WENZEL, CAROL L. AND THOMAS L. ROST.* Section of Plant Biology, University of California Davis, One Shields Ave, Davis, CA, 95616-8537. - Spiral growth in Arabidopsis thaliana roots.
Arabidopsis thaliana roots have closed apical organization
where cell files originate from a specific tier of initial cells. The
root cap/ protoderm (RCP) initials are arranged in a collar around the
columella initials. Periclinal division of the RCP initials gives rise
to the peripheral root cap cells and the first protoderm cell forming
a T-junction. Transverse sections at the level of the initial tier
reveal a spiral pattern of peripheral root cap cells in 2 week old
Arabidopsis thaliana roots grown in sand. The spiral pattern
was suggested to be derived from sequential divisions of the RCP
initials in a particular direction around the collar of initials (1).
Externally, spiral patterns of root growth are also seen in the
epidermal cell file rotations and in the cork-screwing pattern of
roots as they drill downwards. Here we correlate the internal and
external spiral patterns of Arabidopsis thaliana grown in agar
and in different soil conditions. We test the hypothesis that the cell
division pattern causes differential cell expansion around the axis of
a root creating a torque which would lead to cell file rotations and
the cork-screwing growth pattern of roots. (1) Baum SF and Rost TL.
1996. Root apical organization in Arabidopsis thaliana. 1. Root
cap and protoderm. Protoplasma 192: 178-188.
Key words: Arabidopsis thaliana, root, spiral