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Wind-stress induces the initiation of crown roots --Cheng, WY, Cheng, PC, Walden, DB We have discovered that wind load on plants induces the initiation of crown roots. A total of 32 plants (Ohio 43 inbred, two plants per 12 inch pot) were used in this study. Eighteen plants were grown under strictly no air movement conditions, while the other 18 were grown under a constant wind of 9 km/hr (day and night). Two box-fans were used to generate air movement in a growth chamber; pots were rotated every day to simulate changes in wind direction. Plants were grown under 16/8 hours day/night scheme with a high-low temperature of 27/20C, and RH was set at approx 50%. Lighting was provided by a combination of fluorescent lights, high pressure Na and metal halide arc lamps, resulting in an intensity of 1500 foot-candle at the pot level. The results show that the Ohio 43 inbred grew two rows (Figure 1a, 1 and 2) of crown roots from the soil level under no wind conditions, while the wind-blown plants initiated an additional row (Figure 1b, 3) of crown roots at a higher node. Our results suggest that the initiation of crown roots is influenced by the bending stress of the stem resulting from wind load. As indicated by our earlier stem model (Cheng, WY et al., MGCNL 76:27-28, 2002), the maize stem can be described as a "foam stick," a reinforced outer shell, with a spongy interior. The peripheral region can be considered as the steel reinforcing bars and cylinder, and the interconnecting nodal networks (Cheng, WY et al., MGCNL 76:28-29, 2002) are the steel bracings ("rebar") found in a concrete pillar. In the early stage of development, the vasculatures act as the tensile element, while the highly turgid parenchyma cells are the compression element in the model. In the later stage when the parenchyma cells become air-filled, developing a "foamy" texture, the highly lignified para-epidermal bundles become the structural element. The binding between individual para-epidermal vascular bundles by lignified sclerenchyma cells is an important structural development. This binding transforms those loosely parallel arranged vascular bundles into a solid cylindrical structure. Bending of the stem exerts tensile stress in the nodal elements ("rebar"), which may be responsible for orientating the cell division for the initiation of crown roots.

This work was supported by undergraduate scholarships from the Microscopy Society of America and SPIE to WYC.

Figure 1.

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