Activities of Transaminases, Amylases and Proteases during Endosperm Degradation in Normal and Opaque-2 Zea mays L. cv. Maya

Transaminase, amylase and protease activities were comparedin seedlings of normal and Opaque-2 (o2) maize. Transaminaseactivity, greater in normal maize, was highest in the scutellumfrom which it decreased rapidly in activity from day 2 afterimbibition; only low activity was observed in endosperm andaxis tissue. Amylolytic activity, optimal around pH 5, was greater in normalmaize at all stages of endosperm degradation. Activity whichwas low on day 2, rose to a peak on day 6 and declined afterwards.The level of free sugars in the endosperm of normal was higherthan in o2 maize, and in both varieties was highly correlatedwith amylolysis. Protease activity, optimal at pH 3.6, was also greater in normalendosperms and increased up to day 6 and activity was maintainedat this level until around day 14. Although the activity ofall three enzyme systems examined was greater in normal maizethere were no apparent differences in the overall growth ofnormal and o2 seedlings during this period. Zea mays L, maize, corn, endosperm, enzyme activity, transaminase, amylase, protease     

Action of Sorghum Proteinase on the Protein Bodies of Sorghum Starchy Endosperm

Protein bodies isolated from the starchy endosperm of ungerminatedsorghum exhibited some autolytic activity but seemed incapableof significant self-hydrolysis. Enzyme assay, transmission electronmicroscopy, sodium dodecyl sulphate—polyacrylamide gelelectrophoresis and amino acid analysis revealed that a proteinaseextract from germinated sorghum could degrade the protein bodiesin a manner resembling that which takes place in vivo. The proteinbodies were degraded mainly from the periphery. Glutelin (matrixprotein) was first hydrolysed, followed by the prolamin proteinbody protein. Proteinase extracts from both the germ and endospermof germinated sorghum were capable of degrading the proteinbodies. This finding is consistent with the concept that theproteinase is synthesized in the germ and then secreted intothe starchy endosperm during germination. Key words: Sorghum bicolor, protein body degradation, proteinase.     

Tissue-Dependent Expression of the Rice wx+ Gene Promoter in Transgenic Rice and Petunia

The waxy (wx) locus, which controls the amylose synthesis, isknown to be expressed specifically in the endosperm and pollen.To study the tissue-specific regulation of the wx⁺ gene, weintroduced a fusion gene that consisted of the upstream sequenceof the wx⁺ gene and the gene for rß-glucuronidase(GUS) into cells of rice (Oryza sativa L.) and petunia (Petuniahybrida L.). GUS activity was examined in the regenerated transgenicrice and petunia plants. In transgenic rice, the upstream sequenceof the wx⁺ gene was sufficient to direct the tissue-specificexpression of GUS in the endosperm and pollen, and the controlof expression was quantitative. By contrast, in transgenic petunia,the same fusion gene was expressed in pollen but not in theendosperm. These results suggest that the putative cis-actingelements that direct pollen-specific expression are common toor similar in both monocotyledonous and dicotyledonous plants,whereas ciy-elements responsible for the endosperm-specificexpression of the rice wx⁺ gene do not function in petunia,in which development of the endosperm differs from that in rice. ⁴Present address: Division of Biological Sciences, GraduateSchool of Science, Hokkaido University, Kita-ku, Sapporo, 060Japan     

Composition, Degradation and Utilization of Endosperm During Germination in the Oil Palm (Elaeis guineensis Jacq.)

The insoluble carbohydrate and lipid fractions, and -D-galactosidase,ß-D-mannosidase and isocitrate lyase activities werestudied in the various tissues of oil palm (Elaeis guineensisJacq.) kernels prior to and during germination. In ungerminatedkernels insoluble carbohydrate and lipid constituted 36 and47% of endosperm dry weight respectively. During germinationthe thick endosperm cell walls became markedly thinner, concurrentwith a significant decrease in the percentage of insoluble carbohydrateand an increase in -galactosidase and ß-mannosidaseactivity in both degraded and residual endosperm. The proportionof lipid in degraded endosperm also increased significantly.The insoluble carbohydrate appears to be a galactomannan locatedin the secondary walls of the endosperm. No galactomannan wasdetected in oil palm embryos or haustoria. Isocitrate lyasewas present in, and confined to, tissues of the haustorium ofgerminating kernels. The enzyme was not active in endospermat any stage of germination, nor was it active in embryos beforeor at the end of imbibition. The results suggest that galactomannan is the second largestcomponent of oil palm endosperm and that it is utilized morerapidly than lipid during the early stages of germination. Thefact that isocitrate lyase activity is confined to the haustoriumsuggests that in Elaeis gluconeogenesis, the conversion of triglycerideto carbohydrate, takes place entirely within the cotyledon ofthe seed. Elaeis guineensis, galactomannan, galactosidase, germination, isocitrate lyase, mannosidase, oil palm     

Starch-synthesizing Enzymes in the Endosperm and Pollen of Maize

Two mutations, amylose-extender and waxy, which affect the proportion of amylose and amylopectin of starch synthesized in the endosperm of maize (Zea mays L.) seeds, are also expressed in the pollen. However, most mutations that affect starch synthesis in the maize endosperm are not expressed in the pollen. In an attempt to understand the nonconcordance between the endosperm and pollen, extracts of mature pollen grains were assayed for a number of the enzymes possibly implicated in starch synthesis in the endosperm. Sucrose synthetase (sucrose-UDP glucosyl transferase, EC 2.4.1.13) activity was not detectable in either mature or immature pollen grains of nonmutant maize, but both bound and soluble invertase (EC 3.2.1.26) exhibited much greater specific activity (per milligram protein) in pollen extracts than in 22-day-old endosperm extracts. Phosphorylase (EC 2.4.1.1) activity was also higher in pollen than in endosperm extracts. ADP-Glucose pyrophosphorylase (EC 2.7.7.27) activity was much lower in pollen than endosperm extracts, but mutations that drastically reduced ADP-glucose pyrophosphorylase activity in the endosperm (brittle-2 and shrunken-2) did not markedly affect enzymic activity in the pollen. Specific activities of other enzymes implicated in starch synthesis were similar in endosperm and pollen extracts.     

Effect of Benzyladenine on Grain Growth in aestivum wheat

Effect of benzyladenine (BA) on inter and intraspikelet grainsize spectrum in aestivum wheat (cv. Kalyan Sona) has been comparedwith ¹⁴C-uptake of externally added sucrose by the grains andits incorporation in non-starch endosperm lipid fraction. Itis suggested that BA application enhanced the synthesis of membranestructural components required for storage in endosperm. (Received May 8, 1986; Accepted April 2, 1987)     

Inhibition of Gibberellic Acid-induced Starch Mobilization by Salicylhydroxamic acid in Avena fatua L. Seed

Inhibition of GA₃-induced endosperm mobilization in Avena fatuaL. by salicylhydroxamic acid (SHAM), a widely used alternativerespiration inhibitor, was studied. SHAM strongly inhibitedthe GA₃-induced release of reducing sugars in the incubationmedium by 3 mm de-embryonated endosperm segments; at 4 mM SHAM,GA₃-induced sugar release was inhibited by 66–79 per cent.Extracts prepared from segments incubated in 0.05 mM GA₃ with2, 5 and 10 mM SHAM showed 30, 53 and 71 per cent lower -amylaseactivity, respectively, compared to the GA₃-alone treatment.Addition of SHAM (0.5–5 mM) during the enzyme assay hadno effect on the activity of -amylase. Thus, the inhibitionof starch mobilization in endosperm by SHAM is due to inhibitionof the production and not the activity of -amylase. The inhibitionof Avena fatua seedling growth by SHAM reported earlier may,in part, be due to its effect on endosperm mobilization. Since (1) Avena fatua seeds have been shown to have little orno SHAM-sensitive respiration, and (2) concentrations of SHAMnecessary for inhibiting endosperm mobilization were significantlyhigher than those generally necessary for inhibiting alternativerespiration, the inhibition of endosperm mobilization by thiscompound does not appear to involve its effect on alternativerespiration. Avena fatua L., wild oat, -amylase, endosperm, gibberellic acid, salicylhydroxamic acid, seed     

Investigations on the Control of Lettuce Seed Germination at High Temperatures

The activity of sodium hypochlorite solution in relieving thermo-inhibitionof germination of lettuce seed is shown to be due to its chlorinecontent. Results of experiments in which the pericarp, and pericarpand endosperm were removed, together with direct measurementsof penetration forces, suggest that the relief of thermo-inhibitionresults from weakening of the pericarp by the hypochlorite.Differences between the cultivars ‘Cobham Green’and ‘Grand Rapids’ in the contributions made bypericarp and endosperm to germination control at 35 °C aredemonstrated. Key words: Lactuca sativa L, Chlorine, Thermo-inhibition     

Ageing in Triticum durum Seeds: Behaviour of Embryos and Endosperms from Aged Seeds as Revealed by the Embryo-transplantation Technique

The embryo-transplantation technique has been used to studythe behaviour of Triticum embryos and endosperm during the courseof ageing of 1-, 2-, 3-, 4-, and 5-year-old seeds. The resultsshow that the ageing process in Triticum seeds is a progressivephenomenon. It affects both embryo and endosperm as shown by(a) the behaviour of old embryos transplanted on young endosperms,and (b) the deleterious effects of aged endosperms on youngembryos.     

Scavenging of Hydrogen Peroxide in the Endosperm of Ricinus communis by Ascorbate Peroxidase

The fat-storing endosperm of Ricinus communis L. was found tocontain an ascorbate peroxidase (EC 1.11.1.11 [EC] ), which is nearlyas active as catalase (EC 1.11.1.6 [EC] ) in degradation of hydrogenperoxide (H₂O₂) at its physiological concentrations. This ascorbateperoxidase probably functions together with monodehydroascorbatereductase (EC 1.6.5.4 [EC] ) or dehydroascorbate reductase (EC 1.8.5.1 [EC] )and glutathione reductase (EC 1.6.4.2 [EC] ) to remove the H₂O₂ producedduring the transformation of fat to carbohydrate in the glyoxysomes.The activities of these enzymes as well as the content of ascorbateand glutathione increase parallel to the activities of glyoxysomalmarker enzymes during the course of germination. Inhibitionof catalase by aminotriazole results in increases of the ascorbateperoxidase activity and of the glutathione content. All fourenzymes are predominantly localized in the cytosol of the Ricinusendosperm with low activities found in the plastids and themitochondria. The results suggest, that the ascorbate-dependentH₂O₂ scavenging pathway, which has been shown to be responsiblefor the reduction of photosynthetically derived H₂O₂ in thechloroplasts, operates also in the Ricinus endosperm. (Received June 5, 1990; Accepted July 31, 1990)     

Storage-protein Deposition in the Developing Rice Caryopsis in Relation to the Transport Tissues

The developing caryopsis of rice (Oryza sativa L.) was examinedhistologically at successive stages of grain-filling in orderto identify the factors which determine the distribution ofstorage protein in the endosperm, and which terminate the depositionof endosperm protein. The storage protein was deposited at theperiphery of the endosperm, and this distribution was apparentlycaused by the radial pattern of cell development in the endosperm,and by the proximity of the peripheral endosperm cells to thenucellar epidermis. The nucellar epidermis directly surroundsthe endosperm and functions as the pathway for amino acid transportto the endosperm. During the later stages of caryopsis developmentthe nucellar epidermis became compressed by being ‘sandwiched’between the expanding endosperm and the rigid hull (the tightlylocked palea and lemma) which encloses the caryopsis. It isproposed that this compression of the nucellar epidermis blocksthe supply of amino acids to the endosperm and thereby terminatesthe deposition of storage protein in the rice grain. Oryza sativa, rice, caryopsis (development), endosperm, grain filling, nucellar epidermis, storage protein     

Primary dormancy in tomato (Lycopersicon esculentum cv. Moneymaker): studies with the sitiens mutant

Intact wild-type tomato (Lycopersicon esculentum cv. Moneymaker)seeds do not complete germination to the same percentage orat the same speed as intact ABA-deficient sitiens (sit^w) mutantseeds when seeds of both genotypes are imbibed on polyethyleneglycol (PEG) solutions of –0.3 to –1.5 MPa osmoticpotential. However, if the thicker testas of wild-type seedsare removed (stripped) from the micropyle without damaging theendosperm, both the percentage and speed of germination at lowexternal water potential are similar to that of sit^w mutantseeds. Removing the micropylar end of the testa from sit^w seedsdid not enhance either the speed or percentage of germinationon PEG solution. Despite similar germination percentage and speed between strippedwild-type seeds and either stripped or intact sit^w seeds underosmotic stress, some differences in seed metabolism are evidentbetween genotypes. The activity of endo-ß-mannanasewas greater in the endosperm of sit^w mutant seeds compared tothe endosperm of wild-type seeds when seeds were exposed toosmotic stress. Although     

Structure and In Vitro Growth of Zygotic Embryos of Taro (Colocasia esculenta var. antiquorum)

Zygotic embryos of taro, Colocasia esculenta var. antiquorumwere examined using both light and scanning electron microscopyand cultured on Linsmaier-Skoog (LS) medium without the additionof growth regulators. Embryos present within mature seed consistof a hypocotyl-root axis and an undeveloped cotyledon and aresurrounded by two major types of endosperm cells, aleurone andstarchy endosperm. Embryos cultured on LS medium developed intomature plants only in the presence of endosperm tissue. Excisedembryos turned green after 2–4 d in culture and reacheda rapid growth period between days 4 and 6. Culture of taroembryos leading to viable plantlet development depends upon(1) removal of the outer and inner integument, and (2) the presenceof endosperm tissue (including an intact aleurone layer). Colocasia esculenta var. antiquorum, Araceae, taro, embryo culture, integument, endosperm     

Changes in nitrogen contents and in proteolytic activities in different parts of field-grown wheat ears (Triticum aestivum L.) during maturation

Aminopeptidase, carboxypeptidase and neutral endopeptidase activitieswere analyzed in glumes and in kernels of field-grown wheat(Triticum aestivum L.) during ear development. Kernels harvestedon two dates were subdivided into outer pericarp, cross cells,endosperm and embryo. In developing parts with a net nitrogeninflux (young glumes, embryo, endosperm) the aminopeptidaseactivity is high, but in nitrogen-mobilizing tissues (senescingglumes, Outer pericarp) this activity decreases. Carboxypeptidaseis most active in fully expanded tissues. Neutral endopeptidaseshows the highest activity in the nitrogen mobilizing partsand extremely low activity in the embryo and the endosperm. (Received July 15, 1978; )     

Cytochemical Study on the Dormancy-imposing Endosperm of Cercis siliquastrum

Cytochemical observations indicate the occurrence of leucoanthocyanidinsin the protein bodies of Cercis siliquastrum endosperm; theendosperm cell walls give a positive Mayer's test, indicatingmucopolysac-charides. These results are discussed in relationto the endosperm-imposed dormancy of the seed. Cercis siliquastrum, endosperm-imposed dormancy, leucoanthocyanidins, mucopolysac-charides     

On the Structure of Lettuce (Lactuca sativa L.) Endosperm during Germination

Endosperm cells of lettuce (Lactuca sativa L.) are characterizedby thick cell walls and dense cytoplasm which contains numerousprotein bodies. Other organelles such as nucleus, mitochondria,plastids and dictyosomes are typical of plant cells. Light andelectron microscopy reveal that before radicle emergence micropylarcells of endosperm tissue undergo drastic protoplast alterations.These alterations seem to be the only structural modificationsbefore rupturing of the tissue since the walls of the endospermcells seem to degrade only after radicle emergence. The differentialbehaviour of the micropylar area of the endosperm before radicleemergence and the observation that the micropylar cells remainmetabolically active long after radicle emergence while therest of the tissue is almost completely disintegrated, suggeststhat the endosperm cells of the micropylar area may have a roleother than being a main reserve site like the rest of the endosperm. Lactuca sativa L., endosperm structure, seed germination, lettuce     

Metabolism and Translocation of Exogenous Zeatin Riboside in Germinating Seeds and Seedlings of Zea mays

High specific activity [³H]-zeatin riboside (ZR) was suppliedto germinating seed and developing seedlings of Zea mays tostudy its metabolism and translocation The major metabolitesof ZR in endosperm, embryo, and first leaves were adenosine,adenine, and adenine nucleotide When ZR was supplied to theradicle tip a significant proportion of the radioactivity extractedfrom the radicle was identified as zeatin-9-glucoside (Z9G).However, some ZR was also transported to the shoot and vestigialembryo During the initial stage of germination, movement ofzeatin riboside from the embryo to the endosperm was pronouncedbut little movement occurred in the reverse direction Key words: Zea mays cytokinin, zeatin riboside, metabolism, translocation     

Production and secretion of {alpha}-galactosidase and endo-{beta}-mannanase by carob (Ceratonia siliqua L.) endosperm protoplasts

Viable protoplasts were isolated for the first time from maturecarob (Ceratonia siliqua L.) endosperm tissue. After 5 d ofincubation 75% of the protoplasts were viable. During incubationthey underwent vacuolation and produced the carob endospermhydrolases, agalactosidase and endo-ß-mannanase, whichwere secreted in the incubation medium. The secretion of bothenzymes were under Ca²⁺ control. Many characteristics of -galactosidaseand endo-ß-mannanase production by protoplasts werethe same as those of whole endosperms: their production didnot require any hormonal signal and was inhibited in the presenceof ABA or the leachate from the carob endosperm/seed coat. Moderatewater stress (—2.0 MPa) neither affected the activityof these hydrolases nor their secretion by endosperm protoplast.However, when the osmoticum of protoplast incubation mediumwas higher, the production and secretion of both hydrolaseswere reduced. Comparison of the hydrolases activities in theincubation media of leached carob endosperms, which were incubatedunder normal and water stress (—1.5 MPa) conditions, withthe activities of the protoplast-secreted hydrolases indicatedthat (i) carob endosperm cell wall acts as a barrier for thesecreted enzymes and (ii) that water stress reduces the cellwall porosity of the carob endosperm cells, and thus the releaseof the secreted -galactosidase and endo-ß-mannanaseis inhibited. The isolation of carob endosperm protoplasts offersa potent experimental system for the study of aspects of endospermcell physiology, such as enzyme secretion Key words: Abscisic acid, carob endosperm, Ceratonia siliqua L, endo-ß-mannanase, -galactosidase, leachate, protoplasts, water stress     

Spontaneous Chromosome Breakage in Lilium Endosperm

Abnormal mitoses, resulting from chromosome breakage and reunion,occurred in Lilium regale and in the hybrid L. ‘PhyllisCox’ 4 weeks after fertilization. The abnormalities appearedto commence with a single chromatid bridge and in ‘PhyllisCox’ abnormalities accumulated resulting in the formationof multiple bridges, ring chromosomes, fragments, dicentricchromosomes, and micronuclei. Failure of anaphase separationfollowed by restitution resulted in the formation of highlypolyploid nuclei in which mass spontaneous chromosome breakageoccurred. The accumulation of abnormalities in the hybrid endosperm reducedthe mitotic activity and culminated in the failure of the endosperm.This led to the death of the otherwise normal embryo. This sequenceof events is probably of wide importance in the failure of interspecifichybridization.