The regulation of plant cell growth and metabolism by 2,4-dichlorophenoxyacetic acid.

The growth-promoting effects of 2, 4-dichlorophenoxyacetic acid (2,4-D) were studied using cell suspension cultures of sycamore (Acer pseudoplatanus L) Omission of 2, 4-D from the standard culture medium caused a cessation of .growth after an initial period which was dependent on the rate of 2,4-D inactivation, the level of kinetin in the culture medium and the presence or absence of light. Substantial changes in the metabolism of amino acids, particularly serine and glutamic acid, which accompanied the cessation of cell division were studied as possible markers of the final metabolic state, achieved in the absence of 2,4-D, which was not conducive to growth, Clonal 2, 4-D-independent cell lines which varied in their requirements for kinetin were isolated from the 2,4-D-dependent cultures. The responses of these cell lines to anti-metabolites indicated that resistance to 5-bromodeoxy- uridine, 5-methyltryptophan or methotrexate are phenomena which are not prerequisites for auxin- or cytokinin-independence in cultured sycamore cells. A temporary 2,4-D starvation did not induce appreciable synchrony in 2,4-D-dependent cultures which suggests that 2,4-D does not promote cell division by activating a specific cell cycle control point to commit cells to division. 2,4-D appears to act more indirectly by priming cells so that they are prepared for, and capable of division.