Relationship of ribonucleic Acid metabolism in embryo and aleurone to alpha-amylase synthesis in barley

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

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

Adenylate metabolism of embryonic axes from deteriorated soybean seeds

RNA and protein syntheses in axes excised from dry soybean (Glycine max L.) seeds at different levels of deterioration were assayed. Low rates of protein synthesis in slightly deteriorated seeds were not due to losses in ribosomal or soluble fraction activities. However, the lowered rates of RNA and protein syntheses of deteriorated seeds were associated with reduced ATP content of the tissues. Adenine and adenosine conversions to ATP were reduced in deteriorated axes, and these reductions were reflected in reduced incorporation of these compounds into RNA.

A comparison of the activation of ribosomal RNA synthesis during germination of isolated and non-isolated embryos of Triticum aestivum L

Incorporation of [(14)C]uridine into ribosomal RNA and ribosomal RNA precursor fractions was studied in isolated wheat embryos and in embryos remaining within the intact grains during germination. In isolated embryos, radioactive 25S and 18S as well as 31S RNA species appeared already within the first 3 h of germination. In non-isolated embryos, radioactivity could be detected in the mature ribosomal and pre-ribosomal RNA fractions only after 6 h and 12 h germination, respectively. It is concluded that transcription of ribosomal sequences is activated almost immediately in isolated wheat embryos but remains repressed for several hours when the embryo germinates under natural physiological conditions.

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.

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.