Effects of Nutrient Supply on Pre-emergence Growth and Nutrient Absorption in Wheat (Triticum aestivumL.) and Sugarbeet (Beta vulgarisL.)

Nutrient absorption in wheat and sugarbeet was studied duringpre-emergence growth by adding 0, 7, 10.5 or 14 mol m^-3nitrogen(N) to the growth medium. Seedling growth and carbon, N and¹⁵Ncontents of the seedling parts were measured. Differences betweenthe natural abundance of¹⁵N in seeds and in nutrient solutionwere used to determine the proportion of N in the organs originatingfrom seed reserves and from absorption. Absorption began laterfor wheat than for sugarbeet and had less effect on seedlinggrowth. The absorbed N was found mainly in roots. Compared towheat, sugarbeet seedling N content was greatly altered andthe hypocotyl showed increased elongation when nutrients wereadded. Most of the absorbed N was found in the radicle and hypocotylwith less in the cotyledons. Sugarbeet seedling emergence andearly growth could be decreased by adverse conditions occurringafter sowing by affecting mineral availability in the soil orthrough altered root absorption.Copyright 1998 Annals of BotanyCompany Triticum aestivumL., wheat,Beta vulgarisL., emergence, natural isotopic composition, seedling, seed reserves     

Nitrate Stimulation of Mobilization of Seed Reserves in Temperate Cereals: Importance of Water Uptake

Relationships between nitrate (NO^-₃) supply, uptake and assimilation,water uptake and the rate of mobilization of seed reserves wereexamined for the five main temperate cereals prior to emergencefrom the substrate. For all species, 21 d after sowing (DAS),residual seed dry weight (d.wt) decreased while shoot plus rootd.wt increased (15–30%) with increased applied NO^-₃concentrationfrom 0 to 5–20 mM . Nitrogen (N) uptake and assimilationwere as great with addition of 5 mM ammonium (NH⁺₄) or 5 mMNO^-₃but NH⁺₄did not affect the rate of mobilization of seedreserves. Chloride (Cl^-) was similar to NO^-₃in its effect onmobilization of seed reserves of barley (Hordeum vulgare L.).Increased rate of mobilization of seed reserves with additionalNO^-₃or Cl^-was associated with increases in shoot, root and residualseed anion content, total seedling water and residual seed watercontent (% water) 21 DAS. Addition of NH⁺₄did not affect totalseedling water or residual seed water content. For barley suppliedwith different concentrations of NO^-₃or mannitol, the rate ofmobilization of seed reserves was positively correlated (r >0.95)with total seedling water and residual seed water content. Therate of mobilization of seed reserves of barley was greaterfor high N content seed than for low N content seed. Seed watercontent was greater for high N seed than for low N seed, 2 DAS.Additional NO^-₃did not affect total seedling water or residualseed water content until 10–14 DAS. The effects of seedN and NO^-₃on mobilization of seed reserves were detected 10and 14 DAS, respectively. It is proposed that the increasedrate of mobilization of seed reserves of temperate cereals withadditional NO^-₃is due to increased water uptake by the seedlingwhile the seed N effect is due to increased water uptake bythe seed directly. Avena sativa L.; oat; Hordeum vulgare L.; barley; Secale cereale L.; rye; xTriticosecale Wittm.; triticale; Triticum aestivum L.; wheat; nitrate; seed; germination; seed reserve mobilization     

Seed Germination and Seedling Growth in Sopubia delphinifolia - a Hemi-root Parasite: Germination Requirements

Requirements for seed germination (emergence of radicle) andseedling formation (emergence of both radicle and cotyledons)of a hemi-root parasite Sopubia delphinifolia were studied inthe absence of any host stimulus, in Petri dish and asepticcultures. Both water washing in trickling tap water as wellas cold treatment were effective in inducing/stimulating germinationand seedling formation in the light. Although ethrel, an ethylenereleasing compound, stimulated radicle emergence it inhibitedthe emergence of the cotyledons. Light was found to be essentialfor germination; none of the growth substances could replacethe light requirement. Light responses seem to be mediated throughthe phytochrome system. The results indicate that the emergenceof the radicle, its further growth into the root and the emergenceof cotyledons are controlled by different factors. Sopubia delphinifolia, hemi-root parasite, seed germination requirements, pretreatment, seedling formation     

Weakening of muskmelon perisperm envelope tissue 4

Muskmelon (Cucumis melo L.) embryos are enclosed in an envelopeof tissue consisting of a layer of endosperm and a multi-cell-layeredperisperm that the radicle must penetrate for germination tooccur. The force and energy required to penetrate the perispermenvelope tissue were measured using an Instron universal testingmachine at a crosshead speed of 5 mm min^–1 after 0, 10,15, 22, 23, and 25 h of imbibition at 25C. The cellular structureof perisperm envelope tissue surrounding the radicle was observedafter 10, 15, 20, 25, and 48 h of imbibition using scanningelectron microscopy. The force required to puncture 5-mm-long,micropylar seed pieces declined steadily from 1.65 N in driedseeds to 0.65 N after 21 h of imbibition. The penetration energydeclined from 3.0 N mm in dry seeds to 1.1 N mm at 21 h afterthe start of imbibition when the first seeds germinated. Theforce and energy required to penetrate germinated seed pieceswere 0.55 N and 0.9 N mm, respectively, so the net punctureforce and energy needed to rupture the micropylar region ofthe perisperm envelope was roughly 0.10 N and 0.2 N mm at radicleemergence, respectively. Instron measurements of penetrationforce and energy decreased dramatically at crosshead speedsless than the 5 mm min^–1. Crosshead speeds greater than5 mm min^–1 may overestimate the pressure needed to ruptureperisperm and endosperm tissues. Intracellular cracks were firstobserved in SEM images 15 h after the start of imbibition, andafter 20 h cracking was apparent throughout the micropylar regionof the perisperm envelope. The perisperm envelope ruptured inone of two ways, coincident with radicle emergence. In approximately85% of muskmelon seeds, a large crack formed in the perispermenvelope adjacent to the radicle, while in roughly 15 % a circulararea of the perisperm envelope detached during radicle emergence.In dead seeds, the penetration force remained constant from10–24 h after the start of imbibition, and there wereno visible signs of tissue degradation. Cellular degradationand weakening of the perisperm envelope tissue precedes radicleemergence in muskmelon seeds. Key words: Seed, Instron, turgor, cell wall, electron microscopy, Cucumis melo     

Mobilization of nitrogen reserves during regrowth of defoliated Trifolium repens L. and identification of potential vegetative storage proteins

Although it is well established that carbon reserves contributeto shoot regrowth of leguminous forage species, little informationis available on nitrogen reserves except in Medicaqo sativaL. and Trifolium subterraneum L. In this study, reserves werelabelled with ¹⁵N to demonstrate the mobilization of endogenousnitrogen from roots and stolons to regrowing leaves and newstolons during 24 d of regrowth in white clover (Thfolium repensL.). About 55% and 70%, respectively, of the nitrogen contentsof these organs were mobilized to support the regrowth of leaves.During the first 6 d, nitrogen in regrowing leaves came mainlyfrom N reserves of organs remaining after defoliation. Afterthese first 6 d of regrowth, most of the shoot nitrogen wasderived from exogenous nitrogen taken up while the contributionof nitrogen reserves decreased. After defoliation, the buffer-solubleprotein content of roots and stolons decreased by 32% duringthe first 6 d of regrowth. To identify putative vegetative storageproteins, soluble proteins were separated using SDS-PAGE ortwo-dimensional electrophoresis. One protein of 17.3 kDa instolons and two proteins of 15 kDa in roots seemed to behaveas vegetative storage proteins. These three polypeptides, initiallyfound at high concentrations, decreased in relative abundanceto a large extent during early regrowth and then were accumulatedagain in roots and stolons once normal growth was re-established. Key words: White clover, regrowth, ¹⁵N-labelled, vegetative storage proteins, electrophoresis     

Amounts of Nuclear DNA and Internal Morphology of Gibberellin- and Abscisic Acid-deficient Tomato (Lycopersicon esculentum Mill.) Seeds During Maturation, Imbibition and Germination

Using X-ray photography and flow cytometry, the internal morphologyand DNA replication activity of wild type (wt), GA- (gib-1 )and ABA-deficient (sit^w ) tomato (Lycopersicon esculentum Mill.cv. Moneymaker) mutant seeds were studied. During seed formation,from 30 to 45 d after pollination (DAP) the endosperm becomessolid and the seed starts to gain desiccation tolerance. Atthis time significant changes occur in the amounts of DNA inradicle tip cells. At 30 DAP, radicle tip cells of the threegenotypes manifest about 60% of 2C, 30% of 4C and 10% of 8Camounts of DNA. Upon maturation (45 DAP onwards), most cellsin the seeds of the three genotypes arrest in the G₁phase ofthe cell-cycle with 2C amounts of DNA. However, a relativelyhigh proportion of cells with 4C amounts of DNA was detectedin the radicle tip cells ofsit^w compared with wild type andgib-1. At the well-matured stage (60 DAP), there were about 2% ofseeds with free space in wild type andgib-1 , and about 13%insit^w . At the over-matured stage (75 DAP), even more seedswith free space were found insit^w , whereas no increase in theproportion of the seeds with free space was detected in theother two genotypes. In -1.0 MPa PEG-6000 with or without 10µM GA₄₊₇, no germination occurred in well-matured wildtype andgib-1 seeds, whether or not they were dried after harvest.However,sit^w seeds were able to germinate both in over-maturefruit and in -1.0 MPa PEG-6000. Priming of dried seeds in -1.0MPa PEG induced a large amount of free space in almost all seedsof the three genotypes, and nuclear DNA synthesis in the radicletip cells of wild type andsit^w seeds. However, PEG priming offresh (non-dried) seeds had no effect on the amount of freespace and 2C/4C DNA ratios in wild type orgib-1 seeds, but didinduce free space in about 20–25% ofsit^w seeds and provoked4C signals insit^w seeds. Removal of the endosperm and testaopposite the radicle tip of seeds resulted in root protrusion,the induction of free space and an increase of 4C DNA signalsin the three genotypes. It is concluded that ABA is crucialfor the efficient arrest of tomato embryo radicle tip cellsin G₁phase upon maturation, whereas GAs play an important rolein re-initiating 4C DNA levels upon germination. Dormancy; flow cytometry; free space; Lycopersicon esculentum ; maturation; priming; seed; tomato     

Effects of Seed Treatments on the Emergence of Oil Seed Rape Seedlings from Compacted Soil

Imbibition of seeds of oil seed rape (Brassica napus cv Jetneuf)in 10^–3 M aminoethoxyvinylglycine (AVG) or 10^–2silver thiosulphate (Ag⁺) had no effect on germination nor onthe emergence of seedlings from uncompacted or lightly compressedsoil, but significantly reduced emergence from moderately compressedsoil of 68.4 or 143.3 N cm^–2 impedance. Exertion of force by emerging control seedlings against a staticcantilever bar fitted with strain gauges reached a maximum (F_max)of 6 g over 10 h. Higher axial forces were achieved when theseedlings were emerging from compressed soil, without any changein the time required to reach F_max, so that the build-up offorce was considerably (1.8 fold) faster than in uncompressedsoil. This adaptive response to soil impedance was modified by theseed pretreatments employed. Seedlings from AVG or Ag⁺pretreatedseeds produced lower axial forces than controls, and neitherF_max nor the rate at which force developed showed any responseto soil compression. After pretreatment in 10^–3 ethephon or 10^–4 naphthaleneacetic acid (NAA) the seedlings achieved similar F_max to controlseedlings, but responded more rapidly to soil compression sothat the rate of build up of emergence force was 2.3 fold (NAA)or 2.8 fold (ethephon) faster in compressed than in uncompressedsoil. The results suggest that the exertion of force by a seedlingagainst a barrier involves a dynamic response to impedance onthe part of the seedling. This response can be either enhancedor suppressed by substances which affect ethylene productionor ethylene action. Such compounds may have promise for modifyingseedling emergence from impeding soils. Brassica napus, oil seed rape, seedling emergence, soil compaction, ethylene, Ethrel, silver, aminoethoxyvinylglycine, naphthalene acetic acid     

Mobilization of Reserves and Synthesis of Sterols and Triterpenes in Seedlings of Two Canarian Euphorbia Species

Seedlings from Euphorbia canariensis and Euphorbia lambii weregrown in the dark at 25 °C. Protein and triglyceride contentas well as levels of sugars and amino acids in the endospermwere determined during endosperm depletion. In the endospermof Euphorbia canariensis, relatively low levels of amino acids(up to 1 µmol.endosperm^–1) were found of which glutamine/glutamateaccounted for 40% at the stage of radicle emergence. High levelsof amino acids (up to 4 µmol.endosperm^–1) comparedwith sugars (up to 2 µmol sucrose.endosperm^–1) weredetected in the endosperm of Euphorbia lambii. Arginine wasthe main component (28 µmol%) of the amino acids in thistissue. In both species amino acid composition changed graduallyduring endosperm depletion. Cotyledons retained their ability to absorb a variety of watersoluble substrates after removal of the endosperm. ¹⁴C from[U-¹⁴C]sucrose was effectively incorporated into the triterpenesof the laticifers and to a lesser extent into the sterols ofthe seedling. The highest incorporation values were found inyoung seedlings about 2 d after the emergence of the radicle.Seedlings of this age also showed high incorporation rates of¹⁴C from labelled alanine, serine, threonine, valine, leucineand isoleucine into both triterpenols and sterols, but no generalconclusions about metabolic channelling in lipid synthesis couldbe made. Endosperm, Euphorbia canariensis L. Euphorbia lambii Svent., sterols, triterpenols, amino acids, laticifer, biosynthesis     

Seedling Growth in Phaseolus vulgaris L. The Early Growth of Cultivars Selected for Seedling Cold Tolerance

Silbernagel has described a test for selecting cultivars ofPhaseolus vulgaris L. which exhibit rapid seedling emergenceat low temperatures, and using this test has identified threecold-tolerant cultivars. We have compared the growth of thesecultivars with that of three control cultivars. Both at 25/20°C and at 20/15 °C day/night temperatures, Silbernagel'scultivars emerged more rapidly than the controls. This was dueto more rapid hypocotyl elongation, not to earlier germination.Rapid hypocotyl elongation was associated with high relativegrowth rates of the seedling axis and rapid loss in weight ofthe cotyledons. After emergence, cotyledons of all cultivarscontinued to lose weight at a constant exponential rate. Relativegrowth rates of the axes were not constant but declined withtime. There was no evidence that genotypic differences in growthrates before emergence were reflected in growth rates afteremergence. A simple quantitative analysis suggested that thedecline in axis relative growth rate after emergence was dueto a declining contribution from cotyledonary reserves. There were significant differences between cultivars in theinitial weight of the seedling axis. Axis weight (A) was notlinearly proportional to seed weight (S), but the curvilinearallometric relationship A = 0.0773 S^0.697 satisfactorily accountedfor most of the variation in initial axis weight between cultivars.In all cultivars, axis weights at emergence were smaller inthe cool regime than in the warm, because low temperatures depressedaxis relative growth rates relative to the rate of emergence.The biggest difference between the Q₁₀ of relative growth rate,and of emergence rate, and hence the biggest effect of low temperatureon axis weight at emergence, occurred in the cold-susceptiblecultivar Seafarer. However, genotypic cold tolerance duringthe period when growth is dependent on reserves did not appearto guarantee cold tolerance during the main period of growth. Phaseolus vulgaris, L., bean, seedling growth, temperature, cold tolerance     

Growth and Nitrogen Status of Soilless Tomato Plants Following Nitrate Withdrawal from the Nutrient Solution

The effects of withdrawing nitrogen (N) from the nutrient solutionof adult tomato plants growing in rockwool in a greenhouse wereinvestigated over a 6 week period during fruit production. Thetreatment reduced total plant growth after a lag period of about2 weeks. The commercial fruit yield after 6 weeks of N deprivationwas 7.7 kg m^-2compared to 9.3 kg m^-2in control plants. Duringthe experiment, growth of the -N plants was fuelled by N reservescontained in both the substrate (rockwool) and in plant organs.The nitrogen budget calculated for -N plants showed that onlya small amount of organic-N was readily available for internalcycling from organs such as stems. It served mainly to feedgrowing fruits which were the main sinks in the plant. The studyalso established that stores of nitrate-N were fully depletedbut it took 45 d for the -N plants to metabolize completelytheir nitrate reserves. This indicates that internal nitrateis not a readily-accessible store of labile N. An estimationof the critical N concentration (%N_c) in the aerial dry matterwas made from the data. Thus, for a crop yielding about 9.9tons DM ha^-1, %N_cwas close to 2.5%. This result is discussedin light of existing models that describe the ontogenic declinein %N_cin dry biomass of C₃plants. The study indicates that thecurrent regime of N fertilization practised in soilless culturesnot only leads to ineffective nitrogen use but also to largelosses of N to the environment; N concentrations should be decreasedin feeding recipes. The use of N-free nutrient solutions priorto the termination of plant culture may also be a means of limitingthe loss of eutrophying elements, such as nitrate, to the environment.Copyright 2001 Annals of Botany Company Lycopersicon esculentum, tomato, organ dry biomass, critical nitrogen concentration, compartment, rockwool, nitrate interruption, distribution, reserves     

Thermosensitivity in Spring White Lupin

Spring morphotypes of white lupin (Lupinus albus L.) are veryresponsive to cool temperatures during seedling developmentas expressed in a number of subsequent developmental characters.Thermosensitivity was examined in a number of studies whereseedlings were incubated at various stages of development andat differing temperatures. Plants were scored for thermosensitivity,as expressed by the number of mainstem and first order lateralvegetative nodes, at flowering. The stages of radicle emergenceand split seed coat were observed to be the developmental stageswhen mainstem and first-order lateral meristems were most sensitiveto incubation temperature. These data show that the optimumwindow for cold treating spring lupin seed is very narrow andoccurs prior to seedling emergence. Seedlings at radicle emergencestage were incubated at temperatures ranging from 1 to 27 °Cfor 0 to 14 d in 2 d increments. For temperatures less than12 °C, mainstem node number decreased curvilinearly withduration of incubation. For temperatures between 12 and 17 °C,mainstem node number decreased linearly with duration of incubation.However, mainstem node number increased linearly with durationof incubation at temperatures greater than 17 °C. The datashow that 'warm' temperatures during early seedling developmenthave a profound influence on subsequent plant morphology. Responseto 'warm' temperatures is greater than to 'cool' temperaturesand it is suggested that the differential response to warm vs.cold incubation temperatures could account for morphologicaland phenological differences observed within genotypes in fieldstudies among sites and years. The lack of temperature responsein one genotype, 'Start' may indicate thermoneutrality in thisgenotype.Copyright 1995, 1999 Academic Press Lupinus albus L., lupin, vernalization, thermosensitivity, vegetative development     

Effect of Nitrogen Supply on the Grass and Clover Components of Simulated Mixed Swards Grown under Favourable Environmental Conditions I. Carbon Assimilation and Utilization

Simulated mixed swards of Perennial Ryegrass (Lolium perenneL.) cv. S23 and White clover (Trifolium repens L.) cv. S100were grown from seed under a constant 20 °C day/15 °Cnight temperature regime and their growth and carbon economyexamined. The swards received a nutrient solution daily, whichcontained either High (220 mg l^–1) or Low (10 mg l^–1)nitrate N. Rates of canopy photosynthesis and respiration, and final drymatter yields were similar in the two treatments although theproportions of grass and clover differed greatly. The Low-Nswards were made up largely of clover. The grass plants in theseswards had high root: shoot ratios and low relative photosyntheticrates – both signs of N deficiency – and were clearlyunable to compete with the vigorously growing Low-N clover plants.These had higher relative growth rates and dry matter yieldsthan their High-N counterparts. In the High-N swards clovercontributed around 50 per cent to the sward dry weight throughoutthe measurement period despite having a smaller proportion ofits dry weight in photosynthetic tissue (laminae) than grassover much of it. The latter was compensated for, initially bya higher specific leaf area than grass, and later by a higherphotosynthetic rate per unit leaf weight. The results are discussedin relation to observed declines in the clover content of swardsafter the addition of nitrogen fertilizer in the field. Trifolium repens, white clover, Lolium perenne, perennial ryegrass, nitrogen, photosynthesis, carbon balance     

Growth Analysis of Solution Culture-grown Winter Rye, Wheat and Triticale at Different Relative Rates of Nitrogen Supply

At low nitrogen (N) supply, it is well known that rye has ahigher biomass production than wheat. This study investigateswhether these species differences can be explained by differencesin dry matter and nitrogen partitioning, specific leaf area,specific root length and net assimilation rate, which determineboth N acquisition and carbon assimilation during vegetativegrowth. Winter rye (Secale cereale L.), wheat (Triticum aestivumL.) and triticale (X Triticosecale) were grown in solution cultureat relative addition rates (R_N) of nitrate-N supply rangingfrom 0.03–0.18 d^-1and at non-limiting N supply under controlledconditions. The relative growth rate (R_W) was closely equalto R_Nin the range 0.03–0.15 d^-1. The maximalR_W at non-limitingnitrate nutrition was approx. 0.18 d^-1. The biomass allocationto the roots showed a considerable plasticity but did not differbetween species. There were no interspecific differences ineither net assimilation rate or specific leaf area. Higher accumulationof N in the plant, despite the same relative growth rate atnon-limiting N supplies, suggests that rye has a greater abilityto accumulate reserves of nitrogen. Rye had a higher specificroot length over a wide range of sub-optimal N rates than wheat,especially at extreme N deficiency (R_N=0.03–0.06 d^-1).Triticale had a similar specific root length as that of wheatbut had the ability to accumulate N to the same amount as ryeunder conditions of free N access. It is concluded that thebetter adaptation of rye to low N availability compared to wheatis related to higher specific root length in rye. Additionally,the greater ability to accumulate nitrogen under conditionsof free N access for rye and triticale compared to wheat maybe useful for subsequent N utilization during plant growth.In general, species differences are explained by growth componentsresponsible for nitrogen acquisition rather than carbon assimilation.Copyright 1999 Annals of Botany Company Growth analysis, nitrogen, nitrogen productivity, partitioning, specific root length, Secale cereale L.,Triticum aestivum L., X Triticosecale, winter rye, winter wheat, winter triticale.     

The Use of Abscisic Acid to Synchronize Carrot Seed Germination Prior to Fluid Drilling

Abscisic acid (ABA) was used as a reversible block to the progressof carrot seed germination in a practical seed treatment. Pre-treatingseeds with 10^–4M ABA solution at 15 °C for 12 d gave93% germination of viable seeds on subsequent transfer to waterbefore radicle lengths became too long for fluid drilling. Thiscompared with only 31 % without pre-treatment ABA pretreatment significantly increased the synchrony of carrotseed germination and did not affect final percentage germinationor early seedling growth rates. Seedling emergence from ABA-treatedgerminating seeds was earlier and more uniform than from untreatedgerminating seeds and seedlings from both these treatments emergedbefore those from ungerminated seeds Daucus carota L., carrot, germination, seed treatment, fluid drilling, abscisic acid, radicle extension     

Dehydration of germinating perennial ryegrass seeds can alter rate of subsequent radicle emergence

Perennial ryegrass (Lolium perenne L.) seeds (caryopses) germinateat or near the soil surface, where water potential can fluctuatewidely. This study examined germination of ‘Del Ray’perennial ryegrass seeds when imbibition was interrupted bydehydration prior to radicle emergence. Seeds were hydratedfor 0 to 40 h (26C), dehydrated at atmospheric water potentialsof –4, –40, –100 and/or –150 MPa for4–168 h, then rehydrated. Germination (radicle elongation 1 mm), seedling growth, solute leakage, and endogenous abscisicacid (ABA) levels were measured. Treatment differences in finalgermination percentage, seedling growth, and solute leakagewere generally not significant. However, the onset of radicleemergence was delayed and the rate of germination slowed whendehydration at –150 MPa was initiated after 36 or 40 hhydration. Slowed germination rates were not observed when dehydrationwas initiated before 36 h, when dehydration occurred at –4MPa, or when dehydration at –150 MPa was preceded by dehydrationat –4 MPa for 24 h. Exogenous abscisic acid (ABA) concentrationsabove 10^–6 M inhibited germination. However, endogenouswhole seed ABA levels declined during imbibition due to leaching,and did not increase during dehydration treatments that delayedgermination. These results illustrate that rate of late-occurringdehydration treatments is critical in determining subsequentgermination response. We propose that seed response to late-occurringdehydration may be of ecological significance in timing radicleemergence to coincide with adequate soil moisture for seedlingestablishment. Key words: Abscisic acid, seed germination, timing     

The Effect of Salinity Stress upon Protein Synthesis of Germinating Wheat Embryos

Two differently salt-sensitive wheat genotypes were imbibedin 0·4 M NaCl for 72 h or, alternatively, for 48 h andthen transferred to water. Seed germination, fresh weight andprotein synthesis in embryos were determined. The followingdifferences were found in the synthesis of in vivo [³⁵S]methionine-labelledproteins during salt imbibition: (a) a general decrease or disappearanceof polypeptides specific to the radicle emergence phase in thesalt-sensitive genotype; (b) a new synthesis of polypeptideswhich are not found during water imbibition and are common toboth genotypes; (c) a differential synthesis of polypeptidesthat are unique to each cultivar. Upon return to water, salt-inducedproteins ceased to be synthesized while proteins associatedwith an advanced germination phase were actively produced. Theseresults suggest that the expression of 'salt stress' proteinsis related to the adaptation process of seeds to salinity aswell as to the genetic constitution of a selected salt-tolerantgenotype.Copyright 1993, 1999 Academic Press Triticum durum, wheat, embryo, salt stress, protein synthesis     

Carbon and nitrogen content of Noctiluca scintillans in the Seto Inland Sea, Japan

The carbon and nitrogen content of Noctiluca scintillans cellsfrom the Seto Inland Sea, Japan was investigated in order toestimate its biomass in natural samples. The carbon contentof N.scintillans ranged from 123 to 627 ng C cell^–1 witha mean value of 353 ng C cell^–1, or 1.12 to 2.67 fg Cµm^–3 with a mean value of 1.98 fg C µm^–3.The nitrogen content ranged from 36.0 to 232 ng N cell^–1with a mean value of 131 ng N cell^–1, or 0.499 to 0.910fg N µm^–3 with a mean value of 0.694 fg N µm^–3.Total cell carbon and nitrogen increased but the carbon andnitrogen per cell volume decreased with increasing cell volume.The C/N ratio of the cells ranged from 2.3 to 4.4, which wasrelatively low compared with the Redfield ratio. The carbonand nitrogen content was extremely low (91.2 ng C cell^–1,41.8 ng N cell^–1) for starved cells, whereas it was extremelyhigh (528 ng C cell^–1, 205 ng N cell^–1) for cellswhich had ingested the large diatom, Coscinodiscus wailesii.Our results suggest that the carbon and nitrogen content ofN.scintillans varies depending on its physiological conditionand the type of food that it has recently consumed.     

Cytokinins in Germinating Seeds of Phaseolus vulgaris L. II. Transport and Metabolism of 8[14C]t-Zeatin Applied to the Radicle

The application of 8[¹⁴C]t-zeatin to the radicle tips of germinatingPhaseolus vulgaris seeds revealed that cytokinins are transportedrapidly from the embryonic axis to the cotyledons, and are utilizedand metabolized extensively in these organs. The informationobtained on the transportation between the different parts ofthe embryo is consistent with the view that the mobilizationof food reserves from the cotyledons is controlled by cytokininswhich originate in the embryonic axis. Tentative identificationof the radioactive metabolites formed indicate that the appliedzeatin was altered by side-chain cleavage and by substitutionto the adenine ring. Phaseolus vulgaris, bean, germination, cytokinins, transport, radicle     

The role of seed reserves in arbuscular mycorrhizal formation and growth of Leucaena leucocephala (Lam.) de Wit. and Zea mays L.

We show here that seed reserves in Leucaena leucocephala (Lam.) de Wit. and Zea mays L. (maize) are important for mycorrhizal formation and seedling growth. Seed reserve removal reduced mycorrhizal formation markedly in Leucaena but not in maize, except at 15 and 45 days after seed reserve removal. Partial or total removal of seed reserves decreased plant growth and tissue nutrient concentrations in both hosts. Nodule number in Leucaena, which was related positively to plant biomass and mycorrhizal infection levels, was reduced when one or both cotyledons were severed. Leucaena seedlings without or with partial seed reserves had higher nutrient use efficiencies throughout seedling growth. But such an effect was observed only initially in maize. Seed reserve removal increased the specific absorption rates of nutrients in both hosts. Phosphorus absorption rate was significantly and positively related to root infection levels in both Leuceana and maize. Though the growth rates of plants without seed reserves were low initially, these plants had higher growth rates during later stages. We conclude that seed reserves are not only important for seedling growth, but also for mycorrhizal formation and nodulation. Received: 15 July 1999 / Accepted: 6 December 1999     

Potential contributions of vertically migrating Rhizosolenia to nutrient cycling and new production in the open ocean

We present a numerical model of nutrient uptake and photosynthesisduring migrations of the marine diatom Rhizosolenia that wasdeveloped to estimate fluxes of carbon and nitrogen due to thesemigrations in the open ocean. The predicted specific rate ofincrease of Rhizosolenia was 0.11–0.15 day¹, whereas thetotal time for one migration cycle ranged between 3 and 5 days.Using published estimates of Rhizosolenia abundance, we estimatethat new primary production due to Rhizosolenia migrations rangesbetween 0.018 and 0.033 mmol N m^–2 day^–1. Thesevalues represent up to 17% of new production due to turbulentdiffusive fluxes of nitrate into the euphotic zone and are ofthe same order of magnitude as new production due to nitrogenfixation in tropical oceans. Large-scale contributions of Rhizosoleniato oceanic new production are limited by their relatively lowstanding crop. Variations in the formulation of losses withdepth greatly affected gross and net fluxes of carbon and nitrogen.Better characterization of losses of Rhizosolenia and improvedestimates of its abundance will help determine more accuratelythe contributions of Rhizosolenia to global biogeochemical cycles. ¹Present address: Department of Agricultural and EnvironmentalScience, The Queen's University of Belfast New forge Lane, BelfastBT95PX, UK