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At least 19 recordsLinked to original sources
PubMed1979

Spectroscopic properties and chromophore conformations of the photomorphogenic receptor: phytochrome.

Fluorescence lifetimes of 'large (mol. wt. 120,000) and 'small' (mol. wt. 60,000) phytochromes isolated from oat and rye seedlings grown in the dark have been measured at 199 K and 298 K. Phytochrome model compounds have also been studied by phase modulation fluorometrically at 77 K for comparison with lifetime data for phytochrome. It was found that the fluorescence lifetime of 'large' phytochrome was significantly shorter than that of 'small' phytochrome and its chromophore models. The phytochrome chromophore of Pr form has been analyzed by fluorescence polarization, CD, and molecular orbital methods. The fluorescence excitation polarization of 'small' phytochrome and the chromophore model in buffer/glycerol mixture (3 : 1, v/v) at 77 K is very hight (0.4) at the main absorption band and is negative (--0.1) and close to 0 in the near ultraviolet band, respectively. Analyses of the spectroscopic data suggest that the chromophore conformation of Pr and Pfr forms of phytochrome are essentially identical. The induced ellipticity of 'large' rye phytochrome in the blue and near ultraviolet regions was found to be significantly higher than that of 'small' phytochrome, indicating that the binding interaction between the phytochrome chromophore and apoprotein is much tighter in the former than in the latter. In addition, the excitation energy transfer does occur from Trp residue(s) to the chromophore in 'large' phytochrome but not in 'small' Pr. This illustrates one feature of the role played by the large molecular weight apoprotein in the binding site interactions and primary photoprocesses of Pr. Finally, a plausible model for the primary photoprocesses and the mechanism of phytochrome interactions triggered by the Pr leads to Pfr phototransformation have been proposed on the basis of the above results.

Circular Dichroism↗
PubMed2026

DNA-binding activity of PIF7 links phytochrome B signaling to plant responses to vegetation proximity.

PHYTOCHROME INTERACTING FACTORs (PIFs) are transcription factors that act as central signaling hubs in light-regulated processes. All PIFs contain an active phytochrome B-binding motif and a DNA-binding basic helix-loop-helix domain. In the shade-avoider Arabidopsis thaliana, PIF7 is a major promoter of hypocotyl elongation in response to vegetation proximity, becoming active when released from phytochrome B via its active phytochrome B-binding motif. Here we show that PIF7 promotes seedling elongation in other species, including the shade-avoider tomato and the shade-tolerant Cardamine hirsuta, suggesting that PIF7 has retained some of its key functional domains across diverse plants. Through complementation analyses using PIF7 variants lacking either the active phytochrome B-binding or basic helix-loop-helix domain, we demonstrate that, unlike PIF3, PIF7 versions unable to bind phytochrome B remain active regardless of light conditions, whereas loss of DNA-binding capacity fully disrupts PIF7 function. Our results further suggest that phytochrome B interaction imposes a dual regulatory control over PIF7, modulating both its abundance and its phosphorylation state (ie its ability to bind and regulate target genes).

Phytochrome B↗
PubMedDate not supplied

[Phytochrome system and synthesis of lipoquinones in the plastids of etiolated hordeum seedlings].

Short pulses of red light induce in etiolated barley seedlings an enhanced synthesis of plastidic benzoquinones and vitamin K1, which can be reverted by subsequent irradiation with short pulses of far-red. As compared to the dark there is more formation of plastoquinone-9 than alpha-tocopherol. The enhanced formation of vitamin K1 is coupled with a concomitant decrease in the level of the second naphthoquinone vitamin "K". The data show that active phytochrome Pfr, also in its ground state, induces the light triggered lipoquinone synthesis which is connected to thylakoid formation. The red light induction of enhanced plastoquinone-9 synthesis cannot be fully reverted by subsequent far-red and seems to be a very fast phytochrome response.

Chlorophyll↗
PubMedDate not supplied

[The influence of phytochrome on the formation of individual carotenoids in etiolated hordeum seedlings].

Short time red pulses, given 6 times for 5 min within 36 h, induce in etiolated barley seedlings an enhanced synthesis of the main chloroplast carotenoids beta-carotene, violaxanthine, lutein and neoxanthine. The level of antheraxanthine and zeaxanthine decreases by red light treatment. These red light effects are reverted by subsequent short time far-red pulses. The results show that the white light induced change in the accumulation rate of individual carotenoids is initiated and regulated by active phytochrome Pfr. In the case of neoxanthin and zeaxanthin the red light effects cannot be fully reverted by far-red; this points to a very fast phytochrome reaction.

Carotenoids↗
PubMed2025

Water shortage reduces PHYTOCHROME INTERACTING FACTOR 4, 5 and 3 expression and shade avoidance in Arabidopsis.

In agricultural crops, forests and grasslands, water deficit often occurs in the presence of cues from neighbouring vegetation. However, most studies have addressed separately the mechanisms of plant growth responses to these two aspects of the environment. Here we show that transferring Arabidopsis thaliana seedlings to agar containing polyethylene glycol (PEG) to restrict water availability reduces hypocotyl growth responses to shade without simultaneously affecting cotyledon expansion or its response to shade. Hypocotyl growth showed significant triple interaction among water availability, shade and the presence of PHYTOCHROME INTERACTING FACTOR 4 (PIF4), PIF5 and PIF3. Water restriction diminished auxin signalling and the activity of the PIF4, PIF5, PIF3 gene promoters and their transcript levels. The responses of PIF4 expression and hypocotyl growth to PEG were reduced in mutants of its positive morning regulators CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY). The CCA1 and LHY gene promoters also reduced their activity in response to PEG. In addition to the changes in PIF4 levels, post-transcriptional processes also contributed to the PIF4 protein response to PEG. Collectively, these results unveil PIFs as a hub that interlinks shade and drought information to control growth.

Arabidopsis↗
PubMed2026

Phytochrome-interacting factor 1b (SlPIF1b) affects the fruit quality of tomato by regulating chloroplast development.

The increased abundance and functionality of fruit chloroplasts could promote the accumulation of nutrients and flavor in the fruit. Tomato fruit has fully developed fruit chloroplasts, whose abundance and functionality have much untapped potential in improving fruit quality by controlling fruit chloroplast development. Previous studies have identified many regulatory factors that specifically regulate fruit chloroplast development in tomatoes, but there are fewer reports on tomato phytochrome-interacting factors (SlPIFs). Arabidopsis AtPIFs have been implicated in chloroplast development and chlorophyll biosynthesis. In this study, we identified and characterized an SlPIF1b mutant in tomato, named GS, which exhibited a dark green fruit shoulder with enhanced chloroplast development. RNA-seq and genotyping analysis identified a - 21 bp (A → T) mutation in the promoter of SlPIF1b, resulting in the absence of the TATA-box core transcriptional element and inhibiting SlPIF1b transcription. The overexpression of SlPIF1b in GS inhibited chloroplast development of fruits, leading to a lighter green shoulder color, decreased chlorophyll content, reduced photosynthetic activity, diminished starch accumulation, and compromised fruit quality upon ripening. Conversely, the down expression of SlPIF1b significantly enhanced fruit chloroplast development and functionality in fruits, resulting in increased chlorophyll and carotenoid accumulation. Further analysis of expression profile and transcriptional activity indicated that SlPIF1b could bind to G/PBE-box elements present in SlGLK2, SlTKN4, SlCAO1a, SlPOR1, SlPOR3, SlCAB1 and SlCAB1b promoters, thereby inhibiting their expression. This study revealed the specific regulatory mechanism by which SlPIF1b modulates chloroplast development and chlorophyll synthesis in tomato fruit and provided valuable genetic resources and a theoretical basis for tomato quality improvement.

Solanum lycopersicum↗
PubMed1975

The structures of the phytochrome chromophore in both photoreversible forms.

Spectral measurements of phytochrome are performed after unfolding of the peptide chain. By comparison with bile pigments of known structure, structure 1a, containing a hydrogenated ring A, is deduced for the PR chromophore. Its spectral properties indicate that the chromophore of the physiologically active PFR form has lost the double bond of the bridge joining rings A and B.

Bile Pigments↗
PubMed1977

Studies on plant bile pigments, II[1]. Chemical and photochemical oxygenation of a phytochrome Pr chromophore model pigment to purpurins.

The chemical and photochemical oxygenation of 2,3-dihydrooctaethyl-1,19(21,24H)-bilindione (1), as a model for the chromophores of both phytochrome Pr and phycocyanin, has been studied in neutral and alkaline solution, and in the presence of zinc ions. By comparison with octaethyl-1,19(21,24H)-bilindione (5), the influence of ring A hydrogenation on the reactivity of bilins has been assessed. In the dark, 1 is attacked selectively and rapidly at C-5 yielding "purpurins", while 5 reacts slowly, and is attacked predominantly at C-10. Photooxidation of 5 yields the tripyrrinic "purpurin" 7 only. Photoreactivity of 1 is considerably enhanced, yielding "purpurins" and "violins" rapidly. In spite of UV-vis and mass spectroscopic similarities, the "purpurin" 7 differs from the "purpurins" 6a,b by the loss of ring A. The facile cleavage at the C-5 methine bridge and the spectroscopic properties of "purpurins" are discussed.

Models, Chemical↗