Developmental biochemistry of cottonseed embryogenesis and germination: changing messenger ribonucleic acid populations as shown by in vitro and in vivo protein synthesis

Differential, temporal and spatial expression of genes involved in storage oil and oleosin accumulation in developing rapeseed embryos: implications for the role of oleosins and the mechanisms of oil-body formation

The temporal and spatial expression of oleosin and delta 9-stearoyl-ACP desaturase genes and their products has been examined in developing embryos of rapeseed, Brassica napus L. var. Topas. Expression of oleosin and stearate desaturase genes was measured by in situ hybridisation at five different stages of development ranging from the torpedo stage to a mature-desiccating embryo. The temporal pattern of gene expression varied dramatically between the two classes of gene. Stearate desaturase gene expression was relatively high, even at the torpedo stage, whereas oleosin gene expression was barely detectable at this stage. By the stage of maximum embryo fresh weight, stearate desaturase gene expression had declined considerably while oleosin gene expression was at its height. In contrast to their differential temporal expression, the in situ labelling of both classes of embryo-specific gene showed similar, relatively uniform patterns of spatial expression throughout the embryo sections. Immunogold labelling of ultra-thin sections from radicle tissue with anti-oleosin antibodies showed similar patterns to sections from cotyledon tissue. However, whereas at least three oleosin isoforms were detectable on western blots of homogenates from cotyledons, only one isoform was found in radicles. This suggests that some of the oleosin isoforms may be expressed differentially in the various types of embryo tissue. The differential timing of stearate desaturase and oleosin gene expression was mirrored by similar differences in the timing of the accumulation of their ultimate products, i.e. storage oil and oleosin proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Two different Em-like genes are expressed in Arabidopsis thaliana seeds during maturation

Using a radish cDNA probe, we have isolated and characterized two genomic clones from Arabidopsis thaliana (GEA1 and GEA6) encoding two different proteins that are homologous to the "Early methionine-labelled" (Em) protein of wheat. GEA1 differs from GEA6 and Em clones of wheat in that a sequence coding for 20 amino acid residues is tandemly repeated 4 times. These two genomic clones correspond to two genes named AtEm1 and AtEm6. Sequencing of several cDNA clones showed that both genes are expressed. The transcription start site was determined for both genes by RNase mapping. The site of polyadenylation is variable and there is no obvious consensus sequence for polyadenylation at the 3' ends of the genes. mRNA corresponding to GEA6 is present only in nearly dry and dry seeds, whereas the corresponding to GEA1 appears in immature seeds and is maximum in dry seeds. No expression of either gene could be detected in leaf, stem, or floral buds. Expression of both genes could be detected in immature seeds when the siliques were incubated with abscisic acid (ABA), demonstrating that both genes are ABA responsive. However, examination of the 5' upstream region does not reveal any extensive homology, suggesting that regulation of the two genes differs. In situ hybridization with a GEA1 probe demonstrated that the expression of this gene is essentially located in the provascular tissues of the cotyledons and axis of the dry seed as well as in the epiderm and outer layers of the cortex in the embryo axis.

A repeating 11-mer amino acid motif and plant desiccation

Among the proteins that accumulate as plant seeds desiccate are several protein families that are composed principally of a tandemly repeated 11-mer amino acid motif. Proteins containing the same motif accumulate in the desiccating leaves of a desiccation-tolerant plant species. This motif is characterized by apolar residues in positions 1, 2, 5 and 9, and charged or amide residues in positions 3, 6, 7, 8 and 11. An alpha helical arrangement of the 11-mer repeating unit gives an amphiphilic helix whose hydrophobic stripe twists in a right-handed fashion around the helix. Should these proteins dimerize via binding of their hydrophobic faces, a right-handed coiled coil would be formed. Such a structure has not previously been observed. A conceivable function for these proteins in ion sequestration in the desiccated state is proposed.

Differential gene expression during germination and after the induction of adventitious bud formation in Norway spruce embryos

A pulse treatment of embryos of Norway spruce with cytokinin suppresses germinative development and induces the coordinate formation of adventitious buds from subepidermal cell layers. To analyse the patterns of gene expression associated with germination and the alterations induced by the bud induction treatment, we have isolated cDNA clones corresponding to genes that are differentially expressed in cytokinin-treated and untreated in vitro germinating embryos. One category of 14 clones hybridized to transcripts that were abundant specifically during germination. The expression of 8 of these genes was reduced by the bud induction treatment. Four clones, including one identified as a histone H2A gene, recognized transcripts that showed an increased abundance in bud-induced versus in vitro germinating embryos. A second category of 13 clones hybridized to transcripts that increased in abundance during post-germinative development of the seedling. Among these a subset of 8 clones, including an alpha-tubulin clone, corresponds to genes suppressed by the bud induction treatment, whereas 5 clones, including a gene with sequence similarity to polyubiquitin, were unaffected by the treatment. One clone hybridized to a message abundant in the seed, during early germination as well as in the vegetative bud, and showed 60% partial sequence identity to a barley (1----3)-beta-glucanase gene. Genes expressed exclusively in bud-induced or in vitro germinating embryos were not found. The results show that a major difference in gene expression between treated and untreated embryos is related to the shift from extensive cell proliferation to elongation and differentiation that occurs at the transition from germination to post-germinative development, and which is suppressed in the bud-induced embryos.

Gene activity during germination of spores of the fern, Onoclea sensibilis. Cell-free translation analysis of mRNA of spores and the effect of alpha-amanitin on spore germination

Poly(A)-RNA fractions of dormant, dark-imbibed (non-germinating) and photoinduced (germinating) spores of Onoclea sensibilis were poor templates in the rabbit reticulocyte lysate protein synthesizing system, but the translational efficiency of poly(A)+RNA was considerably higher than that of unfractionated RNA. Poly(A)+RNA isolated from photoinduced spores had a consistently higher translational efficiency than poly(A)+RNA from dark-imbibed spores. Analysis of the translation products by one-dimensional polyacrylamide gel electrophoresis showed no qualitative differences in the mRNA populations of dormant, dark-imbibed, and photoinduced spores. However, poly(A)+RNA from dark-imbibed spores appeared to encode in vitro fewer detectable polypeptides at a reduced intensity than photoinduced spores. A DNA clone encoding the large subunit of maize ribulose bisphosphate carboxylase hybridized at strong to moderate intensity to RNA isolated from dark-imbibed spores, indicating the absence of mRNA degradation. Although alpha-amanitin did not inhibit the germination of spores, the drug prevented the elongation of the rhizoid and protonemal initial with a concomitant effect on the synthesis of poly(A)+RNA. These results are consistent with the view that some form of translational control involving stored mRNA operates during dark-imbibition and photoinduced germination of spores.

The Viviparous-1 developmental gene of maize encodes a novel transcriptional activator

The Viviparous-1 (Vp1) gene of maize is specifically required for expression of the maturation program in seed development. We show that Vp1 encodes a 73,335 dalton protein with no detectable homology to known proteins. An acidic transcriptional activation sequence was identified by fusion to the GAL4 DNA-binding domain. Expression of VP1 in maize protoplasts resulted in strong activation (greater than 130-fold) of a reporter gene fused to the promoter of a presumptive target gene. The acidic domain in VP1 was essential for transactivation and could be functionally replaced by the activator sequence of the herpes simplex virus VP16 protein. Our results indicate that VP1 is a novel transcription factor possibly involved in potentiation of a seed-specific hormone response.

Sequence analysis of a cDNA encoding a group 3 LEA mRNA inducible by ABA or dehydration stress in wheat

A cDNA clone (pMA2005) of a Group 3 LEA (late embryogenesis abundant) protein has been sequenced from wheat. The wheat cDNA clone codes for a protein with ten tandem repeats of an 11 amino acid sequence and has homology to other Group 3 LEAs reported in barley, carrot, cotton and rape (L. Dure et al., Plant Mol Biol 12: 475-486, 1989). The deduced amino acid sequence indicates that the wheat protein has a molecular weight of 23,000 and is a basic, hydrophilic protein. Northern analysis with the cDNA clone shows that dehydration of wheat shoot tissue results in increased transcript levels that correlate with increases in endogenous ABA.

Analysis of an ABA-responsive rice gene promoter in transgenic tobacco

We have analyzed in transgenic tobacco the expression of a chimeric gene containing 5' sequences of the rice rab-16B gene fused to the beta-glucuronidase (GUS) reporter gene. This construct, a translational fusion (-482 to +184) including 14 amino acids of the RAB-16B protein, is expressed only in zygotic and pollen-derived embryos. In zygotic embryos, GUS activity begins to accumulate 10 days after flowering (daf), and increases until seed maturation at 25 daf. Immunological measurements of endogenous abscisic acid (ABA) accumulation in these seeds showed a close parallel between hormone levels and GUS activity. However, GUS activity could not be reproducibly induced by treatment of immature embryos with ABA (10 microM). Neither GUS activity nor GUS mRNA could be detected in leaves of transgenic tobacco even after ABA treatment. In contrast, GUS activity could be induced to high levels in pollen-derived embryos by treatment with ABA. Our results show that 482 bp of 5' sequences of the rice rab-16B promoter can confer in transgenic tobacco developmentally regulated expression in embryos but not ABA-responsive expression in vegetative tissues.

Relationship between gene expression and hybrid vigor in primary root tips of young maize (Zea mays L.) plantlets

To provide an insight into the molecular basis of heterosis, we investigated gene expression in primary root tips of a heterotic maize hybrid (B73 × Mo17) and its parental lines (B73 and Mo17). This analysis was carried out (i) by differential plaque hybridization of a recombinant cDNA library made to poly(A) RNA isolated from B73 × Mo17 primary root tips, and (ii) by comparing with two-dimensional gel electrophoresis proteins synthesized in vitro in the rabbit reticulocyte system by poly(A) RNA isolated, at different stages of development, from the three genotypes. The results showed that there are sets of proteins and mRNAs that are differentially synthesized and expressed in the F1 primary root tips in comparison to the parental lines. Moreover, results from the survey of 21 major in-vitrosynthesized polypeptide variants, from mRNAs of primary root tips of the parental lines and their F1 hybrid, indicated that in seven instances hybrid proteins translated in vitro were more abundant or possibly new. In most of the remaining cases, hybrid spots were similar in intensity to the same protein produced by one of the two parental lines.

Transcriptional activities in dry seed nuclei indicate the timing of the transition from embryogeny to germination

To investigate processes regulating the reinitiation of growth and differentiation during seed germination, we have studied the transcriptional activities of sets of genes that are expressed at specific stages of embryogeny and post-germination in the higher plant Brassica napus L. We show that transcripts from a subset of the genes are elongated in nuclei isolated from dry seeds, indicating that these genes are competent to be transcribed in desiccated and quiescent mature embryos. Analysis of the specific transcripts produced in dry seed nuclei indicates that the changes in gene expression patterns associated with germination are not initiated during late embryogeny. The results suggest that the transition from an embryonic to a postgerminative program of development occurs after seeds are rehydrated.

Common amino acid sequence domains among the LEA proteins of higher plants

LEA proteins are late embryogenesis abundant in the seeds of many higher plants and are probably universal in occurrence in plant seeds. LEA mRNAs and proteins can be induced to appear at other stages in the plant's life by desiccation stress and/or treatment with the plant hormone abscisic acid (ABA). A role in protecting plant structures during water loss is likely for these proteins, with ABA functioning in the stress transduction process. Presented here are conserved tracts of amino acid sequence among LEA proteins from several species that may represent domains functionally important in desiccation protection. Curiously, an 11 amino acid sequence motif is found tandemly repeated in a group of LEA proteins of vastly different sizes. Analysis of this motif suggests that it exists as an amphiphilic α helix which may serve as the basis for higher order structure.

Multivariate analyses of polypeptide synthesis in developing maize embryos

Variation in polypeptide synthesis was examined in developing maize embryos of two inbred and two hybrid genotypes. Multivariate analyses were used to evaluate the variation among two-dimensional, electrophoretic separations of polypeptides. Several features of the data set were revealed. Similar developmental patterns were exhibited by all genotypes and no evidence was obtained for differential rates of development for inbreds and hybrids. The differential synthesis of two subsets of polypeptides during embryo development was observed. The multivariate methods employed in this study were a valuable aid in interpreting the results from a large and complex data set.

Temporally modular gene expression during cotyledon development

The regulation of cotton embryogenesis has been addressed by measuring the abundance of 47 mRNAs in cotyledons from the late cotyledon stage through early germination. There are at least 11 distinct classes of coordinately expressed mRNAs. Their expression patterns appear to result from unique combinations of five temporal abundance components. These are associated with the cotyledon stage, the endogenous concentration of free abscisic acid, maturation (reserve accumulation), ovule abscission, and germination. This modularity suggests that only a few global regulatory factors orchestrate gene expression with many genes responding to several of them. Significant expression associated only with postabscission or free abscisic acid is restricted to that of the Lea mRNAs earlier suggested to be a component of the embryo's preparation for desiccation.

Patterns of protein synthesis in dormant and growing vegetative buds of pea

Lateral buds on intact pea plants (Pisum sativum L. cv. Alaska) remain dormant until they are stimulated to develop by decapitating the terminal bud. Using two-dimensional gel electrophoresis, we have examined the protein content of terminal and lateral buds from intact plants and from plants at various times after decapitation. Silver-staining and in-vivo-labeling demonstrated very different sets of proteins. The level of expression of 18 stained and 25 labeled proteins was altered when growth was stimulated; this represents 3.4% and 9.1% of the total proteins detected by each method, respectively. Within 24 h of being stimulated, lateral buds doubled in length and their protein content was qualitatively nearly the same as that of terminal buds. Six hours after decapitation, before the onset of detectable growth, the overall pattern of protein synthesis in lateral buds was more like that of growing lateral buds or of terminal buds than that of dormant lateral buds. Direct application of N(6)-furfurylaminopurine (kinetin) to buds on intact plants stimulated their growth and resulted in the same pattern of protein synthesis as did decapitation. Inhibition of bud growth by addition of indole-3-acetic acid to the stumps of decapitated plants resulted in the synthesis of dormancy-related proteins. Lateral buds at all stages of development incorporated labeled amino acids at similar rates, indicating that metabolic activity is not a component of dormancy in these buds.

High-resolution two-dimensional electrophoresis of plant proteins

A technique for the analysis of plant proteins from seed, leaf, root, and coleoptile tissues by high resolution two-dimensional electrophoresis is described. This technique is based primarily on the procedure of P. O'Farrell (1975, J. Biol. Chem. 250, 4007-4021); however, a number of improvements and simplifications have been introduced. We have found that resolution of polypeptides from a range of plant tissues is improved if the concentrations of nonionic detergent and ampholytes used in the isoelectric focusing (IEF) step are increased to 4 and 5% (w/v), respectively. Further increase in the concentrations of these two components results in gels of decreased resolution and low mechanical strength. We have also found that substitution of n-octyl beta-D-glucopyranoside or 3-[(cholamidopropyl)dimethylammonio]-1-propanesulfonate for Triton X-100 or Nonidet-P40 in the IEF dimension significantly increases the resolution of polypeptides in these gels. This technique also allows minor polypeptide differences between closely related cultivars of plants to be identified.

Sequence and characterization of 6 Lea proteins and their genes from cotton

Lea genes code for mRNAs and proteins that are late embryogenesis abundant in higher plant seed embryos. They appear to be ubiquitous in higher plants and may be induced to high levels of expression in other tissues and at other times of ontogeny by ABA and/or desiccation. Presented here are the genomic and cDNA sequences for 6 of these genes from cotton seed embryos and the derived amino acid sequences of the corresponding proteins.The Lea genes contain the standard sequence features of eucaryotic genes (TATA box and poly (A) addition sequences) and have 1 or more introns. Sequences differences between cDNA and genomic DNA confirm the existence of small multigene families for several Lea genes. The amino acid composition and sequence for the Lea proteins are unusual. Five are extremely hydrophilic, four contain no cys or trp and 4 have sequence domains that suggest amphiphilic helical structures. Hypothetical functions in desiccation survival, based on amino acid sequence, are discussed.

Coordinate accumulation of homeologous transcripts of seven cotton Lea gene families during embryogenesis and germination

One of two related patterns of total transcript accumulation are seen during embryogenesis for 18 cotton Lea (Late embryogenesis-abundant) gene families in the allotetraploid cotton Gossypium hirsutum L. cv Coker 201. Coordinate accumulation in each class is complex, suggesting that Lea mRNA abundance is regulated by several events. Each of the Lea gene families probably contains two active homeologous genes (alloalleles), one in each of cotton's two subgenomes. It is of interest whether both transcripts of a Lea family are regulated the same or whether the complexity of total transcript accumulation is due to different regulation of the two transcripts. The two polypeptides encoded by the homeologous transcripts of 7 Lea families can be distinguished on two-dimensional gels. The majority of Lea transcripts in total RNAs is shown to be functional in vitro throughout development; thus in vitro translation should faithfully measure their relative abundance. The ratio of the two transcripts of each was followed during embryo maturation when Lea transcript concentration increases an average of 70-fold and during the first 12 hr of germination when Lea transcripts decline in concentration an average of 50-fold. For 6 of the Lea families, the relative level of the two transcripts is invariant throughout this period. The two constituent transcripts of the seventh, Lea9, change 5-fold in relative concentration during late maturation and 3-fold during germination. Both transcripts still follow the same temporal pattern of accumulation; only their rates of change are somewhat different. These Lea families are a random sample of the 18 described. If multiple events affect the mRNA abundance of each Lea family, such events then each affect their individual transcripts in a similar way.

Accumulation kinetics of cotton late embryogenesis-abundant mRNAs and storage protein mRNAs: coordinate regulation during embryogenesis and the role of abscisic acid

The accumulation of total RNA transcripts of 18 late embryo-abundant (Lea) gene families, each encoding two closely related Lea mRNAs, was measured in cotyledon total RNA during embryogenesis and germination of Gossypium hirsutum L. by RNA dot hybridization. Transcript abundance of the three storage protein families was also followed. The Lea mRNAs belong to only two related groups of commonly regulated mRNAs. The transcript level of each of the 6 members of Class I has two transient maxima during early maturation and a maximum level at 3 days prior to desiccation. The transcript level of each of the 12 members of Class II increases abruptly in late maturation with a maximum concentration at 3 days before desiccation (Class IIA) or at desiccation (Class IIB). Several patterns of early accumulation also exist within Class II, some overlapping with those of storage protein or Lea Class I mRNAs. The concentrations of Lea mRNAs increase at least 10- to 1700-fold during embryogenesis and decline 15- to 220-fold during the first day of germination. Earlier studies indicated that most Lea mRNAs, but no storage protein mRNAs, are induced in excised embryos exposed to abscisic acid (ABA). Free (+)ABA was measured during embryogenesis using a monoclonal antibody-based ELISA. The ABA concentration shows maxima correlating with the maxima in early Class I Lea mRNA abundance. However, ABA declines during the accumulation of Class I and Class II Lea mRNAs in late embryogenesis. Consequently, ABA could be an endogenous regulator of Class I Lea mRNAs during early maturation but is not the primary regulator of Lea mRNAs during late maturation. In contrast, cotyledon water potential exhibits a decrease that correlates with the late induction of Lea mRNAs. These findings are consistent with the hypothesis that low water potential is the endogenous regulator of some ABA-inducible mRNAs. The cessation of vascular flow to the embryo may also be involved in the disappearance of storage protein mRNAs and the late induction of Lea mRNAs.

Translation efficiency of Lea mRNAs in cotton embryos: minor changes during embryogenesis and germination

In earlier studies, only two major patterns of transcript accumulation were seen for 18 late embryogenesis abundant (Lea) gene families in cotton (Gossypium hirsutum L.) during embryogenesis and early germination. Each of these gene families probably comprises two active alloalleles. The two polypeptides encoded by seven of the Lea families can be distinguished, and analysis of their translation in vitro indicated that regulation of the homeologous transcript abundance was similar in each.In the present study, two-dimensional gel electrophoresis of polypeptides synthesized in excised embryos was employed to determine if LEA polypeptide synthesis is regulated at the translational level. The relative in vivo synthesis rate of each of the two polypeptides of 7 Lea families was compared with the relative concentration of their transcripts measured earlier by in vitro translation. For 4 families, the relative translational efficiencies of the homeologous mRNAs do not change during embryogenesis. However, there are changes of 1.5-3-fold in the other 3 families. The translation efficiencies of all transcripts of 9 of the Lea family mRNAs in vivo can be calculated from the fraction of total protein radioactivity incorporated in each LEA polypeptide family and the fractional abundance of Lea family transcripts measured by RNA dot hybridization. Lea mRNAs are found to be translated at near average rates throughout embryogenesis and early germination. These observations suggest that regulation of Lea gene expression at the translational level is minor.

Abscisic acid induction of cloned cotton late embryogenesis-abundant (Lea) mRNAs

Earlier studies found that cotton (Gossypium hirsutum L.) cotyledons contain several mRNAs which are more abundant during late embryogenesis than in mid-embryogenesis or early germination. They are here termed 'Late embryogenesis-abundant' mRNAs, encoded by Lea loci. Complementary DNA clones for 18 such mRNA sequences, defined at a hybridization criterion of Tm-15°C, were identified in a mature embryo cDNA library by differential cDNA hybridization. At a lower hybridization criterion, some sequence homology was found within several of these cloned Lea mRNA sequences. Each Lea mRNA sequence comprises 0.04-1.3% of mature embryo poly(A)(+) mRNA, a level ten-fold to several hundred-fold higher than in young embryo or 24 h seedling poly(A)(+) mRNA. Of 18 Lea mRNA sequences examined in cultured young embryos, the level of at least 13 are specifically increased by exogenous abscisic acid (ABA), several to a level near that in normal mature embryos. However, the abundance of several of the sequences does not appear to be significantly modulated by ABA. The LEA polypeptides encoded by 10 Lea mRNA sequences were identified by hybrid-arrested translation. They include most of the late embryogenesis-abundant, ABA-inducible, polypeptides previously identified. Preliminary results suggest that many of the individual Lea mRNA sequences are transcribed from 1-3 genes in each of cotton's two subgenomes.

Abscisic acid and the regulation of synthesis of specific seed proteins and their messenger RNAs during culture of soybean embryos

The ability of soybean (Glycine max (L.) Merr.) embryos cultured in vitro in the absence of abscisic acid (ABA) to germinate precociously increased as the embryos matured. Exogenous ABA prevented precocious germination at all stages of development, concentrations below 10(-5) M being partially effective. Growth (fresh weight increase) of mid-maturation embryos was dependent on ABA, and such embryos required ABA for continued synthesis of storage proteins during culture. Two complementary-DNA clones for different members of the family of 11S storage proteins, and one for the 7S storage proteins were used in Northern blot hybridizations to analyze the effects of ABA on the levels of the 11S and 7S mRNAs. In addition, filter hybridizations with in-vivo-labeled [(3)H]polyadenylated RNA to the cloned DNA for one of the 11S proteins were carried out to study transcription of 11S mRNA. Midmaturation embryos cultured with ABA continued to transcribe mRNAs for the storage proteins during the 21 d of culture studied, whereas in the absence of ABA these mRNAs disappeared from the cotyledons within about 5 d. The optimum concentration of ABA for the synthesis of storage-protein mRNAs was 10(-5) M. The effect of ABA on the concentration of 11S mRNAs was stage-dependent. Abscisic acid caused a decrease in the mRNA in embryos cultured at the cotyledon stage; it was necessary for high levels of the mRNA to be achieved in early- and mid-maturation embryos; and it did not reverse the decline in the mRNA levels in embryos cultured at the late-maturation stage.

Altered development of polysomal RNA activity in chick-pea (Cicer arietinum L.) embryonic axes. Effects of abscisic acid and temperature

The in vitro activity of polysomal polyadenylated RNA (poly(A)RNA) was studied using chick-pea (Cicer arietinum L.) embryonic axes subjected to treatments retarding germination (H2O 30°C and abscisic acid [ABA] 30°C) or inducing a false germination (thiourea 30°C) in which normal protein synthesis and growth did not occur. All treatments induced a smaller proportion of poly(A)RNA compared with the control (H2O 25°C). However, poly(A)RNA obtained in the presence of ABA had a similar in vitro activity to that of the control. The translation of mRNA from embryonic axes germinated at high temperatures was extensively blocked (70%) by methyl-7-guanosine-5'-triphosphate, whereas mRNA translation from axes treated with H2O-25°C and ABA was completely blocked (100%), indicating a greater cap dependence in the latter cases. Polyacrylamide gel electrophoresis showed that ABA and H2O-30°C each induced the synthesis of a polypeptide with an approximate Mr of 32 kDa, probably a germination regulator. It is suggested that ABA and high temperatures could regulate germination at the translational level as well as affecting ionic-exchange properties, as has been previously demonstrated (Hernández-Nistal et al. 1983, Physiol. Plant. 57, 273-278).

Method for extraction of proteins from green plant tissues for two-dimensional polyacrylamide gel electrophoresis

A method has been developed for the extraction of proteins from green plant tissues to be used in two-dimensional polyacrylamide gel electrophoresis. Three purification steps were necessary to overcome the problems due to streaking, charge heterogeneity, and other artifacts: After it was ground in liquid nitrogen, the powdered material was stirred in the presence of insoluble polyvinylpyrrolidone for binding phenols, and sodium ascorbate for binding quinones; proteins were precipitated with ammonium sulfate, and the sample was dialyzed. Hundreds of proteins could be detected after Coomassie blue staining using 200 micrograms of proteins from apical buds of Sinapis alba L.

Phytohormone control of translatable RNA populations in sexual organogenesis of the dioecious plant Mercurialis annua L. (2n = 16)

A cell-free translation system was programmed with total, poly(A), non poly(A) and polysomal RNAs from male and female flowers of this plant with separated sexes. The peptide patterns obtained reflected differences in corresponding translatable RNAs. In total RNA products, three peptides were specific for males, two for females. One of the two male-specific polypeptides of high molecular weight was obtained from poly(A) RNAs and a female-specific one from non poly(A) RNAs. Differences between peptides common to both sexes reflected different concentrations of corresponding messengers. Similar results were obtained with polysomal RNAs. The male-specific RNAs were depending on high endogenous auxin concentrations while the female on active cytokinins. Cytokinin feminization of males induced the female-specific RNAs showing cytokinin action at pretranslational stages. Phytohormone roles are discussed.

Developmental biochemistry of cottonseed embryogenesis and germination : XVII. Developmental expression of genes for the principal storage proteins

The developmental time period and the magnitude of expression of the genes for the principal cottonseed storage proteins have been measured by several means. RNA was extracted from cotton cotyledons at stages during embryogenesis and the relative amounts of the mRNAS for these proteins were determined by cell-free translation in the wheat germ system and by dot and northern hybridization of the RNA with cloned cDNA probes representing the three subfamilies of the major storage protein genes. The rates of reassociation in solution of some of the RNAs with one of the cDNA clones were also determined. Data from all four procedures show that the storage protein mRNAs are demonstrable in very small embryo cotyledons, rapidly reach a high abundance level that is maintained during most of embryo growth, and then fall precipitously in amount in the last days of embryogenesis. The expression of all three gene subfamilies appears coordinate.Further, cDNA reverse transcribed from the poly(A)(+) mRNA from a stage of maximum storage protein synthesis was hybridized to saturation with cDNA clones representing each of the subfamilies. These data indicate that the mRNAs for two of the families reach the same relative level in the total mRNA population which is about 15% of the total mRNA mass. The mRNA of the third subfamily comprises only 5% of the total mRNA mass at this stage. This apparent 3∶3∶1 ratio of mRNAs does not change during the period of storage protein synthesis. Based on the amounts of the storage protein species in the mature seed, the mRNAs of each subfamily appear to be translated to the same extent during embryogenesis.

Developmental biochemistry of cottonseed embryogenesis and germination : XVI. Analysis of the principal cotton storage protein gene family with cloned cDNA probes

DNAs complementary to the mRNAs coding for the major cotton 48 kD and 52 kD storage proteins have been cloned and used to characterize the principal cotton storage protein gene family. The principal storage proteins are found to emanate from three subsets of genes that share some homology, as shown by common antigenic determinants shared by the proteins themselves, but that are distinguishable by nucleic acid hybridization. A single sequence subfamily of 2.26 kb mRNAs codes for the 69 kD preproteins (precursors to the mature 48 kD proteins) and two sequence subfamilies of 1.96 kb mRNAs each code for 60 kD preproproteins (precursors to the mature 52 kD proteins). Hybrid arrested translation shows that cloned members of these three subfamilies hybridize only with the mRNAs of a single subfamily at moderate criterion. These three subfamilies comprise all of the principal storage protein mRNAs detectable byin vitro translation. With hybridization at low criterion, some homology has been detected between the two 1.96 kb mRNA families, although no homology has yet been detected between the 2.26 kb mRNA family and either of the two 1.96 kb mRNA families.

Plant seed embryogenesis as a tool for molecular biology

Aspects of the embryogenesis of higher plants that are of interest to molecular and cell biologists are reviewed. What is known about the changing population of developmentally regulated mRNA is summarized, and the properties of the gene products that most distinguish embryogenesis, the nutritional storage proteins, are collated.

Induction of dormancy during seed development by endogenous abscisic acid: studies on abscisic acid deficient genotypes of Arabidopsis thaliana (L.) Heynh

Mutant lines of Arabidopsis thaliana (L.) Heynh., which are characterized by symptoms of withering and the absence of seed dormancy, showed much lower levels of endogenous abscisic acid (ABA) in developing seeds and fruits (siliquae) than the wild type. Reciprocal crosses of wild type and ABA-deficient mutants showed a dual origin of ABA in developing seeds. The genotype of the mother plant regulated a sharp rise in ABA content half-way seed development (maternal ABA). The genotype of the embryo and endosperm was responsible for a second ABA fraction (embryonic ABA), which reached much lower levels, but persisted for some time after the maximum in maternal ABA. The onset of dormancy correlated well with the presence of the embryonic ABA fraction and not with the maternal ABA. Dormancy developed in both the absence and presence of maternal ABA in the seeds. In this respect maternal ABA resembled exogenously applied ABA which did not induce dormancy in ABA-deficient seeds. However, both maternal and applied ABA stimulated the formation of a mucilage layer around the testa, which could be observed during imbibition of the mature seeds. In the mature state, ABA-deficient seeds germinated in the siliquae on the plant, but only when the atmosphere surrounding the plant was kept at high relative humidity. In younger stages germination in siliquae occurred after isolation from the plants and incubation on wet filter paper. Therefore, it seems that limited access to water is the primary trigger for the developmental arrest in these seeds.

Diversity of abundant mRNA sequences and patterns of protein synthesis in etiolated and greened pea seedlings

The diversity of abundant mRNA sequences in various parts of 4-d etiolated pea seedlings (Pisum sativum L. var. Rondo CB) was compared by a cell-free translation of the mRNAs in the presence of [(35)S]methionine and by an analysis of the products by two-dimensional electrofocussing/ electrophoresis (2D separation). The various parts of the seedlings were also examined for the pattern of protein synthesis in vivo. Proteins were labeled by injection of [(35)S]methionine into the cotyledons, followed by 2D separation of the products. Over 95% of the abundant mRNA sequences and newly synthesized abundant polypeptides were shared by all parts of etiolated seedlings, including the cotyledons. However, a few distinct differences were observed when comparing mRNAs of roots and shoots; the most prominent among these were a group of six abundant mRNA sequences found exclusively in shoots. Only about 30% of the polypeptides synthesized on isolated RNA could be traced in equivalent positions on the gels as the polypeptides synthesized in vivo. Analysis of total RNA from light-grown pea seedlings showed the appearance of some twenty-five translation products not found with total RNA from etiolated seedlings, while about nine other translation products disappeared. At least ten of the light-induced RNA sequences were also present after growth in low-intensity red light (λ>600 nm) and are therefore thought to be controlled by the phytochrome system. Comparison of 11-d light-grown pea plants with 4-d light-grown seedlings did not reveal additional translatable RNA sequences, indicating that the major morphogenetic changes that occur after 4 d are not accompanied by significant changes in the pattern of abundant RNA sequences.

Control of enzyme activities in cotton cotyledons during maturation and germination : III. In-vitro embryo development in the presence of abscisic acid

Cotton (Gossypium hirsutum L.) embryos excised from bolls 38-43 d after anthesis and cultured in vitro for 4 d on a nutrient agar medium containing 3.8 μM abscisic acid (ABA) developed enzyme activity and accumulated insoluble protein, neutral lipid, and dry weight similar to embryos maturing on the plant. Inclusion of ABA in the medium prevented precosious germination and allowed continued increases in catalase, malate dehydrogenase, citrate synthase, aspartate aminotransferase, and β-oxidation enzyme activities as well as de-novo synthesis of malate synthase. Isocitrate lyase activity was not detectable in ABA-cultured embryos nor normally-developed embryos. Omission of sucrose from the medium resulted in near-doubling of the development of malate synthase activity, with minimal effects on the other enzyme activities. Addition of Actinomycin D, cordycepin, or cycloheximide to ABA-containing cultures did not overcome the observed inhibition of germination, but severely reduced both the appearance of new malate synthase activity and further production of other related enzyme activities. Thus, development of these enzyme activities in the presence of ABA appears dependent on transcription and translation, while inhibition of germination by ABA at this stage of development is not sensitive to the RNA- and protein-synthesis inhibitors. The results indicate that ABA does not prevent vivipary by suppressing translation of m-RNAs coding for isocitrate lyase and its companion enzymes, as previously proposed.