Madison, Wisconsin
University of Wisconsin
BUFFALO, NEW YORK
State University of New York
LONDON, ONTARIO, CANADA
University of Western Ontario
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.
Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.
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