Onset of nucleic acid synthesis during germination of Pisum sativum L

The nucleosomal repeat length of pea (Pisum sativum) chromatin changes during germination

Pea (Pisum sativum) nuclei have been isolated from ungerminated embryos, developing embryonic axes and seedlings. Morphological and biochemical criteria revealed that preparations were free from contaminants and that nuclei were intact. These circumstances permitted an accurate determination of nucleosomal repeat lengths, the values obtained being 175±4 base pairs for ungerminated embryos, 185±5 base pairs for 62-hours germinated embryonic axes and 185±3 base pairs for 6-day old seedlings. The results seem to indicate that the increase in repeat length is associated with the onset of transcription and/or replication of DNA.

Endomitosis and the effect of gibberellic acid in different Pisum sativum L. cultivars

The evolution of the total amount of DNA in epicotyls and of the amount of DNA per cell nucleus in epicotyl cortex cells during germination was followed in two closely related pea varieties, Pisum sativum cv. Finale and Pisum sativum cv. Rondo. Under etiolating conditions, growth of the cv. Rondo occurs only by cell elongation which is preceded by endomitotic DNA synthesis, while in the cv. Finale growth is the result of cell elongation accompanied by endomitotic DNA synthesis and cell division. The maximum C-level attained in both cultivars under etiolating conditions is 8 C (C=haploid amount of DNA in a gamete cell). Both the maximum C-level reached and the percentage of cells reaching this C-level seem to be under strict genetic control. In both cultivars, light inhibits the endomitotic DNA replication.Neither gibberellic acid (GA3), nor AMO 1618 alter the maximum C-level or the percentage distribution of the C-classes. Both growth regulators are effective, although in an opposite way, only in tissues where cell division occurs or where endomitotic DNA synthesis is blocked, as in light-grown pea epicotyls.

Correlation between deoxyribonuclease activity and DNA replication in the embryonic axes of germinating peas (Pisum sativum L.)

Crude chromatin preparations from pea seedlings contain calcium-dependent deoxyribonuclease activity, at least part of which is endonucleolytic. During germination, there is a dramatic increase in chromatin-bound deoxyribonuclease activity in the embryonic axis immediately prior to the onset of DNA replication. Evidence has been obtained for the presence of an inhibitor of deoxyribonuclease activity in chromatin preparations from embryonic axes not undergoing DNA replication.

Development of nuclease activity in cotyledons of Pisum sativum L

The RNA content of pea cotyledons shows little change during the first five days of germination at 22°C. From day five onwards there is a rapid net degradation of RNA, which continues until day thirteen. The DNA content of the cotyledons increases slightly during the first nine days of germination, after which there is a net decrease. Acid and alkaline ribonuclease activities increase markedly between day one and day five, and then decline between day five and day nine. There is a second increase in the activities of both enzymes from day nine onwards. Soluble deoxyribonuclease activity exhibits a single peak, seven days after the onset of germination. The first increase in acid ribonuclease activity is only partially inhibited by cycloheximide at concentrations which severely inhibit protein synthesis.

Ribonucleic acid synthesis and loss of viability in pea seed

RNA synthesis and protein synthesis in embryonic axis tissue of viable pea (Pisum arvense L. var. N.Z. maple) seed commences during the first hour of germination. Protein synthesis in axis tissue of non-viable pea seed is barely detectable during the first 24 h after the start of imbibition. Nonviable axis tissue incorporates significant levels of [(3)H]uridine into RNA during this period but the level of incorporation does not increase significantly over the first 24 h of imbibition. In axis tissue of non-viable seed during the first hour of imbibition most of the [(3)H]uridine was incorporated into low molecular weight material migrating in advance of the 4S and 5S RNA species in polyacrylamide gels but some radioactivity was incorporated into a discrete species of RNA having a molecular weight of 2.7×10(6). After 24 h, non-viable axis tissue incorporates [(3)H]uridine into ribosomal RNA, the low molecular weight material migrating in advance of the 4S and 5S RNA peak in polyacrylamide gels and a heterogeneous RNA species of molecular weight ranging from 2.2×10(6) to 2.7×10(6). No 4S or 5S RNA synthesis is detectable after 24 h of imbibition in non-viable axis tissue. Axis tissue of viable pea seed synthesises rRNA, 4S and 5S RNA, the low molecular weight material migrating in advance of the 4S and 5S RNA peak in polyacrylamide gels and the rRNA precursor species at both periods of germination studied. Loss of viability in pea seed appears to be accompanied by the appearance of lesions in the processing of rRNA precursor species and a significant loss of RNA synthesising activity.