Utilization of Stored Nitrate during the Anaerobic Germination of Rice Seeds

The presence of nitrate in the seed and its utilization duringanaerobic germination of rice (Oryza sativa L.) were studied.The results indicate that nitrate was reduced and assimilatedby the coleoptile for 11 days during anaerobic growth aftergermination. The importance of the anoxic utilization of nitrateis discussed. (Received June 19, 1992; Accepted January 4, 1993)     

Nucleotide Metabolism during Pine Pollen Germination

The metabolism of purine- and pyrimidine nucleotides in pine pollen (Pinus mugo) grown in suspension cultures have been examined. In the ungerminated dehydrated pollen, the presence of ATP has been demonstrated. Incubation of the pollen in a germination medium leads to an exhaustion of the ATP pool, which is restored with the onset of oxygen uptake. By labelling pollen cultures with ³²P-orthophosphate, it has been possible to quantitate the nucleotide components of the pollen, and thereby to measure changes in the nucleotide pattern at various growth stages. The most marked changes occur during the initial phase of tube growth when a large increase in the ribonucleoside triphosphate and the sugar nucleotide pools is observed. The contents of ATP and UDP-glucose are further increased if starch synthesis is initiated by the addition of sucrose to the culture medium. In order to determine whether nucleotides in pine pollen are synthesized from de novo pathways or via reutilization pathways, from breakdown products of nucleic acids, pollen was incubated with ¹⁴C-labelled precursors of both the de novo and the reutilization pathways. Incorporation experiments established de novo synthesis of ATP and GTP from glycine, and de novo synthesis of CTP and UTP from orotic acid. The operation of pathways for the utilization of exogenous nucleosides was also demonstrated. While uridine, cytidine and adenosine are incorporated into nucleoside triphosphate to a great extent, only minor incorporation of inosine and guanosine is observed. These reutilization pathways might be of importance for the synthesis of nucleotides during tube growth in situ. Addition of inhibitors of glycolysis and oxidative phosphorylation drastically reduces the level of ribonucleoside triphosphates, indicating a rapid turnover of the nucleotide pool.     

Deteriorative Changes in Pea Seeds (Pisum sativum L.) Stored in Humid or Dry Conditions

Seeds stored under various conditions showed deteriorative changesin extremely dry (1% r.h. at 10 °C) or humid (93% r.h. at25 °C) conditions after 6 weeks storage, when little orno loss of viability had taken place; no changes were detectedin intermediate conditions (45% r.h. at 10 °C). The lossof electrolytes from seeds into water increased after 3 weeksof humid storage, and subsequently dead areas developed on thecotyledons of seeds held in either humid or dry conditions.With time in storage some of the seeds in dry conditions showeda reduction in the rate of imbibition, and consequently a lowlevel of electrolyte leakage. Other seeds showed an increasein leakage following dry storage. No change in solute content(sugars, potassium, and electrolytes) was detected in seedsstored in humid conditions, suggesting that the increased electrolyteleakage was caused by an impaired ability to retain solutes.Thus increased leakage was recorded in seeds whose cotyledonscontained no dead areas as revealed by vital staining, and wastherefore attributable to changes in living cells, possiblydeterioration in cell membranes. Viability began to declineafter 6 weeks in humid storage at 25 °C and after 2 d in94% r.h. at 45 °C, but was maintained in both dry and intermediateconditions. The rate at which viability fell in humid storagewas greatly influenced by the initial condition of the seed.     

Changes in Endogenous Growth Kegulators in Loblolly Pine Seeds During the Process of Stratification and Germination

The seeds of loblolly pine (Pirns taeda L.) were cold-stratified for 0, 14, 28, 42, and 56 days. Endogenous growth regulators were extracted from these seeds, and also from the germinating and the 28-day warm stratified seeds. Partially purified extracts were separated on chromatographic paper. The chromatograms were cut into 10 equal segments, and these were tested for biological activity using three different btoassays. The results indicated that the unstratified seeds and those stratified up to a period of 28 days contained very little or no growth promoter (GA-like substances), and a relatively high concentration of an inhibitor (presumably abscisic acid), Following 42-day stratification, the promoter concentration gradually increased while the inhibitor level fell almost to zero. A high level of promoter but no inhibitor was detected in germinating seeds. No auxin-like activity was noted in the unstratified seeds. This activity slowly increased up to a period of 28 days and remained at this level for the subsequent stratification periods. However, the activity greatly increased in the germinating seeds. Very little changes in the levels of growth regulators were noted in warm-stratified seeds as compared to the unstrati-fied controls.     

Localization of Phenolic Compounds in the Root Cap Columella of Six-year-old Dry Seeds of Brassica napus during Imbibition and Germination

In 6-year-old seeds of Brassica napus the columella cells haveno necroses and resemble in structure the cells of the 2-year-oldembryo. The outermost layer of the columella shows a structuresimilar to that of the lateral region of the root cap, as itcontains protein bodies, rare in layers of the columella closerto the promeristem, which, in turn, contain numerous mitochondriaand plastids. Phenolic compounds in the dry embryo are on thesurface of the root cap in the space between the plasmalemmaand the cell wall, and in small vesicles which presumably remainedfrom degradation of ER. Imbibition promotes further extrusionof phenolics outside the plasma membrane. Long sheets of ERare visible after 9 h imbibition. After 24 h phenolics of moredense structure are localized in some dilated parts of the ER.This suggests that new production of defence compounds startswithin 24 h in water, a few hours earlier than in 2-year-oldseeds.Copyright 1994, 1999 Academic Press Brassica napus, phenolics, root columella, germination     

Amino Acid Utilization in Seeds of Loblolly Pine during Germination and Early Seedling Growth (I. Arginine and Arginase Activity)

The mobilization and utilization of the major storage proteins in loblolly pine (Pinus taeda L.) seeds following imbibition were investigated. Most of the seed protein reserves were contained within the megagametophyte. Breakdown of these proteins occurred primarily following radicle emergence and correlated with a substantial increase in the free amino acid pool in the seedling; the majority of this increase appeared to be the result of export from the megagametophyte. The megagametophyte was able to break down storage proteins and export free amino acids in the absence of the seedling. Arginine (Arg) was the most abundant amino acid among the principal storage proteins of the megagametophyte and was a major component of the free amino acid pools in both the seedling and the megagametophyte. The increase in free Arg coincided with a marked increase in arginase activity, mainly localized within the cotyledons and epicotyl of the seedling. Arginase activity was negligible in isolated seedlings. Experiments with phenylphosphorodiamidate, a urease inhibitor, supported the hypothesis that arginase participates in Arg metabolism in the seedling. The results of this study indicate that Arg could play an important role in the nutrition of loblolly pine during early seedling growth.     

The Regulatory Role of the Embryo on the Development of Isocitrate Lyase Activity during Germination of Ponderosa Pine Seeds

The specific activity of isocitrate lyase rapidly increased in the megagametophytic tissue of cold-stratified seeds of ponderosa pine (Pinus ponderosa Laws) prior to and after germination. When the embryo was removed at germination, isocitrate lyase activity continued to develop. However, in the total absence of the embryo, only a small increase in the specific activity of the enzyme was observed. The development of the enzyme was inhibited by cycloheximide, actinomycin D and abscisic acid. The embryo produced an unidentified factor which enhanced the development of isocitrate lyase activity in the megagametophytic tissue. This embryo factor could not be replaced by the hormones indoleacetic acid (IAA), gibberellic acid (GA₃) or benzylaminopurine (BA). Indoleacetic acid had little effect upon enzyme development. Gibberellic acid and benzylaminopurine inhibited isocitrate lyase development in the megagametophytic tissue of the seed.     

Increase in beta-N-Acetylglucosaminidase Activity during Germination of Cotton Seeds

A marked increase in beta-acetylglucosaminidase (2-acetamido-2-deoxy-beta-d-glucoside acetamidodeoxyglucohydrolase, EC 3.2.1.30) activity was observed in the germinating cotyledon of cotton seeds. The enzyme was isolated from cotton seedlings and purified to study its physiological function in the germination of cotton seeds. The purification procedure involves ammonium sulfate fractionation, ion-exchange chromatography, gel filtrations, and concanavalin A-Sepharose 4B chromatography, and the purified beta-N-acetylglucosaminidase was shown to be homogeneous by disc electrophoresis. The molecular weight was estimated to be about 125,000 by gel filtration. The enzyme hydrolyzed both p-nitrophenyl-N-acetyl-beta-d-glucosamine and p-nitrophenyl-N-acetyl-beta-d-galactosamine. When p-nitrophenyl-N-acetyl-beta-d-glucosamine was used as substrate, K(m) and V(max) were 0.625 nanomolar and 228 moles per minute per milligram, respectively, and optimum activity was at pH 5.6. The enzyme liberated beta-linked N-acetyl-glucosamine from chitin, ovalbumin, and pronase-digested wheat germ lectin.     

The Antioxidant System of Wheat Seeds during Germination

The dynamics of peroxidase activity and antioxidant contents in wheat seeds were studied in the course of 24-hour swelling at 5°C (group 1) and 23°C (group 2). Both parameters were 1.5 times higher in seeds of the first group. In the same seeds, peroxidase activity in the endosperm and seed coat increased by factors of 1.5 and 1.8, respectively. Catalytic constants of wheat seed peroxidase were determined in the reactions of o-dianisidine and ascorbic acid peroxidation. In the pH range studied (pH 5–7), K _m proved to change only slightly. In seedlings, an increase in the lipid peroxidation rate was accompanied by an increase in the content of antioxidants. Peroxidase activity increased as the content of antioxidants decreased, and vice versa. Thus, the reciprocal influence of peroxidase and low-molecular antioxidants during seed germination in wheat was revealed.     

Trypsin Inhibitors during Germination of Vigna sinensis Seeds

The trypsin inhibiting activity of cotyledonary extracts of serido beans (Vigna sinensis) falls continuously during germination to a value which represents 5 % of the value for the dry seed. The specific activity is constant over the first three days and then decreases, reaching a level at the seventh day of germination which represents 20 % of the initial value. It is also shown that the axial parts control the disappearance of the trypsin inhibiting activity of the cotyledons. The results presented here seem to indicate a role for these substances in the process of germination.     

Phosphoenolpyruvate Carboxylase during Maturation and Germination Sorghum Seeds: Enzyme Activity and Regulation

Sorghum (Sorghum bicolor (L.) Moench) is a species of great socio-economic and ecological importance for countries in arid and semi-arid climate. In C₄ plants like sorghum, phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) plays a key role in seed development and germination. In this work, the PEPC activity shows an increase followed by a decrease at the early and later stages of maturation, respectively. In germinating seeds, the PEPC activity quickly increases after soaking. The L-malate test and the ratio of PEPC activity determined at pH 8.0 and 7.1, indicates, that PEPC is phosphorylated at the early stages of maturation then becomes dephosphorylated at the later stages and during seed germination, PEPC takes back its phosphorylated form. The determination of the affinity constant showed different K_M depending on the seed developmental stage. As there is no PEPC-C4 isoform in developing sorghum seeds, this result indicates that the different K_M observed during seed maturation could be a result of a post-translational regulation such as phosphorylation or ubiquitination of a pre-existing isoform. This regulation enhances the PEPC activity at early stages of seed development.     

Phytochrome and Seed Germination. III. Action of Prolonged Far Red Irradiation on the Germination of Tomato and Cucumber Seeds

Prolonged irradiation with continuous or intermittent far red prevents the germination of tomato and cucumber seeds. The inhibitory efficiency of intermittent far red decreases with the lengthening of the interval between successive irradiations, and with the increase of temperature. If each far red irradiation is followed by red, germination is restored. Intermittent far red is less inhibitory than intermittent red-far red when red is given immediately before each far red. This effect is more evident when the interval between successive irradiation becomes longer.     

Embryo and Endosperm Metabolism of Barley Seeds during Early Germination

Embryos detached from germinating barley seeds were immersedin tritiated water or solutions containing ¹⁴C-labelled compounds.Amino acids rapidly became radioactive and later acids of theKrebs cycle. Labelled alanine did not give rise to radioactivesucrose.     

Effects of Water Deficit during Germination of Wheat Seeds

Germinating seeds of spring wheat (Triticum aestivum L.) were tolerant to dehydration up to the 4^th day following imbibition and from the 5^th day the seedling survival decreased. Dehydration also inhibited the rate of seed dry mass depletion and seedling dry matter accumulation and increased the content of soluble sugars both in grain and seedlings. Glucose supplied either to dry seeds or to 4-d-old seedlings increased survival of dehydrated seedlings. In contrast, exogenously supplied non-readily metabolizable sorbose and mannose suppressed seedling survival.     

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)     

Changes in Phosphorus Fractions and Phytase Activity of Rice Seeds during Germination

The present experiment provides information on the phosphorus compounds in rice seeds and elucidates the changes they undergo during germination. In ungerminated seeds, the bulk of total-P appears in phytin (about 76 per cent). It is then dephosphorylated in course of germination with a simultaneous accumulation of large amounts of inorganic-P. Lipid-P increases very rapidly from 0 to 24 hours. The increase up to 72 hours is gradual, after which it drops at 96 hours and again rises to a maximum after 120 hours. The ester-P and RNA-P, fractions increase in concentration with time of germination (except 120 hours). Protein-P begins to fall after 48 hours, while DNA-P remains more or less constant throughout the experiment. The two pH optima recorded for phytase activity at 4.0 and 9.0, suggests that there exist two phytases, one acidic and the other alkaline. Both behave similarly during germination with a continuous increase throughout the course of the experiment. The enzyme with an optimal pH at 4 hydrolyses phytin more actively than the other with the pH optimum at 9.0. Phytase shows maximum activity at a stage when most of the phytin has disappeared; the metabolic significance is uncertain.     

On the Role of Stored mRNA in Protein Synthesis in Embryonic Axes of Germinating Vigna unguiculata Seeds

Polyadenylated (poly A⁺) RNAs were prepared from both dry and incubated embryonic axes of Vigna unguiculata seeds and were translated by a wheat germ translation system. Analysis with gel electrophoresis and fluorography showed that translation products of poly A⁺ RNA from dry embryonic axes were nearly the same as those from 2-hour incubated axes but somewhat different from those of 4- to 24-hour incubated axes, and that translation products remained almost unchanged between the 4- and 24-hour stages of postimbibition. The results indicate the possibility that the stored mRNA (poly A⁺ RNA from dry embryonic axes) directs the protein synthesis required for early stages of germination. This is supported by comparison of the in vitro translation products of poly A⁺ RNAs with those of polysomal RNAs. Experiments with α-amanitin, a specific inhibitor of RNA polymerase II (J. Jendrisak 1980 J Biol Chem 255: 8529-8533), suggested that the synthesis of some of the stored mRNA species is resumed as early as 4 hours after the onset of imbibition.     

Biochemical and Morphological Changes in Protein Bodies during Germination of Lentil Seeds

Alvarez, J. and Guerra, H. 1985. Biochemical and morphologicalchanges in protein bodies during germination of lentil seeds.—J.exp. BoL 36: 1296–1303. Protein bodies were extracted from lentil (Lens culinaris Medilk,var. castellana) seeds. Proteins from the protein bodies weredegraded during the first 7 d of germination. In some casesthis mobilization of proteins was accompanied by fusion of theprotein bodies into a large central vacuole. The loss of proteinswas paralleled by an increase in the activity of an enzyme systemthat hydrolysed casein. The different kinds of protein bodiesexhibited structural differences; some displayed uniform material,others coagulated or semi-coagulated material and the thirdkind displayed inclusions. Key words: Lentil, protein bodies, seed germination