Nicotiana tabacum Callus Studies I. Assessment of Growth and Differentiation

Abstract

Summary Nicotiana pith expiants containing bundles of internal phloem attain the same plateau of growth in terms of mass and volume after 14 days as do expiants devoid of internal phloem after 21 days. The lag appears to be related to the time required for the dedifferentiation of the quiescent pith parenchyma. Tracheary element differentiation occurred in controls as well as in all treatments with only indoleacetic acid (IAA), 0.3 mgl−1 being significantly effective. Expiants treated only with kinetin (K) developed small numbers of tracheary elements at all concentrations. Sieve elements were not induced in response to media including K but without IAA or with a high level of IAA (3 mgl−1) in the absence of K. At low and intermediate levels of IAA phloic tissue differentiated at all levels of sucrose (2, 4 and 6%) with the exception of 0.03 mgl−1 IAA, 1 mgl−1 K and 2% sucrose. There was a lack of consistency in the extent of sieve element differentiation. However, when comparing individual combinations of IAA and K among various sucrose levels, more phloem was initiated at 4 than at 2 or 6%.