The lower portion of the mutant na2/na2 (Fig. 1-6) stem has a "normal" stem appearance but the internode length is significantly shortened compared to that found in the wild type (Fig. 1-1, 1-2, 1-8). The cross-sectional views (Fig. 1-4, 1-5) reveal similar nodal and internodal vascular arrangements, as found in the wild type (Cheng et al., Microsc. Microanal. 7:444-445, 2001). However, at a more apical portion of the plant, one frequently observes a continuous "zig-zag" nodal structure; slanted nodes with wedge-shaped internodes characterize this phenotype. Figure 1-2 shows a longitudinal section cutting through the bi-lateral axis of the stem. Figure 1-1 shows a longitudinal section with a sagital cut plane, perpendicular to Fig. 1-2, 1-8. Sandwiched between the slanted nodes, one finds the initiation of axilary buds apparently supplied by the two joining nodal networks (Fig. 1-9 stereogram). The leaf-sheath insertion on the plant is also tilted (Fig. 1-3, indicated by white-line pairs). These results suggest that the lower internodes may have been initiated in the embryonic stage assuming the expression of the na2 is not in effect, while the expression of the allele occurs only in the post-germination growth. The tassel internodes in na2/na2 revert to normal, suggesting that this gene expression is "turned off" in the reproductive organs (Fig. 1-1 and 1-3). A diagrammatic representation of the nodal arrangement is shown in Fig. 1-10.
This article is part of a report by WYC for Siemens Westinghouse Science and Technology Competition (Semi Finalist) and Intel Science Talent Search (2001).
1. (1 and 2) Longitudinal section of na2/na2 in sagital (1)
and bilateral (2), (3) na2/na2 plant showing tilted leaf sheaths
attachment, (4) Cross-section of internode, (5) Cross-section of a nodal
region, (6) na2/na2 plant, (7 and 8) Digested sagital and bilateral
sections, (9) 3D-pair of tilted nodes and ear attachment (E), (10) Diagram
representing a na2/na2 stem.
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