Early Hours Of Germination Research Articles

Heat-Induced Protein and Superoxide Dismutase Changes in Wild Tetraena propinqua ssp. Migahidii Seedlings.

<b>Background and Objective:</b> Heat stress is known as a raise of 5°C or more than the optimal temperature. In this study, we analyzed the effect of heat stress on protein content, protein electrophoretic pattern and Superoxide Dismutase (SOD) profile in three populations of <i>Tetraena propinqua</i> subspecies migahidii. <b>Materials and Methods:</b> Populations of <i>Tetraena propinqua</i> ssp. migahidii were studied. The seeds were subjected to 25 (control), 30, 35 and 40°C for 4, 24 and 48 hrs and 10 days. <b>Results:</b> Heat stress (35 and 40°C) elicited total soluble protein in populations 1 and 2 however reduced in population 3 with increasing exposure time to 10 days. New polypeptides of 23 KD at 4 hrs in population 3 below 35°C and population 2 below 40°C and 28 KD at 48 hrs in population one below 30°C however 20 KD altogether populations below 40°C. The expression of most polypeptides diminished for 4 hrs however induced for 24, 48 hrs and 10 days with increase heat temperature to 40°C relative to their expression among the management seedlings. SOD1 and SOD2 have detected altogether most of the genotypes, however, heat stress (35, 40°C) induced the expression of SOD2 and SOD1 and was altogether genotyped for 10 days as compared with the control. <b>Conclusion:</b> The heat stress caused protein degradation and conjointly induced expression of new synthesized HSPs throughout heat acclimatization may be related to heat injury and the improved thermotolerance in early hours of germination and additional studies are required for its protein identification.

GDP‐mannose transporter contributes to polarity establishment in the filamentous fungus Aspergillus nidulans

GDP‐mannose transporters (Gmt) carry nucleotide sugars from the cytosol across the Golgi apparatus membrane in various eukaryotic organisms including plants and a variety of fungi. Some fungal species such as the yeast Saccharomyces cerevisiae express only one Gmt, while others including A. nidulans express paralogues (GmtA and GmtB) whose individual roles have not been elucidated. As in S. cerevisiae GmtA is localized within the Golgi apparatus which in A. nidulans consists of widely separated cisternae, in contrast to the stacked cisternae of animals and plants. Here we show that GmtB localization is congruent with GmtA in mature hyphae. Real‐time reverse transcriptase PCR shows a gradual decrease in GmtA expression during the first 12 hours of germination while GmtB expression remains high and unchanged during this period. Depletion of GmtB by the glucose repressible alcA promoter causes abnormalities in polarized growth, a developmental event that is initiated during the early hours of germination. Taken together these observations suggest that GmtB plays an important role in establishment of polarized growth. Although GmtA and GmtB reside within the same Golgi compartments they appear to perform independent functions at different developmental stages.Funded by Research Corporation, the Merck/AAAS Undergraduate Science Research Program and NSF RUI

Maize D4;1 and D5 cyclin proteins in germinating maize. Associated kinase activity and regulation by phytohormones

We have previously reported the expression of four different maize D cyclins during seed germination and showed that cytokinins and auxins stimulate the expression of every cyclin in a differential way. In this paper we characterize the behavior at the protein level of two of these cyclins, CycD5 and CycD4;1. Antibodies were raised against CycD5;2 (which very likely also recognizes D5;1) and CycD4;1 and Western blot studies demonstrated that neither BA nor indol-3 acetic acid (IAA) stimulate cyclin accumulation during germination, compared with control levels. However, phytohormones, particularly IAA, modify the kinase activity associated to D cyclins preferentially at early hours of germination. The associated kinase moiety to D cyclins appears to be of a Cdk-A type because this protein immunoprecipitates with D cyclins and because kinase activity is strongly inhibited by both olomoucine and also by a peptide corresponding to the carboxy end of a maize kip related protein (KRP) protein. There is thus no correlation between mRNA and protein expression for these maize D cyclins during seed germination, although phytohormones may stimulate a signaling cascade that stimulates activation of protein kinase activity in cyclin-Cdk complexes.

Expression of maize D‐type cyclins: comparison, regulation by phytohormones during seed germination and description of a new D cyclin

While cloning maize D‐type cyclins previously reported in databases (described as of D1, D2 and D4 types), a fourth D cyclin was cloned that showed high homology (75%) with the D1 cyclin. Because this D1 cyclin has been recently described as a D5‐type cyclin (D5;1), the new cyclin was named D5;2. All maize cyclins have been compared among themselves and among D cyclins from other plant species. All maize D cyclins possess the retinoblastoma protein–binding motif and cyclin boxes but no PEST sequences or destruction box sequences are required for protein degradation. D5 and D2 cyclins also have canonical cyclin‐dependent kinase (Cdk)–phosphorylation sites. Every cyclin showed a different expression pattern during seed germination, standing out cyclin D5;2, which seems to be expressed only during the early stages (equivalent to postmitotic interphase), and cyclin D4;1, which progressively accumulates from an almost undetectable level in dry seed embryo axes. Phytohormones like cytokinins and auxins, which accelerate the germination process, change the expression pattern of all cyclins, with cytokinins promoting an increase in expression during the early hours of germination (by 6 h), whereas auxins promote a constant increase in the levels of three out of the four D cyclins (except D5;1). Cyclin D5;1 is the least expressed of all cyclins in all tissues measured (embryo axes, seedlings and plantlets), and all cyclins are expressed in both meristematic and non‐meristematic tissues. We discuss their relevance for the germination process and plantlet establishment.

Adenylate energy charge during the life cycle ofMyxococcus coralloidesD

The adenylate energy charge of cells of Myoococcus coralloides D has been measured during the different stages of its life cycle. The energy charge of the vegetative cells (0.8) did not change significantly either during glycerol-induced myxospore formation, or during germination of these myxospores. Fruiting body myxospores had a relatively high energy charge (0.65). The adenylate energy charge decreased slightly (from 0.82 to 0.65) throughout fruiting body development and returned to values of vegetative cells in the early hours of germination of fruiting body myxospores. The levels of adenine nucleotide in myxospores in desiccation conditions were similar to those before desiccation.

Biochemical control systems operating in the early hours of germination

This review describes very early biochemical events during imbibition in seeds. It considers the control systems that regulate the production of nucleic acids and proteins when the dry seed first imbibes water. During the ageing of embryos in the dry state, DNA is progressively fragmented with an accumulation of single-stranded breaks. The critical role of DNA repair early in imbibition is considered in the context of genetic integrity of the nuclear template and successful germination.

Biochemical Changes in Germinating Rice Seeds under Saline Stress

Activity of enzymes viz., amylase, ribonuclease, protease and levels of substrates like starch, sugar, RNA, protein, amino acids were studied in endosperms of germinating rice seeds under different levels of salinity. Inereased salinity decreased germination percentage, seedling growth and water uptake by endosperm. Lower concentration of NaCl caused increase in amylase activity but sharp decrease was observed with higher concentration and so was depletion of starch from endosperm. Levels of snrrose, redueing and total sugars decreased with salinity. Suppression of RNase activity and decrease in RNA content of endosperms were observed under salt treatment. The suppression of RNase activity was about 2 and 4 folds with 0.15 M and 0.30 M NaCl respectively. Salinity inhibited the rate of disappearance of protein from endosperm. Increased protease aetivity was noticed up to 48 h followed by sharp decrease during later hours of germination where maximum inhibition of activity with higher salt concentration was observed. Increase in amino acid content during early hours of germination was observed under saline situation but significant decrease was noticed during later stages of germination.

The loss of desiccation tolerance during germination: An ultrastructural and biochemical approach

Rye embryos of high viability and vigour can be imbibed for 1 hour, dehydrated and subsequently rehydrated without harm. However, extension of the imbibition period results in progressive structural damage to cells of both the embryonic root and the coleorhiza. Greatest sensitivity to this treatment is shown by the microtubule assembly system and the plasmalemma which loses its integrity permitting the egress of ribosomes and lipid towards the cell wall. Further stress results in fragmentation of the endoplasmic reticulum, disruption of plastid, mitochondrial and nuclear membranes and the dispersion of the contents of provacuoles. Damage is initiated during the drying of imbibed embryos but it is compounded by subsequent rehydration. Coleorhiza cells, particularly those distal to the root, which normally develop very rapidly during the early hours of germination are most sensitive to desiccation. The onset of sensitivity to desiccation (ca. 3 hours after imbibition) corresponds with a transitory halt in the increasing rate of protein synthesis and with the start of DNA replication. These results are discussed in relation to DNA repair and the “hardening” of seeds to stimulate rapid growth following rehydration.

Nucleic acid and protein synthesis and loss of vigour in germinating wheat embryos

A study has been made of the RNA and protein synthesising systems of wheat embryos isolated from seed lots having high viability but differing in vigour. The rate of RNA and protein synthesis in wheat embryos during the early hours of germination is related to the vigour of the seed lot. The imposition of a stress factor, in the nature of a sub-optimal germination temperature, during germination of isolated wheat embryos magnifies the differences in rates of protein and RNA synthesis between high and low vigour seed. Using cell-free protein synthesising systems it has been demonstrated that an important difference between high and low vigour embryos lies in the relative levels of messenger RNA in the embryo. High vigour embryos contain relatively higher levels of poly A(+)-RNA (i.e. potential mRNA species) than lower vigour embryos and furthermore the level of poly A(+)-RNA in high vigour embryos increases during early germination whilst in lower vigour embryos the level decreases. The difference in poly A(+)-RNA levels accounts, at least partially, for the differences in rates of protein synthesis observed between embryos from high and low vigour wheat seed during early germination at both optimal and sub-optimal germination temperatures.

A comparative study of the fine structure of coleorhiza and root cells during the early hours of germination of rye embryos

The sequences of changes which occur in the fine structure of root and coleorhiza cells of the rye embryo during the first 9 hours of germination are described. Quiescent cells from both tissues characteristically possess no vacuole, a cytoplasm densely packed with ribosomes, lipid droplets largely confined to a peripheral position, a greatly reduced endomembrane system, mitochondria with few cristae and nuclei in which the heterochromatin is condensed. Following imbibition the structure of root cells is elaborated slowly. Microtubules and dictyosomes appear, followed by the development of mitochondrial cristae and endoplasmic reticulum and the dispersion of lipid droplets. A similar pattern of events occurs within coleorhiza cells but at a much enhanced rate. By 6 hours the endomembrane system is highly organized but by 9 hours it has largely disappeared. These observations are discussed in relation to the penetration of the root through the coleorhiza.

Lack of Inhibiting Effects of Abscisic Acid on Seeds ofHaplopappus gracilis(Nutt.) Gray Pregerminated in Water for Short Times

Abscisic acid (ABA) inhibits germination of Haplopappus gracilis seeds. If seeds are germinated in water until radicle protrusion and then transferred to ABA, no inhibiting effect is observed and growth goes on normally. The same behaviour is observed if embryos (i.e. seeds deprived of coats) are pregerminated in water for 12 h. No growth substance (cytokinins or gibberellins) is able to reverse in short times the inhibiting effects of ABA on germination and on resumption of DNA synthesis; hence it is unlikely that some growth regulator synthesized during the early hours of germination can account for a subsequent neutralization of the inhibiting effects of ABA. It is suggested that ABA is metabolized to some compound devoid of hormonal activity in the seeds during the incubation in water.

Dependence of protein synthesis on RNA synthesis during the early hours of germination of wheat embryos

WHEAT EMBRYO germination is characterised by an increase in fresh weight during the first 40 min of imbibition, followed by a lag period of 5 h and finally, a phase of cell elongation during which fresh weight increases at a sustained rate1. An essential step in seed germination is de novo synthesis of proteins, but for the first 40 min it is mediated by preformed mRNA transcribed during embryogenesis2 Previous reports have shown that although there is a 2.5–3-fold increase in the relative rate of protein synthesis during the lag period (40 min–5.5 h)3, there is no appreciable change in the rate of RNA synthesis4–7 With the recently developed sensitive assays for ribonucleoside triphosphates8,9, the rate of RNA synthesis and its mode of regulation in early germination of wheat embryos was reexamined10 In contrast to previous findings4–7, our results clearly show a two- to threefold increase in the rate of RNA synthesis during the lag period of wheat embryo germination This increase in RNA synthesis could conceivably account for the threefold increase in the rate of protein synthesis4 and raises the possibility that protein synthesis may depend on RNA synthesis after the first 40 min of germination We describe here experiments undertaken in wheat (Triticum aestivum L.) embryos to study the effect of inhibition of RNA synthesis on the rate of protein synthesis. Our data suggest that protein synthesis depends on RNA synthesis, and that the substrate level of mRNA is not a rate-limiting determinant for protein synthesis during the early hours of germination.

Induction of petite mutations during germination and outgrowth of Saccharomyces cerevisiae ascospores.

The germination and outgrowth of Saccharomyces cerevisiae ascospores were studied by determining the sensitivity of the ascospores to the action of chemical mutagens. Survival of the ascospores after N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) treatment was low during the first 2 h of germination and then increased and remained constant. Survival of the ascospores after 2-methoxy-6-chloro-9-(3-[ethyl-2-chloroethyl]aminopropylamino)acridine-2HC1 (ICR-170) treatment was constant from 0 to 5 h, but as the ascospores completed outgrowth at 6 h they became more sensitive to killing by ICR-170. Survival of the ascospores remained high during treatment with 2-methoxy-6-chloro-9-(3-[ethyl-2-hydroxyethyl]aminopropylamino)acridine-2HC1 (ICR-170-OH) or 2,7-diamino-10-ethyl-9-phenyl-phenanthridinium bromide. The main classes of mutations screened for were petites and auxotrophs. The induction of petites and auxotrophs by MNNG was independent of the stage of germination and outgrowth treated. Petite induction by ICR-170 was dependent upon the stage of germination and outgrowth treated. The early hours of germination (0 to 3 h) were not sensitive to petite induction. However, there was maximal petite induction at 5 h into germination and outgrowth, followed by a decline. During this same time period, ICR-170 induced less than 1% auxotrophic colonies. This finding is very unusual because ICR-170 induced 15% auxotrophic colonies in starved log-phase cultures of S. cerevisiae. The acridine ICR-170-OH induced no mutations during germination and outgrowth of the ascospores. Ethidium bromide induced petites, and the petite frequency became maximal at 5 h of germination and outgrowth, a result similar to that obtained with ICR-170.

Glucose metabolism of dormant and heat-activated spores of Phycomyces blakesleeanus burgeff

The metabolism of [(14)C]glucose has been studied in Phycomyces spores during dormancy, activation, and the initial stages of germination. Dormant spores are able to take up and metabolize exogenous glucose into different products; the major part of it goes to trehalose synthesis (up to 60% when the external glucose concentration exceeds 10(-3) M). During activation itself (i.e. a prolonged treatment at 50°) there is a general increase of glucose uptake and metabolism, without major changes in the relative rates of (14)C-label distribution in the different fractions (as compared to the metabolism of dormant spores), except for a drop in material insoluble in 80% ethanol and a still higher percentage (73%) going to trehalose synthesis. In the early hours of germination we find an enhancement of the uptake and metabolism of glucose. Trehalose synthesis is practically switched off within 2 h whereas the major part of glucose (65%) is metabolized to CO2 and ethanol-insoluble proteinaceous material.

Protein synthesis and the viability of rye grains. Loss of activity of protein-synthesizing systems in vitro associated with a loss of viability.

A study was made of the integrity of some components of the protein-synthesizing system from viable and non-viable embryos of rye grains. In comparison with viable-embryo components both post-ribosomal supernatant and ribosomal fractions from non-viable embryos are impaired, for neither will fully support polyphenylalanine synthesis in poly(U)-directed cell-free systems. The lesion in the supernatant lies in components other than the tRNA or the aminoacyl-tRNA synthetase, for these are as functional as those present in the fully active cell-free systems from viable embryos. The ribosomes of embryos of lowered viability show considerable fragmentation and degradation of both 18S and 25S rRNA. This breakdown does not, however, account for the complete lack of polypeptide synthesis in the poly(U)-directed non-viable-embryo system, for if provided with viable-embryo supernatant, non-viable-embryo ribosomes will sustain 60% of the viable-embryo ribosome activity. A lesion in non-viable-embryo supernatant has been located in the binding of the aminoacyl-tRNA to the ribosome. The impaired components in both supernatant and ribosomes in systems in vitro may reflect the site of faults in protein synthesis in vivo in the early hours of germination. The development of these lesions during grain storage could contribute to senescence and loss of viability in the embryos of rye.

Metabolism of Barley Seed During Early Hours of Germination

The growth process in germinating barley seeds and its inhibition by actinomycin D and puromycin were investigated. Soon after seeds are imbided, their respiratory activity increases several fold, and the protein- and carbohydrate-synthesizing systems become active. The immediate activation of protein synthesis and its inhibition by actinomycin D and puromycin suggest that the dry seed has all the components necessary for protein synthesis.Although a good correlation exists between the rate of oxygen uptake and that of protein synthesis during the first 12 hr of germination, respiration appears to be independent of protein synthesis during the first 8 hr, as reflected by the insensitivity of the respiratory process to actinomycin D and puromycin. However, after 8 hr both antibiotics reduce oxygen uptake as well as subsequent seedling growth.The distribution of (14)C, derived from labeled glucose during the early hours of barley germination, among various fractions of metabolites, indicated that 50 to 70% of the utilized glucose appeared in (14)CO(2). The rest of the incorporated label appeared in hemicelluloses and starch, water-soluble ethanol-insoluble carbohydrates, and to a lesser extent in proteins and cellulose.

Photosynthesis and Respiration in Germinating Spores of Polytrichum

Photosynthesis and Respiration in Germinating Spores of Polytrichum