Tissue and Cell Culture of 'Passe Crassane' Pears: Amylase Pattern of Cultured Tissues Compared with Whole Fruit

Calluses and cell suspension cultures were initiated from young and fully developed fruits and from stem and petiole tissues of ‘Passe Crassane’ pears. On a dry weight basis, proliferation is significantly higher in tissues from full-grown fruits and petioles. Cullus tissues grown in vitro have a protein content up to 25 times higher than the initial quiescent organ. Three amylase fractions (2 β amylases E, and E₂: 1 α amylase E₃) were isolated by gel filtration on Sephadcx G-100 and isoenzymes revealed in these fractions after polyacrylamide gel electrophoresis. Comparison of amylase activity in actively growing cells and in auxin-starved cell suspensions shows that β-amylase activity is mainly a function of cell growth, while α-amylase activity is more related to the age of the cells. The presence of two isoenzymes in the β-amylase E₂ fraction was found to be highly characteristic of young fruits. The same polymorphism was found in all the strain of tissues thus indicating that tissues grown in vitro retain or revert to a juvenile biochemistry. The growth hormone. 2,4-dichlorophenoxyacetic acid, used to support cell division, is demonstrated to be responsible for the reversion of the β-amylase polymorphism from a mature to a juvenile phenotype in mature fruit explants incubated in vitro. The interest of fruit tissue and cell culture for the study of fruit physiology is questioned and discussed.