Two Spectroscopically and Photochemically Distinguishable Phytochromes in Etiolated Seedlings of Monocots and Dicots *

Abstract

Fluorescence (F) emission spectra of the red‐absorbing phytochrome form (Pr) at 85 K, temperature dependence of the F intensity and the extent of the Pr F changes in the phototransformation of Pr into the first stable photoproduct (lumi‐R) at 85 K (γ1,) and into the far‐red‐absorbing form (Pfr) at 267 K (γ2) were investigated in etiolated shoots and roots of monocots (oat, maize, rice) and dicots (pea, cress). These characteristics monotonously changed as a function of the phytochrome content, [Ptot]: with its decrease to 3‐5% of the maximal values, the F spectrum shifts from 686 nm to 682 nm, its half‐band width rises from 22 nm to ca 25 nm, temperature dependence of Pr F changes its character, γ1, drops down from ca > 0.45 to ca 0.05‐0.10 and γ2 from 0.80–0.82 to 0.70. These data were interpreted in terms of two different phytochromes whose relative concentration varies with [Ptot]: (1) a longer wavelength type with the F maximum at 686 nm, low activation energy of the photoreaction (Ea 3–4 kj/ mol) and high extent of the phototransformation at 85 K (0.49 ± 0.03) and at 267 K (ca 0.85) (Pra); (2) a shorter wavelength type practically inactive at 85 K with F maximum at 682 nm, higher Ea (ca 35 kj/mol) and lower extent of the Pr & Pfr phototransformation (0.70) (Pri). [Pra] widely varies in different parts of the seedlings (up to 100 times) and Pra dominates when [Ptot] is high. The [Pri] is much more constant (variations, <10 times), and it becomes the major one when [Ptot] drops down. The two species are likely to belong to the labile (type 1) and stable pools of pigment and not to be connected with the localization of the pigment in the cell since red‐far‐red preillu‐mination, which is believed to bring about sequestering of the pigment, does not change their relative concentration and properties.

Two Native Pools of Phytochrome A in Monocots: Evidence from Fluorescence Investigations of Phytochrome Mutants of Rice

“…As it was shown elsewhere (19), the spectra of etiolated tissue are represented by the individual spectra of the phytochromes and also by the spectrum of the background fluorescence. In this work, to get individual spectra of phyA, the spectrum of the phyA mutant was subtracted from that of WT and the spectrum of the phyAphyB double mutant was subtracted from the spectrum of the phyB mutant (see below) (Fig.…”

“…We used low‐temperature fluorescence spectroscopy of phytochrome in etiolated tissues as a major experimental approach (16–21). The procedure of the rice seedlings growth, sample preparation and spectral measurements were essentially the same as those reported elsewhere (21).…”

“…The two Pr types were also found in monocots ( i.e. oat, wheat, barley, rice and maize (19–21)), which, similar to dicots, could be attributed to the presence of phyA′ and phyA″, on the basis of their spectroscopic and photochemical properties and their abundance in and distribution among plant species and tissues under different physiological conditions. However, the lack of phyA and phyB mutants of monocots did not allow us to present a rigorous proof that phyA in these plants also exists in the two isoforms.…”

Two modes of the light-induced phytochrome A decline – with and without changes in the proportion of its isoforms (phyA′ and phyA″): evidence from fluorescence investigations of mutant phyA-3D pea

“…The experimental approach was the same as that used earlier (see [11][12][13][14]17,18,21,22] and the literature cited therein). To obtain the phytochrome parameters in the sample, low-temperature (85 K) emission spectra (wavelength of the excitation, k e , 610 or 650 nm) were taken under two different experimental settings (see Figs.…”

“…The proportion of the two phenomenological pools was evaluated using the experimental c 1 values as described in detail in [22] based on the fact that Pr 0 is active at low temperature in the Pr ! lumi-R photoconversion with c 0 1 ¼ 0:49 AE 0:03 and Pr 00 is practically inactive in this photoprocess (c 00 1 !…”