Light dependent formation of -aminolevulinic acid in etiolated leaves of higher plants

Supplementation of Jasmonic acid Mitigates the Damaging Effects of Arsenic Stress on Growth, Photosynthesis and Nitrogen Metabolism in Rice

Experiments were conducted to evaluate the role of exogenously applied jasmonic acid (JA; 0.1 and 0.5 µM) in alleviating the toxic effects of arsenic (As; 5 and 10 µM) stress in rice. Plants treated with As showed considerable decline in growth attributes like height, fresh and dry weight of plant. Arsenic stress reduced the content of δ-amino livulenic acid (δ-ALA), glutamate 1-semialdehyde (GSA), total chlorophylls and carotenoids, with more reduction evident at higher (10 µM) As concentrations, however exogenously supplied JA alleviated the decline to considerable extent. Arsenic stress mediated decline in photosynthetic gas exchange parameters, Fv/Fm (PSII activity) and Rubisco activity was alleviated by the exogenous treatment of JA. Arsenic stress caused oxidative damage which was evident as increased lipid peroxidation, lipoxygenase activity and hydrogen peroxide concentrations however, JA treatment declined these parameters. Treatment of JA improved the activity of nitrate reductase and glutamate synthase under unstressed conditions and also alleviated the decline triggered by As stress. Activity of antioxidant enzymes assayed increased due to As stress, and the supplementation of JA caused further increase in their activities. Moreover, the content of proline, free amino acids and total phenols increased significantly due to JA application under stressed and unstressed conditions. Treatment of JA increased the content of nitrogen and potassium while as reduced As accumulation significantly.

Alleviation of Adverse Effects of Drought Stress on Growth and Nitrogen Metabolism in Mungbean (Vigna radiata) by Sulphur and Nitric Oxide Involves Up-Regulation of Antioxidant and Osmolyte Metabolism and Gene Expression

The influence of drought induced by polyethylene glycol (PEG) and the alleviatory effect of nitric oxide (50 µM) and sulphur (S, 1 mM K2SO4) were studied in Vigna radiata. Drought stress reduced plant height, dry weight, total chlorophylls, carotenoids and the content of nitrogen, phosphorous, potassium and sulphur. The foliar applications of NO and sulphur each individually alleviated the decline, with a greater alleviation observed in seedlings treated with both NO and sulphur. The reduction in intermediates of chlorophyll synthesis pathways and photosynthesis were alleviated by NO and sulphur. Oxidative stress was evident through the increased hydrogen peroxide, superoxide and activity of lipoxygenase and protease which were significantly assuaged by NO, sulphur and NO + sulphur treatments. A reduction in the activity of nitrate reductase, glutamine synthetase and glutamate synthase was mitigated due to the application of NO and the supplementation of sulphur. The endogenous concentration of NO and hydrogen sulphide (HS) was increased due to PEG; however, the PEG-induced increase in NO and HS was lowered due to NO and sulphur. Furthermore, NO and sulphur treatments to PEG-stressed seedlings further enhanced the functioning of the antioxidant system, osmolytes and secondary metabolite accumulation. Activities of γ-glutamyl kinase and phenylalanine ammonia lyase were up-regulated due to NO and S treatments. The treatment of NO and S regulated the expression of the Cu/ZnSOD, POD, CAT, RLP, HSP70 and LEA genes significantly under normal and drought stress. The present study advocates for the beneficial use of NO and sulphur in the mitigation of drought-induced alterations in the metabolism of Vigna radiata.

Alleviation of arsenic toxicity in pepper plants by aminolevulinic acid and heme through modulating its sequestration and distribution within cell organelles

Aminolevulinic acid (ALA) is essential for chlorophyll and heme synthesis. However, whether heme interacts with ALA to elicit antioxidants in arsenic (As)-exposed plants is still unknown. ALA was applied daily to pepper plants for 3 days prior to beginning As stress (As-S). Then, As-S was initiated for 14 days by employing sodium hydrogen arsenate heptahydrate (0.1 mM AsV). Arsenic treatment decreased photosynthetic pigments (chl a by 38% and chl b by 28%), biomass by 24%, and heme by 47% content, but it elevated contents of malondialdehyde (MDA) by 3.3-fold, hydrogen peroxide (H₂O₂) by 2.3-fold, glutathione (GSH), methylglyoxal (MG), and phytochelatins (PCs) and electrolyte leakage (EL) by 2.3-fold along with enhanced subcellular As concentration in the pepper plant's roots and leaves. The supplementation of ALA to the As-S-pepper seedlings enhanced the amount of chlorophyll, heme content, and antioxidant enzyme activity as well as plant growth, while it reduced the levels of H₂O₂, MDA, and EL. ALA boosted GSH and phytochelates (PCs) in the As-S-seedlings by controlling As sequestration and rendering it harmless. The addition of ALA enhanced the amount of As that accumulated in the root vacuoles and reduced the poisonousness of the soluble As in the vacuoles. The ALA treatment facilitated the deposition and fixation of As in the vacuoles and cell walls, thereby reducing the transport of As to other cell organelles. This mechanism may have contributed to the observed decrease in As accumulation in the leaves. The administration of 0.5 mM hemin (H) (a source of heme) significantly enhanced ALA-induced arsenic stress tolerance. Hemopexin (Hx, 0.4 μg L^-1), a heme scavenger, was treated with the As-S plants along with ALA and ALA + H to observe if heme was a factor in ALA's increased As-S tolerance. Heme synthesis/accumulation in the pepper plants was reduced by Hx, which counteracted the positive effects of ALA. Supplementation of H along with ALA + Hx reversed the negative effects of Hx, demonstrating that heme is required for ALA-induced seedling As-S tolerance.

5-Aminolevulinic Acid Induces Chromium [Cr(VI)] Tolerance in Tomatoes by Alleviating Oxidative Damage and Protecting Photosystem II: A Mechanistic Approach

Chromium [Cr(VI)] pollution is a major environmental risk, reducing crop yields. 5-Aminolevunic acid (5-ALA) considerably improves plant abiotic stress tolerance by inducing hydrogen peroxide (H₂O₂) and nitric oxide (NO) signalling. Our investigation aimed to uncover the mechanism of tomato tolerance to Cr(VI) toxicity through the foliar application of 5-ALA for three days, fifteen days before Cr treatment. Chromium alone decreased plant biomass and photosynthetic pigments, but increased oxidative stress markers, i.e., H₂O₂ and lipid peroxidation (as MDA equivalent). Electrolyte leakage (EL), NO, nitrate reductase (NR), phytochelatins (PCs), glutathione (GSH), and enzymatic and non-enzymatic antioxidants were also increased. Foliar application of 5-ALA before Cr treatment improved plant growth and photosynthetic pigments, diminished H₂O₂, MDA content, and EL, and resulted in additional enhancements of enzymatic and non-enzymatic antioxidants, NR activity, and NO synthesis. In Cr-treated tomato seedlings, 5-ALA enhanced GSH and PCs, which modulated Cr sequestration to make it nontoxic. 5-ALA-induced Cr tolerance was further enhanced by sodium nitroprusside (SNP), a NO donor. When sodium tungstate (ST), a NR inhibitor, was supplied together with 5-ALA to Cr-treated plants, it eliminated the beneficial effects of 5-ALA by decreasing NR activity and NO synthesis, while the addition of SNP inverted the adverse effects of ST. We conclude that the mechanism by which 5-ALA induced Cr tolerance in tomato seedlings is mediated by NR-generated NO. Thus, NR and NO are twin players, reducing Cr toxicity in tomato plants via antioxidant signalling cascades.

Melatonin-mediated endogenous nitric oxide coordinately boosts stability through proline and nitrogen metabolism, antioxidant capacity, and Na+/K+ transporters in tomato under NaCl stress

The interactions between nitric oxide (NO) and melatonin in alleviating sodium chloride (NaCl) toxicity in plants are poorly comprehended. Here, the associations between the exogenous application of melatonin and endogenous NO levels in inducing tomato seedlings' defense response during NaCl toxicity were investigated. The results indicated that the application of melatonin (150 μM) increased height (23.7%) and biomass (32.2%), improved chlorophyll (a (137%) and b (92.8%)), and proline metabolisms, and reduced the contents of superoxide anion radicals (49.6%), hydrogen peroxide (31.4%), malondialdehyde (38%), and electrolyte leakage (32.6%) in 40-day-old tomato seedlings grown under NaCl (150 mM) treatment. Melatonin increased the antioxidant defense system in NaCl-stressed seedlings by increasing the activity of the antioxidant enzymes. Melatonin also improved N metabolism and endogenous NO content in NaCl-stressed seedlings by upregulating the activity of enzymes implicated in N assimilation. Furthermore, melatonin improved ionic balance and reduced Na content in NaCl-exposed seedlings by upregulating the expression of genes involved in K/Na ratio homeostasis (NHX1-4) and increasing the accumulation of mineral nutrients (P, N, Ca, and Mg). However, the addition of cPTIO (100 μM; an NO scavenger) reversed the beneficial impacts of melatonin, indicating the effective function of NO in melatonin-induced defense mechanisms in NaCl-stressed tomato seedlings. Therefore, our results revealed that melatonin improves the tolerance of tomato plants during NaCl toxicity by mediating internal NO.

Supplementation of nitric oxide and spermidine alleviates the nickel stress-induced damage to growth, chlorophyll metabolism, and photosynthesis by upregulating ascorbate-glutathione and glyoxalase cycle functioning in tomato

Experiments were conducted to evaluate the role of exogenously applied nitric oxide (NO; 50 µM) and spermidine (Spd; 100 µM) in alleviating the damaging effects of Ni (1 mM NiSO46H2O) toxicity on the growth, chlorophyll metabolism, photosynthesis, and mineral content in tomato. Ni treatment significantly reduced the plant height, dry mass, and the contents of glutamate 1-semialdehyde, δ-amino levulinic acid, prototoporphyrin IX, Mg-prototoporphyrin IX, total chlorophyll, and carotenoids; however, the application of NO and Spd alleviated the decline considerably. Supplementation of NO and Spd mitigated the Ni-induced decline in photosynthesis, gas exchange, and chlorophyll fluorescence parameters. Ni caused oxidative damage, while the application of NO, Spd, and NO+Spd significantly reduced the oxidative stress parameters under normal and Ni toxicity. The application of NO and Spd enhanced the function of the antioxidant system and upregulated the activity of glyoxalase enzymes, reflecting significant reduction of the oxidative effects and methylglyoxal accumulation. Tolerance against Ni was further strengthened by the accumulation of proline and glycine betaine due to NO and Spd application. The decrease in the uptake of essential mineral elements such as N, P, K, and Mg was alleviated by NO and Spd. Hence, individual and combined supplementation of NO and Spd effectively alleviates the damaging effects of Ni on tomato.

Root Exposure to 5-Aminolevulinic Acid (ALA) Affects Leaf Element Accumulation, Isoprene Emission, Phytohormonal Balance, and Photosynthesis of Salt-Stressed Arundo donax

Arundo donax has been recognized as a promising crop for biomass production on marginal lands due to its superior productivity and stress tolerance. However, salt stress negatively impacts A. donax growth and photosynthesis. In this study, we tested whether the tolerance of A. donax to salinity stress can be enhanced by the addition of 5-aminolevulinic acid (ALA), a known promoter of plant growth and abiotic stress tolerance. Our results indicated that root exposure to ALA increased the ALA levels in leaves along the A. donax plant profile. ALA enhanced Na⁺ accumulation in the roots of salt-stressed plants and, at the same time, lowered Na⁺ concentration in leaves, while a reduced callose amount was found in the root tissue. ALA also improved the photosynthetic performance of salt-stressed apical leaves by stimulating stomatal opening and preventing an increase in the ratio between abscisic acid (ABA) and indol-3-acetic acid (IAA), without affecting leaf methanol emission and plant growth. Supply of ALA to the roots reduced isoprene fluxes from leaves of non-stressed plants, while it sustained isoprene fluxes along the profile of salt-stressed A. donax. Thus, ALA likely interacted with the methylerythritol 4-phosphate (MEP) pathway and modulate the synthesis of either ABA or isoprene under stressful conditions. Overall, our study highlights the effectiveness of ALA supply through soil fertirrigation in preserving the young apical developing leaves from the detrimental effects of salt stress, thus helping of A. donax to cope with salinity and favoring the recovery of the whole plant once the stress is removed.

Natural 5-Aminolevulinic Acid: Sources, Biosynthesis, Detection and Applications

5-Aminolevulinic acid (5-ALA) is the key precursor for the biosynthesis of tetrapyrrole compounds, with wide applications in medicine, agriculture and other burgeoning fields. Because of its potential applications and disadvantages of chemical synthesis, alternative biotechnological methods have drawn increasing attention. In this review, the recent progress in biosynthetic pathways and regulatory mechanisms of 5-ALA synthesis in biological hosts are summarized. The research progress on 5-ALA biosynthesis via the C4/C5 pathway in microbial cells is emphasized, and the corresponding biotechnological design strategies are highlighted and discussed in detail. In addition, the detection methods and applications of 5-ALA are also reviewed. Finally, perspectives on potential strategies for improving the biosynthesis of 5-ALA and understanding the related mechanisms to further promote its industrial application are conceived and proposed.

Effects of polyethylene terephthalate (PET) microplastics and acid rain on physiology and growth of Lepidium sativum

This study evaluated the chronic toxicity (30 days) of different sizes of polyethylene terephthalate (PET) microplastics (60-3000 μm) provided alone or in combination with acid rain, on garden cress (Lepidium sativum). Both biometrical and physiological traits have been evaluated: i) percentage inhibition of seed germination, plant height, leaf number and fresh biomass production; ii) oxidative stress responses (hydrogen peroxide; ascorbic acid and glutathione production); iii) impairment in photosynthetic machinery in term of pigments production; iv) aminolevulinic acid and proline production. Results highlighted that different sizes of PET, alone or in combination with acid rain, are able to negatively affect both biometrical and physiological plant traits. In particular, the lower size of microplastics is able to negatively affect growth and development, as well as to trigger the oxidative burst. Regarding the pigments production, PET coupled with acid rain, induced a higher production of Chl-b, and an inhibition of aminolevulinic acid.

Improving growth and photosynthetic performance of drought stressed tomato by application of nano-organic fertilizer involves up-regulation of nitrogen, antioxidant and osmolyte metabolism

Organic fertilizer usage is been introduced into agricultural practices for preventing the damaging effects of chemical fertilizers. Present study investigated the beneficial role of organic fertilizer (nano-vermicompost) on the growth, oxidative stress parameters, antioxidant and nitrogen metabolism, osmolyte accumulation and mineral elements in tomato under drought stress. Drought stress resulted in reduced growth and biomass accumulation by triggering oxidative stress due to excess accumulation of reactive oxygen species (ROS) and reduced mineral uptake. Application of nano-vermicompost proved significantly beneficial in improving growth and mitigating the drought induced growth decline. Nano-vermicompost increased growth and dry matter content and ameliorated the decline in chlorophyll contents, photosynthesis and PSII activity more significantly at higher concentration (100 mg kg-1 soil). ROS accumulation was significantly reduced by nano-vermicompost application thereby enhancing the membrane stability under normal as well as drought conditions. Furthermore, lipid peroxidation and activities of protease and lypoxygenase were significantly reduced. Drought up-regulated antioxidant system and application of nano-vermicompost further enhanced the activities of antioxidant enzymes and the contents of non-enzymatic antioxidant components. Accumulation of osmolytes including proline, glycine betaine and sugars increased significantly due to nano-vermicompost application. Besides, decline in the activity of nitrate reductase and content of essential mineral elements like nitrogen, potassium and phosphorous was also ameliorated by nano-vermicompost application.

Physiological responses of garden cress (L. sativum) to different types of microplastics

In this study, for the first time, acute and chronic toxicity caused by four different kinds of microplastics: polypropylene (PP), polyethylene (PE), polyvinylchloride (PVC), and a commercial mixture (PE + PVC) on Lepidium sativum were evaluated. Parameters considered were: i) biometric parameters (e.g. percentage inhibition of seed germination, plant height, leaf number and fresh biomass productions); and ii) oxidative stress (e.g. levels of hydrogen peroxide, glutathione, and ascorbic acid). On plants exposed to chronic stress chlorophylls, carotenoids, aminolaevulinic acid, and proline productions were, also, evaluated. PVC resulted the most toxic than other plastic materials tested. This study represents the first paper highlighting microplastics are able to produce oxidative burst in tested plants and could represent an important starting point for future researches on biochemical effects of microplastic in terrestrial environments such as agroecosystems.

Spermine application alleviates salinity induced growth and photosynthetic inhibition in Solanum lycopersicum by modulating osmolyte and secondary metabolite accumulation and differentially regulating antioxidant metabolism

Influence of exogenously applied spermine (Spm) on growth and salinity stress tolerance in tomato was investigated. Salinity reduced growth, chlorophyll synthesis and mineral uptake leading to significant reduction in photosynthesis, however Spm application proved beneficial in alleviating the decline to considerable extent. Applied Spm improved nitrate reductase activity, δ-amino levulinic acid content and gas exchange parameters more apparently at 100 μM than 50 μM concentrations. Spm application enhanced the accumulation of compatible osmolytes including proline, glycine betaine and sugars leading to greater tissue water content and photosynthesis. Salinity stress induced oxidative effects were mitigated by Spm treatment reflected interms of reduced accumulation of reactive oxygen species and the activities of protease and lipoxygenase, hence leading to membrane strengthening and protection of their function. Differential influence of exogenous Spm was evident on the functioning of antioxidant system with SOD, GR and APX activities much higher in Spm treated seedlings than CAT and DHAR. Increased synthesis of GSH, AsA and tocopherol in Spm treated seedlings was obvious thereby helping in maintaining the redox homeostasis and the enzymatic antioxidant functioning. Interestingly Spm application maintained the nitric oxide levels higher than control under normal condition while as lowered its concentrations in salinity stressed seedlings depicting existence of probable interaction. Activities of polyamine metabolizing enzymes was up-regulated and the accumulation of secondary metabolites including phenols and flavonoids also increased due to Spm application. Further studies are required to understand the mechanisms clearly.

5-aminolevulinic acid improves salt tolerance mediated by regulation of tetrapyrrole and proline metabolism in Brassica napus L. seedlings under NaCl stress

5-aminolevulinic acid (ALA), a key biosynthetic precursor of tetrapyrroles, is vital for plant growth and adaptation to stress environments. Although exogenous ALA could enhance photosynthesis and biomass accumulation in plants under stress conditions, the underlying physiological and molecular mechanisms governed by ALA in promoting salt tolerance in Brassica napus L. are not yet clearly understood. In the present study, exogenous ALA with the concentration of 30 mg L^-1 was applied to the leaves of B. napus seedlings subjected to 200 mM NaCl. The results showed that NaCl stress decreased the photosynthesis, biomass accumulation, and levels of chlorophyll and heme with the reduction of the concentrations of intermediates including ALA, protoporphyrin IX (Proto IX), Mg-Proto IX, and Pchlide in the tetrapyrrole (chlorophyll and heme) biosynthetic pathway. The transcript levels of genes encoding ALA-associated enzymes and genes encoding Mg-chelatase in the chlorophyll biosynthetic branch were down-regulated, while the expression levels of genes encoding Fe-chelatase in the heme branch were not significantly altered by NaCl stress. Foliar application with ALA enhanced the aboveground biomass, net photosynthetic rate, activities of antioxidant enzymes, accumulation of chlorophyll and heme, and concentrations of intermediates related to chlorophyll and heme biosynthesis in B. napus under 200 mM NaCl. The expression of most genes mentioned above remained constant in ALA-treated plants in comparison with non-ALA-treated plants under NaCl stress. Additionally, exogenous ALA synchronously induced the proline concentration and up-regulated the expression of genes P5CS and ProDH encoding proline metabolic enzymes in the NaCl treatment. These findings suggested that ALA improved salt tolerance through promoting the accumulation of chlorophyll and heme resulting from the increase of intermediate levels in the tetrapyrrole biosynthetic pathway, along with enhancing the proline accumulation in B. napus.

ALA Inhibits ABA-induced Stomatal Closure via Reducing H2O2 and Ca(2+) Levels in Guard Cells

5-Aminolevulinic acid (ALA), a newly proved natural plant growth regulator, is well known to improve plant photosynthesis under both normal and stressful conditions. However, its underlying mechanism remains largely unknown. Stomatal closure is one of the major limiting factors for photosynthesis and abscisic acid (ABA) is the most important hormone in provoking stomatal closing. Here, we showed that ALA significantly inhibited ABA-induced stomatal closure using wild-type and ALA-overproducing transgenic Arabidopsis (YHem1). We found that ALA decreased ABA-induced H2O2 and cytosolic Ca(2+) accumulation in guard cells with stomatal bioassay, laser-scanning confocal microscopy and pharmacological methods. The inhibitory effect of ALA on ABA-induced stomatal closure was similar to that of AsA (an important reducing substrate for H2O2 removal), CAT (a H2O2-scavenging enzyme), DPI (an inhibitor of the H2O2-generating NADPH oxidase), EGTA (a Ca-chelating agent), and AlCl3 (an inhibitor of calcium channel). Furthermore, ALA inhibited exogenous H2O2- or Ca(2+)-induced stomatal closure. Taken together, we conclude that ALA inhibits ABA-induced stomatal closure via reducing H2O2, probably by scavenging, and Ca(2+) levels in guard cells. Moreover, the inhibitive effect of ALA on ABA-induced stomatal closure was further confirmed in the whole plant. Finally, we demonstrated that ALA inhibits stomatal closing, but significantly improves plant drought tolerance. Our results provide valuable information for the promotion of plant production and development of a sustainable low-carbon society.

Physiological and molecular analyses of black and yellow seeded Brassica napus regulated by 5-aminolivulinic acid under chromium stress

Brassica napus L. is a promising oilseed crop among the oil producing species. So, it is prime concern to screen the metal tolerant genotypes in order to increase the oilseed rape production through the utilization of pollutant soil regimes. Nowadays, use of plant growth regulators against abiotic stress is one of the major objectives of researchers. In this study, an attempt was carried out to analyze the pivotal role of exogenously applied 5-amenolevulinic acid (ALA) on alleviating chromium (Cr)-toxicity in black and yellow seeded B. napus. Plants of two cultivars (ZS 758 - a black seed type, and Zheda 622 - a yellow seed type) were treated with 400 μM Cr with or without 15 and 30 mg/L ALA. Results showed that exogenously applied ALA improved the plant growth and increased ALA contents; however, it decreased the Cr concentration in B. napus leaves under Cr-toxicity. Moreover, exogenous ALA reduced oxidative stress by up-regulating antioxidant enzyme activities and their related gene expression. Further, results suggested that stress responsive protein's transcript level such as HSP90-1 and MT-1 were increased under Cr stress alone in both cultivars. Exogenously applied ALA further enhanced the expression rate in both genotypes and obviously results were found in favor of cultivar ZS 758. The ultrastructural changes were observed more obvious in yellow seeded than black seeded cultivar; however, exogenously applied ALA helped the plants to recover their cell turgidity under Cr stress. The present study describes a detailed molecular mechanism how ALA regulates the plant growth by improving antioxidant machinery and related transcript levels, cellular modification as well as stress related genes expression under Cr-toxicity.

Nitric Oxide Mediates 5-Aminolevulinic Acid-Induced Antioxidant Defense in Leaves of Elymus nutans Griseb. Exposed to Chilling Stress

Nitric oxide (NO) and 5-aminolevulinic acid (ALA) are both extremely important signalling molecules employed by plants to control many aspects of physiology. In the present study, the role of NO in ALA-induced antioxidant defense in leaves of two sources of Elymus nutans Griseb. (Damxung, DX and Zhengdao, ZD) was investigated. Chilling stress enhanced electrolyte leakage, accumulation of malondialdehyde (MDA), hydrogen peroxide (H2O2) and superoxide radical in two E. nutans, which were substantially alleviated by exogenous ALA and NO application. Pretreatment with NO scavenger PTIO or NOS inhibitor L-NNA alone and in combination with ALA induced enhancements in electrolyte leakage and the accumulation of MDA, H2O2 and superoxide radical in leaves of DX and ZD exposed to chilling stress, indicating that the inhibition of NO biosynthesis reduced the chilling resistance of E. nutans and the ALA-enhanced chilling resistance. Further analyses showed that ALA and NO enhanced antioxidant defense and activated plasma membrane (PM) H+-ATPase and decreased the accumulation of ROS induced by chilling stress. A pronounced increase in nitric oxide synthase (NOS) activity and NO release by exogenous ALA treatment was found in chilling-resistant DX plants exposed to chilling stress, while only a little increase was observed in chilling-sensitive ZD. Furthermore, inhibition of NO accumulation by PTIO or L-NNA blocked the protective effect of exogenous ALA, while both exogenous NO treatment and inhibition of endogenous NO accumulation did not induce ALA production. These results suggested that NO might be a downstream signal mediating ALA-induced chilling resistance in E. nutans.

Study on salt tolerance with YHem1 transgenic canola (Brassica napus)

5-Aminolevulinic acid (5-ALA) has been suggested for improving plant salt tolerance via exogenous application. In this study, we used a transgenic canola (Brassica napus), which contained a constituted gene YHem1 and biosynthesized more 5-ALA, to study salt stress responses. In a long-term pot experiment, the transgenic plants produced higher yield under 200 mmol L(-1) NaCl treatment than the wild type (WT). In a short-term experiment, the YHem1 transformation accelerated endogenous 5-ALA metabolism, leading to more chlorophyll accumulation, higher diurnal photosynthetic rates and upregulated expression of the gene encoding Rubisco small subunit. Furthermore, the activities of antioxidant enzymes, including superoxide dismutase, guaiacol peroxidase, catalase and ascorbate peroxidase, were significantly higher in the transgenic plants than the WT, while the levels of O2 ·(-) and malondialdehyde were lower than the latter. Additionally, the Na(+) content was higher in the transgenic leaves than that in the WT under salinity, but K(+) and Cl(-) were significantly lower. The levels of N, P, Cu, and S in the transgenic plants were also significantly lower than those in the WT, but the Fe content was significantly improved. As the leaf Fe content was decreased by salinity, it was suggested that the stronger salt tolerance of the transgenic plants was related to the higher Fe acquisition. Lastly, YHem1 transformation improved the leaf proline content, but salinity decreased rather than increased it. The content of free amino acids and soluble sugars was similarly decreased as salinity increased, but it was higher in the transgenic plants than that in the WT.

Mutations in Plastidial 5-Aminolevulinic Acid Biosynthesis Genes Suppress a Pleiotropic Defect in Shoot Development of a Mitochondrial GABA Shunt Mutant in Arabidopsis

Plant developmental processes are co-ordinated with the status of cell metabolism, not only in mitochondria but also in plastids. In Arabidopsis thaliana, succinic semialdehyde (SSA), a GABA shunt metabolite, links the specific mitochondrial metabolic pathway to shoot development. To understand the mechanism of SSA-mediated development, we isolated a succinic semialdehyde dehydrogenase (ssadh) suppressor mutant, affected in its ability to catalyze SSA to succinic acid. We found that pleiotropic developmental phenotypes of ssadh are suppressed by a mutation in GLUTAMATE-1-SEMIALDEHYDE 2, 1-AMINOMUTASE 2 (GSA2), which encodes a plastidial enzyme converting glutatamate-1-semialdehyde to 5-aminolevulinic acid (5-ALA). In addition, a mutation in either HEMA1 or GSA1, two other enzymes for 5-ALA synthesis, also suppressed ssadh fully and partially, respectively. Furthermore, exogenous application of 5-ALA and SSA disturbed leaf development. These results suggest that metabolism in both mitochondria and plastids affect shoot development.

Salt-stress induced modulation of chlorophyll biosynthesis during de-etiolation of rice seedlings

Chlorophyll biosynthesis in plants is subjected to modulation by various environmental factors. To understand the modulation of the chlorophyll (Chl) biosynthesis during greening process by salt, 100-200 mM NaCl was applied to the roots of etiolated rice seedlings 12 h prior to the transfer to light. Application of 200 mM NaCl to rice seedlings that were grown in light for further 72 h resulted in reduced dry matter production (-58%) and Chl accumulation (-66%). Ionic imbalance due to salinity stress resulted in additional downregulation (41-45%) of seedling dry weight, Chl and carotenoid contents over and above that of similar osmotic stress induced by polyethylene glycol. Downregulation of Chl biosynthesis may be attributed to decreased activities of Chl biosynthetic pathway enzymes, i.e. 5-aminolevulinic acid (ALA) dehydratase (EC-2.4.1.24), porphobilinogen deaminase (EC-4.3.1.8), coproporphyrinogen III oxidase (EC-1.3.3.3), protoporphyrinogen IX oxidase (EC-1.3.3.4), Mg-protoporphyrin IX chelatase (EC-6.6.1.1) and protochlorophyllide oxidoreductase (EC-1.3.33.1). Reduced enzymatic activities were due to downregulation of their protein abundance and/or gene expression in salt-stressed seedlings. The extent of downregulation of ALA biosynthesis nearly matched with that of protochlorophyllide and Chl to prevent the accumulation of highly photosensitive photodynamic tetrapyrroles that generates singlet oxygen under stress conditions. Although, ALA synthesis decreased, the gene/protein expression of glutamyl-tRNA reductase (EC-1.2.1.70) increased suggesting it may play a role in acclimation to salt stress. The similar downregulation of both early and late Chl biosynthesis intermediates in salt-stressed seedlings suggests a regulatory network of genes involved in tetrapyrrole biosynthesis.

Young Leaf Chlorosis 2 encodes the stroma-localized heme oxygenase 2 which is required for normal tetrapyrrole biosynthesis in rice

Rice heme oxygenase 2 (OsHO2) mutants are chlorophyll deficient with distinct tetrapyrrole metabolite and transcript profiles, suggesting a potential regulatory role of the stromal-localized OsHO2 in tetrapyrrole biosynthesis. In plants, heme oxygenases (HOs) are classified into the subfamilies HO1 and HO2. HO1 are highly conserved plastid enzymes required for synthesizing the chromophore in phytochromes which mediate a number of light-regulated responses. However, the physiological and biochemical functions of HO2, which are distantly related to HO1, are not well understood, especially in crop plants. From a population of (60)Coγ-irradiated rice mutants, we identified the ylc2 (young leaf chlorosis 2) mutant which displays a chlorosis phenotype in seedlings with substantially reduced chlorophyll content. Normal leaf pigmentation is gradually restored in older plants while newly emerged leaves remain yellow. Transmission electron microscopy further revealed defective chloroplast structures in the ylc2 seedlings. Map-based cloning located the OsYLC2 gene on chromosome 3 and it encodes the OsHO2 protein. The gene identification was confirmed by complementation and T-DNA mutant analyses. Subcellular localization and chloroplast fractionation experiments indicated that OsHO2 resides in the stroma. However, recombinant enzyme assay demonstrated that OsHO2 is not a functional HO enzyme. Analysis of tetrapyrrole metabolites revealed the reduced levels of most chlorophyll and phytochromobilin precursors in the ylc2 mutant. On the other hand, elevated accumulation of 5-aminolevulinic acid and Mg-protoporphyrin IX was observed. These unique metabolite changes are accompanied by consistent changes in the expression levels of the corresponding tetrapyrrole biosynthesis genes. Taken together, our work suggests that OsHO2 has a potential regulatory role for tetrapyrrole biosynthesis in rice.

Exogenous 5-aminolevulenic acid promotes seed germination in Elymus nutans against oxidative damage induced by cold stress

The protective effects of 5-aminolevulenic acid (ALA) on germination of Elymus nutans Griseb. seeds under cold stress were investigated. Seeds of E. nutans (Damxung, DX and Zhengdao, ZD) were pre-soaked with various concentrations (0, 0.1, 0.5, 1, 5, 10 and 25 mg l⁻¹) of ALA for 24 h before germination under cold stress (5°C). Seeds of ZD were more susceptible to cold stress than DX seeds. Both seeds treated with ALA at low concentrations (0.1–1 mg l⁻¹) had higher final germination percentage (FGP) and dry weight at 5°C than non-ALA-treated seeds, whereas exposure to higher ALA concentrations (5–25 mg l⁻¹) brought about a dose dependent decrease. The highest FGP and dry weight of germinating seeds were obtained from seeds pre-soaked with 1 mg l⁻¹ ALA. After 5 d of cold stress, pretreatment with ALA provided significant protection against cold stress in the germinating seeds, significantly enhancing seed respiration rate and ATP synthesis. ALA pre-treatment also increased reduced glutathione (GSH), ascorbic acid (AsA), total glutathione, and total ascorbate concentrations, and the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR), whereas decreased the contents of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), and superoxide radical (O₂^•−) release in both germinating seeds under cold stress. In addition, application of ALA increased H⁺-ATPase activity and endogenous ALA concentration compared with cold stress alone. Results indicate that ALA considered as an endogenous plant growth regulator could effectively protect E. nutans seeds from cold-induced oxidative damage during germination without any adverse effect.

Sigma factor-mediated plastid retrograde signals control nuclear gene expression

Retrograde signalling from plastids to the nucleus is necessary to regulate the organelle's proteome during the establishment of photoautotrophy and fluctuating environmental conditions. Studies that used inhibitors of chloroplast biogenesis have revealed that hundreds of nuclear genes are regulated by retrograde signals emitted from plastids. Plastid gene expression is the source of at least one of these signals, but the number of signals and their mechanisms used to regulate nuclear gene expression are unknown. To further examine the effects of plastid gene expression on nuclear gene expression, we analyzed Arabidopsis mutants that were defective in each of the six sigma factor (SIG) genes that encode proteins utilized by plastid-encoded RNA polymerase to transcribe specific sets of plastid genes. We showed that SIG2 and SIG6 have partially redundant roles in plastid transcription and retrograde signalling to control nuclear gene expression. The loss of GUN1 (a plastid-localized pentatricopeptide repeat protein) is able to restore nuclear (but not plastid) gene expression in both sig2 and sig6, whereas an increase in heme synthesis is able to restore nuclear gene expression in sig2 mutants only. These results demonstrate that sigma factor function is the source of at least two retrograde signals to the nucleus; one likely to involve the transcription of tRNA(Glu) . A microarray analysis showed that these two signals accounted for at least one subset of the nuclear genes that are regulated by the plastid biogenesis inhibitors norflurazon and lincomycin. Together these data suggest that such inhibitors can induce retrograde signalling by affecting transcription in the plastid.

Sigma factor-mediated plastid retrograde signals control nuclear gene expression

Retrograde signalling from plastids to the nucleus is necessary to regulate the organelle's proteome during the establishment of photoautotrophy and fluctuating environmental conditions. Studies that used inhibitors of chloroplast biogenesis have revealed that hundreds of nuclear genes are regulated by retrograde signals emitted from plastids. Plastid gene expression is the source of at least one of these signals, but the number of signals and their mechanisms used to regulate nuclear gene expression are unknown. To further examine the effects of plastid gene expression on nuclear gene expression, we analyzed Arabidopsis mutants that were defective in each of the six sigma factor (SIG) genes that encode proteins utilized by plastid-encoded RNA polymerase to transcribe specific sets of plastid genes. We showed that SIG2 and SIG6 have partially redundant roles in plastid transcription and retrograde signalling to control nuclear gene expression. The loss of GUN1 (a plastid-localized pentatricopeptide repeat protein) is able to restore nuclear (but not plastid) gene expression in both sig2 and sig6, whereas an increase in heme synthesis is able to restore nuclear gene expression in sig2 mutants only. These results demonstrate that sigma factor function is the source of at least two retrograde signals to the nucleus; one likely to involve the transcription of tRNA(Glu) . A microarray analysis showed that these two signals accounted for at least one subset of the nuclear genes that are regulated by the plastid biogenesis inhibitors norflurazon and lincomycin. Together these data suggest that such inhibitors can induce retrograde signalling by affecting transcription in the plastid.

Modulation of chlorophyll biosynthesis by water stress in rice seedlings during chloroplast biogenesis

To understand the impact of water stress on the greening process, water stress was applied to 6-day-old etiolated seedlings of a drought-sensitive cultivar of rice (Oryza sativa), Pusa Basmati-1 by immersing their roots in 40 mm polyethylene glycol (PEG) 6000 (-0.69 MPa) or 50 mm PEG 6000 (-1.03 MPa) dissolved in half-strength Murashige and Skoog (MS)-nutrient-solution, 16 h prior to transfer to cool-white-fluorescent + incandescent light. Chlorophyll (Chl) accumulation substantially declined in developing water-stressed seedlings. Reduced Chl synthesis was due to decreased accumulation of chlorophyll biosynthetic intermediates, that is, glutamate-1-semialdehyde (GSA), 5-aminolevulinic acid, Mg-protoporphyrin IX monomethylester and protochlorophyllide. Although 5-aminolevulinic acid synthesis decreased, the gene expression and protein abundance of the enzyme responsible for its synthesis, GSA aminotransferase, increased, suggesting its crucial role in the greening process in stressful environment. The biochemical activities of Chl biosynthetic enzymes, that is, 5-aminolevulinic acid dehydratase, porphobilinogen deaminase, coproporphyrinogen III oxidase, porphyrinogen IX oxidase, Mg-chelatase and protochlorophyllide oxidoreductase, were down-regulated due to their reduced protein abundance/gene expression in water-stressed seedlings. Down-regulation of protochlorophyllide oxidoreductase resulted in impaired Shibata shift. Our results demonstrate that reduced synthesis of early intermediates, that is, GSA and 5-aminolevulinic acid, could modulate the gene expression of later enzymes of Chl biosynthesis pathway.

Expression of yeast Hem1 controlled by Arabidopsis HemA1 promoter enhances leaf photosynthesis in transgenic tobacco

A gene encoding aminolevulinate synthase (ALA-S) in yeast (Saccharomyces cerevisiae YHem1) was introduced into the genome of tobacco (Nicoliana tabacum) under the control of Arabidopsis thaliana HemA1 gene promoter (AtHemA1 P). All transgenic lines transcribed the YHem1 gene, especially under light condition. The capacity to synthesize ALA and therefore chlorophyll was increased in transformed plants. Determination of gas exchange suggested that transgenic plants had significantly higher level of net photosynthetic rate (P ( n )), stomatal conductance (G ( s )) and transpiration rate (T ( r )), compared to the wild type (WT). Analysis with a modulated chlorophyll fluorometer demonstrated that the genetic transformation also caused a significant increase in photochemical efficiency of PSII ([Formula: see text]), actual photochemical efficiency (Ф ( PSII )), photochemical quenching (qP), electron transfer rate (ETR) and the energy proportion in photochemistry (Pc), but decrease in proportion in heat dissipation (Hd). Chlorophyll-a fast fluorescence measurement and JIP-test indicated that photosynthetic performance index on cross section basis (PI ( CS )) and electron transport flux (ET ( o ) /CS) of transgenic tobacco were increased remarkably. And the probability that a trapped exciton can move a electron into the electron transport chain beyond Q ( A ) (-) (Ψ ( o )) and the density of active reaction centers (RC/CS) were also increased obviously in transgenic tobacco. These results imply that transgenic tobacco plants expressing YHem1 gene had higher photosynthetic capacity and energy conversion efficiency than the WT plants.

Expression of yeast Hem1 gene controlled by Arabidopsis HemA1 promoter improves salt tolerance in Arabidopsis plants

5-Aminolevulinate (ALA) is well-known as an essential biosynthetic precursor of all tetrapyrrole compounds, which has been suggested to improve plant salt tolerance by exogenous application. In this work, the gene encoding aminolevulinate synthase (ALA-S) in yeast (Saccharomyces cerevisiae Hem1) was introduced into the genome of Arabidopsis controlled by the Arabidopsis thaliana HemA1 gene promoter. All transgenic lines were able to transcribe the YHem1 gene, especially under light condition. The chimeric protein (YHem1-EGFP) was found co-localizing with the mitochondria in onion epidermal cells. The transgenic Arabidopsis plants could synthesize more endogenous ALA with higher levels of metabolites including chlorophyll and heme. When the T(2) homozygous seeds were cultured under NaCl stress, their germination and seedling growth were much better than the wild type. Therefore, introduction of ALA-S gene led to higher level of ALA metabolism with more salt tolerance in higher plants.

Mechanism of downregulation of photosystem I content under high-light conditions in the cyanobacterium Synechocystis sp. PCC 6803

Downregulation of photosystem I (PSI) content is an essential process for cyanobacteria to grow under high-light (HL) conditions. In a pmgA (sll1968) mutant of Synechocystis sp. PCC 6803, the levels of PSI content, chlorophyll and transcripts of the psaAB genes encoding reaction-centre subunits of PSI could not be maintained low during HL incubation, although the causal relationship among these phenotypes remains unknown. In this study, we modulated the activity of psaAB transcription or that of chlorophyll synthesis to estimate their contribution to the regulation of PSI content under HL conditions. Analysis of the psaAB-OX strain, in which the psaAB genes were overexpressed under HL conditions, revealed that the amount of psaAB transcript could not affect PSI content by itself. Suppression of chlorophyll synthesis by an inhibitor, laevulinic acid, in the pmgA mutant revealed that chlorophyll availability could be a determinant of PSI content under HL. It was also suggested that chlorophyll content under HL conditions is mainly regulated at the level of 5-aminolaevulinic acid synthesis. We conclude that, upon the shift to HL conditions, activities of psaAB transcription and of 5-aminolaevulinic acid synthesis are strictly downregulated by regulatory mechanism(s) independent of PmgA during the first 6 h, and then a PmgA-mediated regulatory mechanism becomes active after 6 h onward of HL incubation to maintain these activities at a low level.

Gabaculine does not inhibit cytokinin-stimulated biosynthesis of chlorophyll in Pinus nigra seedlings in the dark

Chlorophyll (Chl) accumulation was monitored during black pine (Pinus nigra L.) seed germination for 14 days in the light and in the dark in the presence of gabaculine (GAB) and cytokinin in order to elucidate the regulation of gymnosperm seedling greening in the dark, primarily at the level of aminolevulinic acid formation. In the light, GAB inhibited chlorophyll accumulation in a manner dependent on concentration and developmental stage, and in the dark it showed no effect. Cytokinin, 10(-5) M benzyl adenine (BA) partly overcame GAB-induced inhibition in the light, mainly during earlier developmental stages. In the seedlings grown in the dark, an equal quantity of Chl accumulated in the presence of cytokinin with and without GAB and it was approximately 20-40% higher than in the control seedlings or in the seedlings grown only in the presence of GAB. 5-Amino-levulinic acid (ALA) synthesis was equal in the light and in the dark in seedlings of the same age and seedlings treated with GAB grown in the dark. In the light, GAB inhibited ALA synthetic activity. The results indicate that ALA synthesis is not a rate-limiting step within Chl biosynthesis in pine seedlings grown in the dark.

Temperature-stress-induced impairment of chlorophyll biosynthetic reactions in cucumber and wheat

Chlorophyll (Chl) biosynthesis in chill (7 degreesC)- and heat (42 degreesC)-stressed cucumber (Cucumis sativus L. cv poinsette) seedlings was affected by 90 and 60%, respectively. Inhibition of Chl biosynthesis was partly due to impairment of 5-aminolevulinic acid biosynthesis both in chill- (78%) and heat-stress (70%) conditions. Protochlorophyllide (Pchlide) synthesis in chill- and heat-stressed seedlings was inhibited by 90 and 70%, respectively. Severe inhibition of Pchlide biosynthesis in chill-stressed seedlings was caused by inactivations of all of the enzymes involved in protoporphyrin IX (Proto IX) synthesis, Mg-chelatase, and Mg-protoporphyrin IX monoester cyclase. In heat-stressed seedlings, although 5-aminolevulinic acid dehydratase and porphobilinogen deaminase were partially inhibited, one of the porphyrinogen-oxidizing enzymes, uroporphyrinogen decarboxylase, was stimulated and coproporphyrinogen oxidase and protoporphyrinogen oxidase were not substantially affected, which demonstrated that protoporphyrin IX synthesis was relatively more resistant to heat stress. Pchlide oxidoreductase, which is responsible for phototransformation of Pchlide to chlorophyllide, increased in heat-stress conditions by 46% over that of the control seedlings, whereas it was not affected in chill-stressed seedlings. In wheat (Triticum aestivum L. cv HD2329) seedlings porphobilinogen deaminase, Pchlide synthesis, and Pchlide oxidoreductase were affected in a manner similar to that of cucumber, suggesting that temperature stress has a broadly similar effect on Chl biosynthetic enzymes in both cucumber and wheat.

Photoreduction of protochlorophyllide and its relationship to delta-aminolaevulinic acid synthesis in the leaves of dark-grown barley (Hordeum vulgare) seedlings

The photoreduction of protochlorophyllide (Pchl) in dark-grown leaves of barley (Hordeum vulgare) brings about the synthesis of delta-aminolaevulinic acid (AmLev). Manipulation of the Pchl level in the leaves by incubation in AmLev indicated that the production of AmLev was intimately related to the state of the Pchl reductase ternary complex. Free Pchl reductase that is unassociated with substrate/product appeared at first to be essential for the photoinduction of AmLev synthesis. Experiments on the photoreduction of Pchl in dark-grown leaves exposed to low-energy red-light, however, showed that photoreduction and AmLev synthesis would occur when the Pchl reductase, together with substrate, was maintained at relatively high endogenous concentration. Under such conditions the availability of free reductase protein would be negligible. An alternative scheme is presented, therefore, that can explain many, if not all, of the observations on AMLev synthesis and its close relationship to Pchl reduction, and which is based on a common supply of NADPH for the reduction of glutamate to AmLev and the synthesis of chorophyll(-ide).

Regulation of delta-aminolaevulinic acid synthesis and protochlorophyllide regeneration in the leaves of dark-grown barley (Hordeum vulgare) seedlings

Laevulinic acid (Lev) was used to control the rate of protocholorophyllide (PChl) regeneration in the leaves of dark-grown seedlings of barley (Hordeum vulgare) after a brief light treatment. In the leaves given Lev, at concentrations that severely block the resynthesis of protochlorophyllide, there was a massive overproduction of delta-aminolaevulinic acid (AmLev) that was well in excess of that required for the regeneration of PChl observed in the control leaves. Lev, at low concentrations, slightly delayed regeneration and held up, rather than inhibited, the utilization of the AmLev, which accumulated in the tissues. The overproduction and uncontrolled formation of AmLev also occurred in dark-grown leaves treated with a high concentration of Lev and given a light treatment of just sufficient energy to photoreduce only small quantities of the endogenous PChl. Experiments in which a high level of free PChl was induced by incubating the leaves in AmLev indicated that the active species of PChl was that associated with, and bound to, the PChl reductase protein. The results strongly demonstrate a close relationship between the PChl-protein complex and the ability of the leaves to synthesize AmLev.

Effect of levulinic acid on pigment biosynthesis in Agmenellum quadruplicatum

When levulinic acid was added to a growing culture of the cyanobacterium (blue-green alga) Agmenellum quadruplicatum PR-6, delta-aminoelevulinic acid accumulated in the medium and chlorophyll a synthesis and cell growth were inhibited, but there was a small amount of c-phycocyanin synthesis. The amount of delta-aminolevulinic acid produced in the treated culture did not fully account for the amount of pigment synthesized in the untreated control. Levulinic acid and either sodium nitrate or ammonium chloride were added to nitrogen-starved cultures of PR-6, and delta-aminolevulinic acid production and chlorophyll a and c-phycocyanin content were monitored. When ammonium chloride was added as a nitrogen source after nitrogen starvation, the cells recovered more rapidly than when sodium nitrate was added as a nitrogen source. In cultures recovering from nitrogen starvation, synthesis of c-phycocyanin occurred before synthesis of chlorophyll a.

Biosynthesis of delta-aminolevulinic acid by blue-green algae (cyanobacteria)

When levulinic acid, a competitive inhibitor of delta-aminolevulinic acid dehydratase, was added to growing cultures of blue-green algae (cyanobacteria), delta-aminolevulinic acid was excreted into the medium and cell growth was inhibited.

Biosynthetic events required for lag elimination in chlorophyll synthesis in Euglena

Levulinic acid, a competitive inhibitor of δ aminolevulinic acid dehydratase, cycloheximide, an inhibitor of translation on 89s cytoplasmic ribosomes, and chloramphenicol, an inhibitor of translation on 68s chloroplast ribosomes, are reversible inhibitors of light induced chlorophyll synthesis in resting Euglena gracilis Klebs. When dark grown resting cells are preilluminated for 2 h followed by darkness for 12 h prior to exposure to continuous light, the usual lag period in chlorophyll formation is eliminated. If cycloheximide, chloramphenicol, or levulinic acid are present during either the preillumination period or the subsequent dark period, the lag is reestablished. Only the very beginning of the dark period is sensitive to cycloheximide but the dark period is less sensitive to levulinic acid than is the light period. Exposure of preilluminated cells to cycloheximide or levulinic acid at the time of exposure to continuous illumination completely inhibits chlorophyll synthesis indicating that the potential for rapid chlorophyll synthesis generated by preillumination and a dark period does not result simply from the accumulation of porphyrin precursors. Preillumination has little effect on the development of the capacity to fix CO2 photosynthetically. These results indicate that the control of chlorophyll formation is more complex than in higher plants and a model based on the formation of certain crucial enzymes in the porphyrin pathway, rather than simply upon the accumulation of δ aminolevulinic acid is presented to explain the experimental findings.

Genetic control of chlorophyll biosynthesis in chlamydomonas: analysis of a mutant affecting synthesis of delta-aminolevulinic acid

A Mendelian mutation, r-1, in Chlamydomonas reinhardtii has been isolated which elevates protoporphyrin accumulation of the Mendelian protoporphyrin mutants brS-1 and brC-1 more than 20 fold. This increased protoporphyrin accumulation is shown to result from increased delta-aminolevulinic acid synthesis in the double mutants brS-1 r-1 and brC-1 r-1 over that of brS-1 and brC-1 alone. By itself, the r-1 mutation has no detectable protoporphyrin accumulation and has reduced levels of delta-aminolevulinic acid synthesizing activity, chlorophyll, protoheme, and cytochrome oxidase activity. The low levels of chlorophyll and protoheme in r-1 can be increased by feeding delta-aminolevulinic acid. We hypothesize that r-1 may be a mutation of the gene coding for the delta-aminolevulinic acid synthesizing enzyme which reduces the sensitivity of this enzyme to feedback inhibition by protoporphyrin or heme as well as reducing the overall activity of the enzyme. Evidence is also presented for a single delta-aminolevulinic acid synthesizing enzyme serving both chlorophyll and heme biosynthesis.

Control of chlorophyll synthesis by phytochrome : I. The effect of phytochrome on the formation of 5-aminolevulinate in mustard seedlings

Treatment of mustard (Sinapis alba L.) seedlings with levulinate leads to the inhibition of chlorophyll synthesis and causes the accumulation of 5-aminolevulinate which is only formed in light. A stoichiometric relationship exists between the extent of inhibition of chlorophyll synthesis and 5-aminolevulinate accumulation. The formation of 5-aminolevulinate in continuous white light is increased by pre-irradiation. The effect of the preirradiation can be fully attributed to phytochrome. Under various light conditions the rate of 5-aminolevulinate formation in levulinate-treated seedlings is similar to the rate of chlorophyll accumulation in seedlings not treated with levulinate. This result supports the hypothesis that the phytochrome-controlled chlorophyll accumulation is regulated at the level of the formation of 5-aminolevulinate.

Genetic Regulation of Chlorophyll Synthesis Analyzed with Mutants in Barley

Barley seedlings homozygous both for the xantha-1(35) and tigrina-d(12) mutation accumulate magnesium protopophyrins and other precursors of chlorophyllide constitutively in darkness. The homozygous double mutant xantha-f(10), tigrina-O(34) produces protoporphyrin constitutively. These results provide evidence for the control of chlorophyllide synthesis in higher plants through the products of regulatory genes in the nucleus.