Chlorophyll Precursors Research Articles

Roles of Exogenous 5-Aminolevulinic Acid and Dihydroporphyrin Iron in Chlorophyll Precursor Synthesis and Chlorophyll-Related Enzyme Activities in Wheat Under Different Light Intensities

Aminolevulinic acid (5-ALA) and dihydroporphyrin iron chelates (DHFe) play roles in plant growth regulation under normal and stressful conditions. However, definitive data on their roles in regulating chlorophyll synthesis in wheat are lacking. In this study, the optimal concentrations for foliar-spray application of 5-ALA and DHFe to promote wheat seedling growth and leaf chlorophyll content were assessed. The optimal concentrations of 5-ALA or DHFe (50 mg/L and 0.01 mg/L, respectively) were applied as foliar sprays to seedlings of wheat ‘Bainong 4199’ (high light efficient) and ‘Zhoumai No. 18’ (average light efficient) under different light intensities. Chlorophyll precursor contents and activities of three chlorophyll synthesis-related enzymes were altered, and the combined application of 5-ALA and DHFe more strongly increased the leaf chlorophyll content. 5-ALA significantly increased the contents of the chlorophyll precursors porphobilinogen, uroporphyrinogen III, protoporphyrin IX, and magnesium-protoporphyrin IX, and the activities of 5-amino-ketovalerate dehydratase and uroporphyrinogen III synthase. DHFe resulted in an increase in chlorophyll content but a significant decrease in chlorophyllase activity and protochlorophyllide content. 5-ALA promoted the synthesis of chlorophyll precursors by regulating the activities of 5-amino-ketovalerate dehydratase and uroporphyrinogen III synthase. DHFe decreased chlorophyllase activity, thereby slowing chlorophyll degradation and increasing the chlorophyll content.

Low temperature and high humidity affect dynamics of chlorophyll biosynthesis and secondary metabolites in Cucumber.

During the cold season, low temperature (LT) and high relative humidity (HRH) are significant environmental factors in greenhouses and plastic tunnels, often hindering plant growth and development. The chlorophyll (Chl) biosynthesis inhibitory mechanisms under LT and HRH stress are still widely unclear. To understand how cucumbers seedlings respond to LT and HRH stress, we investigated the impact of these stressors on Chl biosynthesis. Our results revealed that individual LT, HRH and combined LT + HRH stress conditions affected chlorophyll a, b, total chlorophyll and carotenoid content, reducing the levels of these pigments. The levels of Chlorophyll precursors were also markedly reduced under LT and HRH stresses, with the greatest reduction observed in cucumber seedlings exposed to LT + HRH conditions (9/5℃, 95%HRH). The activities of glutamate-1-semialdehyde transaminase (GSA-AT), ALA dehydratase (ALAD), Mg-chelatase, and protochlorophyllide oxidoreductase (POR) were increased under individual LT, HRH, conditions but decreased by combination of LT + HRH stress condition. In addition, Chl biosynthesis related genes (except PBG) were upregulated by the HRH stress but were significantly downregulated under the LT + HRH stress condition in cucumber seedlings. Furthermore, the content of phenols, flavonoids and phenolic acids (cinnamic acid and caffeic acid) were significantly surged under LT + HRH treatment over the control. Histochemical observation showed higher O2- and H2O2 content in cucumber leaves during the LT and HRH stress. The results indicate that LT + HRH stress significantly impairs chlorophyll biosynthesis in cucumber seedlings by drastically reducing pigment accumulation, altering enzyme activity and gene expression. Additionally, LT + HRH stress induces oxidative damage, which further exacerbates the decline in chlorophyll content and affects overall cucumber metabolism.

Critical stages in pea photosynthesis impaired by tetracycline as an environmental contaminant.

The widespread use of antibiotics in intensive animal husbandry, and the agricultural utilization of manure from such farms, imposes a significant burden on the environment. Consequently, the effects of antibiotics should be studied not only in animals and humans but also in all components of biocenoses and agrocenoses. In our study, we analyze the impact of four different concentrations of tetracycline present in soil (0, 5, 50, and 500mg/kg of soil) on the growth and key photosynthesis parameters of pea seedlings: chlorophyll concentration, aminolevulinic acid concentration, aminolevulinic acid dehydrogenase activity, and ribulose bisphosphate carboxylase-oxygenase (RuBisCO) activity. At the lowest tetracycline concentration, chlorophyll content decreased by 13% compared to the control (0 tetracycline), while at the highest antibiotic concentration, it decreased by as much as 27%. Similarly, the decrease in aminolevulinic acid (a chlorophyll precursor) concentration was significant, amounting to 34%. However, the activity of the dehydrogenase enzyme, which consumes this precursor, decreased even more drastically by 51%, indicating significant disturbances in the light phase of photosynthesis. However, the activity of RuBisCO in pea plants subjected to tetracycline was even more severely affected, dropping by 58%, 69%, and 70% in soils with increasing concentrations of tetracycline. The reduction in enzyme activity could only partially be explained by a less pronounced decrease in the quantity of RuBisCO (large subunit) protein, which amounted to 6.5%, 11%, and 35% for tetracycline concentrations of 5, 50, and 500mg/kg of soil, respectively.

Would reducing chlorophyll content result in a higher photosynthesis nitrogen use efficiency in crops?

AbstractDecreasing antenna size is considered a potential option for improving photosynthesis and increasing yield potential. Reducing chlorophyll content has been employed as a strategy to decrease antenna size. One of the commonly mentioned advantages of this approach is its ability to enhance crop nitrogen use efficiency (NUE); however, there is limited field evidence supporting this claim. In this study, we utilized a rice mutant called p35s‐Ami‐YGL1, which exhibits lower chlorophyll content and smaller antenna size, to investigate the effects of modifying leaf chlorophyll content on tissue nitrogen content and NUE. Our results demonstrate that the nitrogen contents in various tissues, including seed tissue, increased on a weight basis in p35s‐Ami‐YGL1 mutants while exhibiting a decrease in C:N ratio. Simultaneously, we observed a reduction in tissue carbon content along with an increase in the levels of chlorophyll precursors such as Proto IX. Specifically, we observed an upregulation in the expression of genes associated with photosynthetic light reactions and chlorophyll metabolism, while there was no increase in the expression of genes involved in the CBB cycle and nitrogen metabolism. In addition, p35s‐Ami‐YGL1 experienced increased photodamage. These findings suggest that the alterations in the C:N ratio and nitrogen content in plants may be attributed to Proto IX‐mediated photodamage and chloroplast reverse transduction signaling. Besides, these results suggest that the observed increase in tissue nitrogen content in p35s‐Ami‐YGL1 does not reflect an increase in plant nitrogen absorption or use efficiency, rather it is a result of stunted carbon fixation capacity.

Mapping and Candidate Gene Analysis of the Low-Temperature-Sensitive Albino Gene OsLTSA8 in Rice Seedlings.

Chloroplasts are organelles responsible for photosynthesis in plants, providing energy for growth and development. However, the genetic regulatory mechanisms underlying early chloroplast development in rice remain incompletely understood. In this study, we identified a rice seedling thermosensitive chlorophyll-deficient mutant, osltsa8, and the genetic analysis of two F2 populations suggested that this trait may be controlled by more than one pair of alleles. Through reciprocal F2 populations and QTL-seq technology, OsLTSA8 was mapped to the interval of 24,280,402-25,920,942 bp on rice chromosome 8, representing a novel albino gene in rice. Within the candidate gene region of OsLTSA8, there were 258 predicted genes, among which LOC_Os08g39050, LOC_Os08g39130, and LOC_Os08g40870 encode pentatricopeptide repeat (PPR) proteins. RNA-seq identified 18 DEGs (differentially expressed genes) within the candidate interval, with LOC_Os08g39420 showing homology to the pigment biosynthesis-related genes Zm00001d017656 and Sb01g000470; LOC_Os08g39430 and LOC_Os08g39850 were implicated in chlorophyll precursor synthesis. RT-qPCR was employed to assess the expression levels of LOC_Os08g39050, LOC_Os08g39130, LOC_Os08g40870, LOC_Os08g39420, LOC_Os08g39430, and LOC_Os08g39850 in the wild-type and mutant plants. Among them, the differences in the expression levels of LOC_Os08g39050 and LOC_Os08g39430 were the most significant. This study will contribute to further elucidating the molecular mechanisms of rice chloroplast development.

A phytoplasma effector destabilizes chloroplastic glutamine synthetase inducing chlorotic leaves that attract leafhopper vectors

Leaf yellowing is a well-known phenotype that attracts phloem-feeding insects. However, it remains unclear how insect-vectored plant pathogens induce host leaf yellowing to facilitate their own transmission by insect vectors. Here, we report that an effector protein secreted by rice orange leaf phytoplasma (ROLP) inhibits chlorophyll biosynthesis and induces leaf yellowing to attract leafhopper vectors, thereby presumably promoting pathogen transmission. This effector, designated secreted ROLP protein 1 (SRP1), first secreted into rice phloem by ROLP, was subsequently translocated to chloroplasts by interacting with the chloroplastic glutamine synthetase (GS2). The direct interaction between SRP1 and GS2 disrupts the decamer formation of the GS2 holoenzyme, attenuating its enzymatic activity, thereby suppressing the synthesis of chlorophyll precursors glutamate and glutamine. Transgenic expression of SRP1 in rice plants decreased GS2 activity and chlorophyll precursor accumulation, finally inducing leaf yellowing. This process is correlated with the previous evidence that the knockout of GS2 expression in rice plants causes a similar yellow chlorosis phenotype. Consistently, these yellowing leaves attracted higher numbers of leafhopper vectors, caused the vectors to probe more frequently, and presumably facilitate more efficient phytoplasma transmission. Together, these results uncover the mechanism used by phytoplasmas to manipulate the leaf color of infected plants for the purpose of enhancing attractiveness to insect vectors.

Comparative transcriptomic analysis to postulate the generation of variegated leaves in Bougainvillea peruviana ‘Thimma’

The underlying mechanism of leaf coloration remains blank in Bougainvillea peruviana ‘Thimma’, which has high ornamental value in urban landscape. In this study, the variegated leaves were comprehensively characterized. Compared to the green leaves, the yellow sectors of variegated leaves had severely disrupted chloroplasts and ruptured thylakoid membranes. The chloroplast number was lower in the yellow sectors of variegated leaves. The chlorophyll and carotenoid contents were extremely lower in the yellow sectors of variegated leaves. Besides, the contents of three key chlorophyll precursors, protoporphyrin IX (Proto IX), magnesium protoporphyrin IX (Mg-Proto IX), and protochlorophyllide (Pchlide), were significantly decreased in the yellow sectors of variegated leaves. The abscisic acid (ABA) content was higher in the yellow sectors of variegated leaves. Moreover, through comparative transcriptome analysis of mature completely green leaves and yellow sectors of variegated leaves, a total of 951 differentially expressed genes (DEGs) were identified. Further annotation analysis indicated that DEGs involved in chlorophyll biosynthesis and the development of chloroplast were downregulated in yellow sectors of variegated leaves, which were likely the main causes of the yellow color phenotype. Additionally, two DEGs were enriched in the ABA biosynthesis, which might inspire future research on correlation between leaf color and hormone. These findings will provide novel insights for leaf coloration regulation in B. peruviana.

Natural Albino Mutant of Daylily (Hemerocallis spp.) Reveals a Link between Drought Sensitivity and Photosynthetic Pigments Metabolism.

Mutant analysis remains one of the main genetic tools for characterising unclarified gene functions in plants, especially in non-model plants. Daylily (Hemerocallis spp.) is a popular perennial ornamental plant grown worldwide. Analysis of daylily mutants can enhance understanding of genes regulating the albino phenotype and improve the cultivar quality of daylily. The natural albino mutant (Alb-⁣/-) was isolated by screening a self-pollinated progeny of daylily cultivar 'black-eyed stella'. Transmission electron microscopy was used in analysing the structure of plastids between mutant and wild-type seedlings. The content of chlorophyll, carotenoids and chlorophyll precursors in plants was measured by ultraviolet spectrophotometry. RNA sequencing and physiological measurements were performed to explore the association between drought tolerance and mutation. All the seedlings of the daylily albino mutants died spontaneously within fifteen days after germination when grown in soil. The carotenoid and chlorophyll content in the leaves of the mutant plants significantly decreased compared with those of the wild-type control. The mutant plants displayed stunted growth, and their leaves were white or light yellow in color. Abnormal plastids such as those showing endomembrane vesiculation and lacking stacking were discovered in the leaves of mutant plants. Furthermore, genetic analysis revealed that a single recessive nuclear gene mutation led to the albino trait, RNA sequencing and real-time quantitative PCR validation showed extensive differences in gene expression between the mutant plants and the wild-type control, and most of the genes related to chlorophyll metabolism were down-regulated, with foldchange ranging from 0.20-0.49. Additionally, the surviving homozygous plants (Alb+⁣/+), which do not contain this mutation, were also isolated by analysing the phenotype of their self-pollinated progeny. The net photosynthesis rate and light saturation point of Alb+⁣/+ were higher than those of heterozygous (Alb+⁣/-) plants. Additionally, the Alb+⁣/+ plants were more tolerant to drought conditions than the Alb+⁣/- plants, suggesting that a heterozygous Alb- mutation is sufficient to negatively affect photosynthetic efficiency and drought tolerance. The albino mutation negatively affects photosynthetic efficiency and drought tolerance, and homozygous mutation is required for the characteristic albino phenotype. This work highlights the link between albino mutation, photosynthetic pigment metabolism and drought sensitivity in daylily.

Conformational variability of cyanobacterial ChlI, the AAA+ motor of magnesium chelatase involved in chlorophyll biosynthesis.

Photosynthesis is an essential life process that relies on chlorophyll. In photosynthetic organisms, chlorophyll synthesis involves multiple steps and depends on magnesium chelatase. This enzyme complex is responsible for inserting magnesium into the chlorophyll precursor, but the molecular mechanism of this process is not fully understood. By using cryogenic electron microscopy and conducting functional analyses, we have discovered that the motor subunit ChlI of magnesium chelatase undergoes conformational changes in the presence of ATP. Our findings offer new insights into how energy is transferred from ChlI to the other components of magnesium chelatase. This information significantly contributes to our understanding of the initial step in chlorophyll biosynthesis and lays the foundation for future studies on the entire process of chlorophyll production.

Salt Stress-Induced Modulation of Porphyrin Biosynthesis, Photoprotection, and Antioxidant Properties in Rice Plants (Oryza sativa).

Salt stress disrupts cellular ion homeostasis and adversely impacts plant growth and productivity. We examined the regulatory mechanisms of porphyrin biosynthesis, photoprotection, and antioxidant properties in salt-stressed rice seedlings. In response to 150 mM NaCl, the rice seedlings exhibited dehydration, reduced relative water content, and increased levels of conductivity, malondialdehyde, and H2O2. The expression levels of the salt-stress-responsive genes NHX1, SOS1, and MYB drastically increased after NaCl treatment. The seedlings grown under NaCl stress displayed declines in Fv/Fm, ΦPSII, rETRmax, and photochemical quenching but increases in nonphotochemical quenching (NPQ) and the expression of genes involved in zeaxanthin formation, BCH, and VDE. Under salt stress conditions, levels of chlorophyll precursors significantly decreased compared to controls, matching the downregulation of CHLD, CHLH, CHLI, and PORB. By contrast, NaCl treatment led to increased heme content at 24 h of treatment and significant upregulations of FC2, HO1, and HO2 compared to controls. Salt-stressed seedlings also increased their expression of CATs (catalases) and APXs (ascorbate peroxidases) as well as the activities of superoxide dismutase, CAT, APX, and peroxidase. Our results indicate that chlorophyll and heme biosynthesis involve the protective strategies for salt stress alleviation through photoprotection by the scavenging of chlorophyll precursors and NPQ as well as activating antioxidant enzymes.

Polystyrene microplastic attenuated the toxic effects of florfenicol on rice (Oryza sativa L.) seedlings in hydroponics: From the perspective of oxidative response, phototoxicity and molecular metabolism

Antibiotics and microplastics (MPs) are two emerging pollutants in agroecosystems, however the effects of co-exposure to antibiotics and MPs remain unclear. The toxicity of florfenicol (FF) and polystyrene microplastics (PS-MPs) on rice seedlings was investigated. FF and PS-MPs caused colloidal agglomeration, which changed the environmental behavior of FF. FF inhibited rice growth and altered antioxidant enzyme (superoxide dismutase, peroxidase, and catalase) activities, leading to membrane lipid peroxidation; impaired photosynthetic systems, decreased photosynthetic pigments (Chlorophyll a, Chlorophyll b, and carotene), chlorophyll precursors (Proto IX, Mg-Proto IX, and Pchlide), photosynthetic and respiratory rates. The key photosynthesis related genes (PsaA, PsaB, PsbA, PsbB, PsbC, and PsbD) were significantly down-regulated. The ultrastructure of mesophyll cells was destroyed with chloroplast swelling, membrane surface blurring, irregular thylakoid lamellar structure, and number of peroxisomes increased. PS-MPs mitigated FF toxicity, and the IBR index values showed that 10 mg∙L−1 PS-MPs were more effective. Metabolomic analysis revealed that the abundance of metabolites and metabolic pathways were altered by FF, was greater than the combined "MPs-FF" contamination. The metabolism of amino acids, sugars, and organic acids were severely interfered. Among these, 15 metabolic pathways were significantly altered, with the most significant effects on phenylalanine metabolism and the citric acid cycle (p < 0.05).

Methyl jasmonate-induced senescence results in alterations in the status of chlorophyll precursors and enzymatic antioxidants in rice plants

We examined the control of chlorophyll biosynthesis and protective mechanisms during leaf senescence induced by methyl jasmonate (MeJA). After MeJA treatment, rice plants displayed evidence of great oxidative stress regarding senescence symptoms, disruption of membrane integrity, H2O2 production, and decreased chlorophyll content and photosynthetic efficiency. After 6 h of MeJA treatment, plants greatly decreased not only their levels of chlorophyll precursors, including protoporphyrin IX (Proto IX), Mg-Proto IX, Mg-Proto IX methylester, and protochlorophyllide, but also the expression levels of the chlorophyll biosynthetic genes CHLD, CHLH, CHLI, and PORB, with the greatest decreases at 78 h. MeJA-treated plants showed a noticeable degradation of light-harvesting chlorophyll-binding proteins (LHCB) at 78 h after MeJA treatment but began to downregulate expression of LHCB at 6 h. Photoprotection, as indicated by nonphotochemical quenching, slightly increased only at 6 h after MeJA treatment. In parallel to the increased activities of superoxide dismutase, catalase (CAT), ascorbate peroxidase (APX), and peroxidase, MeJA-treated plants responded to senescence by markedly upregulating the expression of APX and CAT. Our study demonstrates that rice plants developed protective mechanisms for mitigating oxidative stress by scavenging phototoxic chlorophyll precursors and activating enzymatic antioxidant responses during MeJA-induced senescence.

Identification of Green-Revertible Yellow 3 (GRY3), encoding a 4-hydroxy-3-methylbut-2-enyl diphosphate reductase involved in chlorophyll synthesis under high temperature and high light in rice

Chlorophyll, a green pigment in photosynthetic organisms, is generated by two distinct biochemical pathways, the tetrapyrrole biosynthetic pathway (TBP) and the methylerythritol 4-phosphate (MEP) pathway. MEP is one of the pathways for isoprenoid synthesis in plants, with 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (HDR) catalyzing its last step. In this study, we isolated a green-revertible yellow leaf mutant gry3 in rice and cloned the GRY3 gene, which encodes a HDR participating in geranylgeranyl diphosphate (GGPP) biosynthesis in chloroplast. A complementation experiment confirmed that a missense mutation (C to T) in the fourth exon of LOC_Os03g52170 causes the gry3 phenotype. Under high temperature and high light, transcript and protein abundances of GRY3 were reduced in the gry3 mutant. Transcriptional expression of chlorophyll biosynthesis, chloroplast development, and genes involved in photosynthesis were also affected. Excessive reactive oxygen species accumulation, cell death, and photosynthetic proteins degradation were occurred in the mutant. The content of GGPP was reduced in gry3 compared with Nipponbare, resulting in a stoichiometric imbalance of tetrapyrrolic chlorophyll precursors. These results shed light on the response of chloroplast biogenesis and maintenance in plants to high-temperature and high-light stress.

Cortical cells, xylem vessels, and chlorophyll biosynthesis improved by acetylsalicylic acid and sodium nitroprusside in peach leaves

Objective: Water and nutrients are required for plant growth and development. Transport of water and nutrients from the roots to the shoots occurs in the xylem vessel. Acetylsalicylic acid (ASA) and sodium nitroprusside (SNP) play important roles in plant growth regulation. However, limited information is known about the relationship between SNP and ASA and leaf anatomy. Therefore, the current study was performed to evaluate the hypothesis that ASA and SNP improve leaf cortex and xylem anatomy and chlorophyll biosynthesis in peach. Material and Methods: In the study, the roots of two-year-old peach (Prunus persica (L.) Batsch) cv. Rich May grafted onto GF 677 were treated with 1 mM SNP and 1 mM ASA (except control) through irrigation. One month after the treatments, many leaf histological responses and chlorophyll biosynthesis were evaluated. Results: Both treatments increased stomatal conductance compared to control. Chlorophyll biosynthesis was influenced by the treatments. SNP and ASA increased the concentrations of the chlorophyll precursors compared to control. ASA increased cortex thickness by increasing the number of cortex cell layers. Thus, ASA can affect leaf cell division. Furthermore, SNP and ASA can enhance xylem conduits width. Conclusion: Improvement in xylem conduits may help plants under stress conditions. Therefore, SNP and ASA may be used to improve nutrient and water uptake.

Identification and function analysis of yellow-leaf mutant (YX-yl) of broomcorn millet

BackgroundBroomcorn millet is highly tolerant to drought and barren soil. Changes in chlorophyll content directly affect leaf color, which subsequently leadsleading to poor photosynthetic performance and reduced crop yield. Herein, we isolated a yellow leaf mutant (YX-yl) using a forward genetics approach and evaluated its agronomic traits, photosynthetic pigment content, chloroplast ultrastructure, and chlorophyll precursors. Furthermore, the molecular mechanism of yellowing was explored using transcriptome sequencing.ResultsThe YX-yl mutant showed significantly decreased plant height and low yield. The leaves exhibited a yellow-green phenotype and poor photosynthetic capacity during the entire growth period. The content of chlorophyll a, chlorophyll b, and carotenoids in YX-yl leaves was lower than that in wild-type leaves. Chlorophyll precursor analysis results showed that chlorophyll biosynthesis in YX-yl was hindered by the conversion of porphobilinogen to protoporphyrin IX. Examination of chloroplast ultrastructure in the leaves revealed that the chloroplasts of YX-yl accumulated on one side of the cell. Moreover, the chloroplast structure of YX-yl was degraded. The inner and outer membranes of the chloroplasts could not be distinguished well. The numbers of grana and grana thylakoids in the chloroplasts were low. The transcriptome of the yellowing mutant YX-yl was sequenced and compared with that of the wild type. Nine chlorophyll-related genes with significantly different expression profiles were identified: PmUROD, PmCPO, PmGSAM, PmPBDG, PmLHCP, PmCAO, PmVDE, PmGluTR, and PmPNPT. The proteins encoded by these genes were located in the chloroplast, chloroplast membrane, chloroplast thylakoid membrane, and chloroplast matrix and were mainly involved in chlorophyll biosynthesis and redox-related enzyme regulation.ConclusionsYX-yl is an ideal material for studying pigment metabolism mechanisms. Changes in the expression patterns of some genes between YX-yl and the wild type led to differences in chloroplast structures and enzyme activities in the chlorophyll biosynthesis pathway, ultimately resulting in a yellowing phenotype in the YX-yl mutant. Our findings provide an insight to the molecular mechanisms of leaf color formation and chloroplast development in broomcorn millet.

5-Aminolevulinic acid promotes low-light tolerance by regulating chloroplast ultrastructure, photosynthesis, and antioxidant capacity in tall fescue

The vital signaling molecule 5-Aminolevulinic acid (ALA) plays critical roles in signal transduction and biological modulation under abiotic stresses. In this study, we explored the effects of exogenous ALA on low-light (LL) stress-induced photosynthesis and antioxidant system damage in tall fescue (Festuca arundinacea Schreb.) seedlings. LL stress decreased morphological index values and chlorophyll contents, while also reduced net photosynthetic rate (Pn) and the maximum quantum yield of photosystem II photochemistry (Fv/Fm). Notably, these restrictions were substantially alleviated by exogenous ALA. Moreover, the contents of chlorophyll and its synthetic precursors were significantly increased after ALA treatment. Meanwhile, ALA observably enhanced expression level of FaCHLG, FaHEMA, FaPOR, and FaCAO, which encode the chlorophyll precursors biosynthesis enzymes. Exogenous ALA repaired the damage to the chloroplast ultrastructure caused by LL stress and promoted the formation of ordered thylakoids and grana lamella. ALA also improved Rubisco activity and expression level of the photosynthetic enzyme genes FaRuBP, FaPRK, and FaGADPH. Additionally, application of exogenous ALA decreased relative electrolytic leakage and the accumulation of malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide radicals (O2∙-), and increased the gene expression levels and activity of antioxidant enzymes. The ratios of ascorbic acid (AsA) to dehydroascorbic acid (DHA) and reduced glutathione (GSH) to oxidized glutathione (GSSG) were also increased significantly by application of ALA. Furthermore, all responses could be reversed by treatment with levulinic acid (LA). Thus, these results indicated that ALA protects tall fescue from LL stress through scavenging ROS, improving photosynthetic enzyme activity levels, increasing photosynthetic pigments contents, repairing chloroplast damage, and enhancing the photosynthesis rate.

5-Aminolevulinic Acid-Induced Protoporphyrin IX Fluorescence Imaging for Tumor Detection: Recent Advances and Challenges

5-Aminolevulinic acid (5-ALA) is a natural amino acid and a precursor of heme and chlorophyll. Exogenously administered 5-ALA is metabolized into protoporphyrin IX (PpIX). PpIX accumulates in cancer cells because of the low activity of ferrochelatase, an enzyme that metabolizes PpIX to heme. High expression of 5-ALA influx transporters, such as peptide transporters 1/2, in cancer cells also enhances PpIX production. Because PpIX radiates red fluorescence when excited with blue/violet light, 5-ALA has been used for the visualization of various tumors. 5-ALA photodynamic diagnosis (PDD) has been shown to improve the tumor removal rate in high-grade gliomas and non-muscular invasive bladder cancers. However, 5-ALA PDD remains a challenge as a diagnostic method because tissue autofluorescence interferes with PpIX signals in cases where tumors emit only weak signals, and non-tumorous lesions, such as inflammatory sites, tend to emit PpIX fluorescence. Here, we review the current outline of 5-ALA PDD and strategies for improving its diagnostic applicability for tumor detection, focusing on optical techniques and 5-ALA metabolic pathways in both viable and necrotic tumor tissues.

An oxygen-sensing mechanism for angiosperm adaptation to altitude

Flowering plants (angiosperms) can grow at extreme altitudes, and have been observed growing as high as 6,400 metres above sea level1,2; however, the molecular mechanisms that enable plant adaptation specifically to altitude are unknown. One distinguishing feature of increasing altitude is a reduction in the partial pressure of oxygen (pO2). Here we investigated the relationship between altitude and oxygen sensing in relation to chlorophyll biosynthesis—which requires molecular oxygen3—and hypoxia-related gene expression. We show that in etiolated seedlings of angiosperm species, steady-state levels of the phototoxic chlorophyll precursor protochlorophyllide are influenced by sensing of atmospheric oxygen concentration. In Arabidopsis thaliana, this is mediated by the PLANT CYSTEINE OXIDASE (PCO) N-degron pathway substrates GROUP VII ETHYLENE RESPONSE FACTOR transcription factors (ERFVIIs). ERFVIIs positively regulate expression of FLUORESCENT IN BLUE LIGHT (FLU), which represses the first committed step of chlorophyll biosynthesis, forming an inactivation complex with tetrapyrrole synthesis enzymes that are negatively regulated by ERFVIIs, thereby suppressing protochlorophyllide. In natural populations representing diverse angiosperm clades, we find oxygen-dependent altitudinal clines for steady-state levels of protochlorophyllide, expression of inactivation complex components and hypoxia-related genes. Finally, A. thaliana accessions from contrasting altitudes display altitude-dependent ERFVII activity and accumulation. We thus identify a mechanism for genetic adaptation to absolute altitude through alteration of the sensitivity of the oxygen-sensing system.

SUMO E3 ligase SIZ1 connects sumoylation and reactive oxygen species homeostasis processes in Arabidopsis.

The ubiquitin-like modifying peptide SMALL UBIQUITIN-LIKE MODIFIER (SUMO) has become a known modulator of the plant response to multiple environmental stimuli. A common feature of many of these external stresses is the production of reactive oxygen species (ROS). Taking into account that SUMO conjugates rapidly accumulate in response to an external oxidative stimulus, it is likely that ROS and sumoylation converge at the molecular and regulatory levels. In this study, we explored the SUMO-ROS relationship, using as a model the Arabidopsis (Arabidopsis thaliana) null mutant of the major SUMO-conjugation enhancer, the E3 ligase SAP AND MIZ 1 (SIZ1). We showed that SIZ1 is involved in SUMO conjugate increase when primed with both exogenous and endogenous ROS. In siz1, seedlings were sensitive to oxidative stress imposition, and mutants accumulated different ROS throughout development. We demonstrated that the deregulation in hydrogen peroxide and superoxide homeostasis, but not of singlet O2 (1O2), was partially due to SA accumulation in siz1. Furthermore, transcriptomic analysis highlighted a transcriptional signature that implicated siz1 with 1O2 homeostasis. Subsequently, we observed that siz1 displayed chloroplast morphological defects and altered energy dissipation activity and established a link between the chlorophyll precursor protochlorophyllide and deregulation of PROTOCHLOROPHYLLIDE OXIDOREDUCTASE A (PORA), which is known to drive overproduction of 1O2. Ultimately, network analysis uncovered known and additional associations between transcriptional control of PORA and SIZ1-dependent sumoylation. Our study connects sumoylation, and specifically SIZ1, to the control of chloroplast functions and places sumoylation as a molecular mechanism involved in ROS homeostatic and signaling events.

Hydrogen sulfide improves tall fescue photosynthesis response to low-light stress by regulating chlorophyll and carotenoid metabolisms

Hydrogen sulfide (H2S), as a gaseous messenger molecule, plays critical roles in signal transduction and biological modulation. In the present study, the roles of H2S in regulating chlorophyll (Chl) and carotenoid (Car) contents to improve photosynthesis in tall fescue were investigated under low-light (LL) stress. Compared to control conditions, LL stress significantly reduced total biomass, net photosynthetic rate (Pn), maximal quantum yield of photosystem II (PSII) photochemistry (Fv/Fm), and the contents of Chl and Car. Under exogenous sodium hydrosulfide (NaHS, H2S donor) application, these parameters were enhanced, ultimately increasing photosynthesis. Moreover, exogenous H2S up-regulated the expression of chlorophyll biosynthesis genes while down-regulated chlorophyll degradation genes, resulting in increases in chlorophyll precursors. Components of carotenoids and expression of genes encoding biosynthesis and degradation enzymes varied similarly. Additionally, application exogenous H2S up-regulated expression of FaDES1 and FaDCD. Thus, it enhanced L-cysteine desulfhydrase 1 (DES1, EC 4.4.1.1) and D-cysteine desulfhydrase (DCD, EC 4.4.1.15) activities leading to elevated endogenous H2S. However, these responses were reversed by treatment with hypotaurine (HT, H2S scavenger). These results suggested that H2S is involved in regulating photosynthesis to improve LL tolerance via modulating Chl and Car metabolisms in tall fescue.