Low-intensity Far-red Light Research Articles

SCARECROW-like GRAS protein PES positively regulates petunia floral scent production.

Emission of scent volatiles by flowers is important for successful pollination and consequently, reproduction. Petunia (Petunia hybrida) floral scent is formed mainly by volatile products of the phenylpropanoid pathway. We identified and characterized a regulator of petunia scent production: the GRAS protein PHENYLPROPANOID EMISSION-REGULATING SCARECROW-LIKE (PES). Its expression increased in petals during bud development and was highest in open flowers. Overexpression of PES increased the production of floral volatiles, while its suppression resulted in scent reduction. We showed that PES upregulates the expression of genes encoding enzymes of the phenylpropanoid and shikimate pathways in petals, and of the core regulator of volatile biosynthesis ODORANT1 by activating its promoter. PES is an ortholog of Arabidopsis (Arabidopsis thaliana) PHYTOCHROME A SIGNAL TRANSDUCTION 1, involved in physiological responses to far-red (FR) light. Analyses of the effect of nonphotosynthetic irradiation (low-intensity FR light) on petunia floral volatiles revealed FR light as a scent-activating factor. While PHYTOCHROME A regulated scent-related gene expression and floral scent production under FR light, the influence of PES on volatile production was not limited by FR light conditions.

Low-Intensity Far-Red Light Inhibits Early Lesions That Contribute to Diabetic Retinopathy: In Vivo and In Vitro

Treatment with light in the far-red to near-infrared region of the spectrum (photobiomodulation [PBM]) has beneficial effects in tissue injury. We investigated the therapeutic efficacy of 670-nm PBM in rodent and cultured cell models of diabetic retinopathy. Studies were conducted in streptozotocin-induced diabetic rats and in cultured retinal cells. Diabetes-induced retinal abnormalities were assessed functionally, biochemically, and histologically in vivo and in vitro. We observed beneficial effects of PBM on the neural and vascular elements of retina. Daily 670-nm PBM treatment (6 J/cm(2)) resulted in significant inhibition in the diabetes-induced death of retinal ganglion cells, as well as a 50% improvement of the ERG amplitude (photopic b wave responses) (both P < 0.01). To explore the mechanism for these beneficial effects, we examined physiologic and molecular changes related to cell survival, oxidative stress, and inflammation. PBM did not alter cytochrome oxidase activity in the retina or in cultured retinal cells. PBM inhibited diabetes-induced superoxide production and preserved MnSOD expression in vivo. Diabetes significantly increased both leukostasis and expression of ICAM-1, and PBM essentially prevented both of these abnormalities. In cultured retinal cells, 30-mM glucose exposure increased superoxide production, inflammatory biomarker expression, and cell death. PBM inhibited all of these abnormalities. PBM ameliorated lesions of diabetic retinopathy in vivo and reduced oxidative stress and cell death in vitro. PBM has been documented to have minimal risk. PBM is noninvasive, inexpensive, and easy to administer. We conclude that PBM is a simple adjunct therapy to attenuate the development of diabetic retinopathy.

Missense Mutation in the Amino Terminus of Phytochrome A Disrupts the Nuclear Import of the Photoreceptor

Phytochromes are the red/far-red photoreceptors in higher plants. Among them, phytochrome A (PHYA) is responsible for the far-red high-irradiance response and for the perception of very low amounts of light, initiating the very-low-fluence response. Here, we report a detailed physiological and molecular characterization of the phyA-5 mutant of Arabidopsis (Arabidopsis thaliana), which displays hyposensitivity to continuous low-intensity far-red light and shows reduced very-low-fluence response and high-irradiance response. Red light-induced degradation of the mutant phyA-5 protein appears to be normal, yet higher residual amounts of phyA-5 are detected in seedlings grown under low-intensity far-red light. We show that (1) the phyA-5 mutant harbors a new missense mutation in the PHYA amino-terminal extension domain and that (2) the complex phenotype of the mutant is caused by reduced nuclear import of phyA-5 under low fluences of far-red light. We also demonstrate that impaired nuclear import of phyA-5 is brought about by weakened binding affinity of the mutant photoreceptor to nuclear import facilitators FHY1 (for FAR-RED ELONGATED HYPOCOTYL1) and FHL (for FHY1-LIKE). Finally, we provide evidence that the signaling and degradation kinetics of constitutively nuclear-localized phyA-5 and phyA are identical. Taken together, our data show that aberrant nucleo/cytoplasmic distribution impairs light-induced degradation of this photoreceptor and that the amino-terminal extension domain mediates the formation of the FHY1/FHL/PHYA far-red-absorbing form complex, whereby it plays a role in regulating the nuclear import of phyA.

Light-induced Carbon Dioxide and Oxygen Uptake in Plant Leaves Measured by the Photoacoustic Method¶

Abstract Leaf discs, enclosed in a photoacoustic (PA) chamber, generate two types of PA gas-uptake signals under certain conditions. Type I is manifested by a severe signal decrease that develops slowly under very low-light intensity and often reaches negative values. It is partially reversed by low-intensity far-red light. Type II occurs transiently in modulated far-red light. It is manifested by a rapid and dramatic decrease of the PA signal, upon the addition of short-wave background light, which is subsequently reversed. It differs from type-I uptake in that it occurs at much higher total light intensities. A thorough study, including modulation frequency and atmospheric composition dependencies, indicates different mechanisms for the two types of uptakes. Type-I uptake results from CO2 accumulation in the PA cell by leaf respiration and reflects modulations in CO2 solubilization. Type-II uptake likely reflects oxygen photoreduction in photosystem I, occurring prior to the activation of photosynthesis...

A pathway for the reduction of cytochrome b-559 by Photosystem II in chloroplasts

Cytochrome b-559, which is normally reduced in the dark, was oxidized by preillumination in the presence of N-methyl-phenazonium methosulfate with low intensity far-red light. The average half-time for the photoreduction of oxidized cytochrome b-559 by a long actinic flash ranged from 90 to 110 ms. In the presence of 0.25 μM 3-(3,4-dichlorophenyl)-1,1-dimethylurea the half-time for the photoreduction increased to 230 ms although the extent of the absorbance increase was unchanged. Under similar conditions inhibition of electron transport by 3-(3,4-dichlorophenyl)-1,1-dimethylurea and the increase in the chlorophyll fluorescence show that a large fraction of the Photosystem II reaction centers are blocked. These results are consistent with the concept that electrons are shared between different photosynthetic units by a common pool of plastoquinone and imply that the principle pathway for the reduction of cytochrome b-559 by Photosystem II occurs through plastoquinone. In the presence of the uncoupler gramicidin which stimulates non-cyclic electron transport, the rate of photoreduction of cytochrome b-559 is slower ( t 1 2 = 180 ms ), from which it is inferred that cytochrome b-559 competes with cytochrome f for electrons out of this pool. Comparison of cytochrome b-559 photoreduction and electron transport rates using untreated and KCN-treated chloroplasts indicate that, under conditions of basal electron transport from water to ferricyanide, approximately one-fifth of the electrons from Photosystem II go through cytochrome b-559 to ferricyanide. Further support for this pathway is provided by a comparison of the effect of 2,5-dibromo-3-methyl-6-isopropyl- p-benzoquinone (dibromothymoquinone) on the rates of reduction of cytochrome b-559 and ferricyanide.

Kinetics of the photoreduction of cytochrome b-559 by Photosystem II in chloroplasts

The kinetics of the photoreduction of cytochrome b-559 and plastoquinone were measured using well-coupled spinach chloroplasts. High potential (i.e. hydroquinone reducible) cytochrome b-559 was oxidized with low intensity far-red light in the presence of N-methyl phenazonium methosulfate or after preillumination with high intensity light. Using long flashes of red light, the half-reduction time of cytochrome b-559 was found to be 100±10 ms, compared to 6–10 ms for the photoreduction of the plastoquinone pool. Light saturation of the photoreduction of cytochrome b-559 occurred at a light intensity less than one-third of the intensity necessary for the saturation of ferricyanide reduction under identical illumination conditions. The photoreduction of cytochrome b-559 was accelerated in the presence of dibromothymoquinone with a t 1 2 = 25–35 ms . The addition of uncouplers, which caused a stimulatory effect on ferricyanide reduction under the same experimental conditions, resulted in a decrease in the rate of cytochrome b-559 reduction. The relatively slow photoreduction rate of cytochrome b-559 compared to the plastoquinone pool implies that electrons can be transferred efficiently from Photosystem II to plastoquinone without the involvement of cytochrome b-559 as an intermediate. These results indicate that it is unlikely that high potential cytochrome b-559 functions as an obligatory redox component in the main electron transport chain joining the two photosystems.

Conformational changes of chloroplasts induced by illumination of leaves in vivo

Upon illumination leaves showed both fast absorbance changes and a slow increase in their apparent absorbance (maximum at about 530 mμ) which appeared to be caused by a light-dependent shrinkage reaction of chloroplasts. The extent of shrinkage was strongly influenced by the quality and intensity of exciting light and by the presence or absence of electron acceptors. The following observations pertain to the control of electron flow within the electron transport chain of photosynthesis. 1.1. In N2, shrinkage was promoted by either far-red light or low intensity red light which caused a mediated cyclic electron flow to occur in Photosystem I. Shrinkage was inhibited by illumination with high intensity red light.2.2. Addition of red to a beam of far-red light illuminating a leaf under N2 stimulated shrinkage if the intensities of both beams were sufficiently low and led to inhibition of shrinkage if the red beam was intense. A dark period was required to relieve inhibition.3.3. In CO2-free air, O2 was an electron acceptor and caused shrinkage at higher intensities of red but not at low intensity far-red light. Shrinkage promoted in N2 by far-red or low intensity red light was strongly suppressed by O2 which appeared to interrupt cyclic electron transfer by oxidizing an electron acceptor in the pathway between Photosystem I and NADP+. This view was supported by measurements of cytochrome f changes at 420 mμ. Action spectra indicated also that shrinkage in N2 was a Photosystem I reaction, while in the presence of O2 Photosystems I and II cooperated to produce shrinkage.4.4. While shrinkage was greatly stimulated by low concentrations of O2, when both photosystems were sufficiently excited, increasing O2 concentrations suppressed shrinkage increasingly in the investigated plant species possibly by inhibiting electron flow.5.5. The affinity of the shrinkage reaction for O2 was high. Half maximal stimulation or inhibition of shrinkage was obtained at an O2 concn. of about 1.4 μM in the tissue or 1200 ppm in the gas phase. Half maximal fluorescence quenching by O2 occurred at a similar concentration. The kinetics of shrinkage and of fluorescence during a change in the gas atmosphere from N2 to CO2-free air or vice versa were similar indicating that the effects of O2 on the redox state of the quencher and on the shrinkage were indirect and were both mediated by the same reaction of O2 with a component of the electron transport chain beyond Photosystem I.6.6. Shrinkage caused by electron flow to O2 in air or by the cyclic electron flow in N2 was effectively suppressed by CO2. However, CO2 relieved the inhibition of shrinkage caused by high intensity red light under N2 probably by stimulating electron flow. The affinity of the system for CO2 as judged by the ability of CO2 to act as a fluorescence quencher in N2 in blue light or as an inhibitor of shrinkage in far-red light was higher than that for O2. Half maximal response was obtained in leaves capable of high rates of photosynthesis at a CO2 concn. in the gas phase of 10–20 ppm.7.7. The results indicate that CO2 and O2in vivo both act as electron acceptors of photosynthesis; O2 reduction probably supplies ATP in a pseudocyclic type of photo-phosphorylation. Cyclic electron transfer in the presence of O2 is unlikely to occur except under conditions where the reaction reducing O2 is saturated. The observations support the series model of photosynthesis and do not seem to fit into a model with separate and independent photoreactions.