Hormonal control of messenger ribonucleic acid metabolism in barley aleurone layers

Trails to the gibberellin receptor, GIBBERELLIN INSENSITIVE DWARF1

The researches on the identification of gibberellin receptor are reviewed from the early attempts in 1960s to the identification of GIBBERELLIN INSENSITIVE DWARF1 (GID1) as the receptor in 2005. Unpublished data of the gibberellin-binding protein in the seedlings of adzuki bean (Vigna angularis) are also included, suggesting that the active principle of the gibberellin-binding protein was a GID1 homolog.

Alterations in gene expression in sorghum induced by the host-specific toxin from Periconia circinata

Susceptibility of sorghum to the fungal pathogen Periconia circinata and sensitivity to its host-specific toxin are determined by the semidominant allele at the pc locus. Pretreatment of susceptible seedlings with cycloheximide or cordycepin for 4 hr before treatment with the toxin protected the seedlings against toxin-induced loss of electrolytes and prevented development of disease symptoms. In vivo incorporation of [(3)H]leucine into protein was inhibited 91% and 47% by cycloheximide and cordycepin, respectively, but was not affected by the toxin. Gel electrophoresis and fluorography of in vivo-labeled proteins extracted from non-treated and toxin-treated root tips of near-isogenic susceptible and resistant lines revealed a selective increase in radioactivity of a protein band at M(r) 16,000 only in preparations from toxin-treated susceptible root tips. Two-dimensional gel electrophoresis separated the M(r) 16,000 band into four proteins and confirmed the increased rate of synthesis. Products of in vitro translation were substantially enriched with the four M(r) 16,000 proteins when total RNA from toxin-treated susceptible root tips was used in a cell-free protein-synthesizing system. Because the proteins that increase are common to both susceptible and resistant genotypes, the toxin apparently interferes with a regulatory function, perhaps a function of the pc locus, and thereby alters gene expression in the susceptible genotype. The data suggest but do not establish that phytotoxicity results from the increased rate of synthesis of the specific proteins.

Hormone-induced increase in levels of functional mRNA and alpha-amylase mRNA in barley aleurones

Incubation of barley aleurone cells with gibberellic acid produces a progressive increase in the RNA content of the cells. The activity of poly(A)-containing RNA, measured in an in vitro wheat germ protein-synthesizing system, reaches a maximum approximately 12 hr after hormone addition and declines thereafter. The structurally intact functional mRNA content in these cells, measured as poly(A)-RNA with 5' "caps," also shows a maximum at 12 hr and correlates with the translational capacity of poly(A)-RNA. Activation of mRNA by guanylylation or methylation after addition of gibberellic acid is ruled out. Available evidence indicates that gibberellic acid stimulates protein synthesis by increasing the synthesis of mRNA. Studies with cycloheximide suggest that the induction of synthesis of alpha-amylase mRNA by gibberellic acid requires protein synthesis after hormone addition.

Stability of barley aleurone transcripts: Dependence on protein synthesis, influence of the starchy endosperm and destabilization by GA3

We have studied the stability of Barley aleurone and embryo expressed (Balem) transcripts in aleurone layers. The Per1, Ole1 and Ole2 transcripts are abundant during desiccation and in dry resting seeds, while B12D and B22E transcripts are expressed mainly during seed maturation and germination. From 21 to 40 days post anthesis (DPA) incubation of aleurone layers resulted in a substantial, but differential reduction in the levels of these transcripts. In contrast, Balem transcript levels in aleurone layers of incubated embryoless grains were (except for B22E) similar to those of freshly dissected layers. Cycloheximide lowered transcript levels significantly. This indicates that a protein-synthesis-dependent mRNA-stabilizing mechanism is active in the aleurone cells when attached to the starchy endosperm. At the onset of seed desiccation (40 DPA), half-lives of transcripts to be stored in the dry seed were up to several days longer than the half-life of B22E, which decreases during seed maturation. While the Per1, Ole1 and Ole2 transcript levels decline rapidly in the aleurone layers of mature, germinating seeds, the genes are actively transcribed and their transcripts highly stable in the aleurone of incubated embryoless seeds. The expression of Ole1 and Ole2, as well as Per1, can be repressed 100-1 000-fold by gibberellic acid (GA3) in a dose-dependent manner. Abscisic acid can counteract the GA3 repression. Incubations with transcriptional and translational inhibitors indicate that GA3 inhibits the transcription of these genes and at the same time induces a protein-synthesis-dependent mechanism destabilizing their mRNA molecules present.

Gibberellin-repressible gene expression in the barley aleurone layer

Gibberellins are noted for their ability to induce expression of genes, such as alpha-amylase, in the aleurone layers of cereals. However, a number of mRNA species in the mature imbibed aleurone cell of barley, such as a storage globulin (Heck et al., Mol Gen Genet 239: 209-218 1993), are simultaneously and specifically repressed by gibberellin. In a continuing effort to understand this effect, we report cloning and characterization of two additional cDNAs from barley designated pHvGS-1 and pcHth3 that have high corresponding mRNA levels in the mature imbibed aleurone but are repressed 10-fold or more within 24 h of treatment with gibberellic acid (GA3). The extent of repression was concentration dependent and maximally effective at 10(-6) M GA3. Repression was also noted in the constitutive gibberellin response mutant, slender, in the absence of exogenous GA3. The antagonistic phytohormone, abscisic acid, had no effect or was weakly inductive of the steady-state levels of these mRNAs. During development of the seed, repressible mRNAs are present to different degrees in the maturing aleurone layer and embryo, but not in the starchy endosperm. Some repressible mRNA persists in the mature dry aleurone layer, but is degraded during imbibition, replenished by de novo transcription, and maintained at high steady-state levels until GA3 is perceived. Preliminary investigation suggests that repression is at least partly due to destabilization of the mRNAs which have estimated half-lives of 12 h or greater in the absence of GA3. pcHth3 encodes a member of the gamma-thionin gene family located on chromosome 7. pHvGS-1 corresponds to a gene on chromosome 3 of unknown function.

Barley embryo globulin 1 gene, Beg1: characterization of cDNA, chromosome mapping and regulation of expression

We report identification of a 2189 bp cDNA clone from barley corresponding to a single-copy gene, Beg1 (Barley embryo globulin), on chromosome 4, which encodes a storage globulin. In barley, the major protein reserve in the aleurone layer belongs to the 7S globulin class of proteins found in many seeds. Electrophoretically and antigenically similar proteins are present in the barley embryo. Accumulation of Beg1 mRNA was noted beginning 15-20 days post-anthesis in both the aleurone layer and embryo of the developing barley grain but not in the starchy endosperm. A high level of Beg1 mRNA is also present in the mature imbibed aleurones, which can be repressed by treatment with gibberellic acid. This repressive effect of gibberellin on the levels of Beg1 mRNA is confirmed in the gibberellin response-constitutive mutant, slender, whose aleurone layers do not accumulate Beg1 mRNA even in the absence of applied gibberellic acid. The deduced primary translation product of the Beg1 mRNA is a 63.7 amino acid (72 kDa) protein with homology to maize embryo globulin 1 (GLB1) and a partial sequence of a wheat 7S globulin. The internal amino acid sequence of BEG1 closely matches the N-terminal sequence of isolated barley aleurone globulin. Seven imperfect tandem repeats of 16 amino acids each are present near the N-terminus of BEG1, which conform to the consensus HGEGEREEEXGRGRGR, and contribute to the observed unusual amino acid composition of this protein. A second, distinct barley globulin gene, Beg2, which is homologous to maize Glb2, was detected by Northern and Southern analysis. Beg2 and Beg1 are regulated differently which may indicate variation in storage or utilization properties among the barley globulins.

Regulation and interaction of multiple protein factors with the proximal promoter regions of a rice high pI alpha-amylase gene

The alpha-amylase gene is known to be regulated by the plant hormone gibberellin (GA) in cereal aleurone cells. The accumulation of the mRNA corresponding to a rice high pI alpha-amylase gene, OSamy-c, was stimulated 20-fold by exogenous GA3 in half-seeds lacking embryos. Regulatory regions in the promoter of this high pI sub-family were analyzed. The OSamy-c 5' flanking sequence, spanning positions -231 to +29, was fused upstream of the beta-glucuronidase (GUS) gene coding region. The delivery of this plasmid into rice aleurone cells by the biolistic method resulted in a GA-stimulated synthesis of GUS. Gel retardation assays were performed to study protein-DNA interactions between putative regulatory sequences of OSamy-c and partially purified rice seed extracts. We identified multiple seed-specific protein factors that bind to proximal regions of the OSamy-c promoter between positions -231 and -162. Five different proteins were distinguished based on competitive binding studies. Three protein binding regions were located by footprinting analyses, one of which is located in the conserved sequence also found upstream of other GA-inducible genes. Two protein factors in rice aleurone cells that interact with the putative regulatory sequence do not require GA induction.

Hormonal regulation of alpha-amylase expression in barley aleurone layers : the effects of gibberellic Acid removal and abscisic Acid and phaseic Acid treatments

The expression of alpha-amylase isozymes in barley (Hordeum vulgare L.) aleurone layers is known to be maximally induced between 12 and 20 hours after addition of the phytohormone, gibberellic acid (GA(3)). Addition of another hormone, abscisic acid (ABA), or its metabolite, phaseic acid, during this time period resulted in reduced alpha-amylase expression. Expression of the high isoelectric point alpha-amylase isozyme group was affected much more by both of these treatments than was expression of the low isoelectric point alpha-amylase isozyme group. Addition of either the translation inhibitor cycloheximide or the transcription inhibitor cordycepin prevented the decrease in alpha-amylase mRNA levels after ABA treatment. Cordycepin also prevented the decreases in alpha-amylase expression that result from phaseic acid treatment. Midcourse GA(3) removal experiments were performed to determine whether ABA treatment and the removal of GA(3) have analogous effects on alpha-amylase expression. It was found that cordycepin treatment also prevented decreases in alpha-amylase mRNA levels resulting from GA(3) removal. We conclude that the suppression of alpha-amylase expression caused by ABA or midcourse GA(3) removal is dependent on continuous RNA and protein synthesis.

The effect of abscisic acid on the differential expression of α-amylase isozymes in barley aleurone layers

The treatment of barley aleurone layers with gibberellic acid (GA3) results in the synthesis of two groups of α-amylase isozymes. Addition of abscisic acid (ABA) at the same time as GA3 inhibited the synthesis of both groups of isozymes. However, midcourse ABA addition (12 h or later after GA3) had a more inhibitory effect on the high pI α-amylase group than on the low pI α-amylase group. This midcourse inhibition was detectable within 2 h of ABA addition. Northern analysis results using cDNA probes for the high pI and low pI α-amylase groups paralleled the protein synthesis results for both isozyme groups. High pI α-amylase mRNA levels began to decrease within 2 h of midcourse ABA treatment and were less than 10% of the original level by 4 h. The levels of low pI α-amylase mRNA were decreased less by midcourse ABA addition than were high pI mRNA levels. Cordycepin and cycloheximide blocked the effects of midcourse ABA addition on α-amylase mRNA. These observations indicate that ABA inhibits α-amylase expression at the pretranslational level and that protein and RNA synthesis are required for midcourse ABA action to occur. Our results also show that α-amylase mRNA, which has been thought to be very stable, is degraded after midcourse ABA treatment.

Potassium-Dependent Increase in RNA and Protein Synthesis in the Early Phase of Incubation of the Thermodormant Phacelia tanacetifolia Seeds

The seeds of Phacelia tanacetifolia Benth. cv Bleu Clair incubated at 30 degrees C in the dark did not germinate and did not activate K(+) uptake capacity. The administration of 1 millimolar K(+) in the early phase of incubation stimulated RNA and protein synthesis. The possible role of K(+) in promoting the marcromolecular syntheses during the early phase of germination is discussed.

Heat shock causes destabilization of specific mRNAs and destruction of endoplasmic reticulum in barley aleurone cells

In response to a phytohormone, gibberellic acid, the aleurone layers of barley seeds synthesize and secrete alpha-amylases, which are coded by a set of stable mRNAs. When aleurone layers are subjected to heat shock treatment, the synthesis of alpha-amylase is suppressed while heat shock proteins are induced. The suppression of alpha-amylase synthesis is not the result of translational control as reported in several other systems. Rather, the sequences of alpha-amylase mRNA are rapidly degraded during heat shock as shown by in vitro translation and dot blot hybridization with a cDNA probe. Upon recovery from heat shock, the tissue resumes the synthesis of alpha-amylase in 2-4 hr. However, in the presence of a transcription inhibitor, cordycepin, the resumption of synthesis of alpha-amylase does not take place, indicating that new transcription of alpha-amylase genes is necessary for this recovery process. The degradation of alpha-amylase mRNAs correlates with the rapid destruction of endoplasmic reticulum as observed by electron microscopy, a phenomenon that has not been reported previously as a heat shock response. Since alpha-amylase mRNA is associated with the endoplasmic reticulum via membrane-bound polyribosomes, we suggest that the destruction of the endoplasmic reticulum during heat shock causes the destabilization and the eventual degradation of alpha-amylase mRNA.

The effects of gibberellic acid and abscisic acid on α-amylase mRNA levels in barley aleurone layers studies using an α-amylase cDNA clone

Two cDNA clones were characterized which correspond to different RNA species whose level is increased by gibberellic acid (GA3) in barley (Hordeum vulgare L.) aleurone layers. On the criteria of amino terminal sequencing, amino acid composition and DNA sequencing it is likely that one of these clones (pHV19) corresponds to the mRNA for α-amylase (1,4-α-D-glucan glucanohydrolase, EC 3.2.1.1.), in particular for the B family of α-amylase isozymes (Jacobsen JV, Higgins TJV: Plant Physiol 70:1647-1653, 1982). Sequence analysis of PHV19 revealed a probable 23 amino acid signal peptide. Southern hybridization of this clone to barley DNA digested with restriction endonucleases indicated approximately eight gene-equivalents per haploid genome.The identity of the other clone (pHV14) is unknown, but from hybridization studies and sequence analysis it is apparently unrelated to the α-amylase clone.Both clones hybridize to RNAs that are similar in size (∼1500b), but which accumulate to different extents following GA3 treatment: α-amylase mRNA increases approximately 50-fold in abundance over control levels, whereas the RNA hybridizing to pHV14 increases approximately 10-fold. In the presence of abscisic acid (ABA) the response to GA3 is largely, but not entirely, abolished. These results suggest that GA3 and ABA regulate synthesis of α-amylase in barley aleurone layers primarily through the accumulation of α-amylase mRNA.

Regulation of the synthesis of barley aleurone alpha-amylase by gibberellic Acid and calcium ions

The effects of gibberellic acid (GA(3)) and calcium ions on the production of alpha-amylase and acid phosphatase by isolated aleurone layers of barley (Hordeum vulgare L. cv Himalaya) were studied. Aleurone layers not previously exposed to GA(3) or Ca(2+) show qualitative and quantitative changes in hydrolase production following incubation in either GA(3) or Ca(2+) or both. Incubation in H(2)O or Ca(2+) results in the production of low levels of alpha-amylase or acid phosphatase. The addition of GA(3) to the incubation medium causes a 10- to 20-fold increase in the amounts of these enzymes released from the tissue, and addition of Ca(2+) at 10 millimolar causes a further 8- to 9-fold increase in alpha-amylase release and a 75% increase in phosphatase release. Production of alpha-amylase isoenzymes is also modified by the levels of GA(3) and Ca(2+) in the incubation medium. alpha-Amylase 2 is produced under all conditions of incubation, while alpha-amylase 1 appears only when layers are incubated in GA(3) or GA(3) plus Ca(2+). The synthesis of alpha-amylases 3 and 4 requires the presence of both GA(3) and Ca(2+) in the incubation medium. Laurell rocket immuno-electrophoresis shows that two distinct groups of alpha-amylase antigens are present in incubation media of aleurone layers incubated with both GA(3) and Ca(2+), while only one group of antigens is found in media of layers incubated in GA(3) alone. Strontium ions can be substituted for Ca(2+) in increasing hydrolase production, although higher concentrations of Sr(2+) are required for maximal response. We conclude that GA(3) is required for the production of alpha-amylase 1 and that both GA(3) and either Ca(2+) or Sr(2+) are required for the production of isoenzymes 3 and 4 of barley aleurone alpha-amylase.

Characterization of the increased lysophospholipase activity in gibberellic Acid-treated barley aleurone layers

A lysophospholipase (LPL) activity appears in the aleurone of barley (Hordeum vulgare L. cv Himalaya) half seeds during imbibition on moist agar. Secretion of LPL by half seeds is promoted by GA(3); the increase in secretory rate is almost linear from 10(-10) to 10(-6) molar GA(3). LPL activity is likewise promoted in isolated aleurone layers by GA(3). Its secretion into the incubation medium requires the continued presence of GA(3) and commences after a 10 to 14 hour lag period when 10 millimolar Ca(2+) is present. In the absence of Ca(2+), the lag period remains unchanged but attainment of the maximum secretory rate is delayed. Ca(2+) alone has very little effect either on LPL activity accumulated in the aleurone layer or in the surrounding medium. However, 50 millimolar Ca(2+) together with GA(3) dramatically increase the level of secreted activity and of total (accumulated and secreted) activity.The metabolic inhibitors cycloheximide and actinomycin D inhibit the accumulation of LPL activity in the aleurone and also the secreted activity. Actinomycin D added after the lag period results in a much lower inhibition. The increase in LPL activity in response to GA(3) occurs as a result of de novo synthesis; LPL activity from barley half seeds incubated in 80% D(2)O in the presence of GA(3) undergoes a shift to higher density compared with the activity from similar controls incubated in H(2)O. The characteristics of the GA(3) enhancement of LPL activity are compared specifically with alpha-amylase and generally with other GA(3)-controlled hydrolases.

Effects of abscisic Acid and ethylene on the gibberellic Acid-induced synthesis of alpha-amylase by isolated wheat aleurone layers

Gibberellic acid-induced alpha-amylase synthesis in wheat aleurone layers (Triticum aestivum L. var Potam S-70) escaped from transcriptional control 30 h after addition of the hormone, as evidenced by the tissue's loss of susceptibility to cordycepin. Abscisic acid inhibited the accumulation of alpha-amylase activity when added to the tissue during this cordycepin-insensitive phase of enzyme induction. alpha-Amylase synthesis was not restored by the addition of cordycepin, indicating that the response to abscisic acid was not dependent upon the continuous synthesis of a short lived RNA. When ethylene was added simultaneously or some time after abscisic acid, the accumulation of alpha-amylase activity was sustained or quickly restored. The loss of susceptibility to cordycepin was completely prevented when aleurone layers were incubated with a combination of gibberellic and abscisic acids from the start of the induction period. This effect of abscisic acid was not reversed by ethylene. On the basis of these observations, it is suggested that abscisic acid inhibits both the transcription and translation of alpha-amylase mRNA, and that only the latter site of action is susceptible to reversal by ethylene.The rate of incorporation of [methyl-(14)C]choline into phospholipids was also inhibited by abscisic acid. Ethylene reversed this effect. The effects of abscisic acid and ethylene on phospholipid synthesis were not dependent upon the presence of gibberellic acid. No direct relationship was found between the control of alpha-amylase synthesis and membrane formation by abscisic acid and ethylene.

Modulation by abscisic acid and S-2-aminoethyl-L-cysteine of α-amylase mRNA in barley aleurone cells

The changes in the levels of α-amylase mRNA is barley aleurone layers in response to addition of plant growth regulators have been studied using a cloned α-amylase cDNA as the hybridization probe. An increase in gibberellic acid (GA) concentration in the incubation medium from 10(-9) M to 10(-6) M results in a progressive increase in α-amylase mRNA concentration in the aleurone cells. Detectable levels of α-amylase mRNA appear in the aleurone cells as early as 1 h after addition of GA. The concentration of this mRNA increases for several hours and then declines rapidly. Abscisic acid (ABA) and the amino acid analog S-2-aminoethyl-L-cysteine (AEC) suppress the GA-mediated induction of α-amylase. These compounds appear to affect the level of α-amylase mRNA in aleurone cells as measured byin vitro translation assays and by analysis of RNA blots with α-amylase cDNA probes. It is concluded that the regulation of α-amylase gene expression by ABA is at the level of transcription. Further, a protein factor appears to be required in addition to GA for transcription of α-amylase genes.

Regulation of abscisic acid metabolism in the aleurone layers of barley seeds

The regulation of metabolism of abscisic acid has been investigated in the isolated aleurone layers of barley (Hordeum vulgare L.) seeds. The rate of conversion of abscisic acid to phaseic acid is enhanced by two to five-fold when the tissue is pretreated with 10(-5) M of this hormone. This enhancement can be observed with a pretreatment as short as two hours, and is prevented by transcription and translation inhibitors. The enhancement is accompanied by the appearance of new proteins which are induced by abscisic acid. It is suggested that some of these ABA induced proteins are probably involved in the conversion from abscisic acid to phaseic acid.

Gibberellic acid and abscisic acid modulate protein synthesis and mRNA levels in barley aleurone layers

Using in vivo pulse labeling, changes in the pattern of protein synthesis were detected in isolated barley aleurone layers treated with fibberellic acid (GA3). GA3 greatly altered the relative rates of synthesis of many polypeptides, increasing some, notably α-amylase, and decreasing others. α-Amylase synthesis increased until it was the major product (over 60%) of protein synthesis after 24h. The pulse-labeled pattern of secreted polypeptides was also changed by GA3. There was the expected increase in α-amylase together with a number of other polypeptides but there was reduced secretion of several polypeptides also.Cell-free translation of RNA isolated from control and hormone-treated tissues was used to measure changes in mRNA levels. GA3 caused many changes, particularly in the level of mRNA for α-amylase. In vitro synthesized α-amylase, identified by immunoaffinity chromatography, had an Mr of 46 000. This polypeptide was partially processed to a polypeptide with Mr 44 000 by the addition of dog pancreas membranes to the in vivo translation mixture. The level of mRNA for α-amylase began to increase 2-4 h after GA3 was added and reached a maximum level of about 20% of total mRNA after 16 h. Thus after 16 h, the synthesis of α-amylase as a proportion of total protein synthesis, continued to increase while the level of its mRNA as a proportion of total mRNA remained constant. These results indicate that protein synthesis was modified more extensively than we can account for by changes in mRNA.Abscisic acid (ABA) reversed all of the effects of GA3 on protein synthesis and mRNA levels. It also promoted synthesis of a small number of new polypeptides and increased the level of some mRNAs. GA3 reversed the accumulation of ABA-promoted mRNAs. Although, ABA strongly suppressed the increase in the level of translatable mRNA for α-amylase, there was an even stronger inhibition of enzyme synthesis and accumulation.We conclude that both GA3 and ABA regulate protein synthesis both positively and negatively in aleurone cells largely by regulating levels of mRNA and in the case of α-amylase, possibly also by changing the efficiency of translation of its mRNA.

Endoplasmic Reticulum Formation during Germination of Wheat Seeds : A QUANTITATIVE ELECTRON MICROSCOPE STUDY

This study demonstrates germination-induced ultrastructural changes in wheat (Triticum aestivum L. cv Arthur) aleurone cells. Seeds imbided for 4 hours in water contained endoplasmic reticulum (ER) or ER-like membranes as vesicles or as short segments of membrane associated with the spherosomes on the periphery of aleurone grains. Aleurone cells incubated between 8 and 10 hours contained abundant ER membranes mainly associated with the nuclear envelope and, to a lesser extent, with the spherosomes surrounding the aleurone grain. The membranes located on the periphery of the nucleus occurred as regions of stacked cisternae. When aleurone cells were analyzed by morphometry, the increase in ER during incubation was found to be greater than 2-fold. During the same incubation period, other organelles did not change significantly. The early increase in ER was not affected by gibberellin incubation. Thus, the rapid proliferation of ER observed during the early stages of germination in aleurone cells of wheat is not likely to be controlled directly by gibberellin.

Quantitative and qualitative changes in the endoplasmic reticulum of barley aleurone layers

Changes in the level of the endoplasmicreticulum (ER) marker enzyme cytochrome-c reductase (EC 1.6.2.1) were followed with time of imbibition of de-embryonated half-seeds of barley (Hordeum vulgare L.) and the subsequent incubation of their aleurone layers in gibberellic acid (GA3) and H2O. During imbibition there is an increase in the level of cytochrome-c-reductase activity and in the amount of 280-nm absorbance associated with this enzyme. When aleurone layers are incubated for a further 42 h in water, there is a doubling of the cytochrome-c-reductase activity. In GA3, the activity of cytochrome-c reductase reaches a maximum at 24 h of incubation and thereafter falls to below 70% of its level at the beginning of the incubation period. Changes in the cytochrome-c-reductase activity correlate with changes in the fine structure of the aleurone cell. The ER isolated in low Mg(2+) from aleurone layers incubated in buffer for up to 18 h has buoyant density of 1.13-1.14 g cc(-1) while that from layers incubated in GA3 for 7.5-18 h has a density of 1.11-1.12 g cc(-1). The α-amylase (EC3.2.1.1) isolated with the organelle fraction by Sepharose gel filtration is associated with the ER on isopycnic and rate-zonal density gradients, and its activity can be enhanced by Triton X-100. The soluble α-amylase fraction from Separose-4B columns, on the other hand, is not Triton-activated but is acid-labile. Acid phosphatase (EC3.1.3.2) is distributed in at least three peaks on isopycnic gradients. In low Mg(2+) the second peak of activity has a density of 1.12 g cc(-1) in GA3-treated tissue and 1.13-1.14 g cc(-1) in H2O-treated tissue. With high-Mg(2+) buffers, this peak of phosphatase activity disappears. Acid-phosphatase activity is not enhanced by Triton X-100 nor is it acid-labile.

Screening for barley mutants with altered hormone sensitivity in their aleurone layers

A method, based on the diffusion assay of alpha-amylase on agar plates, was developed to screen for barley (Himalaya) mutants with altered sensitivity to gibberellic acid (GA(3)) or abscisic acid (ABA) in their aleurone layers. The seeds produced by sodium azide-mutagenized barley were screened for their ability to synthesize and secrete alpha-amylase when treated with different combinations of hormones. Various GA(3)-insensitive or supersensitive, ABA-insensitive, temperature-dependent GA(3)-insensitive, and constitutive mutants have been identified. Several stable mutants with altered GA(3) sensitivity were recovered. Two of the homozygous GA(3)-insensitive mutants have been preliminarily characterized. The GA(3)-enhanced production of alpha-amylase and release of phosphatase are hampered in these mutants. However, they have normal stem height, and the uptake of GA(3) by their aleurone layers appears to be the same as that of wild-type barley. They are most likely regulatory mutants affecting both alpha-amylase synthesis and phosphatase release.

Partial purification and characterization of the mRNA for alpha-amylase from barley aleurone layers

The poly(A)-containing mRNA from barley aleurone layers pretreated with gibberellic acid has been purified by phenol-chloroform extraction and repeated oligo[d(pT)]-cellulose chromatography. This RNA has been translated in both the wheat germ and reticulocyte lysate in vitro translation systems with greater than 50% of the synthesized protein being alpha-amylase. The mRNA for alpha-amylase has been further purified by dimethylsulfoxide-formamide-sucrose density gradient centrifugation and by gel electrophoresis. By these methods, its molecular weight has been determined to be 580,000.

Isolation and characterization of polysomes and polyadenylated polysomal RNA from Vicia faba meristematic root cells

Undegraded Vicia faba polysomes from meristematic root cells were obtained after homogenization in a medium of low ionic strength provided that the pH was equal to 9.0. By minimizing the shearing forces during the homogenization step, polysomes were obtained free of mitochondrial and nuclear contaminants, measured by differential spectrophotometry and CsCl gradient centrifugation respectively. Poly(A)-containing RNA was obtained by poly(U)-Sepharose chromatography and shown to be virtually free of rRNA and its average size was 13-15 S. Approximately 9% of the purified preparation was annealed by [3H]-poly(U). Sucrose gradient analysis under denaturing conditions showed that the poly(A)-CONtaining RNA were non-degraded. This RNA was used to direct the synthesis of proteins in a heterologous cell-free system from wheat germ.

Enhancement of polyribosome formation and RNA synthesis of gibberellic Acid in wounded potato tuber tissue

As part of a more detailed study on plant tumorigenesis, the action of gibberellic acid (GA(3)) in wounded potato tuber tissues as a model system has been evaluated. GA(3) stimulates total RNA synthesis in wounded tissues, the optimal concentration being 0.1 micromolar. The responsiveness of the tissue toward the hormone develops with time after wounding. Whereas freshly wounded tissue does not respond at all to the hormone, it becomes competent after about 6 hours, the competence being maximal after 1 day of wound healing.GA(3) enhances the formation of polyribosomes in wounded tissues and stimulates the synthesis of both ribosomal RNAs, transfer RNAs, 5S RNA, and a fraction, which in sucrose density gradients sediments between 18S rRNA and 5S RNA. This fraction contains presumptive mRNA.The hormone, then, is somehow recognized by wounded potato tissue in a time-specific way; the signal is transferred to the genome and triggers the synthesis of various RNA species.

Physiological control of exo- and endoproteolytic activities in germinating wheat and their relationship to storage protein hydrolysis

The effects of gibberellic acid, abscisic acid, cycloheximide, actinomycin D, and cordycepin upon exo- and endoproteolytic activities and storage (gluten) protein hydrolysis in germinating wheat and in incubated embryoless wheat seeds have been studied. Early increases in endoproteolytic activity were insensitive to the addition of gibberellic acid and inhibitors of protein and RNA synthesis. Later increases in endoproteolytic activity were enhanced by gibberellic acid, strongly inhibited by abscisic acid and cycloheximide, and partially inhibited by actinomycin D and cordycepin. Increases in exoproteolytic activity were insensitive to the addition of gibberellic acid, abscisic acid, actinomycin D, and cordycepin but were inhibited in whole seeds when cycloheximide was added in the steeping medium. However, cycloheximide did not inhibit increases in exoproteolytic activity when added to embryoless seeds, to germinating whole seeds, or to seeds which had been stored at 4 C for extended periods of time. Comparison of the effects of gibberellic acid, abscisic acid, and inhibitors of protein and RNA synthesis upon storage protein hydrolysis and their effects upon proteolytic activity indicated that storage protein hydrolysis in germinating wheat is controlled by the rate of hormonally induced de novo synthesis of endoproteolytic enzymes.

Development and Localization of Carboxypeptidase Activity in Embryo-less Barley Half-kernels

Distal half-kernels of barley (Hordeum vulgare L.), after imbibition for 1 day, produced a carboxypeptidase that was active on N-carbobenzoxy-l-phenylalanyl-l-alanine and on N-carbobenzoxy-l-phenylalanyl-l-phenylalanine. For the ensuing 2 days, activity increased linearly and thereafter increased at reduced rates. Electrofocusing of an imbibed half-kernel homogenate produced coincident peaks of activity on both substrates. Experiments with dissected imbibed (3 days) half-kernels showed that the enzyme arose in the aleurone layer. Enzyme production was inhibited by 6-methylpurine, cordycepin, cycloheximide, and p-fluorophenylalanine, and activity was inhibited by phenylmethylsulfonylfluoride. The enzyme did not hydrolyze endopeptidase substrates over a range of pH.Gibberellic acid accelerated the rate of release from the aleurone, but was not essential for release and did not appreciably affect the ultimate amount of carboxypeptidase produced. In these respects, the carboxypeptidase appears to be unique among the known hydrolases produced by barley aleurone tissue.

Comparison of the in vitro translation products of mRNA isolated from suspension cultures of Phaseolus vulgaris grown on maintenance and induction medium

1. Bean cells grown in suspension culture on maintenance medium have been shown to differentiate (xylem and phloem production) when they are transferred to an induction medium containing an increased ratio of naphthylacetic acid to kinetin.-2. Conditions for the extraction and isolation of undegraded mRNA are described. The mRNA has been translated by 2 in vitro protein synthesizing systems; the wheat germ and the mRNA-dependent-reticulocyte-lysate preparations.-3. A greater proportion of the mRNA from cells on maintenance medium coded for high molecular weight products compared with that from cells on induction medium.-4. mRNA from cells on induction medium coded for a relatively large amount of a few polypeptides whereas that from cells on maintenance medium coded for a large number of polypeptides all present in fairly equal amounts.

No Effect of 5-Fluorouracil on the Properties of Purified alpha-Amylase from Barley Half-seeds

alpha-Amylase has been purified from de-embryonated seeds of barley (Hordeum vulgare L. cv. Betzes) which have been incubated on 10(-6)m gibberellic acid (GA(3)) following 3 days of imbibition in buffer. Incubation of the half-seeds in up to 10(-2)m 5-fluorouracil (5-FU) during the entire incubation period, including imbibition, had no effect on any of the following characteristics of purified alpha-amylase: thermal stability in the absence of calcium, molecular weight of the enzyme, isozyme composition, specific activity, or the amount of alpha-amylase synthesized by the aleurone tissue. The synthesis of rRNA and tRNA was strongly inhibited by 5-FU, indicating that the analog had entered the aleurone cells. These results are not in agreement with those of Carlson (Nature New Biology 237: 39-41 [1972]) who found that treatment of barley aleurone with 10(-4)m 5-FU prior to the addition of GA(3) resulted in decreased thermal stability of GA(3)-induced alpha-amylase and who interpreted this as evidence that the mRNA for alpha-amylase was synthesized during the imbibition of the aleurone tissue and independently of gibberellin action. Results of the present experiments indicate that the thermal stability of highly purified alpha-amylase is not altered by treatment of barley half-seeds with 5-FU, and that 5-FU cannot be used as a probe to examine the timing of alpha-amylase mRNA synthesis.

Asparagine synthetase in corn roots

The level of asparagine synthetase is low in 10-mm root tips from corn seedings (Zea mays W64 x W182F) but relatively high in mature root sections taken 20 to 35 mm from the tip. When root tips are excised there is a marked increase in asparagine synthetase over a 5-hour period. In mature root sections, on the other hand, the asparagine synthetase activity declines over the same 5-hour period. The increase in the root tip is sensitive to cordycepin, 6-methylpurine, and cycloheximide, which indicates that both RNA and protein synthesis are involved in the formation of asparagine synthetase in the root tip sections. The glutamine analogue azaserine also inhibits formation of the enzyme in root tips, as does glucose. The increase in the root tip is not sensitive to asparagine. Additions of glucose or asparagine have no effect on enzyme activity in extracts. When cycloheximide, azaserine, or glucose is added to the mature root sections there is no effect on recovered enzyme activity.

Gibberellic Acid enhancement of DNA turnover in barley aleurone cells

When imbibed, deembryonated halfseeds from barley (Hordeum vulgare L., var. Himalaya) are incubated in buffer, the DNA content of the aleurone layer increases 25 to 40% over a 24-hour period. In contrast, the DNA of isolated aleurone layers declines by 20% over the same time period. Gibberellic acid (GA) causes a reduction in DNA levels in both halfseed aleurone layers and isolated aleurone layers. GA also increases the specific radioactivity of [(3)H]thymidine-labeled halfseed aleurone layer DNA during the first 12 hours of treatment. Pulse-chase studies demonstrated that the newly synthesized DNA is metabolically labile.The buoyant density on CsCl density gradients of hormone-treated aleurone DNA is identical with that of DNA extracted from whole seedlings. After density-labeling halfseed DNA with 5-bromodeoxyuridine, a bimodal absorption profile is obtained in neutral CsCl. The light band (1.70 g/ml) corresponds to unsubstituted DNA, while the heavy band (1.725-1.74 g/ml) corresponds to a hybrid density-labeled species. GA increases the relative amount of the heavy (hybrid) peak in halfseed aleurone layer DNA, further suggesting that the hormone enhances semiconservative replication in halfseeds.DNA methylation was also demonstrated. Over 60% of the radioactivity from [(3)H-Me]methionine is incorporated into 5-methylcytosine. GA has no effect on the percentage distribution of label among the bases.It was concluded that GA enhances the rate of DNA degradation and DNA synthesis (turnover) in halfseeds, but primarily DNA degradation in isolated aleurone layers. Incorporation by isolated aleurone layers is due to DNA repair. Semiconservative replication apparently plays no physiological role in the hormone response, since both isolated aleurone layers and gamma-irradiated halfseeds respond normally. The hypothesis was advanced that endoreduplication and DNA degradation are means by which the seed stores and mobilizes deoxyribonucleotides for the embryo during germination.

Evidence for a photoinduced synthesis of poly(A) containing mRNA in Fusarium aquaeductuum

Based on inhibitor studies it has been concluded that in photoregulated processes of plant development, light induces differential gene expression. Using affinity chromatography of double labelled polysomal RNA on poly(U)-sepharose 4B, we were able to demonstrate different (3)H/(14)C ratios for the bound poly(A) containing fraction (mRNA) when compared with the unbound fraction: when [(3)H]uridine was present in the light induced sample and [(14)C]uridine in the dark control, in the bound material the (3)H/(14)C ratio was found to be higher than in the unbound fraction and vice versa. No such shift was observed, when both sample and control were kept in the dark. Our data are interpreted to provide evidence for photoinduced de novo synthesis of mRNA.

Differential effects of actinomycin d and cordycepin in lettuce seed germination and RNA synthesis

Intact lettuce seed germination was inhibited by cordycepin but not by actinomycin D; however, when seeds were clipped at the cotyledonary end, actinomycin D partially inhibited germination. Uptake studies with intact seeds using (3)H-actinomycin D showed that it was unable to reach the embryo prior to radical protrusion. (3)H-Cordycepin uptake studies using intact seeds showed that cordycepin was able to reach the embryo during the first 3 hours of incubation and at subsequent times. The pericarp and endosperm offered resistance to penetration of cordycepin into the embryo. In contrast to actinomycin D, cordycepin markedly inhibited (3)H-uridine incorporation into RNA of intact seeds during the first 10 and 12 hours of incubation. About 60% of (3)H-adenosine incorporation into poly A-RNA was inhibited by cordycepin during 12 hours of incubation, whereas actinomycin D had little effect. RNA synthesis appears to be essential for seed germination.

Preferential stimulation of the plant mRNA synthesis by gibberellic acid

1. Treatment of the etiolated maize seedlings with the plant hormone, gibberellic acid results in a significant enhancement of heavy polyribosome formation. 2. This is accompanied by highly increased incorporation of the labelled RNA precursors into RNA engaged in the polyribosomal complex, as well as by an increased rate of protein synthesis in vivo. 3. Determination of the specific radioactivity of particular RNA classes isolated from polyribosomes reveals that gibberellic acid stimulates mostly the synthesis of the rapidly labelled, non-ribosomal RNA fraction. 4. A considerable amount of this rapidly labelled RNA fraction, whose synthesis is preferentially stimulated by exogenous gibberellic acid contains poly(A) sequences, as shown by affinity chromatography on oligo (dT)-cellulose indicating that phytohormone causes an increased transcription of mRNA in etiolated maize seedlings. 5. When [3H]adenosine served as the RNA precursor it was found that the ratio between the heteropolymeric and polyadenylic parts of the poly(A)-RNA chain markedly changed under gibberellin treatment, suggesting that, in addition to an increased rate of mRNA synthesis, the plant hormone also affects the process of post-transcriptional polyadenylation of the newly made mRNA precursors. Possible extension of the polyadenylate segment in the presence of gibberellin may account for a longer functional half-life of the mRNA synthesized in plants treated with the phytohormone, and may explain significantly enhanced heavy polyribosome formation, as well as a higher efficiency of protein synthesis in plants treated with gibberellic acid.

Response of barley aleurone layers to abscisic Acid

Cordycepin, an inhibitor of RNA synthesis in barley (Hordeum vulgare L.) aleurone cells, does not inhibit the gibberellic acid-enhanced alpha-amylase (EC 3.2.1.1.) synthesis in barley aleurone layers if it is added 12 hours or more after the addition of the hormone. However, the accumulation of alpha-amylase activity after 12 hours of gibberellic acid can be decreased by abscisic acid. The accumulation of alpha-amylase activity is sustained or quickly restored when cordycepin is added simultaneously or some time after abscisic acid, indicating that the response of aleurone layers to abscisic acid depends on the continuous synthesis of a short lived RNA. By analysis of the newly synthesized proteins by gel electrophoresis with sodium dodecylsulfate, we observed that the synthesis of alpha-amylase is decreased in the presence of abscisic acid while the synthesis of most of the other proteins remains unchanged. From the rate of resumption of alpha-amylase production in the presence of cordycepin and abscisic acid, it appears that abscisic acid does not have a measurable effect on the stability of alpha-amylase mRNA.

Polyadenylated RNA from Vicia faba meristematic root cells. Localization and size estimation of the poly (A) segment

After incubating root apices from two-day-old bean seedlings with [3H] adenine the RNA was extracted from whole cells or polysomes, and the poly (A) sequences were isolated by nuclease digestion followed by poly(U)-Sepharose chromatography. The alterations of the RNA molecules due to the various treatments were monitored by sucrose density gradients. It was found that sequential extraction first at pH 7.6 then at pH 9.0 did not result in a separation between RNA poor in poly(A) sequences and poly(A)-rich RNA. Furthermore chromatography analysis of hydrolysates from nuclease-resistant RNA extracted either at pH 7.6 or pH 9.0 revealed that AMP constituted nearly 95% of the bases and that the poly(A) sequences, about 200 bases, were located at the 3' terminus of the polyadenylated RNA. No size difference was found for the poly(A) segment between the pH-7.6-extracted RNA and that extracted at pH 9.0.