Regeneration of Plants From Callus Cultures of Roots Induced by Agrobacterium rhizogenes on Tobacco

Abstract

Summary Plants were regenerated from aseptic callus cultures derived from roots induced by Agrobacterium rhizogenes on tobacco (hairy root tissues). Shoot induction was readily achieved from hairy root calli which had been maintained in tissue culture for about one year. All of the regenerated shoots were able to differentiate roots under the same culture conditions used for normal tobacco and, once transferred to soil, developed into mature flowering plants. The hairy root regenerants show the same overall morphological characteristics of normal plants and are susceptible to infection with both Agrobacterium rhizogenes and Agrobacterium tumefaciens. Their flowers, however, are all characteristically modified in that they show pistils much longer than the stamens (heterostyly). This morphological feature is accompanied by self-sterility. When self-pollination was forced the flowers degenerated into abortive fruits which, in some cases, contained a limited number of viable seeds. Cross-pollination with normal plants and pollen analysis revealed that these heterostylic flowers possess a variable level of pollen sterility ranging between 50 and virtually 100%. The characteristics of the hairy root regenerants are presented and discussed in comparison with those of normal and crown-gall derived plants, in view of their possible utilization in genetic manipulation of higher plants.