AGEING IN PLANT EMBRYOS III. ACCELERATION OF SENESCENCE FOLLOWING ARTIFICIAL AGEING TREATMENT.

An unusual pattern of senescence occurs in the root caps of embryos of Zea mays subjected to an artificial ageing treatment. After an initial reversal of membrane damage in the first stages of germination, precocious senescence was observed in the zone of differentiation of the root cap at the 48-hour stage of germination. These senescent changes occurred suddenly, with apparently normal cells being found immediately adjacent to cells in which the entire protoplast had degenerated. Acid phosphatase activity was confined to lysosome-like organelles in the still-organized cells, but was distributed throughout the ground cytoplasm of the adjacent senescent cells. The degenerative changes appeared to progress from the outermost cells proximally towards the chronologically younger cells. Thus the precipitous senescent changes were probably caused by the release of hydrolases normally confined within lysosomes, and the precocious senescence was due to an acceleration of a genetically-controlled process of ageing. [ABSTRACT FROM AUTHOR]