A Golden2-like transcription factor, BnGLK1a, improves chloroplast development, photosynthesis, and seed weight in rapeseed

Enhancing photosynthetic efficiency is a major goal for improving crop yields under agricultural field conditions and is associated with chloroplast biosynthesis and development.In this study,we demonstrate that Golden2-like 1a(BnGLK1a)plays an important role in regulating chloroplast development and photosynthetic efficiency.Overexpressing BnGLK1a resulted in significant increases in chlorophyll content,the number of thylakoid membrane layers and photosynthetic efficiency in Brassica napus,while knocking down BnGLK1a transcript levels through RNA interference(RNAi)had the opposite effects.A yeast two-hybrid screen revealed that BnGLK1a interacts with the abscisic acid receptor PYRABACTIN RESISTANCE 1-LIKE 1-2(BnPYL1-2)and CONSTITUTIVE PHOTOMORPHOGENIC 9 SIGNALOSOME 5A subunit(BnCSN5A),which play essential roles in regulating chloroplast development and photosynthesis.Consistent with this,BnGLK1a-RNAi lines of B.napus display hypersensitivity to the abscisic acid(ABA)response.Importantly,overexpression of BnGLK1a resulted in a 10%increase in thousand-seed weight,whereas seeds from BnGLK1a-RNAi lines were 16%lighter than wild type.We propose that BnGLK1a could be a potential target in breeding for improving rapeseed productivity.Our results not only provide insights into the mechanisms of BnGLK1a function,but also offer a potential approach for improving the productivity of Brassica species.

Comparative and Phylogenetic Analysis of the Complete Chloroplast Genomes of 19 Species in Rosaceae Family

Rosaceae represents a vast and complex group of species,with its classification being intricate and contentious.The taxonomic placement of many species within this family has been a subject of ongoing debate.The study utilized the Illumina platform to sequence 19 plant species from 10 genera in the Rosaceae.The cp genomes,vary-ing in size from 153,366 to 159,895 bp,followed the typical quadripartite organization consisting of a large single-copy(LSC)region(84,545 to 87,883 bp),a small single-copy(SSC)region(18,174 to 19,259 bp),and a pair of inverted repeat(IR)regions(25,310 to 26,396 bp).These genomes contained 132–138 annotated genes,including 87 to 93 protein-coding genes(PCGs),37 tRNA genes,and 8 rRNA genes using MISA software,52 to 121 simple sequence repeat(SSR)loci were identified.D.arbuscular contained the least of SSRs and did not have hexanotides,A.lineata contained the richest SSRs.Long terminal repeats(LTRs)were primarily composed of palindromic and forward repeat sequences,meanwhile,The richest LTRs were found in Argentina lineata.Except for Argentina lineata,Fragariastrum eriocarpum,and Prunus trichostoma,which varied in gene type and position on both sides of the boundary,the remaining species were found to be mostly conserved according to IR boundary analysis.The examination of the Ka/Ks ratio revealed that only the infA gene had a value greater than 1,indicating that this gene was primarily subjected to positive selection during evolution.Additionally,9 hotspots of variation were identified in the LSC and SSC regions.Phylogenetic analysis confirmed the scientific validity of the genus Prunus L.sensu lato(s.l.)within the Rosaceae family.The separation of the three genera Argentina Hill,Fragariastrum Heist.ex Fabr.and Dasiphora Raf.from Potentilla L.may be a more scientific classification.These results offer fresh perspectives on the taxonomy of the Rosaceae.

Os DXR interacts with Os MORF1 to regulate chloroplast development and the RNA editing of chloroplast genes in rice

Plant chlorophyll biosynthesis and chloroplast development are two complex processes that are regulated by exogenous and endogenous factors. In this study, we identified OsDXR, a gene encoding a reductoisomerase that positively regulates chlorophyll biosynthesis and chloroplast development in rice. OsDXR knock-out lines displayed the albino phenotype and could not complete the whole life cycle process. OsDXR was highly expressed in rice leaves, and subcellular localization indicated that OsDXR is a chloroplast protein. Many genes involved in chlorophyll biosynthesis and chloroplast development were differentially expressed in the OsDXR knock-out lines compared to the wild type.Moreover, we found that the RNA editing efficiencies of ndhA-1019 and rpl2-1 were significantly reduced in the OsDXR knock-out lines. Furthermore, OsDXR interacted with the RNA editing factor OsMORF1 in a yeast two-hybrid screen and bimolecular fluorescence complementation assay. Finally, disruption of the plastidial 2-C-methyl-derythritol-4-phosphate pathway resulted in defects in chloroplast development and the RNA editing of chloroplast genes.

Advancing approach and toolbox in optimization of chloroplast genetic transformation technology

Chloroplast is a discrete,highly structured,and semi-autonomous cellular organelle.The small genome of chloroplast makes it an up-and-coming platform for synthetic biology.As a special means of synthetic biology,chloroplast genetic engineering shows excellent potential in reconstructing various sophisticated metabolic pathways within the plants for specific purposes,such as improving crop photosynthetic capacity,enhancing plant stress resistance,and synthesizing new drugs and vaccines.However,many plant species exhibit limited efficiency or inability in chloroplast genetic transformation.Hence,new transformation technologies and tools are being constantly developed.In order to further expand and facilitate the application of chloroplast genetic engineering,this review summarizes the new technologies in chloroplast genetic transformation in recent years and discusses the choice of appropriate synthetic biological elements for the construction of efficient chloroplast transformation vectors.

OsTHA8 encodes a pentatricopeptide repeat protein required for RNA editing and splicing during rice chloroplast development

In higher plants, the chloroplast is the most important organelle for photosynthesis and for numerous essential metabolic processes in the cell. Although many genes involved in chloroplast development have been identified, the mechanisms underlying such development are not fully understood. In this study, a rice(Oryza sativa) mutant exhibiting pale green color and seedling lethality was isolated from a mutant library. The mutated gene was identified as an ortholog of THA8(thylakoid assembly 8) in Arabidopsis and maize. This gene is designated as OsTHA8 hereafter. OsTHA8 showed a typical pentatricopeptide repeat(PPR) characteristic of only four PPR motifs. Inactivation of OsTHA8 led to a deficiency in chloroplast development in the rice seedling stage. OsTHA8 was expressed mainly in young leaves and leaf sheaths.The OsTHA8 protein was localized to the chloroplast. Loss of function of OsTHA8 weakened the editing efficiency of ndhB-611/737 and rps8-182 transcripts under normal conditions. Y2H and BiFC indicated that OsTHA8 facilitates RNA editing by forming an editosome with multiple organellar RNA editing factor(OsMORF8) and thioredoxin z(OsTRXz), which function in RNA editing in rice chloroplasts. Defective OsTHA8 impaired chloroplast ribosome assembly and resulted in reduced expression of PEP-dependent genes and photosynthesis-related genes. Abnormal splicing of the chloroplast gene ycf3 was detected in ostha8. These findings reveal a synergistic regulatory mechanism of chloroplast biogenesis mediated by RNA, broaden the function of the PPR family, and shed light on the RNA editing complex in rice.

PtrDJ1C,an atypical member of the DJ-1 superfamily,is essential for early chloroplast development and lignin deposition in poplar

The nuclear-encoded factors and the photosynthetic apparatus have been studied extensively during chloroplast biogenesis.However,many questions regarding these processes remain unanswered,particularly in perennial woody plants.As a model material of woody plants,poplar not only has very significant value of research,but also possesses economic and ecological properties.This study reports the Populus trichocarpa DJ-1C(PtrDJ1C)factor,encoded by a nuclear gene,and a member of the DJ-1 superfamily.PtrDJ1C knock-out with the CRISPR/Cas9 system resulted in different albino phenotypes.Chlorophyll fluorescence and immunoblot analyses showed that the levels of photosynthetic complex proteins decreased significantly.Moreover,the transcript level of plastid-encoded RNA polymerase-dependent genes and the splicing efficiency of several introns were affected in the mutant line.Furthermore,rRNA accumulation was abnormal,leading to developmental defects in chloroplasts and affecting lignin accumulation.We concluded that the PtrDJ1C protein is essential for early chloroplast development and lignin deposition in poplar.

OsPPR9 encodes a DYW-type PPR protein that affects editing efficiency of multiple RNA editing sites and is essential for chloroplast development

Photosynthesis occurs mainly in chloroplasts,whose development is regulated by proteins encoded by nuclear genes.Among them,pentapeptide repeat(PPR)proteins participate in organelle RNA editing.Although there are more than 450 members of the PPR protein family in rice,only a few affect RNA editing in rice chloroplasts.Gene editing technology has created new rice germplasm and mutants,which could be used for rice breeding and gene function study.This study evaluated the functions of OsPPR9 in chloroplast RNA editing in rice.The osppr9 mutants were obtained by CRISPR/Cas9,which showed yellowing leaves and a lethal phenotype,with suppressed expression of genes associated with chloroplast development and accumulation of photosynthetic-related proteins.In addition,loss of OsPPR9 protein function reduces the editing efficiency of rps8-C182,rpoC2-C4106,rps14-C80,and ndhB-C611 RNA editing sites,which affects chloroplast growth and development in rice.Our data showed that OsPPR9 is highly expressed in rice leaves and encodes a DYW-PPR protein localized in chloroplasts.Besides,the OsPPR9 protein was shown to interact with OsMORF2 and OsMORF9.Together,our findings provide insights into the role of the PPR protein in regulating chloroplast development in rice.

Isolation of Chloroplasts from Marine Microalga Isochrysis galbana Parke for Their Lipid Composition Analysis

Marine microalga Isochrysis galbana is an important feed species with a high nutritional value.Different from other uni-cellular algae,its cell contains two chloroplasts which are the major sites for lipid synthesis.Here,we optimized a chloroplast isola-tion approach suitable for the isolation of I.galbana chloroplasts and determined the purity and integrity of the isolated chloroplasts through microscopic observations and enzyme activity assay.The chloroplast lipids were analyzed with a ultrahigh-performance li-quid chromatography-Q Exactive Orbitrap-mass spectrometry.This newly developed isolation approach is simple and reliable to isolate chloroplasts with high integrity and purity.The average yield of intact chloroplasts was 15.3%±0.1%.Glycolipids and acyl-glycerols were the main chloroplast lipids.Glycolipids accounted for 56.6%of chloroplast lipid.Digalactosyldiacylglycerol(DGDG),monogalactosyldiacylglycerol(MGDG)and sulfoquinovosyldiacylglycerol(SQDG)were the main glyceroglycolipids.The fatty acyl R1/R2 were mostly 18:4/16:1,18:3/16:1 and 18:4/18:5 in DGDGs,14:0/18:4,18:4/18:5,18:4/18:4 and 18:3/18:4 in MGDGs and 16:0/14:0,16:0/18:3,and 18:4/18:3 in SQDGs.In addition,diacylglycerol(DAG)was the most abundant acylglycerols;the content of 22:6/18:4-DAG was the highest.There was a little amount of glycosphingolipid(GSL)in chloroplast.Digalactosylmonoglyceride(DGMG),monogalactosylmonoglyceride(MGMG),sulfoquinovosylmonoacylglycerol(SQMG),monoglyceride(MAG),phospholi-pids(PLs),ceramide(Cer)and betaine lipids were nearly undetectable in chloroplast.The fatty acid proportions of DGDGs,MGDGs,SQDGs,DAGs,triglycerides(TAGs)and GSLs were either higher or lower than or similar to those of whole-cell.Collectively,our isolation approach is applicable to many aspects of chloroplast biology,and may offer a reference for the isolation of chloroplasts from other marine microalgae.

Patterns of synonymous codon usage bias in chloroplast genomes of seed plants

Codon usage in chloroplast genome of six seed plants （Arabidopsis thaliana, Populus alba, Zea mays, Triticum aestivum, Pinus koraiensis and Cycas taitungensis） was analyzed to find general patterns of codon usage in chloroplast genomes of seed plants. The results show that chloroplast genomes of the six seed plants had similar codon usage patterns, with a strong bias towards a high representation of NNA and NNT codons. In chloroplast genomes of the six seed plants, the effective number of codons （ENC） for most genes was similar to that of the expected ENC based on the GC content at the third codon position, but several genes with low ENC values were laying below the expected curve. All of these data indicate that codon usage was dominated by a mutational bias in chloroplast genomes of seed plants and that selection appeared to be limited to a subset of genes and to only subtly affect codon usage. Meantime, four, six, eight, nine, ten and 12 codons were defined as the optimal codons in chloroplast genomes of the six seed plants.

Effects of Exogenous Silicon on Photosynthetic Capacity and Antioxidant Enzyme Activities in Chloroplast of Cucumber Seedlings Under Excess Manganese

Effects of silicon on photosynthetic parameters and antioxidant enzymes of chloroplast in cucumber seedlings under excess Mn were studied. Compared with the control, excess Mn significantly inhibited net photosynthetic rate （Pn）, stomatal conductance, as well as the maximum yield of the photosystem II photochemical reactions （Fv/Fm） and the quantum yield of photosysytem II electron transport （Φ PSII）, application of Si reversed the negative effects of excess Mn. In the further investigation, it was obtained that application of Si significantly increased the activities of enzymes related with ascorbate-glutathione cycle including ascorbate peroxidase （APX）, dehydroascorbate reductase （DHAR） and glutathione reductase （GR） in cucumber chloroplast under excess Mn, this could be responsible for the lower accumulation of H2O2 and lower lipid peroxidation of chloroplast induced by Mn, and resulted in keeping higher photosynthesis.

Exogenous GSH protects tomatoes against salt stress by modulating photosystem Ⅱ efficiency, absorbed light allocation and H2O2-scavenging system in chloroplasts

The effects of exogenous GSH（reduced glutathione）on photosynthetic characteristics,photosystem Ⅱ efficiency,absorbed light energy allocation and the H2O2-scavenging system in chloroplasts of salt-stressed tomato（Solanum lycopersicum L.）seedlings were studied using hydroponic experiments in a greenhouse.Application of exogenous GSH ameliorated saline-induced growth inhibition,the disturbed balance of Na＋ and Cl- ions and Na＋/K＋ ratios,and the reduction of the net photosynthetic rate（Pn）.GSH also increased the maximal photochemical efficiency of PSⅡ（Fv/Fm）,the electron transport rate（ETR）,the photochemical quenching coefficient（qP）,and the non-photochemical quenching coefficient（NPQ）.In addition,GSH application increased the photochemical quantum yield（Y（Ⅱ））and relative deviation from full balance between the photosystems（β/α-1）and decreased the PSⅡ excitation pressure（1-qP）and quantum yield of non-regulated energy dissipation（Y（NO））in leaves of salt-stressed tomatoes without BSO（L-buthionine-sulfoximine,an inhibitor of key GSH synthesis enzymeγ-glutamylcysteine synthetase）or with BSO.Further,the addition of GSH depressed the accumulation of H2O2 and malondialdehyde（MDA）,induced the redistribution of absorbed light energy in PSⅡ reaction centers,and improved the endogenous GSH content,GSH/GSSH ratio and activities of H2O2-scavenging enzymes（including superoxidase dismutase（SOD）,catalase（CAT）,peroxidase（POD）and key enzymes in the AsA-GSH cycle and Grx system）in the chloroplasts of salt-stressed plants with or without BSO.Therefore,GSH application alleviates inhibition of salt-induced growth and photosynthesis mainly by overcoming stomatal limitations,improving the PSⅡ efficiency,and balancing the uneven distribution of light energy to reduce the risk of ROS generation and to mediate chloroplast redox homeostasis and the antioxidant defense system to protect the chloroplasts from oxidative damage.Thus,GSH may be used as a potential tool for alleviating salt stress in tomato plants.

Effects of potassium deficiency on photosynthesis,chloroplast ultrastructure,ROS,and antioxidant activities in maize(Zea mays L.)

Potassium(K)deficiency significantly decreases photosynthesis due to leaf chlorosis induced by accumulation of reactive oxygen species(ROS).But,the physiological mechanism for adjusting antioxidative defense system to protect leaf function in maize(Zea mays L.)is unknown.In the present study,four maize inbred lines(K-tolerant,90-21-3 and 099;K-sensitive,D937 and 835)were used to analyze leaf photosynthesis,anatomical structure,chloroplast ultrastructure,ROS,and antioxidant activities.The results showed that the chlorophyll content,net photosynthetic rate(P_n),stomatal conductance(G_s),photochemical quenching(q_P),and electron transport rate of PSII(ETR)in 90-21-3 and 099 were higher than those in D937 and 835 under K deficiency treatment.Parameters of leaf anatomical structure in D937 that were significantly changed under K deficiency treatment include smaller thickness of leaf,lower epidermis cells,and vascular bundle area,whereas the vascular bundle area,xylem vessel number,and area in 90-21-3 were significantly larger or higher.D937 also had seriously damaged chloroplasts and PSII reaction centers along with increased superoxide anion(O_2^-·)and hydrogen peroxide(H_2O_2).Activities of antioxidants,like superoxide dismutase(SOD),catalase(CAT),and ascorbate peroxidase(APX),were significantly stimulated in 90-21-3 resulting in lower levels of O_2^-·and H_2O_2.These results indicated that the K-tolerant maize promoted antioxidant enzyme activities to maintain ROS homeostasis and suffered less oxidative damage on the photosynthetic apparatus,thereby maintaining regular photosynthesis under K deficiency stress.

Influence of lanthanum on chloroplast ultrastructure of soybean leaves under ultraviolet-B stress

In order to investigate the effects of lanthanum（Ⅲ） on cell ultrastructure of soybean leaves under elevated ultraviolet-B irradiation （UV-B, 280-320 nm）, the chloroplast ultrastructure of soybean seedlings was studied by hydroponics under laboratory conditions. The resuits showed that the thylakoid in chloroplast was orderly and clearly as soybean leaves were pretreated by La（Ⅲ）. The thylakoid was indis- tinctly disordered, expanded and even indiscoverable in the chloroplast under UV-B stress. The impact on the thylakoid by the high intensity UV-B irradiation （T2） was bigger than that by the low intensity UV-B irradiation （T1）. However, the destruction of the chloroplast structure caused by UV-B stress was alleviated by La（Ⅲ）, and the arrangement of the thylakoid in the chloroplast became orderly and clearly. The effect of the alleviation by La（Ⅲ） under the low intensity UV-B irradiation （T1） was better than that under the high intensity UV-B irradiation （T2）.

Deciphering codon usage patterns and evolutionary forces in chloroplast genes of Camellia sinensis var. assamica and Camellia sinensis var. sinensis in comparison to Camellia pubicosta

Codon usage bias(CUB) is a unique property of genome which refers to non-random usage of synonymous codons in coding sequences. The present study makes an attempt to find out the pattern of CUB in chloroplast(cp) genes among three tea species, i.e., Camellia sinensis var. assamica(Assam tea), Camellia sinensis var. sinensis(Chinese tea) and Camellia pubicosta(wild tea species) as no work on CUB was reported earlier. To understand the patterns of codon usage among the cp genes of three tea groups, we used bioinformatic tools to investigate the protein coding sequences of cp genes. In our present study, the mean nucleobase T was the highest whereas C was the lowest in all the three tea groups. The overall AT content was more than GC content, i.e., genes were AT rich. The scaled chi-square(SCS) value indicated that the CUB of cp genes was low. The codon CGT(Arg) was over-represented in C. sinensis var. sinensis whereas GGA(Pro) was over-represented in C. pubicosta species. Heatmap study revealed that most of the GC ending codons showed positive correlations between codon usage and GC3 while AT ending codons exhibited negative correlations. From neutrality plot analysis, it was evident that natural selection had played a major role, while mutation pressure exerted a minor effect in the CUB of cp genes in three tea groups. Highly significant(P<0.01) positive correlation was found between SCS and synonymous codon usage order(SCUO) of cp genes which suggested that high expression of cp genes was associated with high degree of CUB.

A Comparative Analysis of the Chloroplast Genomes of Four Salvia Medicinal Plants

Herbgenomics is an emerging field of traditional Chinese medicine(TCM)research and development.By combining TCM research with genomics,herbgenomics can help to establish the scientific validity of TCM and bring it into wider usage within the field of medicine.Salvia Linn.(S.Linn.)is a large genus of Labiatae that includes important medicinal plants.In this herbgenomics study,the complete chloroplast(cp)genomes of two Salvia spp.—namely,S.przewalskii and S.bulleyana,which are used as a surrogate for S.miltiorrhiza—were sequenced and compared with those of two other reported Salvia spp.—namely,S.miltiorrhiza and S.japonica.The genome organization,gene number,type,and repeat sequences were compared.The annotation results showed that both Salvia plants contain 114 unique genes,including 80 protein-coding,30 transfer RNA(tRNA),and four ribosomal RNA(rRNA)genes.Repeat sequence analysis revealed 21 forward and 22 palindromic sequences in both Salvia cp genomes,and 17 and 21 tandem repeats in S.przewalskii and S.bulleyana,respectively.A synteny comparison of the Salvia spp.cp genomes showed a high degree of sequence similarity in the coding regions and a relatively high divergence of the intergenic spacers.Pairwise alignment and single-nucleotide polymorphism(SNP)analyses found some candidate fragments to identify Salvia spp.,such as the intergenic region of the trnV–ndhC,trnQ–rps16,atpI–atpH,psbA–ycf3,ycf1,rpoC2,ndhF,matK,rpoB,rpoA,and accD genes.All of the results—including the repeat sequences and SNP sites,the inverted repeat(IR)region border,and the phylogenetic analysis—showed that S.przewalskii and S.bulleyana are extremely similar from a genetic standpoint.The cp genome sequences of the two Salvia spp.reported here will pave the way for breeding,species identification,phylogenetic evolution,and cp genetic engineering studies of Salvia medicinal plants.

Effects of 4f Electron Characteristics and Alternation Valence of Rare Earths on Photosynthesis: Regulating Distribution of Energy and Activities of Spinach Chloroplast

Chloroplasts were isolated from spinach treated with taCl3, CeCl3, and NdCl3. Because of owning 4f electron characteristics and alternation valence, Ce treatment presented the highest enhancement in light absorption, energy transfer from LHC Ⅱ to PS Ⅱ, excitation energy distribution from PS Ⅰ to PS Ⅱ, and fluorescence quantum yield around 680 nm. Compared with Ce treatment, Nd treatment resulted in relatively lower enhancement in these physiological indices, as Nd did not have alternation valence. La treatment presented the lowest enhancement, as La did not have either 4f electron or alternation valence. The increase in activities of whole chain electron transport, PS ⅡDCPIP photoreduction, and oxygen evolution of chloroplasts was of the following order： Ce〉Nd 〉La〉 control. However, the photoreduction activities of spinach PS I almost did not change with La, Ce, or Nd treatments. The results suggested that 4f electron characteristics and alternation valence of rare earths had a close relationship with photosynthesis improvement.

Phylogenetic placement of Cynomorium in Rosales inferred from sequences of the inverted repeat region of the chloroplast genome

Cynomorium is a herbaceous holoparasite that has been placed in Santalales, Saxifragales, Myrtales, or Sapindales. The inverted repeat （IR） region of the chloroplast genome region is slow evolving and, unlike mitochondrial genes, the chloroplast genome experiences few horizontal gene transfers between the host and parasite. Thus, in the present study, we used sequences of the IR region to test the phylogenetic placements of Cynomorium. Phylogenetic analyses of the chloroplast IR sequences generated largely congruent ordinal relationships with those from previous studies of angiosperm phylogeny based on single or multiple genes. Santalales was closely related to Caryophyllales and asterids. Saxifragales formed a clade where Peridiscus was sister to the remainder of the order, whereas Paeonia was sister to the woody clade of Saxifragales. Cynomorium is not closely related to Santalales, Saxifragales, Myrtales, or Sapindales; instead, it is included in Rosales and sister to Rosaceae. The various placements of the holoparasite on the basis of different regions of the mitochondrial genome may indicate the heterogeneous nature of the genome in the parasite. However, it is unlikely that the placement of Cynomorium in Rosales is the result of chloroplast gene transfer because Cynomorium does not parasitize on rosaceous plants and there is no chloroplast gene transfer between Cynomorium and Nitraria, a confirmed host of Cynomorium and a member of Sapindales.

Photosynthetic Characteristics and Ultrastructure of Chloroplast of Cucumber Under Low Light Density in Solar-Greenhouse

The photosynthetic characteristics and ultrastructure of chloroplast of cucumber in solar-greenhouse were studied. The result showed that the photosynthetic rate (Pn), photosyntheticability (A350), carboxylation efficiency, light saturation point and light compensation pointall declined remarkably under low light density, indicating that the photosynthetic characteristicsof cucumber were closely related to light environment. Under low light density, the minimalfluorescence (Fo), alterable fluorescence (Fv), photochemical efficiency of PSⅡ(Fv/Fm), steadyfluorescence in light (Fs), maximal fluorescence (Fm) and actual efficiency of PSⅡ(φPSⅡ)etcincreased, indicating that the photochemical activity and efficiency for solar energy transformationenhanced, thus the light proportion used to electron transport also increased. The chlorophylla, b, a/b and carotenoid of shading leaves decreased. However, the depressed extent of Chl a andChl a/b were obviously larger than that of Chl b. The number of chloroplast and starch grainin cucumber leaves descended, but that of grana and lamella increased as a shaded result. Thesize of chloroplast and starch grain of shading leaves minished.

Effects of different LEDs light spectrum on the growth,leaf anatomy,and chloroplast ultrastructure of potato plantlets in vitro and minituber production after transplanting in the greenhouse

Light spectrum plays an important role in regulating the growth and development of in vitro cultured potato(Solanum tuberosum L.) plantlets. The status of potato plantlets at the end of in vitro stage influences the minituber production after transplanting. With 100 μmol m^-2s^-1 total photosynthetic photon flux density(PPFD), a light spectrum study of 100% red light emitting diodes(LEDs) light spectrum(RR), 100% blue LEDs light spectrum(BB), 65% red+35% blue LEDs light spectrum(RB), and 45% red+35% blue+20% green LEDs light spectrum(RBG) providing illumination at the in vitro cultured stage of potato plantlets for 4 weeks using fluorescent lamp as control(CK) was performed to investigate the effects of LEDs light spectrum on the growth, leaf anatomy, and chloroplast ultrastructure of potato plantlets in vitro as well as the minituber yield after 2 months transplanting in the greenhouse. Compared to CK, RB and RBG promoted the growth of potato plantlets in vitro with increased stem diameter, plantlet fresh weight, plantlet dry weight, and health index. Furthermore, BB induced the greatest stem diameter as well as the highest health index in potato plantlets in vitro. Root activity, soluble protein, and free amino acid were also significantly enhanced by BB, whereas carbohydrates were improved by RR. In addition, thickness of leaf, palisade parenchyma and spongy parenchyma was significantly increased by BB and RBG. Chloroplasts under BB and RBG showed well-developed grana thylakoid and stroma thylakoid. Unexpectedly, distinct upper epidermis with greatest thickness was induced and palisade parenchyma and spongy parenchyma were arranged neatly in RR. After transplanting in the greenhouse for 2 months, potato plantlets in vitro from BB, RB, and RBG produced high percentage of large size tuber. BB improved fresh and dry weights of the biggest tuber but decreased tuber number per plantlet. In addition, RBG increased tuber number as well as tuber fresh and dry weight slightly. Our results suggested monochromatic blue LEDs as well as combined red, blue or/and green LEDs light spectrum were superior to fluorescent lamp spectrum in micro-propagation of potato plantlets. Therefore, the application of RBG was suitable;BB and RB could be used as alternatives.

Effects of Ce^(3+) on Chloroplast Senescence of Spinach under Light

The effects of Ce^3 ＋ on the chloroplast senescence of spinach under light were studied. The results show that when the chloroplasts are illuminated for 1, 5 and 10 min with 500 μmol·cm^-2· min^-1 light intensity, the oxygen evolution rate is rapidly increased. When the chloroplasts are treated for 20, 30 and 40 min with 500 μmol·cm^-2·min^-1 light intensity, the oxygen evolution rate is gradually decreased. While spinach is treated with 16μmol·L^-1 Ce^3＋ , the rate of oxygen evolution of chloroplasts in different illumination time （1,5, 10, 20, 30, 40 min） is higher than that of control, and when illumination time is over 10 min, the reduction of the oxygen evolution rate is lower than that of control. It suggests that Ce^3＋ treatment can protect chloroplasts from aging for long time illumination. The mechanism research results indicate that Ce^3＋ treatment can significantly decrease accumulation of active oxygen free radicals such as O2^- and H2O2, and reduce the level of malondialdehyde （MDA）, and maintain stability of membrane structure of chloroplast under light. It is shown that the redox took place between cerium and free radicals, which are eliminated in a large number, leading to protect the membrane fiom peroxidating.