胚乳和蔗糖对大麦成熟胚无菌苗生长和叶片切段愈伤组织诱导及分化的影响

大麦无菌苗的苗高。苗干重和单位长度、叶片切段的干重均依胚培养时所带胚乳的增多而递增。但叶片切段培养时的愈伤组织诱导率和再分化率并不与胚乳多少正相关。成熟胚培养时蔗糖的供应明显影响叶片切段培养时的愈伤组织诱导率。培养带1/2胚乳的胚,用萌发率高的新鲜种子培养无菌苗时,以不供给蔗糖的有较高的叶段愈伤组织诱导率,用萌发率显著降低的陈种子时,则以育苗时供给6％蔗糖为好。     

Endosperm protein of wheat seed as a determinant of seedling growth

Seed of a Mexican semidwarf wheat (Triticum aestivum L. cv. Inia 66), was obtained from a nitrogen fertilizer field trial grown in Mexico. A high positive correlation was obtained between seed protein content and seedling dry weight after 3 weeks growth (r = +0.92^**). The seedling dry weight was positively related to the protein content of the aleurone layer and endosperm, but not to the embryo. Small, 35 milligrams, high protein seeds (4.7 milligrams protein per seed) produced larger seedlings than large, 45 milligrams, low protein seeds (4.3 milligram protein per seed). There was no difference in the weight or protein content of embryos from low and high protein seeds and their growth was similar. Composite seeds of the two protein levels were produced by transferring embryos from one endosperm type to the other. After 4 weeks, there was no difference between the different embryo types grown on the same endosperm type. High protein endosperm produced more vigorous seedlings regardless of the embryo type grown on it, indicating that the factor(s) responsible for the greater growth of high protein seed is in the endosperm.     

Fructan contents and dry matter deposition in different tissues of the wheat grain during development

The role of fructan metabolism in the assimilate relations of the grain of wheat (Triticum aestivum L.) was investigated by determination of the dry matter and fructan content of grain components at short intervals during grain filling. During the initial phase of rapid expansion, most of the assimilates entering the grain were partitioned to the outer pericarp. A large fraction of these assimilates were used for the synthesis of fructan. Dry matter deposition and fructan synthesis in the outer pericarp ceased at about 5d after anthesis. At the same time, the endosperm and the inner pericarp and testa started to accumulate dry matter at a fast rate. This was also associated with significant fructan synthesis in the latter tissues. The outer pericarp lost about 45% of its former maximum dry weight between 9 and 19 d after anthesis. This loss was due almost entirely to the near complete disappearance of water-soluble carbohydrates, most of which was fructan. The inner pericarp and testa accumulated dry matter until about mid-grain filling. The fructan contents of the inner pericarp and testa and the endosperm decreased slowly towards the end of grain filling. Most of the fructans in the inner pericarp and testa and the endosperm had a low molecular weight, whereas higher molecular weight fructans predominated in the outer pericarp. The embryo did not contain fructan. The presence of low molecular weight fructans in the endosperm cavity at mid-grain filling was confirmed. It is suggested that fructan synthesis is closely linked to growth-related water deposition in the different tissues of the wheat grain and serves to sequester the surplus of imported sucrose.     

Lectins in castor bean seedlings

The amounts of the two lectins (ricin and Ricinus communis agglutinin) in tissues of castor bean seedlings were followed during germination and early growth. For measurement, lectins in extracts were separately eluted from Sepharose columns; an antibody to the agglutinin was also used to detect the lectins by immunodiffusion. The endosperm of the dry seed contains 3.5 mg total lectin (5.6% of the total seed protein), which declines by 50% by day 4 and more rapidly thereafter as the tissue is completely consumed. The cotyledons of the dry seed also contain lectins but the amounts are less than 1% of those in the endosperm, and, as in the endosperm, they are constituents of the albumin fraction of the isolated protein bodies. No lectins were detected in the green cotyledons of 10-day seedlings that had been exposed to light from day 5. The embryonic axes of 2-day seedlings contained very small amounts of lectins but they were not detectable in the aerial parts of seedlings grown for 3 weeks or in cells from endosperm grown in tissue culture.

The ability of proteinases and glycosidases (isolated from endosperm of 4-day seedlings) to hydrolyze the lectins was examined. No hydrolysis of the two lectins was observed, but the subunits, separated by reduction with 2-mercaptoethanol, were hydrolyzed slowly by a proteinase and some release of mannose was observed in the presence of the glycosidases. Ricin was converted to its subunits by cysteine and an enzyme in an endosperm extract accelerated chain separation by glutathione.

     

Dynamics of nutrient remobilisation from seed of wheat genotypes during imbibition,germination and early seedling growth

The changes in nutrient content of grain tissues and seedling parts of two wheat genotypes (Triticum aestivum L., Excalibur and Janz) with low or high seed Zn content were followed from imbibition to early seedling development (12 days). The grains were separated into seed coat, endosperm and embryo, while the seedlings were separated into roots and shoots. The dry weight of the seed coat did not change throughout the experimental period, whereas the endosperm weight declined rapidly from day 4 onward. The weight of embryo did not show any difference between and within cultivars. About a half of seed Zn was remobilised into shoot and roots during 12 days of growth, regardless of the initial seed Zn content in both genotypes. The seed coat contained 55–77% of the total seed nutrients in the two wheat genotypes, except in the case of S (around 40%). Manganese, Fe, Ca, K, and P were remobilised effectively from the seed coat as well as from the endosperm, while remobilisation of Zn and Cu was relatively less from the seed coat than from the endosperm. After 10 days of growth, all nutrients monitored were completely remobilised from the endosperm. Remobilised K was directed primarily into shoots; an increase in K content in shoots was relatively higher than the accumulation of dry matter, with a consequent increase in K concentration in shoot tissue. The remobilisation of some nutrients (eg. Fe, Ca and Zn) from various grain tissues during inbibition, germination and early growth is different from the remobilisation in more mature plants.     

Osmoregulation, growth and sucrose accumulation in germinated Trigonella foenum-graecum (fenugreek) seeds treated with polyethylene glycol

Germinated seeds of Trigonella foenum-graecum L. (fenugreek) were grown in water or in polyethylene glycol (PEG) solutions. After endosperm removal, the water relations, growth, dry weight, sucrose and reducing sugar content of the embryo were determined. Under water sstress conditions, water content and osmotic potential (π₀) at saturation, growth and dry weight were lower than in non-stressed controls. The reduction in dry weight indicated a lower uptake of solutes from the endosperm and the decrease in π₀ was not accompanied by an increase in the amount of the accumulated solutes. It is suggested that embryos of stressed fenugreek seeds control osmotic potential by reduction of water uptake and that this results in reduction of growth. Embryos isolated from germinated seeds ("naked" embryos) were grown in water or in PEG solutions, with or without galactose (as an external solute source substituting for the endosperm). The results indicate that a decrease in the external solute did not account for growth reduction under conditions of water stress, and that decreased solute transport to the embryo may be important. The sucrose contents of "naked" embryos and of embryos from whole seeds were higher after PEG treatment, while reducing sugar contents were lower compared to non-stressed controls. The increased sucrose accumulation may be due to decreased sucrose hydrolysis.     

Effects of irradiance and water supply on grain development in wheat

The effects of two levels of irradiance and of water supply on grain development in two cultivars of winter wheat were studied by imposing treatments during the phases of cell production and cell expansion in the endosperm. The storage capacity of the grain was determined by cell number in the endosperm, which was reduced by both treatments during the cell production phase. Changes in cell number caused by the treatments were due to changes in the rate of production of cells; the duration of the cell production phase was constant. Weight per grain at maturity was proportional, both within and between cultivars, to the number of endosperm cells, except when treatments altered the supply of assimilate to the grain during the cell expansion phase. Reducing irradiance and water during the cell expansion phase decreased the rate of accumulation of dry matter in the grain and reduced weight per grain at maturity, with no effect on the duration of grain filling. Shrivelled grain resulted from a failure of the endosperm cells to fill completely, and was characterised by a reduction in the number of ‘B’-type starch granules.     

Inhibitors of endogenous proteinases in Scots pine seeds: Fractionation and activity changes during germination

Resting seeds of Scots pine (Pinus sylvestris L.) contain inhibitors which inhibit the proteinase activity present in germinating seeds but have no effect on trypsin or chymotrypsin. When a crude inhibitor preparation was chromatographed on Sephadex G-75, the inhibitor activity separated into four peaks with elution volumes corresponding to the molecular weights 24,000, 14,600, 14,000, and 9000. Each of the inhibitors affected both the hydrolysis of haemoglobin at pH 3.7 and the hydrolysis of casein at pH 5.4 and 7.0 by proteinase extracts prepared from “germinating” endosperms. These results suggest that one major proteinase was possibly acting in all the assays. In resting seeds inhibitor activity was present in both the embryo and the endosperm, the activity (per mg dry weight) in the embryo being about 2-fold that in the endosperm. In the endosperms of germinating seeds the inhibitor activity per seed decreased at about the same rate as total N and dry weight. In the seedlings the activity per seedling remained approximately constant. The patterns of the activity changes suggest that the inhibitors do not control the breakdown of storage proteins; a more probable function is the protection of other cellular components from the high proteinase activities required for the rapid proteolysis during germination.     

Light and the correlation of chloroplast development and coupling of phosphorylation to electron transport

Coupling of phosphorylation to electron transport was examined by measuring the photosynthetic control ratio for broken wheat plastids isolated from seedlings at different greening stages. The photosynthetic control ratio progressively increased during greening and tight coupling was noted after granal stacking and thylakoid elongation. ADP impaired nonphosphorylating (state 2) electron transport rates of plastids at extremely early stages of greening and interfered with photosynthetic control measurements. Partially developed plastids exhibited low nonphosphorylating electron flow rates but did not exhibit high phosphorylating or uncoupled electron transport rates to the same extent as nearly developed plastids. Prolamellar body dispersal, primary thylakoid production, and the development of photosynthetic control were stimulated equally by 48 minutes of low irradiance, in cycles of 2 minutes every 2 hours, or by 9 hours of continuous light of moderate irradiance. Wheat plastids that greened for 6 hours in continuous light of moderate intensity did not exhibit photosynthetic control or much differentiation beyond the etioplast stage. It is concluded that plastid differentiation and the development of photosynthetic control early in greening under continuous light were limited by developmental time (dark time) rather than by either light intensity or duration.     

Effect of lateral far-red light supplementation on the growth and morphology of birch seedlings and its interaction with mineral nutrition

The effects of lateral far-red light (FR) and nutrient supply on the growth and nitrogen accumulation of silver birch (Betula pendula) seedlings were studied with the objective of testing the following hypotheses: (1) silver birch seedlings grow taller in response to increased FR irradiance received from the side; (2) this response is modulated by the nutritional status of the seedlings; and (3) an increase in lateral FR irradiance, and concomitant decrease in red to far-red photon ratio, affects the carbon and nitrogen economies of the seedlings. Two factorial experiments, each with two levels of mineral nutrient availability and two light treatments (background 'white' light with and without additional lateral FR simulating light reflected by neighbours in a sparse canopy) were done with small seedlings. The two experiments differed in PAR irradiance. The results of these experiments were that (1) stem elongation rate was increased by lateral FR addition, (2) there was no interaction between this effect and the nutritional status of the seedlings, and (3) neither whole plant accumulation of nitrogen nor dry weight increment was affected by lateral FR under either mineral nutrient supply regime.     

Mineral reserves in castor beans: the dry seed

Elemental composition and distribution of the mineral reserves in the endosperm and embryo tissues of Ricinus communis cultivars Hale and Zanzibarensis were investigated. Energy dispersive x-ray analysis was used to determine the elemental composition of the globoid crystals, while atomic absorption spectrometry allowed quantification of the elements, particularly Ca, in various seed regions. No major differences were found between the two cultivars with regard to the elemental distribution in globoid crystals. While the majority of globoid crystals contained P, K, and Mg, the occasional one also contained Ca. In extremely rare instances, Fe was detected in globoid crystals. Ca-containing globoid crystals were more common in provascular cell protein bodies in the stem and radicle. Polarized light microscopy, micro-incineration, and acid solubility tests demonstrated the presence of calcium oxalate crystals in the innermost testa which adheres to the endosperm and is often mistakenly identified as endosperm. Atomic absorption spectrometry revealed that most of the calcium present in castor bean seeds is localized in the testa. On a perseed-region basis, the much larger endosperm contains more Ca than does the embryo. However, on a unit-weight basis, the radicle-plus-stem regions contain considerably more Ca than does the cotyledon or endosperm, an observation that is consistent with the observed distribution pattern for Ca-containing globoid crystals.     

Degradation of the endosperm cell walls of Lactuca sativa L., cv. Grand Rapids

The timing of mobilisation of lipid, sucrose, raffinose and phytate in lettuce seeds (achenes) (cv. Grand Rapids) has been examined. These reserves (33%, 1.5%, 0.7%, 1.4% of achene dry weight, respectively) are stored mostly in the cotyledons. Except for a slight degradation of raffinose and increase in sucrose, there is no detectable reserve mobilisation during germination. The endosperm (8% of seed dry weight), which has thick, mannan-containing cell walls (carbohydrate, 3,4% of seed dry weight), is completely degraded within about 15h following germination. Mannanase activity increases about 100-fold during the same period and arises in all regions of the endosperm. Also during this period sucrose and raffinose are degraded and fructose and glucose accumulate in the embryo. The endosperm hydrolysis products are taken up by the embryo, and are probably used as an additional reserve to support early seedling growth. However, endosperm cell-wall carbohydrates, such as mannose, are not found as free sugars. Lipid and phytate are degraded in a later, second phase of mobilisation. Low levels of sucrose are present in the embryo, mostly in the cotyledons, and large amounts of fractose and glucose (14% of seedling dry weight at 3 days after sowing) accumulate in the hypocotyl and radicle. It is suggested that sucrose, produced in the cotyledons by gluco-neogenesis, is translocated to the axis and converted there to fructose and glucose.     

Changes in Cytokinin Activity during Seed Germination in Rice (Oryza sativa L.)

Cytokinin activity was determined in dry mature rice seeds,in endosperm and embryo tissues 24, 48 and 72 over imbibitionand in radicles 96 h after germination. Cytokinins with chromatographicproperties similar to zeatin, zeatin riboside, zeatin glucosideand zeatin riboside glucoside were datected in embryo and endosperm,but only the latter two were detected in mature seeds. Cytokininactivity was low during early toges of germination. Qualitativeand quantitative changes in cytokinins were observed in bothembryo and endosperm. The presence of higher cytokinin activityin the endosperm than in the embryo during the first 24 h aftergermination suggests that the endosperm may supply cytokininsuntil the embryo is able to synthaize its own cytokinins. Thepossible significance of high cytokinin glucoside activity inthe embryo early during germination and high cytokinin activityin the radicle during the later stages is discussed. Oryza sativa L., rice, cytokinin, germination, seed     

A structural study of germination in celery (Apium graveolens L.) seed with emphasis on endosperm breakdown

Germination of celery seed occurred after 6 d of imbibition in light. During this time the embryo enlarged at the expense of the adjacent endosperm cells and at the time of germination was 2–3 times as long as in the dry seed. Breakdown of the endosperm cells near the root cap preceeded radicle emergence. None of these changes occurred in darkness.Endosperm digestion began adjacent to the embryo and spread radially. In degrading cells, the aleurone grains often became larger and fewer in number. The cell walls were modified and appeared to undergo partial degradation. Ultimately the cells seemed to lose their contents. In cells adjacent to the root cap, similar changes occurred except there was a transient appearance of starch grains. Radial progression of endosperm breakdown also occurred in isolated endosperm treated with gibberellin A₄₊₇.The results indicate that (1) the stimulus for breakdown of celery endosperm emanates from the embryo in response to light; (2) the stimulus may be a gibberellin because changes in endosperm cells and the sequence of endosperm digestion during germination resemble the responses of isolated endosperm to gibberellin; and (3) the radial progression of endosperm breakdown during germination may be the result of a sequential response of cells to a uniformly applied stimulus rather than the result of gradual embryo expansion.     

Isolation and characterization of rice phytochrome A mutants

To elucidate phytochrome A (phyA) function in rice, we screened a large population of retrotransposon (Tos17) insertional mutants by polymerase chain reaction and isolated three independent phyA mutant lines. Sequencing of the Tos17 insertion sites confirmed that the Tos17s interrupted exons of PHYA genes in these mutant lines. Moreover, the phyA polypeptides were not immunochemically detectable in these phyA mutants. The seedlings of phyA mutants grown in continuous far-red light showed essentially the same phenotype as dark-grown seedlings, indicating the insensitivity of phyA mutants to far-red light. The etiolated seedlings of phyA mutants also were insensitive to a pulse of far-red light or very low fluence red light. In contrast, phyA mutants were morphologically indistinguishable from wild type under continuous red light. Therefore, rice phyA controls photomorphogenesis in two distinct modes of photoperception--far-red light-dependent high irradiance response and very low fluence response--and such function seems to be unique and restricted to the deetiolation process. Interestingly, continuous far-red light induced the expression of CAB and RBCS genes in rice phyA seedlings, suggesting the existence of a photoreceptor(s) other than phyA that can perceive continuous far-red light in the etiolated seedlings.     

Proteolytic activity and nitrogen transfer in maize seeds during imbibition

Ethanol-soluble and insoluble nitrogen and protease activity in maize seeds during imbibition period of 6 to 60 h at 30 ± 2 °C were determined both in light and in the dark. In light, soluble and insoluble nitrogen in the embryo were similar to that in the dark. But the increase in soluble nitrogen in the endosperm up to 38 h was higher in light than in the dark. Decrease in insoluble nitrogen was correlated with increase in soluble nitrogen, the level always being higher in the dark. Light increased protease activity also in the endosperm. Among various light qualities, red light was most effective in inducing proteolysis, and loss of nitrogen from the endosperm. Further, the growth and organic nitrogen of primary leaves from seedlings raised from light pretreated seeds were better than those from dark pretreated ones.     

Seeds of tomato (Lycopersicon esculentum Mill.) which develop in a fully hydrated environment in the fruit switch from a developmental to a germinative mode without a requirement for desiccation

Seed water content is high during early development of tomato seeds (10–30 d after pollination (DAP)), declines at 35 DAP, then increases slightly during fruit ripening (following 50 DAP). The seed does not undergo maturation drying. Protein content during seed development peaks at 35 DAP in the embryo, while in the endosperm it exhibits a triphasic accumulation pattern. Peaks in endosperm protein deposition correspond to changes in endosperm morphology (i.e. formation of the hard endosperm) and are largely the consequence of increases in storage proteins. Storage-protein deposition commences at 20 DAP in the embryo and endosperm; both tissues accumulate identical proteins. Embryo maturation is complete by 40 DAP, when maximum embryo protein content, size and seed dry weight are attained. Seeds are tolerant of premature drying (fast and slow drying) from 40 DAP.Thirty-and 35-DAP seeds when removed from the fruit tissue and imbibed on water, complete germination by 120 h after isolation. Only seeds which have developed to 35 DAP produce viable seedlings. The inability of isolated 30-DAP seed to form viable seedlings appears to be related to a lack of stored nutrients, since the germinability of excised embryos (20 DAP and onwards) placed on Murashige and Skoog (1962, Physiol. Plant. 15, 473–497) medium is high. The switch from a developmental to germinative mode in the excised 30- and 35-DAP imbibed seeds is reflected in the pattern of in-vivo protein synthesis. Developmental and germinative proteins are present in the embryo and endosperm of the 30- and 35-DAP seeds 12 h after their isolation from the fruit. The mature seed (60 DAP) exhibits germinative protein synthesis from the earliest time of imbibition. The fruit environment prevents precocious germination of developing seeds, since the switch from development to germination requires only their removal from the fruit tissue.Abbreviations DAP days after pollination - kDa kilodaltons - SP1-4 storage proteins 1–4 - SDS-PAGE sodium dodecyl sulphate-polyacrylamide gel electrophoresis - HASI hours after seed isolation - MS medium Murashige and Skoog (1962) medium This work is supported by National Science and Engineering Research Council of Canada grant A2210 to J.D.B.     

Catalase activity in developing seedling of opium poppyPapaver somniferum L

Catalase is an enzyme unique to glyoxysomes in developing poppy seedlings. Catalase activity is very low in endosperm and in embryo of germinating poppy seeds. During postgerminative growth and development the enzyme activity increases rapidly with maximum in endosperm on day 2 and in developing seedling on day 3. A rapid decline of enzyme activity parallells the extension growth of poppy seedlings. Three electrophoretic forms of catalase have been detected in isolated glyoxysomes and partially purified catalase preparation. Electron microscopic observation indicates the presence of catalase in glyoxysomes of parenchyma cells of poppy seedling cotyledons. Numerous lipid bodies and electron-dense deposits in vacuoles are the most characteristic feature of these cells.     

Reserve mobilization in the Arabidopsis endosperm fuels hypocotyl elongation in the dark, is independent of abscisic acid, and requires PHOSPHOENOLPYRUVATE CARBOXYKINASE1

Arabidopsis thaliana is used as a model system to study triacylglycerol (TAG) accumulation and seed germination in oilseeds. Here, we consider the partitioning of these lipid reserves between embryo and endosperm tissues in the mature seed. The Arabidopsis endosperm accumulates significant quantities of storage lipid, and this is effectively catabolized upon germination. This lipid differs in composition from that in the embryo and has a specific function during germination. Removing the endosperm from the wild-type seeds resulted in a reduction in hypocotyl elongation in the dark, demonstrating a role for endospermic TAG reserves in fueling skotomorphogenesis. Seedlings of two allelic gluconeogenically compromised phosphoenolpyruvate carboxykinase1 (pck1) mutants show a reduction in hypocotyl length in the dark compared with the wild type, but this is not further reduced by removing the endosperm. The short hypocotyl phenotypes were completely reversed by the provision of an exogenous supply of sucrose. The PCK1 gene is expressed in both embryo and endosperm, and the induction of PCK1:beta-glucuronidase at radicle emergence occurs in a robust, wave-like manner around the embryo suggestive of the action of a diffusing signal. Strikingly, the induction of PCK1 promoter reporter constructs and measurements of lipid breakdown demonstrate that whereas lipid mobilization in the embryo is inhibited by abscisic acid (ABA), no effect is seen in the endosperm. This insensitivity of endosperm tissues is not specific to lipid breakdown because hydrolysis of the seed coat cell walls also proceeded in the presence of concentrations of ABA that effectively inhibit radicle emergence. Both processes still required gibberellins, however. These results suggest a model whereby the breakdown of seed carbon reserves is regulated in a tissue-specific manner and shed new light on phytohormonal regulation of the germination process.     

Impaired stem-growth responses to blue-light irradiance in light-grown transgenic tobacco seedlings overexpressing Avena phytochrome A

The effects of blue light (B) on stem extension-growth were compared in light-grown seedlings, of tobacco overexpressing Avena phytochrome A and its isogenic wild type (WT). Under natural radiation, lowering the levels of B reaching the whole shoot promoted stem extension growth in WT but not in transgenic seedlings. Under controlled conditions, the seedlings were exposed to white light (WL) or WL minus B, each one provided at two different irradiances. In WT seedlings stem extension growth was promoted by lowering B at both irradiance levels. In transgenic seedlings a reduction of B was promotive only at low irradiance levels. The seedlings were also grown under WL, WL minus B, WL minus red light (R) and far-red light (FR) or WL minus R, FR and B. In the WT, lowering B promoted stem extension growth irrespective of R+FR levels. In the transgenics, B was effective only at very low levels of R+FR (i.e. at low phytochrome cycling rates). Lowering the Pfr levels at the end of the day promoted extension growth in wild type and transgenic seedlings. Responses to B were not observed in transgenic seedlings having low Pfr levels at the end of the day. The results suggest that the overexpressed phytochrome A acts mainly via irradiance-dependent reactions. When these reactions are highly expressed, B responses are not observed.