Effect of the auxin, 2‐(2‐methyl‐4‐chloro‐phenoxy)propionic acid, on cell cycle regulation in maize embryonic tissues

Abstract

During seed maturation, cells from embryonic tissues stop division at different phases of the cell cycle. In maize, neither these phases nor the effect of exogenous auxin on them are known. Disinfected whole maize ( Zea mays L. Mexican commercial hybrid H30) seeds or sectioned embryonic axes were incubated in Murashige and Skoog medium, with or without 2‐(2‐methyl‐4‐chlorophenoxy)propionic acid (MCPP), a synthetic auxin. For some in vitro experiments, radioactive [ 3 H]‐thymidine was also added. After the stated incubation period, meristems of mesocotyl, primary and seminal roots from embryonic axes were dissected, fixed, and analyzed under a microscope. The percentage of mitotic indices was recorded. In the labeling experiments, labeled and non‐labeled percentage of mitotic figures (MI %) were determined. It was found that cell division is a programmed event in the meristematic tissues of maize embryonic axes. Populations of cells entering cell division were obseved during the germination process. The mesocotyl was the first tissue to divide, followed by seminal and primary roots. Meristematic cells from dry embryos are arrested during the G 2 and G 1 phases of the cell cycle. MCPP has a differential effect, stimulating G 2 cells to enter cell division. It is concluded that MCPP might regulate the cell cycle at specific points.