Effects of the Introduction of Agrobacterium tumefaciens T-DNA ipt Gene in Nicotiana tabacum L. cv. Petit Havana SR1 Plant Cells

Transformation of tobacco leaf discs with the ‘cytokinin’ ipt</it> gene yielded several transgenic callus tissue lines, respective to the kind of ipt</it> construction present in the A. tumefaciens</it> cointegrates. Those calli containing an active ipt</it> gene were able to grow hormone-autotrophically and showed an increased endogenous cytokinin level in comparison with controls. Analysis of endogenous IAA level did not allow any quantitative correlation with the cytokinin content. However, a minimal level of auxin seems to be necessary to obtain hormone-autotrophic growth. Exogenously supplied NAA significantly reduced the endogenous cytokinin content without modifying growth characteristics. The varying chlorophyll content in the different callus lines elicited the study of the ultrastructure of the plastids. The controls contained small plastids, often filled with starch or accumulated vesicles that did not allow observation of the internal membrane system. The ‘Pssu-ipt</it>’ line, having a higher cytokinin content, showed plastids with an internal membrane system consisting of stroma and grana thylakoids, but this structure was lost during subculture. Swollen thylakoids appeared, the amount of starch was reduced and vesicles were accumulating.