Plant Physiol, February 2001, Vol. 125, pp. 900-911
Asymmetric Subcellular mRNA Distribution Correlates with
Carbonic Anhydrase Activity in Acetabularia
acetabulum1
Kyle A.
Serikawa,2*
D. Marshall
Porterfield, and
Dina F.
Mandoli
Department of Botany (K.A.S., D.F.M.) and Center for Developmental
Biology (D.F.M.), University of Washington, Seattle, Washington 98195;
and Department of Biological Sciences, University of Missouri, Rolla,
Missouri 65409 (D.M.P.)
The unicellular green macroalga Acetabularia
acetabulum L. Silva is an excellent system for studying
regional differentiation within a single cell. In late adults,
physiologically mediated extracellular alkalinity varies along the long
axis of the alga with extracellular pH more alkaline along the apical
and middle regions of the stalk than at and near the rhizoid.
Respiration also varies with greater respiration at and near the
rhizoid than along the stalk. We hypothesized that the apical and
middle regions of the stalk require greater carbonic anhydrase (CA)
activity to facilitate inorganic carbon uptake for photosynthesis.
Treatment of algae with the CA inhibitors acetazolamide and
ethoxyzolamide decreased photosynthetic oxygen evolution along the
stalk but not at the rhizoid, indicating that CA facilitates inorganic
carbon uptake in the apical portions of the alga. To examine the
distribution of enzymatic activity within the alga, individuals were
dissected into apical, middle, and basal tissue pools and assayed for
both total and external CA activity. CA activity was greatest in the apical portions. We cloned two CA genes (AaCA1 and
AaCA2). Northern analysis demonstrated that both genes
are expressed throughout much of the life cycle of A.
acetabulum. AaCA1 mRNA first appears in early adults.
AaCA2 mRNA appears in juveniles. The
AaCA1 and AaCA2 mRNAs are distributed
asymmetrically in late adults with highest levels of each in the apical
portion of the alga. mRNA localization and enzyme activity patterns
correlate for AaCA1 and AaCA2, indicating
that mRNA localization is one mechanism underlying regional
differentiation in A. acetabulum.
1
This work was supported by the U.S. National
Science Foundation (postdoctoral grant to K.A.S. and grant no.
IBN-9630618 to D.F.M.).
2
Present address: Department of Biochemistry, Box 357350, University of Washington, Seattle, WA 98195.
*
Corresponding author; email kyles{at}u.washington.edu; fax
206-543-4822.
© 2001 American Society of Plant Physiologists
