RNA Metabolism and Membrane-Bound Polysomes in Relation to Globulin Biosynthesis in Cotyledons of Developing Field Beans (Vicia fabaL.)

Abstract

In cotyledon cells of developing field beans the RNA content per cell does not change in the second half of developmental period 2, whereas globulin biosynthesis continues. The constant RNA content per cell results from an equilibrium between RNA synthesis and degradation. All types of RNA are synthesized until the end of globulin biosynthesis, but poly(A)-containing RNA was preferentially labelled during maximum globulin formation.During stage 2 of seed development the poly(A)-containing RNA fraction represents a discrete peak in the 12 -18-S region on agarose gels and corresponds to the peak of poly(A)-containing RNA isolated from polysomes. %-Amanitin inhibits selectively the labelling of poly(A)-containing RNA and concomitantly globulin formation. Translation of total poly(A)-containing RNA, free and membrane-bound polysomes in a cell-free wheat germ system demonstrates that the globulins are preferentially produced on membrane-bound polysomes and that poly(A)-containing RNA includes the mRNA for both vicilin and legumin.

Expression of Storage Protein Genes in Developing Wheat (Triticum aestivum L.) Seeds

“…In a separate experiment, where total endosperm polysomes from Cheyenne wheat were extracted in the presence of heparin and isolated by ultracentrifugation (I 1), the radioactivity of the isolated polysomal RNA varied qualitatively with seed age in a way similar to that described above for total RNA (data not shown). These findings are similar to observations reported for RNA synthesis in seeds of legumes (22,23) and sorghum (14).…”

“…Developmental studies of cereal seeds have included investigations of in vitro protein synthesis capacity of maize endosperm polysomes (15, 24), protein (7) and nucleic acid synthesis (28) in wheat, and nucleic acid synthesis in sorghum (14), but the synthesis and stability of mRNA have not been extensively examined, and most relevant observations have been made on legume seeds (10,22,23). This report examines RNA and protein synthesis as functions of development in the wheat kernal via in vivo labeling of RNA and protein of developing wheat kernels, and in vitro translation of kernel RNA.…”

Sequestration of Pea Reserve Proteins by Rough Microsomes

“…: 2). This result provided further evidence that polypeptides pro- (27) demonstrated that in beans, Phaseolus vulgaris and Viciafaba, respectively, the cotyledon reserve proteins are also synthesized by membrane-bound polysomes. These studies on the synthetic capacity of membrane-bound polysomes confirm earlier speculations based on indirect evidence-the proliferation of the RER (8,9,12,26) and an increase in membrane-bound polysomes (9) with the onset of reserve protein synthesis-that membrane-bound polysomes were the cellular site of synthesis of reserve proteins.…”

“…Proteins accumulating in the protein body of legume seeds therefore must be synthesized elsewhere in the cell. Although there were originally inconclusive and conflicting results, recent investigations demonstrating preferential synthesis of reserve proteins in cell-free systems driven by polysomes released from membranes have provided evidence that the RER is the cellular site of synthesis of these proteins (7,18,27).…”

“…Proteins accumulating in the protein body of legume seeds therefore must be synthesized elsewhere in the cell. Although there were originally inconclusive and conflicting results, recent investigations demonstrating preferential synthesis of reserve proteins in cell-free systems driven by polysomes released from membranes have provided evidence that the RER is the cellular site of synthesis of these proteins (7,18,27).In this study, we have examined the synthetic capabilities of free polysomes, polysomes released from membranes, and rough microsomes to establish the role of the RER in the synthesis of pea reserve proteins. The results demonstrate that polysomes released from membranes and polysomes associated with rough microsomal vesicles direct the in vitro synthesis of polypeptides related to reserve proteins whereas free polysomes do not.…”