Improved sensitivity of genetic complementation of nitrate reductase deficient mutants via protoplast fusion.

An improved rapid assay for complementation testing of mutants of Nicotiana tabacum deficient in nitrate reductase is described. The test is based on measurement of in vivo nitrate reductase activity in 7 to 10 day old cultures derived from fusion-treated protoplast mixtures of the respective mutants as a criterion for complementation. It allows to detect complementing hybrids induced by the conventional droplet fusion technique in small numbers of protoplasts per assay (8×10(4)).