Characterization of a non-abscission mutant in Lupinus angustifolius. I. Genetic and structural aspects

A spontaneous mutant, Abs(-), that does not abscise any organs despite an a pparently normal pattern of growth and senescence was isolated from among p lants of Lupinus angustifolius cv. 'Danja'. Abs- was found to be a recessiv e single gene mutation, and it was proposed that the gene for the original mutant phenotype, referred to as Abs(-), be designated abs1. An artificiall y induced mutant allelic to abs1 was also obtained and a non-allelic mutant phenotype, Delabs (delayed abscission), which was designated abs2. Morphol ogical and cytological features of the abscission process under conditions of natural and ethylene-induced senescence were compared in the wild-type p arent and Abs- mutant. In the parent genotype abscission under natural cond itions is similar to many other species, consisting of a stage of cell divi sion forming an abscission zone, activation of the cytoplasm of zone cells, dissolution of the middle lamella, disorganization of fibrillar wall struc ture, and cell separation. A slightly different pattern of abscission zone development was observed for ethylene-treated explants of the parent, mainl y with respect to features of cell division and cell enlarge ment. In Abs- no abscission occurred for any abscission sites under conditions of natural senescence or with ethylene treatment of small shoot explants. However rel atively normal abscission zones were differentiated at all sites in the mut ant except that extensive cell walt disorganization did not occur. Ethylene production by leaves or other organs of the mutant was no different from t hat of Danja. Application of copper salts or hydrogen peroxide, droughting, waterlogging, or application of abscisic acid (ABA) increased ethylene pro duction equally in both genotypes but did not result in abscission in the m utant. Release of root cap border cells, the only other cell separation pro cess examined, was similar in each genotype. The study concludes that the m utation is quite specific to the abscission process and may be due to a lac k of or delay in the expression of hydrolytic enzyme(s) associated specific ally with abscission zone differentiation and separation.