Effects of Indoleacetic Acid on Growth Without Mitosis & on Mitotic Activity in Absence of Growth by Expansion.

The effects of indoleacetic acid (IAA) on plant growth and development have been intensively studied for more than three decades. Some effects are reflected in changes in cell size, while others (e.g., adventitious roots, calluses, & tumors) involve an overall expansion with cell proliferation (1, 5. 20, 21, 35). Complementary systems have recently been found for studying in intact organisms A: mitotic activity in the absence of over-all growth by expansion (viz., dormant lettuce seeds, 13-15), and B: growth and differentiation without significant deoxyribonucleic acid (DNA) synthesis, mitosis, and cell division (viz., wheat grown from gamma-irradiated grain, 9, 11). In this paper we report the effects of IAA on these two systems, with particular reference to interactions of IAA with kinetin on cell division (29), and we suggest how such effects might underlie various actions of auxin as a regulator of normal growth. as a herbicide, and as a causative agent in the production of plant tumors.