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QUANTITATIVE ULTRASTRUCTURAL CHANGES IN TUNICA AND CORPUS CELLS OF THE SHOOT APEX OF NICOTIANA TABACUM DURING THE TRANSITION TO FLOWERING
Author(s) -
Kanchanapoom Malee L.,
Thomas Judith F.
Publication year - 1987
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1987.tb08602.x
Subject(s) - tunica , vacuole , biology , meristem , tunica media , ultrastructure , nicotiana tabacum , botany , microbiology and biotechnology , cytoplasm , shoot , biochemistry , endocrinology , smooth muscle , gene
Very distinct ultrastructural differences in organelle composition in the cells of tunica and corpus layers in the central part of shoot apices of the quantitative short‐day plant, Nicotiana tabacum L. cv. NCTG‐22, were observed during the 17‐day transition period from vegetative to reproductive growth. Under short‐day conditions, changes in the tunica layer included the eventual reduction in cross sectional areas of cells, nuclei, vacuoles, and proplastids, while mitochondrial cross sectional area increased throughout the course of the induction period. From the measurable changes of several of the organelles, tunica cells appeared to respond to induction sooner than corpus cells. After one exposure the relative volume of tunica cell nuclei in short‐day plants was larger than in long‐day controls, but thereafter became smaller than controls. Enlargement of nuclei profiles in corpus cells in response to induction did not occur until after seven exposures, subsequently decreasing below control values. In addition, after one inductive exposure, vacuolar density was reduced in the tunica cells of induced meristems, yet at the same time in corpus cells vacuole density increased slightly and decreased only much later. An early increase in proplastid density in tunica cells of induced meristems was a further indication that these cells responded sooner than corpus cells to the photoperiodic stimulus. The changes in organellar composition of tunica and corpus cells, including nuclei, vacuoles, and proplastids, suggests that each layer was independent in readjustment of rate of growth towards the new pattern of development. That tunica cells seemed to respond sooner than corpus cells to the inductive signal may indicate that, at least in this species, the epidermis (i.e., tunica) plays a dominant role in controlling the initial morphogenetic change.