In vivo Studies on the Occurrence of Stored mRNA in Embryonic Axes of Vigna unguiculata Seeds

-Amanitin and cordycepin at various concentrations were testedfor their inhibitory effect on the fresh weight increase ofVigna unguiculata embryonic axes after the onset of imbibitionand on the incorporation rate of ³H-labeled leucine into proteinin axes of the 36–38 h stage. -Amanitin at 0.5–5µ/Kg/ml clearly exerted an inhibitory effect on both thefresh weight increase and the protein synthesis. This drug at1 µg/ml, however, showed no significant effect on theprotein synthesis at an early stage of imbibition (4 h), whereascycloheximide was a very potent inhibitor. By experiments inwhich ‘dry’ axes were allowed to imbibe 3H-lebeledadenosine solution for 4 and 12 h in the presence of -amanitin,it was found that poly A⁺RNA was newly synthesized to some extentin axes as early as 4 h after the onset of imbibition and thatthe drug effectively inhibited the poly A⁺RNA synthesis. Theresults may indicate the occurrence of stored mRNA in embryonicaxes of V. unguiculata seeds. (Received June 11, 1983; Accepted August 16, 1983)     

The Role of ABA in the Control of Apple Seed Dormancy Re-appraised by Combined Gas Chromatography-Mass Spectrometry

Measured by GC—MS²—SIR³, endogenous ABA⁴ in embryonicaxes of seeds of Malus pumila L. cv. Golden Delicious decreased8-fold and cotyledon ABA by only 60%, during 10–50 d ofstratification at 5 ?C, after ABA leaching during an initial24 h soaking. During stratification, the percentage germinationof embryos transferred to 17?C showed a significant linear dependenceon log_e of ABA levels in the axes at transfer. Between 50 and70 d, ABA levels increased markedly in axes and testa both ofstratified seeds and seeds allowed to re-dry at 17 ?C afterinitial soaking. The ability of fully stratified axes with elevatedendogenous ABA to germinate indicated that stratification haddecreased their ABA sensitivity. Changes in cotyledon ABA couldnot account for the promotory effect of cotyledons on germinationduring the first 30 d of stratification. Loss of testa inhibitionof germination during stratification was not linked with changesin testa ABA. Stratification markedly increased the sequestrationin the axes of exogenous ABA supplied via the cotyledons. Changesboth in axis ABA levels and sensitivity were thus correlatedwith dormancy release, but subject to modifying control by thecotyledons and testa not involving ABA. Rehydration of driedseeds affected axis ABA later during storage via mechanismsunconnected with dormancy. Key words: ABA, seed dormancy, stratification     

Cotyledonary mRNA Species and Germinability of Immature Vigna unguiculata Seeds

We have defined four stages in the development of cowpea seeds:I(9–11 days after flowering), II (13–15), HI (17–19)and IV (22–24). Poly A⁺ RNA fractions were prepared fromcotyledons of developing (stages I–IV) and germinating(0, 12, 24 and 48 h after imbibition) seeds. Poly A⁺ RNAs fromstages I–III exhibited high translation activities witha maximum at stage II, and the activity was markedly reducedat stage IV. In cotyledons of germinating seeds, the translationactivity was low until 12 h after the onset of imbibition butrose thereafter. Analysis of in vitro translation products withSDS-polyacrylamide gel electrophoresis and fluorography showedthat the abundant mRNA population underwent a distinct changebetween stages II and III of seed development. Since the mRNApopulation at stage III was very similar to that of stage IV(mature seeds), it appears that, as far as mRNA species areconcerned, the prerequisites for germination are fully availablein the developing seeds by stage III. This assumption was supportedby the fact that immature seeds at stage III exhibited highgermination rates and normal axial growth and produced -amylaseat levels similar to those produced by mature seeds. Severalpolypeptides which have been regarded as translation productsof stored mRNA (poly A⁺ RNA from dry seeds) were detected atearlier stages of germination. (Received September 29, 1988; Accepted January 25, 1989)     

Dimethipin (2,3-Dihydro-5,6-dimethyl-1,4-dithiin 1,1,4,4-tetraoxide) Effects on Soybean Seedling Growth and Metabolism

Three-day-old dark-grown soybean [Glycine max (L.) Merr.] seedlingswere transferred to 2 mM CaSO₄ or 10^–5 M dimethipin in2 nM CaSO₄ and root-fed via liquid culture. Plants were placedin continuous darkness or in continuous white light (200 µE.m^–2?s^–11,PAR) at 25?C. Dimethipin inhibited root and shoot elongationin dark-grown plants after 24 h and 48 h, respectively. In thelight, root elongation was inhibited also after 24 h, but hypocotylelongation was not significantly affected. Extractable phenylalanineammonia-lyase (PAL) activity per axis in dimethipin-treateddark-grown axes was not generally affected but, in the lightdimethipin caused a significant decrease in PAL activity (24to 96 h). Total soluble hydroxyphenolics in axes were not affectedby dimethipin in light- or dark-grown plants. Anthocyanin andchlorophyll levels were lowered in hypocotyls of dimethipin-treatedplants after 48 to 96 h. Soluble protein in hypocotyls of light-or dark-grown seedlings was not substantially affected by dimethipin.Nitrate reductase (NR) activity (per organ) was generally notaffected by dimethipin in light-grown cotyledons, but in theroots of these seedlings, NR activity was significantly decreased.Proteolytic enzyme activity using three substrates (leucine-p-nitroanilide,LPNA; proline-p-nitroanilide, PPNA; and benzoylarginine-p-nitroanilide,BAPA) indicated little effect on enzyme activities per organin roots and hypocotyls. These data suggest that dimethipinat low concentrations can cause significant growth inhibitionin soybean seedlings grown in either light or darkness and thatfurthermore, extractable activities of some enzymes associatedwith nitrogen metabolism and secondary metabolism are alteredby this chemical. Light also plays a role in the activity ofthis chemical. (Received November 29, 1983; Accepted January 25, 1984)     

Lipid Synthesis and Ultrastructure of the Laticifers of Etiolated Euphorbia lathyris Seedlings

In 6–14-day-old etiolated seedlings of Euphorbia lashyrisa latex triterpene synthesis of 19 µg day^–1 wasrecorded. This production was proportional to stem growth. Laticiferdistribution in the cotyledons and stem was studied. In ultra-thinsections the occurrence of many mitochondria was observed. A¹⁴C-latex triterpene synthesis was measured after ¹⁴C-glucoseand ¹⁴C-sucrose uptake by the cotyledons in which most of the¹⁴C-triterpenes were synthesized. ¹⁴C-incorporation into theselipids from [1^–14C]glucose, [6-¹⁴C]glucose and [3,4^–14points to a glycolytic catabolism of glucose prior to terpenesynthesis. The possible involvement of mitochondria in thissynthesis is discussed. Euphorbia lathyris, triterpene synthesis, laticifer, latex, mitochondria, ultrastructure     

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

The application of 8[¹⁴C]t-zeatin to the cotyledons of germinatingbean seeds demonstrated that cytokinins are not readily exportedfrom the cotyledons to the embryonic axis during the early stagesof this process. In the cotyledons the applied zeatin is metabolizedextensively to metabolites which are polar and which occur atR_F 0·2–0·5 on paper chromatograms. Thesemetabolites are stable and are not readily exported from thecotyledons. In contrast the metabolites found at R_F 0–0·2are more readily exported. When exported to the radicles andplumules a large proportion of the translocated metaboliteswere converted to compounds which on paper co-chromatographedwith zeatin. This seems to suggest that the embryonic axis hasthe capacity to synthesize cytokinins and that some of the metabolitesformed during its catabolism can also be used for its synthesis. Phaseolus vulgaris, bean, germination, cytokinins, transport, cotyledons     

Synthesis of Translatable mRNA for Phytochrome during Imbibition in Embryonic Axes of Pisum sativum L.

The activity of translatable mRNA for phytochrome was measuredin excised embryonic axes of Pisum sativum L. during imbibitionboth in the dark and under continuous irradiation with whitelight. When measured in cell-free protein synthesis systemsof both rabbit reticulocyte lysate and wheat germ extract, theactivity of translatable mRNA for phytochrome was not detectedin dry quiescent axes but increased rapidly after imbibitionin the dark. After 24 h imbibition, the level of translatablemRNA for phytochrome, in terms of the incorporation of [³⁵S]methioninein the wheat germ system, was ca. 0.0034% of total translatablemRNA. In the presence of 0.5 µg ml^–1 -amanitin,the appearance of translatable mRNA for phytochrome was inhibitedby 60%, while 2 µg ml^–1 -amanitin was almost completelyinhibitory. This indicates that the synthesis of translatablemRNA for phytochrome in embryonic axes begins upon imbibition. When the axes were imbibed under continuous white light, theactivity of phytochrome mRNA increased as rapidly during thefirst 3 h as in the dark. After this time, the activity wasmarkedly lower than in the dark. Nevertheless, during the 24h of imbibition, activity in the light was always found to bemore than half of that in the dark. These results indicate thatin germinating pea axes the level of translatable mRNA for phytochromeis partially repressed by light. (Received June 5, 1985; Accepted September 2, 1985)     

In vitro Propagation of Red Cabbage (Brassica oleracea L. var. capitata)

By manipulation of various growth regulators and physical conditions,plants have been regenerated from excised roots, stem segments,cotyledons, leaves, and callus cultures of red cabbage (Brassicaoleracea var. capitata) grown under in vitro conditions. Shootbuds were induced on isolated root segments (1 cm long) culturedon Murashige and Skoog's medium and the frequency of bud formationwas greatly enhanced by the addition of kinetin (0.5 part 10^–6).Callus obtained from the seeds, cotyledons, and hypocotyl segmentscultured on a medium fortified with 2,4-D (1 part 10^–6),kinetin (0.1 part 10^–6), and coconut milk (10%, v/v) hasbeen repeatedly subcultured. The callus is slow growing, andon transference to a kinetin (2 parts 10^–6) and IAA (2parts 10^–6) medium underwent morphogenesis to give riseto plants. The significance of the propagation of red cabbageby in vitro culture is pointed out.     

The Inhibitory Effect of (2-Chloroethyl)-trimethylammonium Chloride on Chlorophyll and Protein Synthesis in Lettuce Cotyledons, and its Reversal by Potassium

Germinated seeds of Lactuca sativa (L.) were placed in Petri-dishesin (2-chloroethyl)-trimethyl-ammonium chloride (CCC; 0.005–0.05M), KN0₃ (0.01 M), and KC1 (0.01 M) solutions, and incubatedfor 2 or 5 days under continuous light. CCC strikingly arrestedchlorophyll accumulation, and retarded cotyledon growth relativelylittle. The retardant inhibited ¹⁴C-leucine incorporation intobulk proteins of the cotyledons. KN0₃ and KC1 promoted cotyledongrowth and chlorophyll synthesis per cotyledon by about 150per cent, and about doubled protein synthesis. Potassium saltscompletely reversed the inhibitory effects of CCC on chlorophylland protein synthesis. It is suggested that the inhibition ofgreening by CCC is dependent on a prior inhibition of proteinsynthesis.     

Changes in ubiquitin and ubiquitin-protein conjugates during seed formation and germination

Changes in both free ubiquitin and ubiquitin-protein conjugateswere followed in cotyledons of lupin (Lupinus albus L.) duringthe course of seed formation, from the flower to the dry seed,and during germination and seedling growth, from the dry seedto the senescing cotyledons. The observed levels of ubiquitinconjugates, detected by immunoblotting using antiubiquitin antibodiesand by autoradiography using ¹²⁵I-labelled ubiquitin, suggestan intense involvement of the ubiquitin-mediated proteolyticpathway during the highly regulated phases of seed formationand germination. High amounts of free ubiquitin are presentat all stages in all tissues examined. With the exception ofthe dry seed, the high molecular mass ubiquitin-protein conjugatesare also present at all stages. Higher amounts of these conjugateswere found during the initial stages of pod development andseed germination and during the most active phases of storageprotein deposition and degradation. Germination and seedlinggrowth in total darkness not only delays the degradation ofthe storage proteins, but also extends the period characterizedby the presence of a high amount of these conjugates. No suchconjugates were detected in the dry seeds, probably reflectingthe extremely low metabolic activity observed in these organs.A number of smaller molecular mass polypeptides were also detectedat different stages of seed development, germination and seedlinggrowth. Of particular interest is the abrupt accumulation ofan abundant 20 kDa polypeptide in the cotyledons during the4th day after imbibition, which is maintained in high amountsin these organs, rapidly declining after about 12–14 d.The pattern of accumulation of the 20 kDa polypeptide is controlledneither by light nor by the embryo axes, and large variationsin its concentration are observed during heat shock. Key words: Ubiquitin, ubiquitin-protein conjugates, seed storage proteins, protein synthesis, protein degradation     

Effects of Temperature on Growth and Protein and RNA Syntheses of Excised Vigna mungo Embryonic Axis

Embryonic axes excised from dry Vigna mungo seeds cultivatedon wet filter paper grew well at 27°C, but did poorly below15°C. The increase in fresh weight at 27°C was completelyinhibited by both cycloheximide and a-amanitin. Excised axescould grow well at 15°C only if cultivated at 27°C forthe first 12 h. Also, excised axes cultivated at 15°C forseveral days grew well when transferred to 27°G. These resultssuggest that the ability of the axes to grow is retained duringcultivation at 15°C, even when no growth occurs, and thatonly the initial stage of cultivation requires high temperaturesfor growth. The incorporation of ³H-leucine into protein in the excisedaxes during the first 6 h of cultivation at 15°C was muchslower than that at 27°C. The incorporation rate at 15°Gduring the second 6 h was, however, considerably high. In contrast,the incorporation of ³H-uridine into the total RNA fractionat 15°C was much slower during the first and the second6 h as compared to that at 27°C, suggesting a differencein the response to temperature between protein and RNA synthesesin the axes. (Received February 9, 1983; Accepted August 4, 1983)     

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     

Soya Bean Seed Growth and Maturation In vitro without Pods

Immature Glycine max (L.) Merrill seeds, initially between 50and 450 mg f. wt, were grown and matured successfully in vitro.Excised seeds were floated in a liquid medium containing 5 percent sucrose, minerals and glutamine in flasks incubated at25 °C under 300 to 350 µE m^–2 s^–1 fluorescentlight. During 16 to 21 d in culture, seeds grew to a matured. wt of 100 to 600 mg per seed at an average rate of 5 to 25mg d. wt per seed d^–1 depending on initial size. Growthrates were maximal during the first 8 to 10 d in vitro but declinedwith loss of green colour in the cotyledons. Seed coats rupturedwith rapid cotyledon expansion during the first 2 d in culture.Embryos were tolerant to desiccation and 80 to 90 per cent germinatedif removed from culture before complete loss of green colour.The growth of excised seeds in vitro exceeded the growth ofseeds in detached pods, but when windows were cut in pods topermit direct exposure of seeds to the medium, seed growth wascomparable. Glycine max (L.) Merrill, soya bean, seed culture, seed growth, seed maturation, germination     

STUDIES ON HOMOSERINE DEHYDROGENASE IN PEA SEEDLINGS

Partially purified homoserine dehydrogenase was prepared frompea seedlings. The optimum pH for this enzyme is approximately 5.4. The K_mvaluesfor ASA and TPNH are 4.6xl0^–4Af and 7.7xl0^–5M, respectively.This enzyme can also utilize DPNH but less effectively thanTPNH. In contrast with yeast homoserine dehydrogenase whichis insensitive to — SH reagents, the pea enzyme is inhibitedalmost completely by 10^–4MPCMB and 10^–5MHgCl₂, theinhibition being removed by 10^–2M thioglycolate. Homoserinedehydrogenase was found not only in decotylized seedlings, butalso in cotyledons. The significance of this enzyme in homoserine biosynthesis ingerminating pea seeds has been discussed. (Received February 20, 1961; )     

Control of Seed Growth in Soya Beans [Glycine max (L.) Merrill]

The seed is the primary sink for photosynthate during reproductivegrowth and an understanding of the mechanisms controlling therate of seed growth is necessary to understand completely theyield production process. The growth rate of individual seedsof seven soya bean [Glycine max (L.) Merrill] cultivars withgenetic differences in seed size varied from 10.8 to 3.9 mgseed^–1 day^–1. The growth rates were highly correlatedwith final seed size. The growth rate of cotyledons culturedin a complete nutrient medium was highly correlated with thegrowth rate of seeds developing on the plant and with finalseed size. The number of cells per seed in the cotyledons variedfrom 10.2 to 5.7 x 10⁶ across the seven cultivars. The numberof cells per seed in the cotyledons was significantly correlatedwith final seed size and the seed growth rate both on the plantand in the culture medium. The data suggest that genetic differencesin seed growth rates are controlled by the cotyledons and thenumber of cells in the cotyledons may be the mechanism of control. Glycine max L., soya bean, seed size, growth rate, cell number, sink activity     

Ageing of Cucumber and Onion Seeds: Phospholipase D, Lipoxygenase Activity and Changes in Phospholipid Content

Cucumber (Cucumis sativus L. cv. Mesa) and onion (Allium cepaL. cv. Rijnsburger Heldis) seeds were rapidly aged at 40 °Cand 74% relative humidity. Onion seeds were also slowly agedat 40 °C with 15% relative humidity for 11 months and onemore month at 28% relative humidity. Significant loss of totaland individual phospholipids was an early event during bothstorage treatments. With slow ageing of onion, loss of phosphatidylcholineoccurred several months before loss of viability and vigourwas detected. Phosphatidic acid, the lipid product of phospholipaseD action, increased during rapid ageing of both cucumber andonion. Phosphatidic acid was present in onion seeds before theageing treatments and its content remained unchanged in theslowly aged seeds. There was 1600 (cucumber) and 2000 (onion)times more phospholipase D activity (6 x 10⁵ and 2·9x 10⁵ nmol g^–1 d^–1 in cucumber and onion, respectively)in crude extracts from non-aged seeds than was required to accountfor the fastest fall in phospholipids (72, 372 and 144 nmolg^–1 d^–1 for cotyledons and radicles of cucumberand onion, respectively, over the first 9 d [cucumber] or 1d [onion] of ageing) and fastest increase in phosphatidic acid(7, 162 and 37 nmol g^–1 d^–1). How accurate a guidethe in vitro activity of phospholipase D was to the in vivoactivity was unclear. However, the considerable excess activityseen with the formation of phosphatidic acid supports the proposalthat hydrolysis of phospholipids by phospholipase D is a firststep in deterioration during ageing. Substantial lipoxygenaseactivity was also detected (58 x 10³ and 54 x 10³ nmol g^–1d^–1 respectively, for non-aged cucumber and onion seeds).However, the increase in conjugated dienes (an early productof peroxidation) in ageing cucumber seeds was comparativelysmall (90 nmol g^–1 d^–1 over 21 d ageing), and increasein malondialdehyde could not be detected, indicating that peroxidationmay not have been a major factor in cucumber. The increase inconjugated dienes during rapid ageing of onion seeds was larger(1·5 x 10³ nmol g^–1 d^–1 over days 0–2of rapid ageing), much greater than the decrease in phospholipidacyl groups (260 nmol g^–1 d^–1 over days 0–2of rapid ageing) indicating the occurrence of peroxidation offatty acids released from reserve as well as from membrane lipids.This higher level of conjugated dienes during onion ageing wasthe main difference between cucumber and onion, indicating thatthe level of peroxidation could be an important difference betweenfast and slow ageing seeds. However, peroxidation is not theonly possible deleterious process since hydrolysis of the normalmembrane phospholipids to phosphatidic acid increased the contentof non-bilayer-forming lipids and this too could be a directmembrane-destabilizing consequence of phospholipase D actionduring ageing. Key words: Cucumis sativus L. (cucumber), Allium cepa L. (onion), seed ageing, phospholipase D, lipoxygenase, phospholipids     

Factors Affecting the Biosynthesis of Abscisic Acid

Incorporation of labelled mevalonate into abscisic acid (ABA)has been demonstrated in the cotyledons of mature avocado seeds,embryos and endosperms of developing wheat seeds, and avocadostems. The increase in ABA concentration on wilting parallelsthe increased incorporation of [2^–14C)mevalonate intoABA in avocado leaves and stems, suggesting that the increasein ABA content occurs by synthesis rather than by release froma stored precursor. Incorporation of [2^–14C]mevalonateby avocado mesocarp segments is unaffected by an 18 per centwater loss. The ABA content of roots was hardly affected bya 30 per cent water loss, indicating that the wilt-activatedmechanism is not fully operative in these tissues. Submerged Ceratophyllum plants and submerged parts of Callitricheshoots show a twofold increase in ABA content on wilting whereasthe aerial rosettes of the latter plant show a sixfold increase.This suggests that the occurrence of the wilt-induced mechanismis affected by previous growth conditions as well as by themorphology of the tissue.     

Protein Synthesis During Rehydration, Germination and Seedling Growth of Naturally and Precociously Matured Soybean Seeds (Glycine max)

Soybean seeds [Glycine max (L.) Merr.] synthesize de novo andaccumulate several non-storage, soluble polypeptides duringnatural and precocious seed maturation. These polypeptides havepreviously been coined ‘maturation polypeptides’.The objective of this study was to determine the fate of maturationpolypeptides in naturally and precociously matured soybean seedsduring rehydration, germination, and seedling growth. Developingsoybean seeds harvested 35 d after flowering (mid-development)were precociously matured through controlled dehydration, whereasnaturally matured soybean seeds were harvested directly fromthe plant. Seeds were rehydrated with water for various timesbetween 5 and 120 h. Total soluble proteins and proteins radio-labelledin vivo were extracted from the cotyledons and embryonic axesof precociously and naturally matured and rehydrated seed tissuesand analyzed by one-dimensional PAGE and fluorography. The resultsindicated that three of the maturation polypeptides (21, 31and 128 kDa) that had accumulated in the maturing seeds (maturationpolypeptides) continued to be synthesized during early stagesof seed rehydration and germination (5–30 h after imbibition).However, the progression from seed germination into seedlinggrowth (between 30 and 72 h after imbibition) was marked bythe cessation of synthesis of the maturation polypeptides followedby the hydrolysis of storage polypeptides that had been synthesizedand accumulated during seed development. This implied a drasticredirection in seed metabolism for the precociously maturedseeds as these seeds, if not matured early, would have continuedto synthesize storage protein reserves. Glycine max (L.) Merr, soybean, cotyledons, maturation, germination/seedling growth     

Protein Modification and Utilization of Starch in Soybean (Glycine max L. Merr.) Seed Maturation

Seeds of soybean (Glycine max L. Merr.) harvested at variousstages of development and allowed to dry in intact pods undergoa maturation process and are viable. Defatted powders of seedharvested 24–66 d after flowering were extracted to yieldbuffer-soluble and alkali-soluble proteins. Imposition of amaturation process increased the level of buffer-soluble proteinsbut had no effect on the disulflde content of these proteins.After undergoing maturation, seeds showed an accumulation ofbuffer-soluble polypeptides in the molecular weight range of43–94 kD. Maturation may be associated with the synthesisof specific polypeptides having a molecular weight of approximately85 kD. Alkali-soluble proteins, which represents the storageproteins, did not show any responses to maturation. Their quantityincreased substantially during seed development and the disulfidelevel was only half that of buffer-soluble proteins, attaininga maximum value of 10.9 mol S per 10⁵ g protein. Matured seedat all harvest dates had a final starch content close to thatof normal seed, 10–20 mg g^–1, and soluble sugarswere maintained at quite high levels, 51–83 mg g^–1.The metabolic program for synthesis and degradation of starchseems quite rigidly followed and is independent of harvest dateor of attachment to the parent plant. Soybean seeds retain considerablesoluble proteins and soluble sugars throughout maturation, andthese collectively may be important in maintaining a desiccationresistant structure.     

Transport and Metabolism of Dihydrozeatin Riboside in Germinating Lupin Seeds

[³H]-dihydrozeatin riboside was applied selectively to the embryonicaxes or to the cotyledons of germinating lupin (Lupinus luteusL. cv. Weiko III) seeds 6 h following the start of imbibition.There was little transport of dihydrozeatin riboside from embryoto cotyledons up to 6 h after the application, but a substantialamount of radioactivity had moved into the cotyledons at theend of the 10 h incubation period. However, there was no detectablemovement of [³H]-dihydrozeatin riboside from the cotyledonsto the embryonic axis. This indicated a highly polarized movementof cytokinins during the early stages of seed germination. Exogenouslyapplied [³H]-dihydrozeatin riboside was found to be very stable,both when applied to the embryonic axes and cotyledons of intactseed, or following excision, and there was little metabolismwith only small amounts of radioactivity found associated withdegradative metabolites. The embryonic axis of this specieshas recently been found to synthesize cytokinins within 12 hfrom the start of imbibition, and the results of this studyindicate that the embryo-derived cytokinin is probably transportedto the cotyledons where it accumulates and subsequently participatesin the control of cotyledon function. Key words: Lupinus luteus, cytokinin transport and metabolism, dihydrozeatin riboside, seed germination