|Johri, M - TATA INST FUND RES INDIA|
|Coe Jr, Edward|
Submitted to: Genetica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 5, 1994
Publication Date: N/A
Interpretive Summary: We carried out these experiments to determine how the cells of the embryo of corn progress to form the fully developed corn plant. At the time the seed is planted it contains some groups of cells already destined to form the lower parts of the plant, some committed to the areas where reproductive parts (the ears and the tassel) will be formed, and some with less restricted commitments. The experiments detailed in this paper show that an upward-advancing progression defines all of the parts of the plant, all within two weeks of sowing. Combined with previous studies by this laboratory, this information rounds out a definitive picture of development in this crop. This knowledge impacts understanding of the effects of applying targeted cultural conditions (i.e., When might leaf number be increased or decreased by conditions? Which leaves might be affected? Can ear level be modified?). Prospects for genetic modification of these subdivisions and commitments through selective breeding are opened by this knowledge, and targeting is made possible for developmental stages or cells toward which physiological or genetic manipulations may be directed.
Technical Abstract: The formation of the lower nodes and internodes in maize and the progression of their differentiation was investigated by generating clonal sectors from cells of the apical meristem. Marked clones were induced by irradiating dry seeds and 2-, 8-, and 13-day-old seedlings heterozygous for visible genetic markers. The linear extent and the apparent number of cells generating internodes 2-6, which normally remain condensed, were traced by promoting elongation with gibberellic acid. At the mature seed stage, internodes 2 and 3 are undergoing longitudinal expansion and each is represented by two or three layers of cells. Internodes 4 and 5 are in the process of radial expansion and are represented by a single layer of cells. At nodes 2-4, the cells for leaves and internodes have separated, but such a separation has not occurred for nodes 5 and 6. The formation and expansion of the basal 6 internodes progresses from the base toward distal nodes. Analysis of sectors induced at the seedling stages, 2, 8, and 13 days, shows that the formation of middle and top internodes also progresses similarly. Each advancing separation of groups of leaf units, then leaf from internode, then distal and proximal parts of internodes, is a characteristic progression at all levels of the development of the plant.