Distribution of vascular bundles in Ohio43/KYS stem --Cheng, WY, Cheng, PC, Walden, DB Throughout the maize plant, most of the longitudinal vascular bundles travel through a number of nodes where side branching occurs (Fig. 1). In other than the nodal region, it seems that no interconnections occur. The longitudinal vascular bundles form branches just before entering the nodal region (Fig. 1); these vascular branches in turn form an interconnecting network. We observed that most of the branches are derived from the cortex of the stem while the vasculatures in pith tend to pass through with few connections. Where the leaf initiates, the vascular bundles form an intense array (Fig 1), which shows as dark radiating structures (A) in the MRI image (Cheng et al., MGCNL 75:8, 2000)

Figure 2 shows the internode cross sectional area and the distribution of bundles in cortex (the para-epidermal zone 1 is 19% of the total cross sectional area) and pith (89%) in four Ohio43/KYS plants at the stage of silking. The numbering system adapted places the top ear above the internode #12 (Fig. 2a). The tassel begins above internodes #2-3 and the top crown roots initiate at the node above internodes #19-20. The results indicate a maximum bundle number at the ground level (#19) and demonstrate a general exponential reduction in the number of vascular bundles and cross-section area toward the apex of the plant. However, a shoulder in the curve was observed around the ear-bearing node (internodes 12-16) as the large number of vascular bundles supplying the ear (Fig. 2b-e).

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. Vascular bundles below and through a node. Note the branching before the vasculatures enter the node (black arrow). V: vascular bundles, White Arrow: Direction of Apex.

Figure 2. (a) Diagrammatic representation of the using internode numbering system used in this article, (b) number of vasculatures in zone 1, (c) number of vasculatures in pith (core), (d) number of total vasculatures, (e) cross sectional area.

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