Habituation of plant cells does not mean insensitivity to plant growth regulators

Fully habituated organogenic and nonorganogenic sugarbeet calluses reacted to application of the synthetic auxin [3-benzo(b) selenienyl] acetic acid by changes in growth and ethylene production. Treatment of fully habituated cells of periwinkle with 2,4-dichlorophenoxyacetic acid led to the decrease of free cytokinin contents (isopentenyl adenine, zeatin riboside, and zeatin) during the late exponential phase of growth. The polyamine contents were also modified and the capacity to biotransform secologanin into ajmalicine was decreased. Treatment of the habituated periwinkle cells with zeatin greatly increased the amount of a polypeptide of 16 kDa; this response was more marked than that displayed by the auxin-dependent line. These data show that hormone-independent calluses and cell suspensions can retain some sensitivity to growth hormones. However, differences of responses were observed between the auxin-dependent lines and the habituated lines.