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 on each 3 mm
diameter curd piece. The mutagen generated numerous morphological and pigment mutations without significantly
affecting shoot regeneration from explants . Thirty one resistant shoots were recovered from 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 resistant shoots which survived subculture,
only one showed consistently elevated levels of endogenous proline . During early shoot culture passages, proline
levels were 3 .6-4.7 times higher than controls, but this was 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 efforts are directed towards regenerating solid mutants from resistant sectors .
These will then be evaluated for any alteration in frost tolerance
