Relationship of endogenous abscisic Acid to sucrose level and seed growth rate of soybeans

It has been proposed that abscisic acid (ABA) may stimulate sucrose transport into filling seeds of legumes, potentially regulating seed growth rate. The objective of this study was to determine whether the rate of dry matter accumulation in seeds of soybeans (Glycine max L.) is correlated with the endogenous levels of ABA and sucrose in those sinks. The levels of ABA and sucrose in seed tissues were compared in nine diverse Plant Introduction lines having seed growth rates ranging from 2.5 to 10.0 milligrams dry weight per seed per day. At 14 days after anthesis (DAA), seeds of all genotypes contained less than 2 micrograms of ABA per gram fresh weight. Levels of ABA increased rapidly, however, reaching maxima at 20 to 30 DAA, depending upon tissue type and genotype. ABA accumulated first in seed coats and then in embryos, and ABA maxima were higher in seed coats (8 to 20 micrograms per gram fresh weight) than in embryos (4 to 9 micrograms per gram fresh weight. From 30 to 50 DAA, ABA levels in both tissues decreased to less than 2 micrograms per gram fresh weight. Levels of sucrose were also low early in development, less than 10 milligrams per gram fresh weight at 14 DAA. However, by 30 DAA, sucrose levels in seed coats had increased to 20 milligrams per gram fresh weight and remained fairly constant for the remainder of the filling period. In contrast, sucrose accumulated in embryos throughout the filling period, reaching levels greater than 40 milligrams per gram fresh weight by 50 DAA. Correlation analyses indicated that the level of ABA in seed coats and embryos was not directly correlated to the level of sucrose measured in those tissues or to the rate of seed dry matter accumulation during the linear filling period. Rather, the ubiquitous pattern of ABA accumulation early in development appeared to coincide with water uptake and the rapid expansion of cotyledons occurring at that time. Whole tissue sucrose levels in embryos and seed coats, as well as sucrose levels in the embryo apoplast, were generally not correlated with the rate of dry matter accumulation. Thus, it appears that, in this set of diverse soybean genotypes, seed growth rate was not limited by endogenous concentrations of ABA or sucrose in reproductive tissues.     

Cessation of assimilate uptake in maturing soybean seeds

In vitro assimilate uptake and metabolism were evaluated in embryos of known age isolated from seeds at mid-podfilling through physiological maturity. The capacity of isolated Wye soybean embryos to take up exogenous [¹⁴C]sucrose dropped nearly 4-fold in less than 1 week at incipient cotyledon yellowing. This drop in rate of sucrose uptake coincided with cessation of seed growth as well as rapid decline in leaf photosynthetic rate that preceded leaf yellowing. Conversely, the rate of [³H]glutamine uptake by cotyledons increased as they yellowed. Yellow cotyledons also rapidly converted exogenous [³H]glutamine to ethanolinsoluble components, but converted little exogenous [¹⁴C]sucrose to ethanol-insoluble components, primarily because of greatly reduced sucrose uptake. Sustained import and metabolism of amino acids remobilized from senescing leaves may prolong seed growth beyond loss of photosynthetic competency and sucrose availability.     

Sucrose Concentration at the Apoplastic Interface between Seed Coat and Cotyledons of Developing Soybean Seeds

The apoplastic sucrose concentration at the interface between cotyledons and surrounding seed coats of developing soybeans (Glycine max L. Merr. cv Wye) was found by three indirect methods to be in the range of 150 to 200 millimolar. This is an order of magnitude higher than has been reported elsewhere for soybean. It was also higher than the overall sucrose concentrations in the cotyledons and seed coats, each of which was approximately 90 millimolar. By defoliating plants 24 hours before measurement, both the overall sucrose concentration in the cotyledons and the interfacial apoplastic sucrose concentration were reduced by three-fourths. However, there was no day/night difference in overall tissue sucrose concentration of cotyledons or seed coats from intact plants suggesting the existence of a homeostatic mechanism compensating for the diurnal photosynthetic cycle. About 7 hours were required for a tritiated polyethylene glycol-900 solution to fully permeate developing cotyledons (from ~220 milligram fresh weight embryos), implying high diffusion resistance through the tissue.

These results indicate that a high interfacial sucrose concentration may exist in vivo. They suggest that the saturable carrier-mediated component of sucrose uptake may be of little physiological significance in the outermost cell layers of the cotyledons.

     

Abscisic Acid Levels in Soybean Reproductive Structures during Development

Abscisic acid (ABA) concentrations and growth rates of developing soybean (Glycine max [L.] Merr. cv. Wye) seeds and pod walls were determined from anthesis to maturation using high pressure liquid chromatographic techniques. Developing soybean seeds contain up to 12,200 ng/g fresh weight of ABA compared to 330 ng/g fresh weight for pod walls. In the developing seeds ABA levels correlated with growth rates, being the highest during the most active growth period of seed enlargement, and then decreasing to less than 10 ng/g fresh weight at maturity. Higher levels of ABA were found to occur in the cotyledons and seed coats than the root-shoot axes at 21 days postanthesis. The time required for excised root-shoot axes to initiate growth in liquid culture decreased as seed development progressed and ABA levels of the seeds declined.     

Regulation by ABA of beta-Conglycinin Expression in Cultured Developing Soybean Cotyledons

The regulation of cotyledon-specific gene expression by exogenously applied abscisic acid (ABA) was studied in developing cultured cotyledons of soybean (Glycine max L. Merr. cv Provar). When immature cotyledons were cultured in modified Thompson's medium, the addition of ABA resulted in an increased concentration of the β-subunit of β-conglycinin, one of the major storage proteins of soybean seeds. The amount of the α′-and α-subunits of β-conglycinin was relatively unaffected by the ABA treatment. When fluridone, an inhibitor of carotenoid biosynthesis that has been shown to decrease ABA levels in plant tissues, was added to the medium the level of ABA and the β-subunit decreased in the cotyledons. Increasing the concentration of sucrose in the culture medium caused an increase in the concentration of ABA and β-subunit in the cotyledons. When in vitro translation products from RNA isolated from cotyledons cultured with ABA were immunoprecipitated with antiserum against β-conglycinin, there was an increased amount of pre-β-subunit polypetide compared to the translation products from RNA isolated from control cotyledons. The pre-β-subunit polypeptide was not detected in translation products from RNA isolated from fluridone-treated cotyledons. Nucleic acid hybridization reactions showed that the level of β-subunit mRNA was higher in ABA-treated cotyledons compared to the control, and was lower in the fluridone-treated cotyledons. We have shown that exogenous ABA is able to modulate the accumulation of the β-subunit of β-conglycinin in developing cultured soybean cotyledons.     

Translocation of iron from soybean cotyledons

Soybean seeds, Glycine max L. Merrill, were produced by plants treated from anthesis to seed maturity with ⁵⁹Fe supplied as ferric ethylenediaminedi (o-hydroxyphenylacetate). Seed coats accounted for 7.4% of dry seed weight and had Fe concentrations 5 times greater than the embryos. After germinating 2 days, cotyledons contained 69.6% and radicles 5.0% of original seed Fe. Fractions of seed Fe unavailable to seedlings were: 19.8% in seed coats, 1.7% in germination paper, 0.1% in the water under germinating seeds, and 3.8% unaccounted for. Every 3 days seedlings received nutrient solution without Fe or with 10 μm ferric ethylenediaminedi (o-hydroxyphenylacetate) and developed as deficient Fe or normal Fe plants. The deficient Fe cotyledons on day 18 retained 13% of the labeled Fe originally present. Cotyledons of normal Fe plants retained 50 to 70% of their original Fe. Moreover, cotyledons of the normal Fe plants accumulated externally supplied Fe and finally contained twice the quantity of Fe originally present. Stem exudate collected above cotyledons of deficient Fe plants contained 5.3 μm⁵⁹Fe. Electrophoresis of exudate showed that most of the ⁵⁹Fe migrated anodically as a single band and was in the position of ferric citrate.     

Controlling seed development and seed size in Vicia faba: a role for seed coat-associated invertases and carbohydrate state

We previously provided evidence that seed coat-associated invertase is involved in controlling the carbohydrate state of developing seeds and, by this way, triggering developmental processes (Weber et al . (1995) Plant Cell , 7, 1835–1846). To verify our postulate, we compared seed development of two genotypes of Vicia faba differing in seed weight. The seed coat of the large-seeded genotype formed a higher number of parenchymatous cell layers and matured later. VfCWINV1 encoding a cell wall-bound invertase is expressed in the unloading zone of the seed coat. mRNA levels peaked later in 'large' coats and mRNA was present in more cell layers over a longer time period. Cell wall-bound invertase activity revealed a similar accumulation pattern, obviously generating the high hexose conditions present in the endospermal cavity bathing the premature cotyledons and thus controlling their carbohydrate state. High hexose conditions were correlated with an extended mitotic activity of the 'large' cotyledons. In 'large' and 'small' cotyledons, sucrose levels rose when hexoses decreased apparently terminating cell divisions and initiating differentiation and storage activities. This developmental switch was delayed in 'large' embryos. To prove the outlined relationship, sucrose was added in vitro to mitotically active cotyledons. This treatment favoured nuclear expansion and starch accumulation over cell division. In contrast, a hexose-based medium maintained cell divisions. We conclude that development of the embryo is coordinately regulated with that of the maternal seed coat which controls, by metabolic signals, the phase of cell division of the embryo and consequently also seed size.     

The Importance of Genetically Determined Seed Coat Characteristics to Seed Quality in Grain Legumes

Comparisons of five pairs of isogenk lines of peas, differingonly in the A gene for seed coat colour showed that white seeds(genotype aa) imbibed more rapidly than coloured seeds (AA),suffered greater imbibition damage revealed by dead tissue onthe cotyledons, and higher solute leakage. Seed-coat pigmentationwas closely associated with slow water uptake, since when expressionof the A gene was suppressed by the recessive pollens gene,the resulting white seeds {palpal AA) imbibed rapidly. The slowwater uptake by coloured seeds was not due to the restrictionof water entry by the seed coat since the differences in imbibitionrate were maintained when a portion of the seed coat was removedand seeds were imbibed with the exposed cotyledon in contactwith moist filter paper. Imbibition of similarly treated seedsby immersion in polyethylene glycol solutions (1–4%) whichincreased the seed/solution wettability, had little effect onthe water uptake of coloured seeds compared to imbibition inwater whereas that of white seeds increased in the first 10mins imbibition. Poor wettability of the inner surface of colouredseed coats did not therefore explain the slow imbibition ofthese seeds. The white seed coats loosened rapidly during imbibitionwhilst the coloured seed coats remained closely associated withthe cotyledons suggesting that the adherence of the seed coatto the cotyledons and therefore the ease of access of waterbetween the testa and cotyledons determines the rate of imbibition.The rapid water uptake by white-coated seeds and the subsequentimbibition damage may explain the high incidence of infectionof these seeds by the soil-bome fungus Pythhan after 2 d insoil. Improved seed quality and emergence may therefore be achievedby breeding for seed coat characteristics leading to reducedrates of imbibition Pisum sativum, isogenic lines, A gene, seed coat colour, imbibition, imbibition damage, wettability, pollens gene, seed quality, grain legumes     

Temperature and oxygen effects on C-photosynthate unloading and accumulation in developing soybean seeds

The environmental sensitivity of the processes associated with the import of photosynthate by developing soybean seeds was investigated within intact fruit and with excised, immature embryos. Intact pods of field-grown (Glycine max [L.] Merr.) Amsoy 71 soybeans were subjected to localized regimes of 0, 21, or 100% O₂ and 15, 25, or 35°C during pulsechase translocation experiments and, 2.5 hours later, the uptake and distribution of ¹⁴C-photosynthate among dissected fruit tissues determined. In other experiments, excised embryos were incubated in [¹⁴C]sucrose solutions under various experimental conditions to separate the effects of these treatments on accumulation by the embryos from those which may operate on phloem unloading in the maternal seedcoat.     

Seed Water Relations and the Regulation of the Duration of Seed Growth in Soybean

Soybean [Glycine max (L.) Merrill] seeds and cotyledons weregrown in an in vitro culture system to investigate the relationshipsbetween cell expansion (net water uptake by the seed) and drymatter accumulation. Seeds or cotyledons grown in a completenutrient medium containing 200 mol m^–3 sucrose continueddry matter accumulation for up to 16 d after in planta seedsreached physiological maturity (maximum seed dry weight). Seedor cotyledon water content increased throughout the cultureperiod and the water concentration remained above 600 g kg^–1fresh weight. These data indicate that the cessation of seeddry matter accumulation is controlled by the physiological environmentof the seed and is not a pre-determined seed characteristic.Adding 600 mol m^–3 mannitol to the medium caused a decreasein seed water content and concentration. Seeds in this mediumstopped accumulating dry matter at a water concentration ofapproximately 550 g kg^–1. The data suggest that dry matteraccumulation by soybean seeds can continue only as long as thereis a net uptake of water to drive cell expansion. In the absenceof a net water uptake, continued dry matter accumulation causesdesiccation which triggers maturation. Key words: Glycine max (L.) Merrill, solution culture, duration of seed growth, water content, dry matter accumulation     

Virus-induced gene silencing in soybean seeds and the emergence stage of soybean plants with Apple latent spherical virus vectors

Virus-induced gene silencing (VIGS) has great potential as a reverse-genetics tool in plant genomics. In this study, we examined the potential of VIGS in soybean seeds and the emergence stage of soybean plants using Apple latent spherical virus (ALSV) vectors. Inoculation of an ALSV vector (soyPDS-ALSV) carrying a fragment of the soybean phytoene desaturase (soyPDS) gene into soybean seedlings resulted in a highly uniform photo-bleached phenotype, typical of PDS inhibition, on the upper leaves throughout plant growth. The photo-bleached phenotype was also found on all immature pods, all seed coats, and about 50% embryos of seeds on soybean plants infected with soyPDS-ALSV. Infection with an ALSV vector (soyIFS2-ALSV) having a fragment of soybean isoflavone synthase 2 (soyIFS2) gene also led to a reduction of the levels of both soyIFS2- and soyIFS1- mRNAs and an isoflavone content in the cotyledons of about 36% mature seeds of infected soybean plants. Furthermore, VIGS of soyPDS was induced in the next generation plants by the seed transmission of soyPDS-ALSV. Thus ALSV vectors will be useful for studying gene functions in the reproductive stages and early growth stages, such as emergence and cotyledon stages, in addition to the vegetative stages of soybean plants.     

Effect of Water Deficits on Seed Development in Soybean : II. Conservation of Seed Growth Rate

Water deficits during seed filling decrease seed size in soybean (Glycine max L.). This may result from a reduction in the supply of assimilates from the maternal plant and/or an inhibition of seed metabolism. To determine whether maternal or zygotic factors limited seed growth, we examined the effects of a plant water deficit on the supply of sucrose to and its utilization by developing embryos. Plants were grown in the greenhouse, and water deficits were imposed by withholding water for a period of 6 days during linear seed fill. When water was withheld, leaf water potential decreased rapidly, inhibiting canopy photosynthesis completely within 3 days. However, seed dry weight (nodes 7-11) continued to increase at or near the control rate. The level of total extractable carbohydrates in leaf, stem, and pericarp tissue decreased by 70, 50, and 45%, respectively, indicating that reserves were mobilized to support seed growth. Cotyledon sucrose content decreased from about 60 milligrams per gram dry weight to 30 milligrams per gram dry weight. Similarly, the concentration of sucrose in the interfacial apoplast of the cotyledons decreased from approximately 100 millimolar to 50 millimolar. However, the rate of sucrose accumulation by excised embryos, measured in a short-term in vitro assay, increased in response to the water deficit. These results indicate that both source and sink activity in soybean are altered by water deficits to maintain the flux of assimilates to the developing embryos. This may explain why seed growth is maintained, albeit for a shorter duration, when soybean is exposed to water deficits during the seed filling period.     

Photoperiodically Induced Changes in Seed Growth Rate of Soybean as Related to Endogenous Concentrations of ABA and Sucrose in Seed Tissues

Short-day photoperiods can increase the partitioning of assimilatesto filling seeds of soybean (Glycine max L. Merr.), resultingin higher seed growth rates. The plant growth substance ABAhas been implicated in the regulation of assimilate transferwithin filling soybean seeds. Thus, we hypothesized that anincreased concentration of endogenous ABA in seeds may enhancesucrose accumulation and seed growth rate of soybeans exposedto short-day photoperiods. Plants of cv. Hood 75 were grownin a greenhouse under an 8-h short-day photoperiod (SD) until11 d after anthesis (DAA) of the first flower, when half ofthe plants were transferred to a night-interruption (NI) treatment(3 h of low-intensity light inserted into the middle of thedark period). Plants remaining in SD throughout seed developmenthad seed growth rates 43% higher than that of plants shiftedto NI (7·6 mg seed^–1 d^–1 vs. 5·3 mgseed^–1 d^–1). On a tissue-water basis, the concentrationof ABA in SD seeds increased rapidly from 7.6 µmol l^–1at 11 DAA to 65·2 µmol l^–1 at 18 DAA, butthen declined to 6·6 µmol l^–1 by 39 DAA.In contrast, the concentration of ABA increased more slowlyin NI seeds, reaching only 47·4 µmol l^–1by 18 DAA, peaking at 57·0 µmol l^–1 on 25DAA, and declining to 10·2 µmol l^–1 by 39DAA. The concentration of sucrose in SD embryos peaked at 73·5mmol l^–1 on 25 DAA and remained relatively constant forthe remainder of the seed-filling period. In NI, the concentrationof sucrose reached only 38·3 mmol 1^–1 by 25 DAA,and peaked at 61·5 µmol l^–1 on 32 DAA. Thusin both SD and NI, sucrose accumulated in embryos only afterthe peak in ABA concentration, suggesting that ABA may havestimulated sucrose movement to the seeds. The earlier accumulationof ABA and sucrose in SD suggests that ABA may have increasedassimilate availability during the critical cell-division period,thus regulating cotyledon cell number and subsequent seed growthrate for the remainder of the seed-filling period. Glycine max L. Merr. cv. Hood 75, soybean, assimilate partitioning, abscisic acid, photoperiod, source-sink     

Turgor-dependent unloading of photosynthates from coats of developing seed of Phaseolus vulgaris and Vicia faba. Turgor homeostasis and set points

Key physiological characteristics of turgor-dependent efflux of photosynthates were examined using excised coats and cotyledons of developing Phaseolus vulgaris (cv. Redland Poineer) and Vicia faba (cv. Coles Prolific) seed during the linear phase of seed fill. Exposure to solutions of high osmotic potential inhibited net uptake of [¹⁴C]sucrose by cotyledons at developmental stages less than 60% of their final dry weight. The effect could not be fully reversed by transferring cotyledons to solutions set at lower osmotic potentials. The inhibition became apparent at osmotic potentials that were higher than those that caused stimulation of efflux from seed coats. Net [¹⁴C]sucrose uptake by cotyledons at more advanced stages of development was unaffected by external osmotic potential. Specified tissue layers were removed from seed coats by pretreatment with pectinase. Efflux studies with the pectinase-modified coats of Phaseolus and Vicia seed demonstrated that the cellular site of turgordependent efflux was the ground parenchyma and thin-wall parenchyma transfer cells, respectively. Coats subjected to long-term (hours) incubations, under hypo-osmotic conditions, exhibited the capacity for turgor regulation. This was mediated by turgor-dependent efflux of solutes. The solutes exchanged were of nutritional significance to the developing embryo. The relationship between efflux and coat turgor was characterised by a turgor-independent phase at low turgors. Once turgor exceeded a minimal value (set point), efflux increased in proportion to the magnitude of the turgor deviation (error signal) from the set point. For coats of sink-limited seed of Vicia and Phaseolus, efflux exhibited apparent saturation at turgors above 0.25 and 0.5 MPa respectively. The putative turgor set point and slope of the turgor-dependent component of efflux varied with seed development, the prevailing source/sink ratio and genetic differences in seed growth rate. The nature of these kinetic variations was compatible with the competitive ability of the seed. A turgor homeostat model is proposed that incorporates the observed functional attributes of turgor-dependent efflux. Operationally, the model provides a mechanistic basis for the integration of assimilate demand by the cotyledons with assimilate import into and unloading from the seed coat.     

Permeability of seed coats to water as related to drying conditions and metabolism of phenolics

The seed coat of Pisum elatius is normally impermeable to water. When seeds are dried in the absence of oxygen their coats are totally permeable to water. Structural differences are observed between permeable and impermeable seed coats. In the genus Pisum, species with normally impermeable seed coats have a high content of phenolics and of catechol oxidase, while seed coats of P. sativum contain very little catechol oxidase and have a very low content of phenolics. Such differences are not noted in the cotyledons. We hypothesized that during dehydration of seeds, oxidation of phenolic compounds in seed coats through catalysis of catechol oxidase in presence of O₂ might render the seed coats impermeable to water.     

Somatic embryogenesis from immature zygotic embryos of annatto (<Emphasis Type="Italic">Bixa orellana</Emphasis> L.)

Summary In order to establish a protocol for somatic embryogenesis of annatto, Bixa orellana L., seeds (70 d after anthesis) from field-grown orchards had their coats dissected off, and immature zygotic embryos were excised aseptically from immature seeds collected from field-grown trees and used as explants. Embryos were cultured onto MS medium supplemented with or without different combinations of plant growth regulators and activated charcoal. Direct somatic embryogenesis was induced on explants incubated either in Murashige and Skoog (MS), 2,4-dichlorophenoxyacetic acid (2,4-D), and/or kinetin-supplemented media after 25 d of culture. The highest frequencies of embryogenesis and embryos per explant were obtained on medium containing 2.26 μM 2.4-D, 4.52μM kinetin, and 1.0 gl⁻¹ activated charcoal. The presence of charcoal was critical in increasing embryos per explant, to reduce the time to obtain somatic embryos, and mainly to prevent callus proliferation and subsequent indirect somatic embryogenesis. No embryogenic response was achieved when mature embryos were used. It was also observed that embryogenic response was significantly affected by genotype. Histological investigations revealed that primary direct somatic embryos differentiated exclusively from the protodermis or together with the outer ground meristem cell layers of the zygotic embryo axis, and from the protodermis of zygotic cotyledons. Diverse morphological differences, including malformed embryos, were observed among somatic embryos. In spite of the high frequencies of histodifferentiation of all embryo stages, a very low conversion frequency to normal plants from somatic embryos was observed.     

Seed distribution of four co-occurring grasses around Artemisia halodendron shrubs in a sandy habitat

In a natural population of the perennial semi-shrub Artemisia halodendron in a shifting sandy habitat in the Horqin Desert of eastern Inner Mongolia, six isolated adult A. halodendron individuals of similar canopy size were chosen as target plants. The density of seeds in the top 5 cm soil depth around shrubs was measured using transects aligned to the four main wind directions and at different distances from the shrub base on both the windward and leeward sides. The effects of shrub presence on seed distribution of four co-occurring grasses were examined by linking seed distribution to seed traits. Of the four species, Setaris viridis and Eragrostis pilosa had small but similar seed mass, while Chloris virgata and Aristida adscensionis had large but similar seed mass. The species were grouped into two cohorts: small-seeded vs. large-seeded cohorts, and shrub presence effects on seed distribution of both cohorts were examined. We found marked difference in the seed distribution pattern among species, especially between the small-seeded and large-seeded cohorts. The small-seeded cohort had significantly higher seed accumulation on the windward than the leeward sides in the most and least prevailing wind directions and much higher seed accumulation on the leeward than the windward sides in the second and third most prevailing wind directions, while opposite patterns occurred in the large-seeded cohort. Four species also showed marked variation in the seed distribution pattern among transects and between windward and leeward sides of each transect. This study provided further evidence that shrubs embedded in a matrix of herbaceous plants is a key cause of spatial heterogeneity in seed availability of herbaceous species. However, seed distribution responses to the presence of shrubs will vary with species as well as with wind direction, sampling position (windward vs. leeward sides of the shrub) and distance from the shrub.     

Concentrations of Abscisic Acid and Indole-3-Acetic Acid in Soybean Seeds during Development

Concentrations of abscisic acid (ABA) and indole-3-acetic acid (IAA) in seed parts were determined during reproductive development of soybean plants (Glycine max [L.] Merr. cv `Chippewa 64'). The concentration of ABA and IAA changed independently in individual seed parts with time. Measurement of the level of ABA and IAA in whole seeds masked the changes which occurred in individual seed tissues. The concentration of ABA was generally highest and that of IAA was generally lowest in the embryonic axis of soybean seeds. In the testa, the IAA concentration was generally highest while the ABA concentration was generally the lowest compared to other parts of the seed.     

Sugar transport into protoplasts isolated from developing soybean cotyledons : I. Protoplast isolation and general characteristics of sugar transport

A procedure is described to isolated functional protoplasts from developing soybean (Glycine max L. Merr. cv Wye) cotyledons. Studies of sucrose and hexose uptake into these protoplasts show that the plasmalemma of cotyledons during the stage of rapid seed growth contains a sucrose-specific carrier which is energetically and kinetically distinct from the system(s) involved in hexose transport. For example, sucrose, but not hexose uptake: (a) is inhibited by alkaline pH and the nonpermeant SH modifier, p-chloromercuribenzene sulfonic acid; (b) is stimulated by fusicoccin; (c) shows both a saturable and a linear component of uptake in response to substrate concentration; and (d) displays a sharp temperature response (high Q₁₀ value and high activation energies).     

Reduced phytic Acid content does not have an adverse effect on germination of soybean seeds

Altering the level of phytic acid phosphorus by nutritional means had no effect on the ability of soybean (Glycine max L. [Merr.], cv `Williams 79') seeds to germinate under laboratory or greenhouse conditions. Dry matter moved out of the cotyledons at similar rates whether the germinating seeds initially contained low (0.19), medium (0.59), or high (1.00 milligram per seed) phytic acid phosphorus. Growth of roots and shoots from 3 to 9 days after planting was similar for seeds containing low and medium levels of phytic acid phosphorus. The medium level of phytic acid resembles that found in field-grown seed, so it is clear that soybean seeds normally contain a phosphorus reserve far above that needed for germination and early seedling growth.