Early steps in cold sensing by plant cells: the role of actin cytoskeletonand membrane fluidity

Many plants acquire freezing tolerance through cold acclimatization (CA), a prolonged exposure to low but non-freezing temperatures at the onset of wi nter. CA is associated with gene expression that requires transient calcium influx into the cytosol. Alfalfa (Medicago sativa) cells treated with agen ts blocking this influx are unable to cold acclimatize. Conversely, chemica l agents causing increased calcium influx induce cold acclimatization-speci fic (cas) gene expression in alfalfa at 25 degrees C. How low temperature t riggers calcium influx is, however, unknown. We report here that induction of a CA-specific gene (cas30), calcium influx and freezing tolerance at 4 d egrees C are all prevented by cell membrane fluidization, but, conversely, are induced at 25 degrees C by membrane rigidification. cas30 expression an d calcium influx at 4 degrees C are also prevented by jasplakinolide (JK), an actin microfilament stabilizer, but induced at 25 degrees C by the actin microfilament destabilizer cytochalasin D (CD). JK blocked the membrane ri gidifier-induced, but not the calcium channel agonist-induced cas30 express ion at 25 degrees C. These findings indicate that cytoskeleton re organizat ion is an integral component in low temperature signal transduction in alfa lfa cell suspension cultures, serving as a link between membrane rigidifica tion and calcium influx in CA.