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 Suspensor Haustoria of Some Species of Crotalaria Linn

The structure and function of the suspensor has been studiedin eight species of Crotalaria, in all of which it shows a differentiationinto an upper and a lower part. The peripheral cells of thelower part project out and act as haustorial structures forthe absorption of nutrition from the surrounding endosperm.In G. retusa and G.striata these processes are very long andtubular attacking the surrounding endosperm and nucellar tissuesand extending even into the integumental layers. Remains ofthe suspensor are recognizable even in the mature seed. Thecells of the suspensor possess chloroplasts so that this organalso has a photosynthetic function in addition to its haustorialactivity.     

Structural Aspects of Cluster Root Development and their Possible Significance for Nutrient Acquisition in Grevillea robusta (Proteaceae)

Light microscopy (LM), scanning (SEM) and transmission electronmicroscopy (TEM) were used to study structure and function ofcluster roots inGrevillea robusta . These roots were developedduring growth ofG. robustaseedlings in modified Hoagland's solutionlacking phosphate. Cluster rootlets formed root hairs, basipetally,only after completing their determinate development. The rootlethairs branched in two ways and some had apical swelling. Rootletswith hairs produced two different forms of exudate, one fibrousand the other globular in nature. The fibrous material appearedto be synthesised in the cortical cells. It is released by exocytosisfrom the epidermis. Rootlet hairs produced only fibrous exudate.They attached firmly to pieces of vermiculite. The significanceof cluster roots is discussed within the context of patchy soilresources. Grevillea robusta ; Silky oak; Proteaceae; cluster roots; morphology; mucilage; nutrient acquisition; root exudates     

Fertilizing Pollen Tubes Parasitise Ovary Wall in Grevillea

Tissue-invasive pollen tube branching occurs in an Australianshrub, Grevillea banksii R.Br. (Proteaceae). Parenchyma andphloem of the ovary wall are soon infiltrated after fertilization,by intercellular branches and the lumina of xylem elements areentered. Ovular tissues are not affected. Grevillea banksii, pollen, haustoria, ovary wall     

Floral Structure, Stigma Receptivity and Pollen Viability in Relation to Protandry and Self-incompatibility in Silky Oak (Grevillea robusta A. Cunn.)

The reproductive biology of Grevillea robusta growing underexotic conditions in Kenya and Australia is reported. The speciesshowed both protandry and a self-incompatibility mechanism.The stigma was wet and papillate with a distinct groove in themiddle. The anthers dehisced prior to anthesis, when the perianthopened. Stigmatic receptivity began 1 d after anthesis, withthe greatest pollen germination rates and longest pollen tubesobtained 2 d after anthesis. Nectar secretion commenced withpollen dehiscence and was abundant at anthesis. Most stigmaticgrooves opened widely 1–2 d after anthesis and stigmasshowed taller papillae and abundant secretion. Controlled pollinationsgave a greater fruit set from cross-pollination (5.9% in Apriland 17.5% in July) than open-pollination (0.1% in April and3.3% in July). No fruit set from self-pollination was obtainedin April, and very few fruit set for geitonogamous (two outof 1622; 0.1%) or for autogamous (one out of 2707 flowers; 0.04%)pollination treatments in July. Following self-pollination,growth of pollen tubes was poorer than in other treatments,and was generally arrested in the upper style. Cross-pollinatedflowers produced normal and straight pollen tubes, while self-pollentubes had growth abnormalities. Most of the open-pollinatedflowers were found without pollen or with only self-pollen ontheir stigmas indicating that the amount of cross-pollen reachingthe stigma under open-pollination may be a factor limiting seedproduction. Flowers shed soon after the fertilization phasewere those with ungerminated pollen or no pollen. Although avery low rate of selfing may occur, G. robusta presents a self-incompatibilitysystem and allogamy is its primary breeding behaviour.Copyright2000 Annals of Botany Company Grevillea robusta, silky oak, Proteaceae, protandry, controlled pollinations, receptivity, pollen-tube growth, self-incompatibility, pollination     

Changes in Nuclear DNA Content, Cell and Nuclear Size, and Frequency of Cell Division in the Cotyledons of Brassica napus L. during Embryogenesis

Cellular behaviour was examined during embryogenesis in Brassicanapus to test whether or not polyploidy occurs in the cotyledonsduring the phase of oil deposition. Nuclear DNA content, nuclearand cell size, and the mitotic index were measured in the cotyledonson various days post anthesis (dpa). In squashed monolayersfrom 15 dpa cotyledons, a polyploid (>5C) population wasdetected together with a substantial number of cells in G2 (4C).Nuclear volume was measured on sectioned tissues and, at 15dpa, the range of values from the cotyledons (40–500 *m³)contrasted with that in the vestigial suspensor and endosperm(50–> 600 µm³). At 15 dpa the nuclear volumedata suggest that whilst cells in the cotyledons were in Gland G2 many endosperm and suspensor cells were polyploid. Thus,polyploidy observed in the squashed monolayers was probablydue to contaminating endosperm/suspensor cells. At 25 and 35dpa, polyploidy was not detected; all cells were in Gl (2C)and cell area increased. The mitotic index peaked at 20 dpabefore declining and given the narrower distribution of nuclearvolumes at 25 and 35 dpa (50–300 µm³), these dataare consistent with cell arrest in Gl. Thus, polyploidy wasnot detected in the cotyledons of B. napus which differs fromwhat is known about cellular development in legume cotyledons. Key words: Brassica napus L., DNA, nuclear volume     

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     

Injury-induced Cyanogenesis in Vegetative and Reproductive Parts of Two Grevillea Species and their F1 Hybrid

When leaves of three Grevillea species were macerated, hydrogencyanide was only released from the soft, immature ones. Thebark but not wood of young stems was weakly cyanogenic. Thegreatest concentration of cyanoglucosides occurred in peduncles,flower buds, open flowers, immature seeds and germinants. Nocyanide was released from nectar, pedicels, dry fruit, elaiosomesand dry walls mature seeds. Addition of ß-glucosidase,and sometimes water only, increased cyanogenesis in young leaves,bark, some seed and fruit walls, and embryos of mature seeds.The endogenous levels of ß-glucosidase were sufficientto release all the cyanide present in at least 80% of cases. Young leaves and germinants of G. bipinnatifida (resprouter)released more cyanide than those of G. banksii, while flowerbuds, stigmatic region, styles, perianths and ovaries of G.banksii (non-sprouter) released far more cyanide than thoseof G. bipinnatifida. The interspecific and intraplant distributionof cyanoglucosides is consistent with the expected impact ofbeneficial and herbivorous animals on long term fitness of thesespecies. The F1 hybrid (G. 'Robyn Gordon') tended to have intermediatecyanoglucoside levels between the two putative parents.Copyright1993, 1999 Academic Press Grevillea bipinnatifida, G. banksii, G. 'Robyn Gordon', cyanide, herbivory, ß-glucosidase, cyanogenesis     

Seed Development in a Shrunken Endosperm Barley Mutant

Seg8 is one of eight barley (Hordeum vulgare L.) mutants whoseendosperm development is affected by the maternal plant genotype.This study was initiated to determine the nature and onset ofabnormal development to provide a basis for further studiesaimed at understanding the mechanism of genetic control. Seeddevelopment and synthesis and accumulation of reserve substanceswere compared between seg8 and its normal counterpart, cv. Klages.Light microscopic examination showed that the mutant phenotypeappeared as early as 4 d after anthesis (DAA), and seg8 graindry weight was significantly lower than cv. Klages by 8 DAA.Grain cell number was significantly lower in seg8 by 8 DAA,indicating an early termination of cell division. The mutanthad a lower starch concentration and higher sucrose concentration,also evident at 8 DAA. Rates of [¹⁴C]sucrose incorporation intostarch in excised half seeds were similar in both genotypesat 2 and 4 DAA, but at 8 and 12 DAA seg8 had a lower rate. Totalprotein concentration was not significantly different betweenthe two genotypes throughout endosperm development. These resultsindicate that the mutation affects cell division and starchaccumulation prior to 8 DAA. It is not known if the reductionin starch biosynthesis and accumulation results from a reducedcapacity for starch or a defect in starch biosynthesis. Hordeum vulgare L., barley, shrunken endosperm mutant, endosperm development, starch, protein, endosperm cell number     

Investigations on Growth and Metabolism of Plant Cells: IV. Evidence on the Role of the Coconut-Milk Factor in Development

By the carrot-assay method it has been shown that the wateryendosperm of coconut contains the growth-promoting coconut-milkfactor at all stages of development. Some activity is shownby the parts of the immature embryo but not by the solid endosperm. Sources of analogous activity are in the endosperm of Zea maysin the milk stage, the gelatinous content of immature fruitsof Fuglans regia, and the young gametophyte of Ginkgo biloba.The data for other cases examined suggest that the materialdevelops best in nutritive tissues associated with delayed embryodevelopment.     

Studies on Mature Seeds of Cuscuta pedicellata and C. campestris by Electron Microscopy

The seeds of Cuscuta pedicellata have been investigated by transmissionand scanning electron microscopy. Additional observations havebeen made on seeds of C. campestris by SEM only. The seed coatconsists of an outer single epidermis, two different palisadelayers, and an inner multiparenchyma layer. The outer epidermalwall in C. pedicellata has a thick cuticle and zones rich inpectic substances. The thicker ‘U-shaped’ cell wallsin the outer palisade layer are strengthened by a wall layerof hemicellulose. The inner palisade layer has thick walledcells with a ‘light line’. The inner cell wall ofthe compressed multiparenchyma layer has a thin cuticle. A fairlythick cuticle is positioned directly on the endosperm surface.The aleurone cell walls are different from the remaining endospermwalls. The latter are thick and believed to be of galactomannans.There is a ‘clear’ zone between the plasmalemmaand the cell wall in the aleurone cells. The embryo cells arepacked with lipids and proteins. In Cuscuta campestris mostendosperm has been absorbed during the seed development. Theembryo apex has two minute leaf primordia. The features of theCuscuta seeds are discussed in relation to functional and environmentalconditions. Cuscuta pedicellata, Cuscuta campestris, seed, seed coat, cuticle, cell walls, endosperm, aleurone cells, galactomannan, embryo, TEM, SEM     

An Unusual Cytoplasmic Component in Euphorbia peplus L. Endosperm

The coenocytic endosperm of Euphorbia peplus contains a complexsystem of flat, tightly-stacked membrane saccules which havea sinuous profile and a smooth or smooth-rough surface. Theyare joined by membrane-to-membrane links. The usual ergastoplasmiccisternae are an integral component of this system which canessentially be regarded as a sui generis from of endoplasmicreticulum.Copyright 1995, 1999 Academic Press Euphorbia peplus, TEM, ultrastructure, endosperm, endoplasmic reticulum, cell organelles     

Structure and In Vitro Growth of Zygotic Embryos of Taro (Colocasia esculenta var. antiquorum)

Zygotic embryos of taro, Colocasia esculenta var. antiquorumwere examined using both light and scanning electron microscopyand cultured on Linsmaier-Skoog (LS) medium without the additionof growth regulators. Embryos present within mature seed consistof a hypocotyl-root axis and an undeveloped cotyledon and aresurrounded by two major types of endosperm cells, aleurone andstarchy endosperm. Embryos cultured on LS medium developed intomature plants only in the presence of endosperm tissue. Excisedembryos turned green after 2–4 d in culture and reacheda rapid growth period between days 4 and 6. Culture of taroembryos leading to viable plantlet development depends upon(1) removal of the outer and inner integument, and (2) the presenceof endosperm tissue (including an intact aleurone layer). Colocasia esculenta var. antiquorum, Araceae, taro, embryo culture, integument, endosperm     

Ageing in Triticum durum Seeds: Behaviour of Embryos and Endosperms from Aged Seeds as Revealed by the Embryo-transplantation Technique

The embryo-transplantation technique has been used to studythe behaviour of Triticum embryos and endosperm during the courseof ageing of 1-, 2-, 3-, 4-, and 5-year-old seeds. The resultsshow that the ageing process in Triticum seeds is a progressivephenomenon. It affects both embryo and endosperm as shown by(a) the behaviour of old embryos transplanted on young endosperms,and (b) the deleterious effects of aged endosperms on youngembryos.     

Tissue-Dependent Expression of the Rice wx+ Gene Promoter in Transgenic Rice and Petunia

The waxy (wx) locus, which controls the amylose synthesis, isknown to be expressed specifically in the endosperm and pollen.To study the tissue-specific regulation of the wx⁺ gene, weintroduced a fusion gene that consisted of the upstream sequenceof the wx⁺ gene and the gene for rß-glucuronidase(GUS) into cells of rice (Oryza sativa L.) and petunia (Petuniahybrida L.). GUS activity was examined in the regenerated transgenicrice and petunia plants. In transgenic rice, the upstream sequenceof the wx⁺ gene was sufficient to direct the tissue-specificexpression of GUS in the endosperm and pollen, and the controlof expression was quantitative. By contrast, in transgenic petunia,the same fusion gene was expressed in pollen but not in theendosperm. These results suggest that the putative cis-actingelements that direct pollen-specific expression are common toor similar in both monocotyledonous and dicotyledonous plants,whereas ciy-elements responsible for the endosperm-specificexpression of the rice wx⁺ gene do not function in petunia,in which development of the endosperm differs from that in rice. ⁴Present address: Division of Biological Sciences, GraduateSchool of Science, Hokkaido University, Kita-ku, Sapporo, 060Japan     

Ontogeny, Structure and Breakdown of Protein Bodies in Linum usitatissimum Linn.

In Linum usitatissimum protein bodies are observed in the cellsof endosperm and embryo. They originate in vacuoles. Proteinbodies have both crystalloid and globoid inclusions. The breakdownoccurs by vacuolization and fragmentation. Linum usitatissimum, seed, embryo, endosperm, protein bodies     

Effects of Parental Embryo and Endosperm Mitotic Cycle Times on Development of Hybrids Between Barley and Rye

Seven different barley/rye crosses were made using genotypeshaving close (predicted compatible) or dissimilar (predictedincompatible) mean cell doubling times. The relative successof the crosses was determined by a cytological study of earlyhybrid seed development and by the yield of 16-day-old hybridembryos. The results support the hypothesis that parental developmentalrates must be similar for successful hybridization. The degenerationof the hybrid endosperm occurred earlier in the predicted incompatiblecrosses than in the more compatible ones. Fewer hybrid embryoswere harvested at day 16 from predicted incompatible crossesthan from compatible crosses. We conclude that development ofhybrid embryos depends on the early stages of endosperm developmentand that mitotic rates in parental endosperms are more importantthan in embryos. Hordeum vulgare L., Secale cereale L., barley, rye, hybrid, mean cell doubling time, embryo, endosperm     

Metabolism and Translocation of Exogenous Zeatin Riboside in Germinating Seeds and Seedlings of Zea mays

High specific activity [³H]-zeatin riboside (ZR) was suppliedto germinating seed and developing seedlings of Zea mays tostudy its metabolism and translocation The major metabolitesof ZR in endosperm, embryo, and first leaves were adenosine,adenine, and adenine nucleotide When ZR was supplied to theradicle tip a significant proportion of the radioactivity extractedfrom the radicle was identified as zeatin-9-glucoside (Z9G).However, some ZR was also transported to the shoot and vestigialembryo During the initial stage of germination, movement ofzeatin riboside from the embryo to the endosperm was pronouncedbut little movement occurred in the reverse direction Key words: Zea mays cytokinin, zeatin riboside, metabolism, translocation