Factors affecting the onset of deoxyribonucleic acid synthesis during wheat embryo germination. Study of the changes in DNA polymerases A, B and C and the pool of DNA precursors

Abstract

DNA synthesis starts about 12 h after water imbibition in wheat embryos. We have determined that noticeable amounts of labelled thymidine are found inside the embryo only after 6 hr of germination. DNA polymerase C from ungerminated wheat embryos decreased markedly in activity during the first hours of germination, whereas the activities of DNA polymerases A and B increased, having a maximum at about 15 h or germination. Serological evidence has suggested a clear antigenic relationship between DNA polymerases A and C. Although the pool of ATP increases rapidly after water imbibition, the increase in the pool of dNTP species was much slower.

Maize Thymidine Kinase Activity Is Present throughout Plant Development and Its Heterologous Expression Confers Tolerance to an Organellar DNA-Damaging Agent

“…Our results agree with those obtained on other monocots; in wheat embryos, DNA synthesis increases at 12 h after water imbibition [ 6 ] as well as in maize [ 12 , 24 ] with a concomitant rise in TK activity [ 7 ]. We found that during germination of maize the NSPT activity also can be detected but did not vary during the imbibition as TK1 activity, thus highlighting the role of TK1 in providing dTPP for DNA synthesis at these early stages.…”

“…Our results agree with those obtained on other monocots; in wheat embryos, DNA synthesis increases at 12 h after water imbibition [6] as well as in maize [12,24] with a concomitant rise in TK Figure 6. Expression of ZmTK1 in Arabidopsis TK1 double mutant allows the plants to develop in presence of CIP.…”

“…In plants, an ATP-dependent activity of thymidine phosphorylation was detected during germination of wheat [ 6 ] and maize [ 7 ] seeds. Also, a few TK genes have been described in plant species; in rice, TK mRNA levels are higher in mature as well as in meristematic tissues, thus the pyrimidine salvage pathway might function in other events requiring DNA synthesis, such as DNA repair.…”

Multiple deoxyribonucleic acid polymerases from quiescent wheat embryos. Purification and characterization of three enzymes from the soluble cytoplasm and one from purified mitochondria

“…Wheat enzyme B has a 3'and 5'-exonuclease activity, as well as a 'proof-reading' capacity. This kind of activity is not shown by enzymes A and C. The latter two enzymes seem to be antigenically related, as is shown in the following paper (Castroviejo et al, 1979). Another interesting similarity with the yeast enzyme is that the enzyme having exonuclease activity in yeast is not able to use synthetic RNA primers for DNA synthesis.…”