East Amherst, New York
Williamsville East High School
Buffalo, New York
State University of New York
London, Ontario, Canada
University of Western Ontario
The vascular development in the na2/na2 mutant --Cheng, WY, Cheng, PC, Walden, DB The phenotype of nana2 (na2/na2, Fig 1-6) is characterized by its stubby dwarf appearance. As reported earlier, the longitudinal sections of stem of na2/na2 generally appear similar to the wild-type but with significantly shorter internodes (Cheng et al., Microsc. Microanal. Vol. 6, Supp 2:692-693, 2000). However, in the 2001 summer nursery (an excellent growing season) in London, Ontario, we observed an interesting characteristic (described below) of the mutant in more than 60 homozygous na2/na2 plants. This phenotypic expression was also observed in two plants previously in our 1999 and 1998 summer crop (relatively poor growing sessions).

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).

Figure 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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