Spontaneous forward mutation versus reversion frequencies for maize Adh1 in pollen.

Reliable quantitative data on spontaneous, specific gene mutation frequencies in higher plants and animals are few. Detergents include low natural frequencies and difficulty in obtaining in excess of 10(6) scorable organisms or gametophytes. The alcohol dehydrogenase-1 gene (Adh1 gene; ADH enzyme EC 1.1.1.1.), as expressed in pollen grains, is among the exceptionably suitable; much is known about the maize ADHs, Adh1 function is totally dispensible in an aerobic environment and maize pollen is a trinucleate gametophyte which expresses much of its haploid genome, including Adh1. In particular, there have been two recent methodological advances. First, I am able to cytochemically stain pollen, before or after in vitro germination, for the presence of above 5% normal ADH activity. And second, ADH1- pollen grains survive allyl alcohol (C=C-C-OH) vapour concentrations which kill ADH1+ grains; this selection scheme was developed for yeast by Megnet. My genetic resolution is approximately one mutant (Adh1+-->ADH-) per 10(7) chemically selected, viable gametophytes, and one (phenotypic) revertant (Adh1--->ADH+) per 10(8) unselected gatetophytes. In this note, I compare spontaneous forward mutant frequency with previously published revertant frequencies for one naturally occurring and six ethyl methanesulphonate-induced Adhl-deficient (Adh1-) alleles.