituted 36 and47% of endosperm dry weight respectively. During germinationthe thick endosperm cell walls became markedly thinner, concurrentwith a significant decrease in the percentage of insoluble carbohydrateand an increase in -galactosidase and ß-mannosidaseactivity in both degraded and residual endosperm. The proportionof lipid in degraded endosperm also increased significantly.The insoluble carbohydrate appears to be a galactomannan locatedin the secondary walls of the endosperm. No galactomannan wasdetected in oil palm embryos or haustoria. Isocitrate lyasewas present in, and confined to, tissues of the haustorium ofgerminating kernels. The enzyme was not active in endospermat any stage of germination, nor was it active in embryos beforeor at the end of imbibition. The results suggest that galactomannan is the second largestcomponent of oil palm endosperm and that it is utilized morerapidly than lipid during the early stages of germination. Thefact that isocitrate lyase activity is confined to the haustoriumsuggests that in Elaeis gluconeogenesis, the conversion of triglycerideto carbohydrate, takes place entirely within the cotyledon ofthe seed. Elaeis guineensis, galactomannan, galactosidase, germination, isocitrate lyase, mannosidase, oil palm     

Determination of Inositol in Inbred and Hybrid Corn (Zea mays) Seedlings

Four inbred (W_f9, Hy₂, B₁₀, and 38–11) plus three hybrid(W_f9 x 38.11, US13, and B₁₀ x Hy2) corn (Zea mays) seedlingstrains (minus seed coat and endosperm) were assayed for totaland free myoinositol content, using a mutant inositol-less straino Neurospora crassa. Over a 120-h germination period, it wasfound that the concentration of total myoinositol decreasedin both of the respective varieties. The inbred corn seedling strains, assayed in this study, appearto demonstrate a lower decrease in total myoinositol than dothe hybrids, over the same 120-h germination period. Concomitantly,the hybrid strains have a higher percentage increase in freemyoinositol than do the inbred varieties, over the same germinationtime period. The hybrid corn seedling strains appear to havea greater capacity to mediate the metabolism of total to freemyoinositol, during the early stages of germination, comparedto the inbred varieties.     

Identification of a new bioregulator acting in ultralow doses in bulb onion (Allium cepa L.)

A bioregulator that has physicochemical and biological properties similar to a group of bioregulators isolated from various animal tissues has been found in the bulb onion (Allium cepa L.). It was determined that the biological action of the plant bioregulator is determined by a peptide with molecular weight of 4036 +/- 2 Da whose 18-C-terminal amino acid sequence consisted of 18 residues. On models of seed germination of some vegetable cultures, the ability of the bioregulator isolated from supernatant of onion extract in ultralow doses (10(-13) mg of protein/ml) to inhibit growth and development was demonstrated.     

Relationship between the ATP content measured at three imbibition times and germination of onion seeds during storage at 3, 15 and 30C

The possibility of using ATP content as an indicator of seedquality was studied in onion seeds {Allium cepa cv. Wdenswil).The percentage germination and ATP content of imbibed seedswere compared during 145 weeks of storage at three temperatures(3, 15 and 30C). ATP content, which was undetectable in airdriedseeds (moisture content: 9%, w/w), increased rapidly as a functionof imbibition time, as did the fresh weight and respirationrate, reaching a steady-state level after about 17 h. After36 weeks of storage, the rate of ATP formation was greater forthe seeds stored at 3C than for those kept at 15 and 30C.Furthermore, the onset of ATP synthesis was delayed. These phenomena,which are likely to be an expression of seed ageing, are usefulindicators, allowing the prediction of the loss of seed viabilitybefore the decrease in percentage germination which occurredbeyond 36 weeks of storage. In addition, the correlation betweenATP content and germination capacity of seeds during 145 weeksof storage was excellent (r=0.95 at 15C and 0.97 at 30C),provided that a 17 h-imbibition time, specific for onion seeds,was chosen. These results are discussed in terms of the controversyconcerning the correlation between the ATP content and germinationpercentage of seeds. Key words: Allium cepa, ageing, bioenergetic metabolism, seed quality, temperature storage