Modulation by phytochrome of the blue light-induced extracellular acidification by leaf epidermal cells of pea (Pisum sativum l.): a kinetic analysis.
Blue light induces extracellular acidification, a prerequisite of cell expansion, in epidermis cells of young pea leaves, by stimulation of the proton pumping-ATPase activity in the plasma membrane. A transient acidification, reaching a maximum 2.5-5 min after the start of the pulse, could be induced by pulses as short as 30 msec. A pulse of more than 3000 micromol m-2 saturated this response. Responsiveness to a second light pulse was recovered with a time constant of about 7 min. The fluence rate-dependent lag time and sigmoidal increase of the acidification suggested the involvement of several reactions between light perception and activation of the ATPase. In wild-type pea plants, the fluence response relation for short light pulses was biphasic, with a component that saturates at low fluence and one that saturates at high fluence. The phytochrome-deficient mutant pcd2 showed a selective loss of the high-fluence component, suggesting that the high-fluence component is phytochrome-dependent and the low-fluence component is phytochrome-independent. Treatment with the calmodulin inhibitor W7 also led to the elimination of the phytochrome-dependent high-fluence component. Simple models adapted from the one used to simulate blue light-induced guard cell opening failed to explain one or more elements of the experimental data. The hypothesis that phytochrome and a blue light receptor interact in a short-term photoresponse is endorsed by model calculations based upon a three-step signal transduction cascade, of which one component can be modulated by phytochrome.
Elzenga
J T
JT
Laboratory of Plant Physiology, Department of Plant Biology, University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands. j.t.m.elzenga@biol.rug.nl
Staal
M
M
Prins
H B
HB
D000143:Acids; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D018532:Pisum sativum / Q000502:physiology / Q000528:radiation effects*; D010834:Phytochrome / Q000502:physiology*; D019441:Plant Epidermis / Q000166:cytology; D018515:Plant Leaves / Q000166:cytology / Q000502:physiology*
D000143:Acids; D010834:Phytochrome