Fluorescence spectroscopy and photochemistry of phytochromes A and B in wild-type, mutant and transgenic strains of Arabidopsis thaliana

Phytochrome (P) was characterized in etiolated seedlings of wild-type, mutant and transgenic strains of Arabidopsis with the use of low-temperature (85 K) fluorescence spectroscopy and photochemistry. The position (lambda(max)) of the Pr emission spectrum, its intensity (F-0) proportional to [P-tot] and the extent of the Pr-->lumi-R phototransformation at 85 K (gamma(1)) were shown to vary depending on the plant strains and tissues used, while the extent of the Pr-->Pfr transformation at 273 K (gamma(2)) remained relatively constant. Depletion of phyA (frel-1 in Nagatani et al., Plant Physiol. 102 (1993) 269-277, and fhy2-2 in Whitelam et al., Plant Cell 5 (1993) 757-768) resulted in a steep decrease of F-0 to approximate to 10%. The phyB mutant (hy3-Bo64 in Reed et al., Plant Cell 5 (1993) 147-157) revealed a slight reduction (by approximate to 20%) of F-0 while lambda(max) and gamma(1) remained practically unaffected. In phyAphyB mutant no P emission was observed. Overexpression of oat phyA (13k7 and 21k15 in Boylan and Quail, Proc. Natl. Acad. Sci. USA 88 (1991) 10806-10810) brought about an increase of F-0 by two to three times, a shift of lambda(max) to 685 nm and an increase of gamma(1) to 0.3-0.4. On the contrary, an increase of F-0 (up to 40%) in Arabidopsis and rice phyB overexpressors (ABO and RBO in Wagner et al., Plant Cell 3 (1991) 1275-1288) was followed by a decrease of gamma(1) values to 0.13-0.14. These data together with the results on phyB (Ih) mutant of cucumber prove the existence of the two phyA populations with high (phyA') and low (phyA ") photochemical activity at low temperatures. PhyB emits maximally in the same region as phyA in Arabidopsis (approximate to 683 nm) and at shorter wavelength (< 680 nm) in rice. It is characterized by low photochemical activity at 85 K (gamma(1) less than or equal to 0.05)) and can be attributed in this respect to the same pigment type as phyA ". (C) 1998 Elsevier Science S.A.