Antioxidase System of a Rice Mutant with Low Chlorophyll b

[Objective] The mitigative effect of antioxidase system of a rice mutant with low chlorophyll b on photooxidative damage was studied.[Method] A rice mutant with low chlorophyll b and its wild type were taken as experimental materials to comparatively research their peroxide (H2O2) contents, the activity and isozymes of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in chloroplast.[Result] Compared with the wild type, there were many kinds of SOD, POD and CAT isozymes in leaf cells and chloroplast cell of mutant, and the activity of SOD, POD and CAT isozymes in leaf cells and chloroplast cell of mutant was also correspondingly higher. Under intense light condition, the H2O2 content of chloroplast in mutant was less than that in the wild type. [Conclusion] The higher activity of scavenging active oxygen can relieve the photooxidative damage made by excessive light energy of intense light on photosynthetic membrane, which is an important reason for higher photosystem Ⅱ (PS II) stability of this mutant.

Study on a Mutant with Low Content Chlorophyll b in a High Yielding Rice and Its Photosynthesis Properties

A high yielding rice mutant ( Oryza sativa L. cv. Zhenhui 249) with low chlorophyll b was recently discovered in the field. The mutant was mainly characterized by the decrease of the content of extrinsic antennae complex. This variation was shown in the stage when the leaves were expanding. When the leaves are at the final developmental stage, the content would approach to that of the wild type. It was discovered that only moderate amount of chlorophyll b decreased in this mutant. The photosynthetic apparatus of the mutant was rather stable in the whole life span of the leaf. The extrinsic antennae complex of the mutant might make efficient use of light and meanwhile reduce the production of O -· 2.

Variations in chlorophyll content, stomatal conductance, and photosynthesis in Setaria EMS mutants

Chlorophyll (Chl) content,especially Chl b content,and stomatal conductance (G_s) are the key factors affecting the net photosynthetic rate (P_n).Setaria italica,a diploid C_4 panicoid species with a simple genome and high transformation efficiency,has been widely accepted as a model in photosynthesis and drought-tolerance research.The current study characterized Chl content,G_s,and P_n of 48 Setaria mutants induced by ethyl methanesulfonate.A total of 24,34,and 35 mutants had significant variations in Chl content,G_s,and P_n,respectively.Correlation analysis showed a positive correlation between increased G_s and increased P_n,and a weak correlation between decreased Chl b content and decreased P_n was also found.Remarkably,two mutants behaved with significantly decreased Chl b content but increased P_n compared to Yugu 1.Seven mutants behaved with significantly decreased G_s but did not decrease P_(n )compared to Yugu 1.The current study thus identified various genetic lines,further exploration of which would be beneficial to elucidate the relationship between Chl content,G_s,and P_n and the mechanism underlying why C_4 species are efficient at photosynthesis and water saving.

Changes in Chlorophyll Fluorescence of Rice Mutants Induced by High Hydrostatic Pressure

Three mutants of rice (Oryza sativa L. ), Mutant 1, Mutant 2 and Mutant 3, which were selected by high hydrostatic pressure (75 MPa), and their parent Yuexiangzhan were used to study the changes in chlorophyll fluorescence during different growth stages. In all the three mutants, the function of PSⅡ was improved, F_v/F_m ratio of mutants increased compared to their parent at tillering and heading stage, and ΦPSⅡ also improved except for Mutant 2 at heading stage. Similar to their parent, the mutants exhibited slight photoinhibition at noon and almost complete recovery to initial levels of 6:00 after 18:00 at heading stage. At milking stage, the photoinhibition in the mutants was obvious, and recovered rapidly compared to the parent. Yields of individual plant and grain/straw ratio were also higher in three mutants than the parent. Results indicated that characteristics of chlorophyll fluorescence in leaves of mutants and their photoinhibition in the field had changed. It is suggested that high hydrostatic pressure induction could be applied as a new effective approach in high-yield rice breeding in the future.

Genetic Analysis and Molecular Mapping of a Novel Chlorophyll-Deficit Mutant Gene in Rice

A rice etiolation mutant 824ys featured with chlorophyll deficiency was identified from a normal green rice variety 824B. It showed whole green-yellow plant from the seedling stage, reduced number of tillers and longer growth duration. The contents of chlorophyll, chlorophyll a, chlorophyll b and net photosynthetic rate in leaves of the mutant obviously decreased, as well as the number of spikelets per panicle, seed setting rate and 1000-grain weight compared with its wild-type parent. Genetic analyses on F1 and F2 generations of 824ys crossed with three normal green varieties showed that the chlorophyll-deficit mutant character was controlled by a pair of recessive nuclear gene. Genetic mapping of the mutant gene was conducted by using microsatellite markers and F2 mapping population of 495R/824ys, and the mutant gene of 824ys was mapped on the short arm of rice chromosome 3. The genetic distances from the target gene to the markers RM218, RM282 and RM6959 were 25.6 cM, 5.2 cM and 21.8 cM, respectively. It was considered to be a new chlorophyll-deficit mutant gene and tentatively named as chill（t）.

Effect of Low Content Chlorophyll on Distribution Properties of Absorbed Light Energy in Leaves of Mutant Rice

This paper reported the diurnal variations of photochemical efficiency of PSII, thermaldissipation rate and other physiology process in the low content chlorophyll mutant rice andits wild type under field conditions, and analyzed the difference of absorbed light distributionbetween the two rice varieties in a day. The results showed that the mutant had poor absorbedlight because of its little light absorption coefficient, but higher electron transportg ratecould partly reduce the disadvantageous effect of deficient absorbed light in mutant. Comparedwith wild-type rice, the mutant had less excess excitation energy and the fraction of absorbedlight allocated to photochemical process was more.

Characterization of a Novel Chlorophyll-Deficient Mutant Mt6172 in Wheat

Identification of new chlorophyll-deficient mutants will provide materials for studying signaling components and pathways between plastid and nucleus. A novel chlorophyll-deficient mutant, named Mt6172, was obtained by spaceflight environment induction. Genetic analysis showed that its inheritance was controlled by nuclear and cytoplamic genes. Leaf color of its self-fertilized progenies was albino, narrow-white striped, or green. Only a few cells with abnormal chloroplasts were observed in albino plants and white section of narrow-white striped plants. These chloroplasts had obvious flaws in inner structure, and granum lamellae was extremely disordered. The narrow-white striped plants were characterized with green- and-narrow-white striped leaves, and the width of stripes between different plants was even, their plant height, number of productive tillers, and 1 000-grain weight were lower than those of the wild type. The narrow-white striped plants and the wild type had significant difference in the value of potential activity of photosystem II at all tested stages. At elongation stage, which was impacted the most seriously, effective quantum yield significantly decreased, whereas the energy for photoprotection and photodamage significantly increased. changes of electron transport rate, photochemical dissipation, Under different photosynthetic active radiation conditions, and effective quantum yield were different, electron transport rate was more impacted than other parameters. Therefore, the leaf morphology and inheritance of mutant Mt6172 was different from the other reported mutants in wheat, and it was a novel mutant of chloroDhvll deficiency.

Analysis of Chloroplast Ultrastructure,Photosystem Ⅱ Light Harvesting Complexes and Chlorophyll Synthesis in a Chlorophyll-Less Rice Mutant W2555

A comparative study on chloroplast ultrastructure and light harvesting complex of photosystem Ⅱ （LHC Ⅱ） was conducted between a new rice mutant （W2555） and its wild type （WT）. The chloroplasts of W2555 had less thylakoids and grana stacks compared with the wild type. There was no significant change in the composition of LHC Ⅱ polypeptide in W2555, while a decline had been noted in LHC Ⅱ content. Northern blot analysis with a specific cab gene probe showed no appreciable difference in the LHC Ⅱ mRNA level between the W2555and its wild type. The precursors of chlorophyll synthesis, 6-aminolevulinic acid （ALA） and porphobilinogen （PBG） were over accumulated in W2555, but the other precursors were all decreased. These results indicated that the decreased level of LHC Ⅱ in the mutant W2555 was attributed to the change of cab gene transcription, but a blockage in chlorophyll biosynthesis due to the formation of uroporphyrinogen Ⅲ （Urogen Ⅲ）.

玉米光合突变体hcf136(high chlorophyll fluorescence 136)的转录组分析

玉米是典型的C_4作物,其光合作用由花环结构的两种细胞(叶肉细胞和维管束鞘细胞)共同完成。玉米hcf136(high chlorophyll fluorescence 136)突变体叶肉细胞叶绿体不能形成基粒从而丧失了PSII活性,但维管束鞘细胞的叶绿体发育不受影响,是研究玉米C_4光合机理的好材料。本研究利用转录组测序(RNA-Seq)技术,通过对高光和低光下野生型和hcf136突变体不同叶片部位进行转录组分析发现,PSII相关基因的转录未发生明显差异,表明PSII复合体的缺失是非转录水平变化所引起。此外,突变体中淀粉合成受阻,糖降解、糖转运及Cu^(2+)转运等代谢过程加剧,且一些转录因子表达发生显著变化。该结果对进一步深入研究玉米HCF136基因的功能提供了参考。

DWARF and SMALL SEED1,a Novel Allele of OsDWARF,Controls Rice Plant Architecture,Seed Size,and Chlorophyll Biosynthesis

Plant architecture is a vital agronomic trait to control yield in rice(Oryza sativa L.).A dwarf and small seed 1(dss1)mutant were obtained from the ethyl methanesulfonate(EMS)mutagenized progeny of a Guizhou glutinous landrace cultivar,Lipingzabianhe.The dss1 mutant displayed phenotypes similar to those of brassinosteroid(BR)deficient mutants,such as dwarfing,dark green and rugose erect leaves,small seeds,and loner neck internode panicles with primary branching.In our previous study,the underlying DSS1 gene was isolated,a novel allele of OsDWARF(OsBR6ox)that encodes a cytochrome P450 protein involved in the BR biosynthetic pathway by MutMap technology.In this work,we confirmed that a Thr335Ile amino acid substitution residing in DSS1/OsDWARF was responsible for the dwarf,panicle architecture,and small seed phenotypes in the dss1 mutants by genetic transformation experiments.The overexpression of OsDWARF in the dss1 mutant background could not only recover dss1 to the normal plant height and panicle architecture but also rescued normal leaf angles,seed size,and leaf color.Thus,the specific mutation in DSS1/OsDWARF influenced plant architecture,seed size,and chlorophyll biosynthesis.

Physical-chemical and Agronomical Analysis of a Leaf Color Mutant of Rice

[Objective] This study was to investigate the physical-chemical properties and the agronomical traits of a leaf color mutant K7231,so as to provide scientific basis for its use as breeding material.[Method]Before heading,the contents of chlorophyll and soluble sugar of leaf color mutant K7231 were measured,and its agronomic traits after mature were investigated.[Result]The contents of chlorophyll and soluble sugar of leaf color mutant K7231 before heading assumed a regular change law.Except the lower yield,K7231 performed similar agronomic traits compared with the CK.[Conclusion]This study provided scientific basis for the utilization of this mutant.

Photosynthetic Characteristics of Flag Leaves in Rice White Stripe Mutant 6001 During Senescence Process

Physiological, biochemical and electron microscopy analyses were used to investigate the photosynthetic performance of flag leaves in rice white stripe mutant 6001 during the senescence process. Results showed that the chlorophyll content at the heading and milk-ripe stages in rice mutant 6001 were about 34.78% and 3.00% less than those in wild type 6028, respectively. However, the chlorophyll content at the fully-ripe stage in rice mutant 6001 was higher than that in wild type 6028. At the heading stage, the net photosynthetic rate （Pn） in rice mutant 6001 was lower than that in wild type 6028. Rice mutant 6001 also exhibited a significantly slower decrease rate of Pn than wild type 6028 during the senescence progress, especially at the later stage. Furthermore, Ca2^-ATPase, Mg~^-ATPase and photophosphorylation activities exhibited the similar trends as the Po. During the senescence process, the 68 kDa polypeptide concentrations in the thylakoid membrane proteins exhibited a significant change, which was one of the critical factors that contributed to the observed change in photosynthesis. We also observed that the chloroplasts of rice mutant 6001 exhibited higher integrity than those of wild type 6028, and the chloroplast membrane of rice mutant 6001 disintegrated more slow during the senescence process. In general, rice mutant 6001 had a relatively slower senescence rate than wild type 6028, and exhibited anti-senescence properties.

Construction and Genetic Analysis of Murine Hepatitis Virus Strain A59 Nsp16 Temperature Sensitive Mutant and the Revertant Virus

Coronaviruses (CoVs) are generally associated with respiratory and enteric infections and have long been recognized as important pathogens of livestock and companion animals. Mouse hepatitis virus (MHV) is a widely studied model system for Coronavirus replication and pathogenesis. In this study,we created a MHV-A59 temperature sensitive (ts) mutant Wu"-ts18(cd) using the recombinant vaccinia reverse genetics system. Virus replication assay in 17C1-1 cells showed the plaque phenotype and replication characterization of constructed Wu"-ts18(cd) were indistinguishable from the reported ts mutant Wu"-ts18. Then we cultured the ts mutant Wu"-ts18(cd) at non-permissive temperature 39.5°C,which "forced" the ts recombinant virus to use second-site mutation to revert from a ts to a non-ts phenotype. Sequence analysis showed most of the revertants had the same single amino acid mutation at Nsp16 position 43. The single amino acid mutation at Nsp16 position 76 or position 130 could also revert the ts mutant Wu"-ts18 (cd) to non-ts phenotype,an additional independent mutation in Nsp13 position 115 played an important role on plaque size. The results provided us with genetic information on the functional determinants of Nsp16. This allowed us to build up a more reasonable model of CoVs replication-transcription complex.

PHYSIOLOGICAL ASPECTS OF A HIGH-CO_2 REQUIRING MUTANT AND THE HIGH-CO_2 GROWING CELLS OF THE CYANOBACTERIUM SYNECHOCOCCUS PCC7942

A new chemically mutagenic mutant of Synechococcus PCC7942 named high-CO2 re-quiring mutant, which could grow at 4% CO2 but could not grow at air levels of CO2, was isolated. Com-parative studies on some physiological aspects of the mutant and high-cO2 growing cells (growing at 4%CO2 ) were conducted. The result showed that the mutant had lower growing rate, about 1/40th photosyn-thetic affinity to inorganic carbon, 25% lower carbonic anhydrase (CA) activity, lower quenching rate ofchlorophyll fluoresence, and about 1/2 alkalinization rate of the medium. The CA activity responses ofthe two types of cells to different concentrations of CO2 were determined. Upon the addition of inorganiccarbon (Ci), the rate of active Ci uptake described by the rate of chlorophyll fluorescence quenching ofthe mutant was obviously lower compared with that of the high-CO2 growing cells; the size of the internalinorganic carbon pool size determined by the extent of fluorescence quenching Of the mutant was alsosmaller.

基于光合突变池的雨生红球藻优异性状藻株挖掘

雨生红球藻(Haematococcus pluvialis Flotow)是天然虾青素的主要来源,其高成本、低效率的规模化生产难以满足市场需求。建立快速获得优质突变株的筛选策略有助于提高雨生红球藻的种质资源开发效率,获得虾青素高富集的优质藻株。以雨生红球藻NIES-144为出发藻株,通过甲基磺酸乙酯(ethyl methylsufone,EMS)诱变和高光处理获得光合突变池。以叶绿素荧光参数为检测指标能够快速筛选出生长速率和虾青素积累能力发生变化的突变藻株。结果显示,从该光合突变池中随机选取11株藻株的增殖能力和虾青素积累能力均与原始对照株存在不同程度的差异,45%的突变株在增殖能力和虾青素积累能力方面显著优于对照株。该结果表明雨生红球藻的光化学活性与增殖和其虾青素积累能力之间存在着紧密的联系,证实基于光合突变池挖掘优异性状雨生红球藻的策略具有可行性,为微藻优良藻株的获取提供新思路。

Thermostability of photosynthesis in two new chlorophyll b-less rice mutants

Leaves of the two new chlorophyll b-less rice mutants VG28-1, VG30-5 and the wild type rice cv. Zhonghua 11 were subjected to temperatures 28, 36, 40, 44 and 48℃ in the dark for 30 min or gradually elevated temperature from 30℃ to 80℃ at 0.5℃/min. The thermostability of photosynthetic apparatus was estimated by the changes in chlorophyll fluorescence parameters, photosynthetic rate and pigment content, chloroplast ultrastructure and tissue location of H2O2 accumulation. There were different patterns of Fo-temperature curves between the Chl b-less mutants and the wild type plant, and the temperature of Fo rising threshold was shifted 3℃ lower in the Chl b-less mutants (48℃) than in the wild type (51℃). At temperature up to about 45℃, chloroplasts were swollen and thylakoid grana became misty accompanied with the complete loss of photosynthetic oxygen evolution in the two Chl b-less mutants, but chloroplast ultrastruc- ture in the wild type showed no obvious alteration. After 55℃ exposure, the disordered thylakoid and significant H2O2 accumulation in leaves were found in the two Chl b-less mutants, whereas in the wild type plant, less H2O2 was accumulated and the swollen thylakoid still maintained a cer- tain extent of stacking. A large extent of the changes in qP, NPQ and Fv/Fm was consistent with the Pn decreasing rate in the Chl b-less mutants during high temperature treatment as compared with the wild type. The results indicated that the Chl b-less mutants showed a tendency for higher thermosensitivity, and loss of Chl b in LHC II could lead to less thermostability of PSII structure and function. Heat damage to photosynthetic apparatus might be partially attributed to the in- ternal oxidative stress produced at severely high temperature.

Functional Accumulation of Antenna Proteins in Chlorophyll b-Less Mutants of Chlamydomonas reinhardtii

The green alga Chlamydomonas reinhardtii contains several light-harvesting chlorophyll a/b complexes （LHC）- four major LHCIIs, two minor LHClIs, and nine LHCIs. We characterized three chlorophyll b-less mutants to assess the effect of chlorophyll b deficiency on the function, assembly, and stability of these chlorophyll a/b binding proteins. We identified point mutations in two mutants that inactivate the CAO gene responsible for chlorophyll a to chlorophyll b conversion. All LHClIs accumulated to wild-type levels in a CAO mutant but their light-harvesting function for photosystem II was impaired. In contrast, most LHCIs accumulated to wild-type levels in the mutant and their light-harvesting capability for photosystem I remained unaltered. Unexpectedly, LHCl accumulation and the photosystem I functional antenna size increased in the mutant compared with in the wild type when grown in dim light. When the CAO mutation was placed in a yellow-in-the-dark background （yid-BF3）, in which chlorophyll a synthesis remains limited in dim light, accumulation of the major LHClIs and of most LHCls was markedly reduced, indicating that sustained synthesis of chlorophyll a is required to preserve the proteolytic resistance of antenna pro- teins. Indeed, after crossing yid-BF3 with a mutant defective for the thylakoid FtsH protease activity, yid- BF3-ftshl restored wild-type levels of LHCI, which defines LHCI as a new substrate for the FtsH protease.

珍珠芦荟失绿突变体‘MT-1’的农艺性状、解剖结构、光合特性和代谢组特征分析

为阐明珍珠芦荟叶色突变的变异机制,以珍珠芦荟(Aristaloe aristata)叶色失绿突变体‘MT-1’及其叶色正常种质‘WT-18’为试材,对其表型特征、叶片超微结构、光合色素含量、叶绿素荧光参数、差异代谢产物等方面进行了对比研究。结果表明,与‘WT-18’相比,突变体‘MT-1’从幼叶开始呈现出黄化条斑现象,且株型变小、生长缓慢;气孔数量少且小,形状由长方形变成正方形;叶绿体数量及内部片层数量变少、体积也明显变小;光合色素(叶绿素a、叶绿素b和类胡萝卜素)含量和叶绿素荧光动力参数(F_o、F_m、F_v/F_m、ФPSⅡ、qP、qN和ETR)均显著降低。‘MT-1’和‘WT-18’的代谢产物差异明显,KEGG代谢通路分析表明,大多数差异代谢物富集到氨基酸代谢、糖代谢、脂类代谢、核酸代谢、次级代谢产物生物合成等途径。因此,叶绿体相关基因的改变可能是发生叶色失绿突变的重要原因。

黄瓜叶色突变体遗传机制的研究

从黄瓜雌性系 9110G中发现能稳定遗传的叶色突变体。该突变体子叶和第 1～ 2片真叶最初为金黄色 ,叶绿素含量约为正常株的 3/5 ,但随着叶片的生长这些叶片逐渐转绿。该突变体叶色黄主要是由叶绿素降低引起的 ,与类胡萝卜素无关。通过对亲本、F1、BC及F2 后代观察和叶绿素测定 ,证明该突变体是细胞核遗传 ,由单一隐性基因控制 ,并且绿色对黄色为不完全显性。该突变性状是研究光合系统和基因定位的好材料 。

水稻叶绿素合成缺陷突变体及其生物学研究进展

叶绿素是植物叶绿体内参与光合作用的重要色素,叶绿素合成缺陷突变是一类明显的性状突变,其在理论研究和实际应用方面均具有重要的意义.本文介绍了国内外在水稻叶绿素合成缺陷突变体的发掘、作用机理及其基因定位等方面的研究进展.