Auxin autonomy

Auxin Autonomy and Auxin Sensitivity Can Be Separate Phenomena... 

The Physiological Basis for Auxin Autonomy in Tobacco Teratomas... 

Both N. tabacum and N, glutinosa can compensate for mutant tms genes of Agrobacterium tumefaciens and grow rapidly as friable and unorganized tissues on hormone-free growth medium. In neither species does compensation result from increased lAA accumulation, and low levels of ACC in A66-transformed cells provide further evidence that auxin activity remains low. Hence, auxin autonomy of cultured crown-gall cells is not necessarily related to the auxin content of the tissue. 

Analysis of several clones of A66-transformed A. tabacum showed that cells exhibiting a high degree of auxin autonomy could be either auxin sensitive or auxin resistant. Thus, auxin autonomy and auxin sensitivity can be separate phenomena and are likely controlled by different mechanisms. Gibberellin A3 can substitute for auxin and support the growth of auxin-dependent teratoma cells, and therefore GAs may be the shoot-derived growth factors accounting for hormone independence of complex teratomas in culture. 

Nicotiana tabacum shows an attenuated response to tms mutant strains. This weakened reaction is characterized by a slower rate of tumor development and by the formation of shoots (teratomas). Cloned teratoma lines are hormone independent in culture [11], but hormone autonomy of the teratoma is dependent on shoot formation [7,30]. It appears, therefore, that compensation for tms mutations in A. tabacum teratomas occurs via growth factors, possibly auxin, produced in developing shoots. 

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