SELECTION OF HYDROXYPROLINE-RESISTANT PROLINE-ACCUMULATING MUTANTS OFCAULIFLOWER (BRASSICA-OLERACEA VAR BOTRYTIS)

A procedure is described by which hydroxyproline-resistant lines could be selected from regenerating curd tissue of cauliflower. Mutagenesis was by N-nitroso-N-ethylurea, supplied as a drop of 0.3 mM solution o n each 3 mm diameter curd piece. The mutagen generated numerous morpho logical and pigment mutations without significantly affecting shoot re generation from explants. Thirty one resistant shoots were recovered f rom more than six thousand explants mutagenised on regeneration medium supplemented with 3 mM hydroxyproline, while none was obtained from a similar number of non-mutagenised controls. Out of twenty-three resis tant shoots which survived subculture, only one showed consistently el evated levels of endogenous proline. During early shoot culture passag es, proline levels were 3.6-4.7 times higher than controls, but this w as reduced to 1.6 times after 10-12 culture passages in the absence of hydroxyproline. Possible reasons for this decline are discussed. Leaf strip assays suggest resistant shoots may be chimeras and current eff orts are directed towards regenerating solid mutants from resistant se ctors. These will then be evaluated for any alteration in frost tolera nce.