Interaction of Cryptochrome 1, Phytochrome, and Ion Fluxes in Blue-Light-Induced Shrinking of Arabidopsis Hypocotyl Protoplasts1

Abstract

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-redabsorbing 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 Ca 2؉ 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.

The Rice COLEOPTILE PHOTOTROPISM1 Gene Encoding an Ortholog of Arabidopsis NPH3 Is Required for Phototropism of Coleoptiles and Lateral Translocation of Auxin

“…The growth of red light-grown maize coleoptiles was inhibited transiently after the onset of continuous blue light (Wang and Iino, 1997). This response was thought to be mediated by cryptochrome 1 because it showed some similarities with the protoplast shrinking response mediated by cryptochrome 1 (Wang and Iino, 1998). However, the transient growth inhibition in maize coleoptiles occurred within 10 min of blue light irradiation, and the lag time was shorter than 1 min.…”

Blue Light Receptors and Signal Transduction

“…The fact that overexpression of Arabidopsis CRY1 in transgenic tobacco also resulted in a short hypocotyl phenotype suggests that the cry1 signaling process is conserved in different plant species. Complex functional interactions of cry1 with phytochromes have been analyzed in a number of studies using Arabidopsis or tomato mutant lines impaired in both types of photoreceptors (Casal and Boccalandro, 1995;Ahmad and Cashmore, 1997;Ahmad et al, 1998b;Casal and Mazzella, 1998;Neff and Chory, 1998;Wang and Iino, 1998;Hennig et al, 1999aHennig et al, , 1999bFolta and Spalding, 2001a;Weller et al, 2001).…”

Cryptochrome 1 Contributes to Blue-Light Sensing in Pea

“…Also, the cry1 and phyA-dependent suppression of hypocotyl elongation by blue light in early seedling development is antagonized by phyB (Folta and Spalding, 2001). Finally, cry1-mediated blue-light effects on membrane polarization in Arabidopsis hypocotyl protoplasts are enhanced by prior activation of phyA or phyB (Wang and Iino, 1998). The molecular basis for these physiological interactions is not yet known.…”