Gibberellic acid causes increased synthesis of RNA which contains poly(A) in barley aleurone tissue

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.

Carcinogenic effect of gibberellin A3 in Swiss albino mice

Gibberellin A3 is a plant growth regulator used in many countries, including Egypt, to increase the growth of fruits and vegetables. The carcinogenic effect of gibberellin A3 was investigated in this study with Swiss albino mice. Administration of gibberellin A3 by gavage for 22 months induced a significant increase in their body weights. Tumors were induced in 18% of the males and 36% of the females and were located in the skin of the axillary region (sebaceous adenomas), breast (adenocarcinomas), and lung (adenocarcinomas and secondary metastatic deposits from breast tumors). Bronchocentric granulomas were induced in animals exposed to gibberellin A3 for 14 months. These results indicate that gibberellin A3 was carcinogenic in mice.

Polyamine metabolism and its relation to response of the aleurone layers of barley seeds to gibberellic Acid

Polyamine metabolism and its relation to the induction of alpha-amylase formation in the aleurone layers of barley seeds (Hordeum vulgare cv Himalaya) in response to gibberellic acid (GA(3)) has been investigated. A high-performance liquid chromatographic system has been employed for qualitative and quantitative analyses of putrescine (Put), cadaverine (Cad), spermidine (Spd), spermine (Spm), and agmatine (Agm).Active polyamine metabolism occurs in the aleurone cells of deembryonate barley half seeds during imbibition. The aleurone layers isolated from fully imbibed half seeds contain about 880 nanomoles of Put, 920 nanomoles of Spd, and 610 nanomoles of Spm as free form per gram tissue dry weight while the levels of Cad and Agm are relatively low. The polyamine levels do not change significantly in the aleurone layers in response to added GA(3) (1.5 micromolar) during the 8-hour lag period of the growth substance-induced formation of alpha-amylase. Also, the polyamine levels are not altered by the presence of abscisic acid (3 micromolar) which inhibits the enzyme induction by GA(3). Kinetic studies show that both applied [U-(14)C]ornithine and [U-(14)C]arginine are primarily incorporated into Put during 2 hours of incubation, but the incorporation is not significantly affected by added GA(3). Additionally, added GA(3) does not affect the uptake and turnover of [1,4-(14)C]Put, nor does it affect the conversion of Put --> Spd or Spd --> Spm. Treatment of the aleurone layers with GA(3) for 2 hours results in no significant changes in the total activities or the specific activities of ornithine decarboxylase and arginine decarboxylase.Experiments with polyamine synthesis inhibitors demonstrate that the level of Spd in the aleurone layers could be substantially reduced by the presence of methylglyoxal-bis(guanylhydrazone) (MGBG) during imbibition. MGBG treatment does not affect in vivo incorporation of [8-(14)C] adenosine into ATP. The lower the level of Spd the less alpha-amylase formation is induced by added GA(3). The reduction of GA(3)-induced alpha-amylase formation by MGBG treatment can be either completely or partially overcome by added Spd, depending upon the concentration of MGBG used in the imbibition medium. The results indicate that the early action of GA(3), with respect to induction of alpha-amylase formation in barley aleurone layers, appears to be not on polyamine metabolism. However, polyamines, particularly Spd, may be involved in regulation of the growth substance-dependent enzyme induction.

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.

Gibberellic-acid-regulated expression of α-amylase and six other genes in wheat aleurone layers

The effect of gibberellic acid (GA3) on gene expression in wheat aleurone cells has been characterised. In-vitro translation of polyadenylated RNA indicated that α-amylase and other messenger-RNA (mRNA) species increase in relative concentration in GA3-treated tissue. At least one mRNA species declines in relative level in response to GA3. There is also a GA3-dependent, four-fold increase in the level of polyadenylated RNA. This effect is largely the result of increased levels of many mRNA species which are also present in untreated tissue. Seven GA3-induced polyadenylated RNA species including the Amyl α-amylase gene product have been cloned as complementary DNA in the plasmid pBR322. These cloned DNAs have been used as hybridisation probes to show that the GA3-induced increase in α-amylase mRNA is more prolonged than the accumulation of the other GA3-regulated mRNA species. A polyadenylated-RNA sequence showing reduced concentration in GA3-treated tissue has also been cloned.

In Vitro Synthesis and Processing of Wheat alpha-Amylase : TRANSLATION OF GIBBERELLIC ACID-INDUCED WHEAT ALEURONE LAYER RNA BY WHEAT GERM AND XENOPUS LAEVIS OOCYTE SYSTEMS

Wheat (Triticum aestivum) RNA was used to program synthesis of the alpha-amylase protein by Xenopus laevis oocytes. A 41,500-dalton protein was made which was identified as alpha-amylase by immunoprecipitation with rabbit anti-alpha-amylase antiserum raised against the purified wheat protein and by its co-migration with authentic alpha-amylase on sodium dodecyl sulfate polyacrylamide gels. Synthesis of alpha-amylase was dependent upon injection of RNA extracted from gibberellic acid-induced aleurone layers from wheat. The amount of alpha-amylase produced was proportional to the amount of RNA injected and reached a plateau within 4 hours after injection. When the same RNA was translated in a wheat germ cell-free translation system, a 43,000-dalton protein was produced. Addition of dog pancreas microsomal membranes to the wheat germ translation system resulted in processing of the alpha-amylase protein to a form which co-migrated with authentic alpha-amylase purified from malted wheat and with the protein synthesized in oocytes.

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.

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.

The measurement of plant polyadenylic acid by hybridisation with radioactive polyuridylic acid

Saturation hybridisation of polyadenylic acid with [(3)H]polyuridylic acid is described. Under conditions of [(3)H]poly(U) excess, poly(A) is detected in the RNA of a number of higher plants. The ribonuclease resistant hybrids melt sharply when subjected to thermal denaturation. Plant RNA which contains poly(A) sequences detected by [(3)H]poly(U) hybridisation is polydisperse in molecular weight. Data presented shows that the amount of poly(A) in plant RNA is variable. This technique is useful for the qualitative and quantitative detection of poly(A) sequences in higher plant RNA.

A rapid technique for the estimation of polynucleotide adenylyltransferase and ribonucleic Acid polymerase in plant tissues

Nucleic acid-dependent polynucleotide adenylytransferase (EC 2.7.7.19) and ribonucleic acid polymerase (EC 2.7.7.6) have been partially purified from maize tissues (Zea mays L.) utilizing ammonium sulfate precipitation and batch diethylaminoethylcellulose chromatography. The technique is applicable to the simultaneous processing of up to eight samples of plant tissue and affords a rapid and reproducible means of assaying these two enzymes from small quantities of kernels or seedlings. The kinetic characteristics of the partially purified enzymes resemble those from more extensively purified preparations.

The occurrence and distribution of poly(a) ribonucleic Acid in soybean

The occurrence and distribution of poly(A) sequences in the RNA of soybean (Glycine max var. Wayne) have been studied. Only one of the two species of AMP-rich RNA contains poly(A). D-RNA does not contain detectable poly(A) sequences. The TB-RNA is the poly(A) RNA in this system. At least a part (up to 50% or more) of the mRNA in polyribosomes contains a poly(A) sequence. The poly(A) RNA is heterodisperse in size but has a mean size of approximately 18S (2,000 nucleotides) in urea and formamide gels. The poly(A) fragment resulting from ribonuclease A and T(1) digestion migrates as a broad band overlapping the 4 to 5.8S regions of the gels with a mean size of somewhat greater than 5S. No evidence was found for the occurrence of a discrete oligo(A) fragment in the poly(A) RNA; however, oligonucleotides which migrate faster than the poly(A) fraction were observed in preparations which were not bound to oligo(dT) cellulose prior to electrophoresis. This oligonucleotide region was enriched in AMP (up to about 65%) as would be expected after ribonuclease A and T(1) digestion.

Poly(A)-containing RNA from Petroselinum hortense: isolation, properties and messenger function in vitro

Cell suspension cultures from parsley (Petroselinum hortense Hoffm.) were labelled in vivo with [2-3H] adenosine. The RNA isolated from the ribosomal pellet was fractionated on an oligo(dT)-cellulose column. Approximately 1.5% of the RNA, representing about 15% of the total radioactivity, was retained at high salt concentrations and eluted at low ionic strength. As determined by two independent methods, this fraction contained poly(A) segments with an average length of about 80 nucleotides. It was active as template in a cell-free system from wheat germ, directing the synthesis of peptides ranging in molecular weight from about 4000-40000 daltons.

Isolation and translation of plant messenger RNA

A fraction of the RNA species isolated from Lemna gibba G-3 consists of molecules with attached sequences of polyadenylic acid. This polyadenylic acid-containing fraction, separated from total RNA by adsorption onto oligothymidylic acid-cellulose, was shown to be mRNA by its ability to serve as template in a cell-free translation system derived from wheat germ. The products of translation were characterized by electrophoresis. This method permitted the comparison of mRNA from plants grown under different light conditions. Such plants were shown to possess qualitative and quantitative differences in their mRNA complements.

Hormonal control of messenger ribonucleic acid metabolism in barley aleurone layers

Ribonucleic acid containing poly(adenylic acid) [poly(A)-RNA] is present in barley aleurone layers. This poly(A)-RNA becomes labeled with radioactive precursors of RNA during the incubation of isolated aleurone layers with or without gibberellic acid. However, the rate of synthesis of poly(A)-RNA is enhanced by gibberellic acid. This enhancement begins within 3-4 hr of addition of the hormone and reaches a maximum, which is about 50-60% over the control, 10-12 hr after addition of the hormone. Cordycepin inhibits total RNA as well as poly(A)-RNA synthesis in barley aleurone layers. However, cordycepin inhibits the hormone-controlled synthesis of alpha-amylase (EC 3.2.1.1) only if it is added 12 hr or less after gibberellic acid. The insensitivity of alpha-amylase production to cordycepin after 12 hr of gibberellic acid treatment suggests that alpha-amylase is translated from stable messenger RNA.