Redistribution of Nutrient Elements from Cotyledons of Two Species of Annual Legumes During Germination and Seedling Growth

The distribution of dry matter and various mineral nutrientsbetween testa and embryo of seeds of Lupinus albus and L. angustifoliusis described It was found that lupin seeds at either end ofa pod contained less dry matter and minerals than seeds in themiddle of the fruit. The transport of dry matter, N, P, K, S,Ca, Mg, Na, Fe, Zn, Mn and Cu from cotyledons of parent seedsof both species to the seedling axis was measured from germinationto the time of cotyledon death. N, P, K and S were retrievedfrom cotyledons with over 90 per cent efficiency, dry matter,Mg, Na, Fe, Zn, Mn and with 59–90 per cent efficiency,and Ca with 26–31 per cent efficiency. There was littlechange in the efficiency of nutrient retrieval from cotyledonswhen seedlings were grown in different culture media. Both speciesshowed a linear relationship between the loss of each elementand dry matter throughout the experiment, and a similar proportioningbetween root and shoot of the amount of a specific nutrientmobilized from cotyledons of parent seeds. Lupinus albus L., Lupinus angustifolius L., lupin, transport, of dry matter and mineral nutrients     

Osmoregulation,solute distribution,and growth in soybean seedlings having low water potentials

Soybean (Glycine max (L.) Merr.) seedlings osmoregulate when the supply of water is limited around the roots. The osmoregulation involves solute accumulation (osmotic adjustment) by the elongating region of the hypocotyls. We investigated the relationship between growth, solute accumulation, and the partitioning of solutes during osmoregulation. Darkgrown seedlings were transplanted to vermiculite containing 1/8 (0.13 x) the water of the controls. Within 12–15 h, the osmotic potential of the elongating region had decreased to-12 bar, but it was-7 bar in the controls. This osmoregulation involved a true solute accumulation by the hypocotyls, since cell volume and turgor were virtually the same regardless of the water regime. The hypocotyls having low water potentials elongated slowly but, when deprived of their cotyledons, did not elongate or accumulate solute. This result indicated a cotyledonary origin for the solutes and a dependence of slow growth on osmotic adjustment. The translocation of nonrespired dry matter from the cotyledons to the seedling axis was unaffected by the availability of water, but partitioning was altered. In the first 12 h, dry matter accumulated in the elongating region of the 0.13 x hypocotyls, and osmotic adjustment occurred. The solutes involved were mostly free amino acids, glucose, fructose, and sucrose, and these accounted for most of the increased dry weight. After osmotic adjustment was complete, dry matter ceased to accumulate in the hypocotyls and bypassed them to accumulate in the roots, which grew faster than the control roots. The proliferation of the roots resulted in an increased root/shoot ratio, a common response of plants to dry conditions.Osmotic adjustment occurred in the elongating region of the hypocotyls because solute utilization for growth decreased while solute uptake continued. Adjustment was completed when solute uptake subsequently decreased, and uptake then balanced utilization. The control of osmotic adjustment was therefore the rate of solute utilization and, secondarily, the rate of solute uptake. Elongation was inhibited by unknown factors(s) despite the turgor and substrates associated with osmotic adjustment. The remaining slow elongation depended on osmotic adjustment and represented some optimum between the necessary inhibition for solute accumulation and the necessary growth for seedling establishment.     

Influence of UV-B Radiation on Early Seedling Growth and Translocation of 65Zn from Cotyledons in Cotton

The influence of UV-B radiation from filtered or unfiltered fluorescent sunlamps on early seedling growth and translocation of ⁶⁵Zn from cotyledons to the shoot was examined in two cultivars of cotton, Acala and Gregg. Ten-day-old seedlings which had been irradiated in the greenhouse for 6 h continuously each day for 14 days with 0.81 or 1.61 W × m^-2 UV-B radiation under two unfiltered FS-40 sunlamps, showed pronounced phytotoxic damage. This was characterized at first by bronzing and glazing of the cotyledons and later by upward curling of the leaves and abscission. Leaf expansion, dry matter accumulation, and mobilization of ⁶⁵Zn from the cotyledons was severely impaired in the young developing shoot under unfiltered UV-B radiation. A significant stress response also was observed in seedlings exposed to 0.61 W × m^-2 UV-B radiation through a polystyrene filter and 0.73 W × m^-2 UV-B radiation through a cellulose-acetate filter. This stress response was characterized by the formation of a red pigment in the petioles of the cotyledons, reduced leaf expansion, and reduced transport of ⁶⁵Zn. Control seedlings exposed to 0.03 W × m^-2 UV-B radiation through a mylar filter were green, had maximum leaf size and dry-matter accumulation, and had the greatest percentage of ⁶⁵Zn translocated from the cotyledons.     

Seed-specific overexpression of a potato sucrose transporter increases sucrose uptake and growth rates of developing pea cotyledons

During the storage phase, cotyledons of developing pea seeds are nourished by nutrients released to the seed apoplasm by their maternal seed coats. Sucrose is transported into pea cotyledons by sucrose/H+ symport mediated by PsSUT1 and possibly other sucrose symporters. PsSUT1 is principally localised to plasma membranes of cotyledon epidermal and subepidermal transfer cells abutting the seed coat. We tested the hypothesis that endogenous sucrose/H+ symporter(s) regulate sucrose import into developing pea cotyledons. This was done by supplementing their transport activity with a potato sucrose symporter (StSUT1), selectively expressed in cotyledon storage parenchyma cells under control of a vicilin promoter. In segregating transgenic lines, enhanced [(14)C]sucrose influx into cotyledons above wild-type levels was found to be dependent on StSUT1 expression. The transgene significantly increased (approximately 2-fold) transport activity of cotyledon storage parenchyma tissues where it was selectively expressed. In contrast, sucrose influx into whole cotyledons through the endogenous epidermal transfer cell pathway was increased by only 23% in cotyledons expressing the transgene. A similar response was found for rates of biomass gain by intact cotyledons and by excised cotyledons cultured on a sucrose medium. These observations demonstrate that transport activities of sucrose symporters influence cotyledon growth rates. The attenuated effect of StSUT1 overexpression on sucrose and dry matter fluxes by whole cotyledons is consistent with a large proportion of sucrose being taken up at the cotyledonary surface. This indicates that the cellular location of sucrose transporter activity plays a key role in determining rates of sucrose import into cotyledons.     

Independence of nitrogen supply and seed growth in soybean: studies using an in vitro culture system

The effect of N supply on soybean (Glycine max L. Merrill) seedgrowth was investigated using an in vitro liquid culture system.Sucrose was maintained at 200 mM and N was supplied by asparagineand methion-ine in a 6.25:1 molar ratio. Media N concentrationsfrom zero to 270 mM had little effect on cultured cotyledondry matter accumulation rate for 7 or 14 d, but rates approachedzero after 21 d when there was no N in the media. Only 17 mMN was required for maximum cotyledon growth rate up to 21 d.Cotyledon N accumulation and concentration increased in directproportion to the N concentration in the media. The N concentrationin cotyledons from a high protein genotype was higher than anormal genotype at all media N levels (0–270 mM). Solublesugar and oil concentrations in the cotyledons were highestat zero media N and decreased as media N increased. These datasuggest that the concept of seed N demand, which is thoughtto cause senescence in soybean, is incorrect. Soybean seedscan accumulate dry matter without accumulating N and apparentlyneed only minimal supplies of N (17 mM) to maintain the metabolicenzymes necessary to sustain dry matter accumulation. Geneticdifferences in seed protein concentration seem to be regulatedby the cotyledons not the supply of N. Key words: Seed N demand, seed dry matter accumulation, in vitro culture     

The effect soaking pea seeds with or without seedcoats has on seedling growth

Pea seeds (Pisum sativum L. `Alaska') with intact seedcoats (WC) and with seedcoats removed (WOC) were soaked in distilled water for 24 hours at 20°. The water, containing the pea diffusate, was decanted after the second, fourth, sixth, eighth, twelfth, and twenty-fourth hour and analyzed for total nitrogen, α-amino nitrogen, carbohydrate, and total solute dry weight. The seeds were germinated at 20° in a 16 hour photoperiod of 300 foot candles. Stem lengths and dry weights of roots, shoots and cotyledons were determined after 4, 11, and 18 days of growth. WOC seeds imbibed more water than WC seeds during the 24 hour imbibition period. Diffusates from WOC seeds always contained more solute than diffusates from WC seeds. Maltose, glucose, and fructose were not detected in the early diffusates from WOC seeds but were found in WC seed diffusates at all times. Seedlings from WC seeds had longer stems than those from WOC seeds. The dry weight of stems and roots of WC seedlings was greater than those from WOC seedlings. The dry weight of cotyledons from 18 day-old WC seedlings was less than from WOC seedlings. Water absorption by WC seeds was slower than by WOC seeds. Removal of the seedcoat allowed rapid imbibition resulting in seed injury presumably because of the loss of solutes which included monosaccharides, disaccharides, amino acids, and other nitrogen containing compounds. These results are consistent with the hypothesis that rapid imbibition disrupts membrane organization leading to reduction of seedling growth.     

Characterizing the interaction between fire ants (Hymenoptera: Formicidae) and developing soybean plants

This research characterizes the interaction between the fire ants Solenopsis invicta Buren and developing soybean plants. Phagostimulant studies showed that fire ant foraging on soybean seeds increased once the seeds imbibed water. During seedling development over a 5-d germination period, fire ant foraging shifted from the stem/cotyledons to the roots, despite continual increases in fresh weights for each region, and the fact that stem/cotyledon tissue contained the majority of food reserves. Carbohydrate analysis showed that although 2-d-old seedlings had higher concentrations of phagostimulant carbohydrates, especially sucrose, than tissues of mature plants, all tissues analyzed had enough of these sugars to induce a phagostimulant response. Fire ant association with seeds/seedlings germinated in soil resulted in reduced seedling vigor, as determined by a doubling of seedling emergence time, a threefold increase in malformed seedlings, and visible damage to cotyledons. Seeds germinated and grown to mature plants in association with fire ants, allocated 43% more assimilate into pods, but produced 28% less root dry matter, 11% less total dry matter, and there was an 81% reduction in the number of root nodules compared with control plants. We propose that reduced root development and inhibitions of nodule formation would be major yield limiting factors under field conditions. This work demonstrates that fire ant damage to soybeans is not limited to seedling establishment and that more research should be directed at the subterranean activities of the fire ant.     

Stimulation of cytokinins and chlorophyll synthesis in cucumber cotyledons by triadimefon

Triadimefon [1-(4-chlorophenoxy)-3,3-dimethyl-1-(1,2,4-triazol-1-yl)-2-butanone] changes the morphology and partitioning of dry matter in cucumber ( Cucumis sativus L. cv. National Pickling) seedlings. The dry weights, potassium and cytokinin levels in the cotyledons and roots of the treated seedlings were higher, whereas the hypocotyl weights were lower than the controls. When etiolated intact seedlings or cotyledons excised from triadimefon-pretreated dark-grown seedlings were exposed to light, chlorophyll synthesis in the pretreated cotyledons was stimulated. Triadimefon does not have cytokinin-like activity in the cucumber cotyledon greening bioassay, but appears to induce the plants to produce more cytokinims, probably by stimulating root growth. Hence it is proposed that the stimulation of chlorophyll production by triadimefon in cucumber cotyledons is mediated by maintaining high levels of potassium and cytokinins in the cotyledons.     

Virus diseases of cacao in West Africa; effect of virus infection on growth and water content of cacao seedlings

Apparently healthy cacao seedlings were compared with those infected before planting with 'swollen shoot' viruses. The leaf area and the fresh and dry weights of each organ were measured. Infected plants were lower in dry weight, leaf area, relative growth rate and net assimilation rate; a smaller proportion of the dry matter was in the leaves and lateral roots, a larger proportion in stems and tap roots. Infection caused extensive necrosis of the lateral roots, and reduced the rate of depletion of reserves in the cotyledons and the water content of the plant. Many of these effects were apparent within a month of infection and planting.     

Comparative effects of gibberellic acid and N6-benzyladenine on dry matter partitioning and osmotic and water potentials in seedling organs of dwarf watermelon

Apical applications of 0.2 μg N⁶-benzyladenine (BA), a synthetic cytokinin, or 5 μg of gibberellic acid (GA₃) significantly enhanced hypocotyl elongation in intact dwarf watermelon seedlings over a 48-h period. Accompanying the increase in hypocotyl length was marked expansion of cotyledons in BA-treated seedlings and inhibition of root growth by both compounds. A study on dry matter partitioning indicated that both growth regulators caused a preferential accumulation of dry matter in hypocotyls at the expense of the roots; however, GA₃ elicited a more rapid and greater change than did BA. In comparison to untreated seedlings, BA decreased total translocation of metabolites out of the cotyledons. Water potentials of cotyledons and hypocotyls were determined by allowing organs to equilibrate for 2 h in serial concentrations of polyethylene glycol 4000. Osmotic potentials were determined by thermocouple psychrometry. During periods of rapid growth in cotyledons and hypocotyls of BA-treated seedlings and in hypocotyls of GA-treated seedlings, the osmotic potential increased and the turgor pressure decreased in relation to untreated seedlings, indicating that cell wall extensibility was being increased. Osmotic potentials were lower in hypocotyls of GA-treated than in those of BA-treated seedlings, even though growth rates were higher in GA-treated seedlings, indicating that the latter treatment was generating more osmotically active solutes in hypocotyls.     

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     

Regulation of the Export of Potassium, Nitrogen, Phosphorus, Magnesium and Dry Matter from the Endosperm of Etiolated Oat Seedlings (Avena sativa, cv. Victory)

The rates of export of potassium, nitrogen, phosphorus, magnesiumand dry matter from the endosperm of dark-grown oat seedlingsover a germination period of 7 days have been measured. It isreported that there is a curvilinear relationship between therate of export of individual elements and dry matter and thatthe relationship is different for each element. During the earlystages of germination the reserves of all four elements weredepleted more rapidly than total dry matter. K was exportedmost quickly, followed by N, then P and Mg. The rates of exportof K and N relative to dry matter decreased progressively withtime during a 7-day period in which 90 per cent of the K, 85per cent of total N and about 80 per cent of total dry matterwere exported. The rates of depletion of P and Mg reserves relativeto the export of dry matter also decreased for a time, but thenbegan to increase again, and in the case of Mg export reacheda level similar to that of dry matter towards the end of theexperimental period. The relative rates of export of the four elements and dry matterwere the same whether the seedlings were grown with their rootsimmersed in quarter-strength Hoagland solution or in 10^–4M calcium chloride solution. When a high concentration of potassiumphosphate was supplied to the roots the rates of export of Kand P from the endosperm were reduced relative to the exportof dry matter, but transport of N and Mg was unaffected. It is concluded that the rates of transport of K, N, P and Mg,as well as of total dry matter from the endosperm of oat seedlingsare controlled on the one hand by mobilization of stored materialsin the endosperm and on the other hand by the strengths of sinksfor individual elements in the axis. Both components in this‘push-pull’ system are regulated by growth of theaxis.     

Reduction of linolenate content in soybean cotyledons by a substituted pyridazinone

The effect of a substituted pyridazinone, 4-chloro-5-(dimethylamino)-2-phenyl-3(2H)-pyridazinone (San 9785), on the reduction of linolenate content was examined in the cotyledons of the soybean cv. Century and a low linolenate mutant of soybeans, C1640, cultured in vitro. No apparent changes in dry matter and total fatty acid accumulation were observed in the cotyledons developing in the presence of San 9785. However, a significant reduction of linolenate content with a corresponding increase in linoleate resulted from growth of the cotyledons in culture medium containing San 9785. San 9785 had a greater effect on decreasing the linolenate content in cotyledons excised in early developmental phases than later stages from both the wild type and mutant soybeans. This result supports other observations that the biosynthesis oflinolenate relative to the other major fatty acids of soybean cotyledons declines in later developmental stages. The compound becomes progressively less effective in reducing the content of linolenate during seed development in the mutant than in the wild type. Both San 9785 and the mutation result in changes in phosphatidylcholine molecular species which indicates the presence of a number oflinolenate desaturation systems in developing soybean cotyledons. The possible biochemical nature of the mutation is discussed.     

Promotion of Hypocotyl Elongation in Watermelc Seedlings by 6-Benzyladenine

Hypocotyl elongation under white fluorescent light was aboutdoubled in dwarf watermelon (Citrullus lanatus0 (Thunb.) Matsu.and Nakai) seedlings treated with 0.1 to 0.3 µg apicaland 3 x 10–6 to 10.3 M root applications of 6-benzyladenine(BA). BA-enhancement of growth occurred primarily during thefirst 48 h after treatment. Increased hypocotyl length in BA-treatedseedlings was attributed more to longer cells than to an increasein cell number. Early hypocotyl growth of normal seedlings wasalso significantly enhanced by BA although final hypocotyl lengthwas not substantially affected. Benzyladenine caused expansion of cotyledons and, at higherdoses, lateral expansion of hypocotyls. BA-induced increasesin fresh weight of cotyledons and hypocotyls were accompaniedby an increase in dry weight of hypocotyls at the expense ofroots which had less dry matter than untreated seedlings.     

Effect of cadmium and nickel on mobilisation of food reserves and activities of hydrolytic enzymes in germinating pigeon pea seeds

Inclusion of cadmium as cadmium chloride and nickel as nickel chloride in media differentially induced dry matter mobilisation from cotyledons of germinating pigeon pea seeds. Cadmium depressed the activities of total amylase, protease, acid phosphatase and peroxidase in germinating seeds. The activities of these enzymes were stimulated at the lower concentrations of nickel and suppressed at the higher ones. This dual response of hydrolytic enzymes to cadmium and nickel is postulated to account for the promotory and inhibitory effects of these heavy metals on dry matter mobilisation.     

Effects of accumulation of 3-O-Methylglucose on levels of intracellular glycerol inDunaliella tertiolecta

Regulation of the concentration of osmotic solute was studied inDunaliella tertiolecta grown at an external salinity ranging between 0.5 and 1.5 mol/L NaCl. The total solute content of the cells was increased by applying 3-O-methylglucose (8 mmol/L), which was not metabolized, but accumulated at concentrations ranging between 7.5 and 12.5 μmol per mg dry mass within 2 h after its addition to the medium. 3-O-Methylglucose uptake resulted in a decreased concentration of glycerol, the solute mainly responsible for adaptation ofD. tertiolecta to high external salinity. 3-O-Methylglucose had no direct effect on the pathway of glycerol synthesis or degradation after external salinity increased or decreased, respectively. Thus, 3-O-methylglucose had no direct effects on glycerol metabolism, and it can bo assumed that it acts solely as an inert osmotic solute with the cells. 3-O-Methylglueose accumulation increased the respiration rate, as expected from an active transport.     

Free Amino Acid, Protein and Water Content Changes Associated with Seed Development in Araucaria angustifolia

The free amino acid, protein, water and dry matter contents were determined during the seed development of Araucaria angustifolia. Soluble and insoluble proteins in the mature seed represent 4.2 % of the fresh matter. The embryonic axis stored the greatest amount of soluble proteins, while cotyledons both with the embryonic axis showed the largest quantities of insoluble proteins in the mature seed. The greatest concentration of free amino acids was detected during the stage when cotyledons start to develop. Glutamic acid, aspartic acid, alanine and serine were predominant in the whole seed while arginine, lysine and γ-aminobutyric acid were present in great amounts only in cotyledons and embryonic axis. Although megagametophyte was important as a source of free amino acids, it was not the major protein storage organ in the mature seed. In the embryogenetic process, the rise of cotyledons is closely related to physiological and biochemical changes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Transport of Materials from the Cotyledons during Germination of Seeds of the Garden Pea (Pisum sativum L.)

After the first week of germination the relationship betweenthe amounts of total dry matter, nitrogen, phosphorus, sulphur,and potassium transferred to the axis from the cotyledons inthe intact plant remained approximately constant irrespectiveof the conditions of growth. It is proposed that the ratio inwhich the individual elements are transported is determinedby the proportions in which they are released by the storagecells. Deviation from this ratio during the first week of germination,and over a longer period in deshooted plants is attributed tocompetition for the available nutrients between actively metabolizingcells in the cotyledons and axis. It is demonstrated by steam-girdling that movement of materialsfrom the cotyledons into the shoot probably occurs via the phloem.Calcium is mobile in the phloem during the early stages of germination,possibly because the amount of free calcium in the cotyledonsis high.     

Role of transpiration from fruits in phloem transport and fruit growth in tomato fruits

Sink activity of fruits had been suggested to vary depending on transpiration of fruits. In this study, the effect of transpiration on dry matter accumulation was evaluated in tomato ( Lycopersicon esculentum Mill.). Fruits of cv. Saturn at 14 days after anthesis were enclosed in chambers and aerated with dried (<15% RH) or moistened (>90% RH) air. These treatments did not cause any significant differences in fruit fresh weight, dry weight, percentage of dry matter, and concentration of soluble sugars within 5 days of the treatment, or the import of ¹⁴C within 18 h after the application of ¹⁴CO₂ to the source leaves. However, displacement transducer measurement of each fruit showed a 40% reduction in growth rate in response to exchange of moistened air with dried air. When fruits of cv. Momotaro were exposed to transpiration treatments from the beginning of visible fruit enlargement until the ripening stage, the fruits exhibited 20% reduction in growth and lower accumulation of dry matter at harvest following treatment with dried air. These results suggested that higher transpiration reduced both water accumulation and dry matter accumulation. In contrast, when fruit growth was mechanically restricted by enclosing the fruits in a chamber packed with glass beads, and dried or moistened air was passed through the spaces between the glass beads, fruits exhibited higher dry matter accumulation under dried air treatment conditions. The results show that only under artificial conditions would transpiration of fruits potentially drive carbohydrate transport; it does not serve as a limiting step of carbohydrate transport to tomato fruits under normal circumstances.