Comparative Ultrastructural Features of Secreting and Nonsecreting Glandular Trichomes of Two Genotypes of Nicotiana tabacum L.

A genotypic difference in Nicotiana tabacum L. for the secreting capability of glandular trichomes was used to determine if the secretory function had an ultrastructural basis. Ultrastructural features of young expanding leaves of two genotypes that differ in the secreting capability of their glandular trichomes were determined. The secreting glandular trichomes of T.I. 1068 and the nonsecreting glandular trichomes of T.I. 1406 had multicellular stalks and six- to eight-celled heads. The secreting type had well-developed chloroplasts and other cytoplasmic organelles, but no secretory pathway was evident. Nonsecreting trichomes lacked chloroplasts but did have unusual inclusions in the cytoplasm. These inclusions, which were either membrane-bound or free in the cytoplasm, appeared to develop from the aggregation of membranous material. We hypothesize that the gene responsible for the lack of secreting capability interrupted normal chloroplast development and that chloroplasts in N. tabacum trichomes are necessary for the synthesis of certain exudate compounds.