Action Of Photoreceptors Research Articles

Shedding light on the chromatin changes that modulate shade responses.

Perception of vegetation proximity or plant shade informs of potential competition for resources by the neighboring vegetation. As vegetation proximity impacts on both light quantity and quality, perception of this cue by plant photoreceptors reprograms development to result in responses that allow plants to compete with the neighboring vegetation. Developmental reprogramming involves massive and rapid changes in gene expression, with the concerted action of photoreceptors and downstream transcription factors. Changes in gene expression can be modulated by epigenetic processes that alter chromatin compaction, influencing the accessibility and binding of transcription factors to regulatory elements in the DNA. However, little is known about the epigenetic regulation of plant responses to the proximity of other plants. In this manuscript, we review what is known about plant shade effects on chromatin changes at the cytological level, that is, changes in nuclear morphology and high order chromatin density. We address which are the specific histone post-transcriptional modifications that have been associated with changes in shade-regulated gene expression, such as histone acetylation and histone methylation. Furthermore, we explore the possible mechanisms that integrate shade signaling components and chromatin remodelers to settle epigenetic marks at specific loci. This review aims to be a starting point to understand how a specific environmental cue, plant shade, integrates with chromatin dynamics to implement the proper acclimation responses.

The remediation of drought stress under VAM inoculation through proline chemical transformation action

This article discussed the enhanced drought tolerance under arbuscular mycorrhizal (AM) inoculation and normal growth of plants which linked with the activity of photoreceptors. The photoreceptor action in dual symbiosis under drought stress showed not only the high photosynthetic activity but also provide information about the broad range of physiological responses. The pot experiment conducted in a natural environment where drought condition was observed twice a week via regular irrigation with water up to twelve months. Plants analysis showed the high contents of water, hydrogen peroxide, carotenoids, proline, antioxidant enzymes like super dismutase (SOD) and catalase(CAT) in both leaves and roots with a large surface area of leaves over control. The elevated concentration of hydrogen peroxide (0.04 ± 0.0 μmol/g) coupled with singlet oxygen species was the main modified molecular mechanism which was operative in drought condition. The accretion of proline under drought stress in dual symbiosis (32.3 ± 0.3 μg/mL) was related to the highest branching pattern of young leaves and the chemical transformation of reactive oxygen species (ROS) including H2O2 and 3O2 into useful molecules like water and triplet molecular oxygen. The higher contents of carotenoids (5.0 ± 1.2 mg/g) in drought over control (4.8 ± 1.6 mg/g) and AM plant (4.9 ± 1.2 mg/g) was found to be supportive in the conversion of singlet oxygen into triplet one.

Shining a light on the Arabidopsis circadian clock.

The circadian clock provides essential timing information to ensure optimal growth to prevailing external environmental conditions. A major time-setting mechanism (zeitgeber) in clock synchronization is light. Differing light wavelengths, intensities, and photoperiodic duration are processed for the clock-setting mechanism. Many studies on light-input pathways to the clock have focused on Arabidopsis thaliana. Photoreceptors are specific chromic proteins that detect light signals and transmit this information to the central circadian oscillator through a number of different signalling mechanisms. The most well-characterized clock-mediating photoreceptors are cryptochromes and phytochromes, detecting blue, red, and far-red wavelengths of light. Ultraviolet and shaded light are also processed signals to the oscillator. Notably, the clock reciprocally generates rhythms of photoreceptor action leading to so-called gating of light responses. Intermediate proteins, such as Phytochrome interacting factors (PIFs), constitutive photomorphogenic 1 (COP1) and EARLY FLOWERING 3 (ELF3), have been established in signalling pathways downstream of photoreceptor activation. However, the precise details for these signalling mechanisms are not fully established. This review highlights both historical and recent efforts made to understand overall light input to the oscillator, first looking at how each wavelength of light is detected, this is then related to known input mechanisms and their interactions.

Light signaling in photosynthetic eukaryotes with ‘green’ and ‘red’ chloroplasts

Light drives one of the most important processes on earth–photosynthesis. Besides providing the energy for carbon reduction, it is also an important signaling source, which largely influences the acclimation and adaptation behavior of algae and plants. Two different ways of light perception can be differentiated: direct and indirect light signaling. Direct light signaling is based on the action of photoreceptors. Indirect light signaling originates from the photosynthetic light reaction and is either based on the redox state of the photosynthetic electron transport chain or on reactive oxygen species. Especially the indirect signaling raises a specific challenge for plants and algae: while the signal perception occurs in the chloroplast, the largest part of the target genes is located in the nucleus, i.e. the triggering signal needs to cross several membranes. Green algae and plants (the ‘greens’) achieved to establish mechanisms which transfer the so called ‘retrograde’ signal from the chloroplast into the nucleus. Besides identifying the primary light triggers and regulated target genes, researchers discovered a bunch of secondary messengers, which may connect the light trigger with the target genes in a signaling network. Still, the exact signaling cascades are basically unknown so far.The knowledge about direct light signaling in organisms with ‘red’ plastids (red algae and those with secondary red plastids, such as stramenopiles, hacrobians and dinoflagellates) is comparatively little compared to the ‘greens’. However, it is clearly advancing and interesting novelties were found in recent years, e.g. the discovery of the aureochrome photoreceptor class. In contrast, the knowledge about indirect light signaling in these organisms is still in its infancy. Given their ecological importance in the aquatic environment and for global net primary production, this lack of information needs to be removed in future research. This review aims at providing a comparatively short summary about light signaling in the ‘greens’, while gathering most of the information available for the ‘reds’, which may attract researchers to start studying light signaling in this largely neglected group.

The signal transducing photoreceptors of plants

Light signals are amongst the most important environmental cues regulating plant development. In addition to light quantity, plants measure the quality, direction and periodicity of incident light and use the information to optimise growth and development to the prevailing environmental conditions. Red and far-red wavelengths are perceived by the photoreversible phytochrome family of photoreceptors, whilst the detection of blue and ultraviolet (UV)-A wavelengths is conferred by the cryptochromes and phototropins. Higher plants contain multiple discrete phytochromes, the apoproteins of which are encoded by a small divergent gene family. In Arabidopsis, two cryptochrome and two phototropin family members have been identified and characterized. Photoreceptor action regulates development throughout the lifecycle of plants, from seed germination through to architecture of the mature plant and the onset of reproduction. The roles of individual photoreceptors in mediating plant development have, however, often been confounded by redundant, synergistic and in some cases mutually antagonistic mechanisms of action. The isolation of mutants null for individual photoreceptors and the construction of mutants null for multiple photoreceptors have therefore been paramount in elucidating photoreceptor functions. Photoreceptor action does not, however, operate in isolation from other signalling systems. The integration of light signals with other environmental cues enables plants to adapt their physiology to changing seasonal environments. This paper summarises current understanding of photoreceptor families and their functions throughout the lifecycle of plants. The integration of light signals with other environmental stimuli is also discussed.

Photoreceptors and signals in the photoperiodic control of development

ABSTRACTMany plant species are sensitive to changes in the seasons, especially with regard to their reproductive behaviour. Sexual or vegetative reproductive structures are often only formed at times of the year when days are sufficiently long, or short. Plants perceive daylength in the leaves, but reproductive changes occur in shoot apices in response to the movement of signals throughout the plant. There is good evidence that phytochrome A is an essential component of the daylength‐sensing mechanism in long‐day plants, and preliminary evidence suggests a potential interaction between phytochrome C and daylength sensitivity in short‐day plants. The sensitivity of reproductive processes to photoperiodic control is directly altered by photoreceptor action, particularly in the case of phytochrome B, which has a major influence on whether flowering or tuberization occurs under non‐inductive conditions in both long‐ and short‐day plants, but is not involved in daylength measurement. The signals which move from leaves to the sites of reproductive development are not known, but there is good evidence that gibberellins may be important and some preliminary indication that brassinosteroids might also be involved in photoperiodic signalling.

Identification of phytochrome B amino acid residues mutated in three newphyBmutants ofArabidopsis thaliana

The growth and development of plants is regulated by light via the action of photoreceptors which are responsive to the red/far-red, blue and UV regions of the spectrum. Phytochrome B (the apoprotein of which is encoded by the PHYB gene) is one of the red/farred absorbing photoreceptors active in this process. In this paper, the isolation and characterization of three new EMS-induced mutations of Arabidopsis which confer phytochrome B deficiency are described. Complementation analysis showed that these mutations (phyB-101, phyB-102 and phyB-104) were allelic with PHYB. DNA sequence analysis showed that all three mutants contain nucleotide substitutions in the PHYB gene sequence. phyB-101 carries a nucleotide substitution within the second exon of the PHYB gene. This G-to-A substitution is a missense mutation that converts a glutamate residue at position 812 of the phytochrome B apoprotein to a lysine residue. phyB-102, another missense mutant, carries a C-to-T substitution which converts a serine residue at position 349 of the phytochrome B apoprotein to a phenylalanine residue. phyB-104 carries a premature stop codon as a result of a G-to-A mutation 1190 bp downstream of the ATG start codon of the PHYB sequence. The missense mutations in phyB-101 and phyB-102 cause significant alterations in the predicted secondary structure of their respective mutant polypeptides, and identify amino acid residues playing crucial roles in phytochrome B function, assembly or stability.

Regulation of gene expression by light

The past year has seen significant advances in the biochemical, genetic and molecular dissection of the light signal transduction and developmental pathways that lead to photoregulated gene expression in higher plants. A major part of recent research has focused on the assignment of biological functions to the various photoreceptors, the genetic dissection of the photoreceptor action pathways, and the identification of the cis-acting sequences and trans-acting factors that regulate the downstream light-regulated genes.

INDUCTION OF Trichoderma SPORULATION BY NANOSECOND LASER PULSES: EVIDENCE AGAINST CRYPTOCHROME CYCLING

An important question in the study of photoreceptor action in morphogenesis is whether the chromophore is unidirectionally photobleached, or whether it is recycled, allowing each receptor molecule to be counted more than once. The common soil fungus Trichoderma harzianum grows vegetatively in the dark and sporulates in response to a pulse of blue or UV-A light. Colonies were grown at 26 degrees C, transferred to 3 degrees C, illuminated with non-saturating light, and then put back at 26 degrees C to sporulate. The fluence-response curves for photoinduction in the cold and at 26 degrees C were identical, indicating that there are no enzymatic transduction processes during irradiation. Regions of the perimeter of dark-grown colonies were given single pulses (maximum duration, 30 ns) at 355 nm with a neodymium laser. We obtained a complete fluence-response curve for the laser pulses, which agreed with data for irradiations in the second to minute range. Photoinduction at 3 degrees C, and validity of Bunsen-Roscoe reciprocity from nanoseconds to minutes, support the hypothesis that the inductive event is a simple first-order photobleaching reaction.

Phototropism of maize coleoptiles Influences of light gradients

The lateral fluence-rate gradients in unilaterally irradiated maize (Zea mays L.) coleoptiles were calculated on the basis of the proportions of P fr (far-red-absorbing form of phytochrome) measured spectroscopically in transverse slices of the coleoptiles (top 1 cm). The results showed the occurrence of significant gradients that are wavelength-dependent. The gradient at 449 nm was steeper than those measured at 516, 534 and 551 nm, which were steeper than that measured at 665 nm. The ratios between the sides proximal and distal to the light source were, for example, 1:0.12 (449 nm), 1:0.23 (534 nm), and 1:0.28 (665 nm). Fluence-response curves for coleoptile phototropism (first positive curvature produced by less than 100 s unilateral irradiation) were measured at 449, 516, 534 and 551 nm. Comparison of the threshold fluences indicated that the responsiveness to 551 nm is about 10(4.8) less than that to 449 nm. Increasing wavelengths led to a decrease in maximal curvature, which correlated with the decrease of the fluence-rate ratios between the proximal and distal sides. Phototropic fluence-response curves were also measured using bilateral irradiation (449 nm). In one set of experiments, the fluence ratio was kept constant (either 1:1/2, 1:1/4 or 1:1/16) and the total fluence was varied, and in the other set the fluence applied to one side was kept constant and the fluence ratio was varied. A simple model based on the assumption that only one photoreaction occurs, and that the response is a function of the difference between the proximal and distal sides in the local photoreceptor action was tested. A fluence-response curve for this local photoreceptor action was calculated based on the fluence-rate ratio and the phototropic fluence-response curve measured for 449 nm. This curve was used, in conjunction with the measured fluence-rate ratios, as a basis for calculating phototropic fluence-response curves for other wavelengths and those for 449 nm obtained with bilateral irradiation. The calculated fluence-response curves showed excellent agreement with the experimental data. It is concluded that the threshold for maize coleoptile phototropism reflects the apparent photoconversion cross-section of the blue-light receptor whereas the maximal curvature depends on the steepness of the light gradient across the coleoptile.