Interaction of cryptochrome 1, phytochrome, and ion fluxes in blue-light-induced shrinking of Arabidopsis hypocotyl protoplasts.
Protoplasts isolated from red-light-adapted Arabidopsis hypocotyls and incubated under red light exhibited rapid and transient shrinking within a period of 20 min in response to a blue-light pulse and following the onset of continuous blue light. Long-persisting shrinkage was also observed during continuous stimulation. Protoplasts from a hy4 mutant and the phytochrome-deficient phyA/phyB double mutant of Arabidopsis showed little response, whereas those from phyA and phyB mutants showed a partial response. It is concluded that the shrinking response itself is mediated by the HY4 gene product, cryptochrome 1, whereas the blue-light responsiveness is strictly controlled by phytochromes A and B, with a greater contribution by phytochrome B. It is shown further that the far-red-absorbing form of phytochrome (Pfr) was not required during or after, but was required before blue-light perception. Furthermore, a component that directly determines the blue-light responsiveness was generated by Pfr after a lag of 15 min over a 15-min period and decayed with similar kinetics after removal of Pfr by far-red light. The anion-channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid prevented the shrinking response. This result, together with those in the literature and the kinetic features of shrinking, suggests that anion channels are activated first, and outward-rectifying cation channels are subsequently activated, resulting in continued net effluxes of Cl- and K+. The postshrinking volume recovery is achieved by K+ and Cl- influxes, with contribution by the proton motive force. External Ca2+ has no role in shrinking and the recovery. The gradual swelling of protoplasts that prevails under background red light is shown to be a phytochrome-mediated response in which phytochrome A contributes more than phytochrome B.
Botanical Gardens, Faculty of Science, Osaka City University, Kisaichi, Katano-shi, Osaka 576, Japan.
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D017360:Arabidopsis / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects*; D029681:Arabidopsis Proteins; D056931:Cryptochromes; D003470:Culture Media; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D018546:Hypocotyl / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects*; D017136:Ion Transport; D008027:Light; D009579:Nitrobenzoates / Q000494:pharmacology; D017956:Photoreceptor Cells, Invertebrate; D010834:Phytochrome / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D011523:Protoplasts / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects*; D043562:Receptors, G-Protein-Coupled; D014638:Vanadates / Q000494:pharmacology
D029681:Arabidopsis Proteins; C538962:CRY1 protein, Arabidopsis; D056931:Cryptochromes; D003470:Culture Media; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins; D009579:Nitrobenzoates; D010940:Plant Proteins; D043562:Receptors, G-Protein-Coupled; C119828:cry protein, Drosophila; D010834:Phytochrome; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D014638:Vanadates