Leaf Mutant Research Articles

Transcriptional profile of genes involved in ascorbate glutathione cycle in senescing leaves for an early senescence leaf (esl) rice mutant

To clarify the complex relationship between ascorbate–glutathione (AsA–GSH) cycle and H2O2-induced leaf senescence, the genotype-dependent difference in some senescence-related physiological parameters and the transcript levels and the temporal patterns of genes involved in the AsA–GSH cycle during leaf senescence were investigated using two rice genotypes, namely, the early senescence leaf (esl) mutant and its wild type. Meanwhile, the triggering effect of exogenous H2O2 on the expression of OsAPX genes was examined using detached leaves. The results showed that the esl mutant had higher H2O2 level than its wild type at the initial stage of leaf senescence. At transcriptional level, the association of expression of various genes involved in the AsA–GSH cycle with leaf senescence was isoform dependent. For OsAPXs, the transcripts of two cytosolic OsAPX genes (OsAPX1 and OsAPX2), thylakoid-bound OsAPX8, chloroplastic OsAPX7 and peroxisomal OsAPX4 exhibited remarkable genotype-dependent variation in their expression levels and temporal patterns during leaf senescence, there were significantly increasing transcripts of OsAXP1 and OsAPX7, severely repressed transcripts of OsAPX4 and OsAPX8 for the esl rice at the initial leaf senescence. In contrast, the repressing transcript of OsAPX8 was highly sensitive to the increasing H2O2 level in the senescing rice leaves, while higher H2O2 concentration resulted in the enhancing transcripts of two cytosolic OsAPX genes, OsAPX7 transcript was greatly variable with different H2O2 concentrations and incubating duration, suggesting that the different OsAPXs isoforms played a complementary role in perceiving and scavenging H2O2 accumulation at various H2O2 concentrations during leaf senescence. Higher H2O2 level, increased AsA level, higher activities of APX and glutathione reductase (GR), and relatively stable GSH content during the entire sampling period in the leaves of esl mutant implied that a close interrelationship existed between AsA level and APX activity in the ongoing senescence of rice leaves. The GSH supply in rice leaves was not the limiting factor for the efficient maintenance of AsA–GSH cycle, despite the senescence-related change in GR activity between the two rice genotypes.

Reflectance variation within the in-chlorophyll centre waveband for robust retrieval of leaf chlorophyll content.

The in-chlorophyll centre waveband (ICCW) (640–680 nm) is the specific chlorophyll (Chl) absorption band, but the reflectance in this band has not been used as an optimal index for non-destructive determination of plant Chl content in recent decades. This study develops a new spectral index based solely on the ICCW for robust retrieval of leaf Chl content for the first time. A glasshouse experiment for solution-culture of one chlorophyll-deficient rice mutant and six wild types of rice genotypes was conducted, and the leaf reflectance (400–900 nm) was measured with a high spectral resolution (1 nm) spectrophotometer and the contents of chlorophyll a (Chla), chlorophyll b (Chlb) and chlorophyll a+b (Chlt) of the rice leaves were determined. It was found that the reflectance curves from 640 nm to 674 nm and from 675 nm to 680 nm of the low-chlorophyll mutant leaf were drastically steeper than that of the wild types in the ICCW. The new index based on the reflectance variation within ICCW, the difference of the first derivative sum within the ICCW (DFDS_ICCW), was highly sensitive (r = −0.77, n = 93, P<0.01) to Chlt while the mean reflectance (R_ICCW) in the ICCW became insensitive (r = −0.12, n = 93, P>0.05) to Chlt when the leaf Chlt was higher than 200 mg/m2. The best equations of R-ICCW and DFDS_ICCW yielded an RMSE of 78.7, 32.9 and 107.3 mg/m2, and an RMSE of 37.4, 16.0 and 45.3 mg/m−2, respectively, for predicting Chla, Chlb and Chlt. The new index could rank in the top 10 for prediction of Chla and Chlt as compared with the 55 existing indices. Additionally, most of the 55 existing Chl-related VIs performed robustly or strongly in simultaneous prediction of leaf Chla, Chlb and Chlt.

Identification and Gene Mapping of an early senescence leaf 4 Mutant of Rice

ABSTRACTAn early senescence leaf 4 (esl4) mutant of rice (Oryza sativa L.) displayed yellowing followed by severe chlorosis of the leaf apex and margin from the late jointing stage to maturity. The content of photosynthetic pigments in the mutant was significantly lower than in wild‐type plants, and abnormalities in cell structure were detected in the mutant leaf blade. Stomatal conductance and rates of photosynthesis and transpiration were lower in esl4 than in wild‐type plants. Furthermore, compared with the wild‐type, the activities of superoxide dismutase and catalase were significantly lower in esl4, whereas peroxidase activity was significantly higher in esl4. Genetic analysis indicated that the early senescence of esl4 was controlled by a recessive nuclear gene. A population of 879 F2 mutants was used to fine‐map the ESL4 gene to chromosome 4 between the insertion and deletion primers S4–42 and S4–67. This 63‐kb stretch encodes 12 uncharacterized open reading frames. Quantitative real‐time polymerase chain reaction analysis (qRT‐PCR) revealed that levels of SGR transcripts were considerably more abundant in esl4 than in wild‐type. These results provide a foundation for map‐based cloning and functional analysis of the ESL4 gene.

Effect of EMS on Induced Morphological Mutants and Chromosomal Variation in Cowpea (&lt;i&gt;Vigna unguiculata&lt;/i&gt; (L.) Walp)

Effect of EMS (ethyl methane sulphonate) on induced morphological mutants and chromosomal variation in cowpea was studied using five different doses of mutagen along with a control in randomized blocked design with three replications. The morphological mutants there are two types of viable and chlorophyll mutants. Viable mutant contains tall, dwarf, early maturity, late maturity, leaf mutants pod mutant and flower mutants. The frequency of chlorophyll mutant contains albino, xantha and viridis. This concentration can damage or modify important components of plant cells and have been reported to affect the morphology, anatomy, biochemistry and physiology of plants differentially depending on the concentration level. These effects include changes in the cellular structure and metabolism of the plants e.g., dilation of thylakoid membranes, alteration in photosynthesis, modulation of the antioxidative system and accumulation of phenolic compounds. The morphological and chromosomal variation was found to be mutagen sensitive in somatic cells of cowpea. It was found to increase with increasing the concentration of EMS in Cowpea plants. The chemical mutagen like ethyl methane sulphonate induces high frequency of chromosomal changes like anaphasic bridge; anaphasic laggard, anaphasic bridge and clumbing of chromosome were including control plants also observed.

LSCHL4 from Japonica Cultivar, Which Is Allelic to NAL1, Increases Yield of Indica Super Rice 93-11

The basic premise of high yield in rice is to improve leaf photosynthetic efficiency and coordinate the source-sink relationship in rice plants. Quantitative trait loci (QTLs) related to morphological traits and chlorophyll content of rice leaves were detected at the stages of heading to maturity, and a major QTL (qLSCHL4) related to flag leaf shape and chlorophyll content was detected at both stages in recombinant inbred lines constructed using the indica rice cultivar 93-11 and the japonica rice cultivar Nipponbare. Map-based cloning and expression analysis showed that LSCHL4 is allelic to NAL1, a gene previously reported in narrow leaf mutant of rice. Overexpression lines transformed with vector carrying LSCHL4 from Nipponbare and a near-isogenic line of 93-11 (NIL-9311) had significantly increased leaf chlorophyll content, enlarged flag leaf size, and improved panicle type. The average yield of NIL-9311 was 18.70% higher than that of 93-11. These results indicate that LSCHL4 had a pleiotropic function. Exploring and pyramiding more high-yield alleles resembling LSCHL4 for super rice breeding provides an effective way to achieve new breakthroughs in raising rice yield and generate new ideas for solving the problem of global food safety.

Effect of EMS on Induced Morphological Mutants and Chromosomal Variation in Cowpea (&lt;i&gt;Vigna unguiculata&lt;/i&gt; (L.) Walp)

Effect of EMS (ethyl methane sulphonate) on induced morphological mutants and chromosomal variation in cowpea was studied using five different doses of mutagen along with a control in randomized blocked design with three replications. The morphological mutants there are two types of viable and chlorophyll mutants. Viable mutant contains tall, dwarf, early maturity, late maturity, leaf mutants pod mutant and flower mutants. The frequency of chlorophyll mutant contains albino, xantha and viridis. This concentration can damage or modify important components of plant cells and have been reported to affect the morphology, anatomy, biochemistry and physiology of plants differentially depending on the concentration level. These effects include changes in the cellular structure and metabolism of the plants e.g., dilation of thylakoid membranes, alteration in photosynthesis, modulation of the antioxidative system and accumulation of phenolic compounds. The morphological and chromosomal variation was found to be mutagen sensitive in somatic cells of cowpea. It was found to increase with increasing the concentration of EMS in Cowpea plants. The chemical mutagen like ethyl methane sulphonate induces high frequency of chromosomal changes like anaphasic bridge; anaphasic laggard, anaphasic bridge and clumbing of chromosome were including control plants also observed.

Leaf phenomics: a systematic reverse genetic screen for Arabidopsis leaf mutants.

The study and eventual manipulation of leaf development in plants requires a thorough understanding of the genetic basis of leaf organogenesis. Forward genetic screens have identified hundreds of Arabidopsis mutants with altered leaf development, but the genome has not yet been saturated. To identify genes required for leaf development we are screening the Arabidopsis Salk Unimutant collection. We have identified 608 lines that exhibit a leaf phenotype with full penetrance and almost constant expressivity and 98 additional lines with segregating mutant phenotypes. To allow indexing and integration with other mutants, the mutant phenotypes were described using a custom leaf phenotype ontology. We found that the indexed mutation is present in the annotated locus for 78% of the 553 mutants genotyped, and that in half of these the annotated T-DNA is responsible for the phenotype. To quickly map non-annotated T-DNA insertions, we developed a reliable, cost-effective and easy method based on whole-genome sequencing. To enable comprehensive access to our data, we implemented a public web application named PhenoLeaf (http://genetics.umh.es/phenoleaf) that allows researchers to query the results of our screen, including text and visual phenotype information. We demonstrated how this new resource can facilitate gene function discovery by identifying and characterizing At1g77600, which we found to be required for proximal-distal cell cycle-driven leaf growth, and At3g62870, which encodes a ribosomal protein needed for cell proliferation and chloroplast function. This collection provides a valuable tool for the study of leaf development, characterization of biomass feedstocks and examination of other traits in this fundamental photosynthetic organ.

Chloroplast dysfunction causes multiple defects in cell cycle progression in the Arabidopsis crumpled leaf mutant.

The majority of research on cell cycle regulation is focused on the nuclear events that govern the replication and segregation of the genome between the two daughter cells. However, eukaryotic cells contain several compartmentalized organelles with specialized functions, and coordination among these organelles is required for proper cell cycle progression, as evidenced by the isolation of several mutants in which both organelle function and overall plant development were affected. To investigate how chloroplast dysfunction affects the cell cycle, we analyzed the crumpled leaf (crl) mutant of Arabidopsis (Arabidopsis thaliana), which is deficient for a chloroplastic protein and displays particularly severe developmental defects. In the crl mutant, we reveal that cell cycle regulation is altered drastically and that meristematic cells prematurely enter differentiation, leading to reduced plant stature and early endoreduplication in the leaves. This response is due to the repression of several key cell cycle regulators as well as constitutive activation of stress-response genes, among them the cell cycle inhibitor SIAMESE-RELATED5. One unique feature of the crl mutant is that it produces aplastidic cells in several organs, including the root tip. By investigating the consequence of the absence of plastids on cell cycle progression, we showed that nuclear DNA replication occurs in aplastidic cells in the root tip, which opens future research prospects regarding the dialogue between plastids and the nucleus during cell cycle regulation in higher plants.

Characterization and mapping of a spotted leaf mutant in rice (Oryza sativa)

Characterization and mapping of a spotted leaf mutant in rice (Oryza sativa)

Identification of a Geranylgeranyl reductase gene for chlorophyll synthesis in rice.

Geranylgeranyl reductase (CHL P) catalyzes the reduction of geranylgeranyl diphosphate to phytyl diphosphate, and provides phytol for both Chlorophyll (Chl) and tocopherol synthesis. In this study, we isolated a yellow-green leaf mutant, 502ys, in rice (Oryza sativa). The mutant exhibited reduced level of Chls, arrested development of chloroplasts, and retarded growth rate. The phenotype of the 502ys mutant was controlled by by a recessive mutation in a nuclear gene on the long arm of rice chromosome 2. Map-based cloning of the mutant resulted in the identification of an OsChl P gene (LOC_Os02g51080). In the 502ys mutant, a single base pair mutation was detected at residue 1279 in DNA sequence of the gene, resulting in an amino acid change (Gly-206 to Ser) in the encoded protein. HPLC analysis of Chls indicated that the majority of Chl molecules are conjugated with an unsaturated geranylgeraniol side chain, in addition to small amount of normal Chls in the mutant. Furthermore, the mutant phenotype was complemented by transformation with the wild-type gene. Therefore, this study has confirmed the 502ys mutant resulted from a single base pair mutation in OsChl P gene.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-3-201) contains supplementary material, which is available to authorized users.

Characterization and mapping of a spotted leaf mutant in rice (Oryza sativa).

Spotted leaf mutant belongs to a class of mutants that can produce necrotic lesions spontaneously in plants without any attack by pathogens. These mutants have no beneficial effect on plant productivity but provide a unique opportunity to study programmed cell death in plant defense responses. A novel rice spotted leaf mutant (spl30) was isolated through low-energy heavy ion irradiation. Lesion expression was sensitive to light and humidity. The spl30 mutant caused a decrease in chlorophyll and soluble protein content, with marked accumulation of reactive oxygen species (ROS) around the lesions. In addition, the spl30 mutant significantly enhanced resistance to rice bacterial blight (X. oryzae pv. oryzae) from China (C1-C7). The use of SSR markers showed that the spl30 gene was located between markers XSN2 and XSN4. The genetic distance between the spl30 gene and XSN2 and between spl30 and XSN4 was 1.7 cM and 0.2 cM, respectively. The spl30 gene is a new gene involved in lesion production and may be related to programmed cell death in rice. The ability of this mutant to confer broad resistance to bacterial blight provides a model for studying the interaction between plants and pathogenic bacteria.

Leaf chloroplast ultrastructure and photosynthetic properties of a chlorophyll-deficient mutant of rice

Leaf chloroplast ultrastructure and photosynthetic properties of a natural, yellow-green leaf mutant (ygl1) of rice were characterized. Our results showed that chloroplast development was significantly delayed in the mutant leaves compared with the wild-type rice (WT). As leaves matured, more grana stacks formed concurrently with increasing leaf chlorophyll (Chl) content. Except for the lower intercellular CO2 concentration, the ygl1 plants had a higher leaf net photosynthetic rate, stomatal conductance, and transpiration rate than those of the WT plants. Under equal amounts of Chl, the excitation energy of PSI and PSII was much stronger in the mutant than that in the WT. The ygl1 plants showed higher nonphotochemical quenching and lower photochemical quenching. They also exhibited higher actual photochemical efficiency of PSII with a higher electron transport rate. Under the light of 200 &mu;mol(photon) m-2 s-1, the ygl1 mutant showed lesser deepoxidation of violaxanthin in the xanthophyll cycle than WT, but it increased substantially under strong light conditions. In conclusion, the photosynthetic machinery of the ygl1 remained stable during leaf development. The plants were less sensitive to photoinhibition compared with WT due to the active xanthophyll cycle. The ygl1 plants were efficient in both light harvesting and conversion of solar energy.

The maize pentatricopeptide repeat gene empty pericarp4 (emp4) is required for proper cellular development in vegetative tissues

The empty pericarp4 (emp4) gene encodes a mitochondrion-targeted pentatricopeptide repeat (ppr) protein that is involved in the regulation of mitochondrial gene expression and is required for seed development. In homozygous mutant emp4-1 kernels the endosperm is drastically reduced and the embryo is retarded in its development and unable to germinate. With the aim of investigating the role of emp4 during post-germinative development, homozygous mutant seedlings were obtained by cultivation of excised immature embryos on a synthetic medium. In the mutants both germination frequency as well as the proportion of seedlings reaching the first and second leaf stages were reduced. The anatomy of the leaf blades and the root cortex was not affected by the mutation, however severe alterations such as the presence of empty cells or cells containing poorly organized organelles, were observed. Moreover both mitochondria and chloroplast functionality was impaired in the mutants. Our hypothesis is that mitochondrial impairment, the primary effect of the mutation, causes secondary effects on the development of other cellular organelles. Ultra-structural features of mutant leaf blade mesophyll cells are reminiscent of cells undergoing senescence. Interestingly, both structural and functional damage was less severe in seedlings grown in total darkness compared with those exposed to light, thus suggesting that the effects of the mutation are enhanced by the presence of light.

Phenotypic characterization of the CRISPA (ARP gene) mutant of pea (Pisum sativum; Fabaceae): a reevaluation.

Leaf form and development are controlled genetically. The ARP genes encode MYB transcription factors that interact with Class 1 KNOX genes in a regulatory module that controls meristem-leaf determinations and is highly conserved in plants. ARP loss of function alleles and subsequent KNOX1 overexpression cause many unusual leaf phenotypes including loss or partial loss of the ability to produce a lamina and production of "knots" on leaf blades. CRISPA (CRI) is the ARP gene in pea, and a number of its mutant alleles are known. We made morphological and anatomical evaluations of cri-1 mutant plants while controlling for genetic background and for heteroblastic effects, and we used aldehyde fixation and resin preparations for anatomical analysis. Further, we compared gene expression in WT and cri-1 shoot tips and HOP1/PsKN1 and CRI expression in other leaf mutants. The cri-1 plants had more extensive abnormalities in the proximal than in the distal regions of the leaf, including ectopic stipules, narrow leaflets, and shortened petioles with excessive adaxial expansion. "Knots" were morphologically and anatomically variable but consisted of vascularized out-pocketing of the adaxial leaflet surface. HOP1/PsKN1 and UNI mRNA levels were higher in cri-1 shoot tips, and some auxin-regulated genes were lower. Low LE expression suggests that the GA level is high in cri-1 shoot tips. The CRISPA gene of pea suppresses KNOX1 genes and UNI and functions to (1) maintain proximal-distal regions in their appropriate positions, (2) restrict excessive adaxial cell proliferation, and (3) promote laminar expansion.

Increasing total leaf alkaloid concentrations in periwinkle (Catharanthus roseus) by combining the macro-mutant traits of two induced leaf mutants (‘necrotic leaf’ and ‘nerium leaf’)

SummaryThe leaves of periwinkle (Catharanthus roseus) are a source of the highly-valued anti-cancer alkaloids, vincristine and vinblastine. Increasing the concentrations of leaf alkaloids is an important objective of research programmes on this species because of their high medicinal and commercial value and their naturally low concentrations in plants.Two ethyl methanesulphonate (EMS)-induced macro-mutants, ‘necrotic leaf’ and ‘nerium leaf’, with enhanced concentrations of total leaf and root alkaloids compared to their parental variety,‘Dhawal’, have been identified.These two mutants were crossed and double-mutant recombinants expressing both macro-mutant traits, ‘necrotic leaf’ and ‘nerium leaf’, were isolated from the F2 generation to determine the possibility of further increasing the concentration of total leaf alkaloids. Fourteen F5 generation double-mutant recombinant lines were evaluated along with the two parental macro-mutants and the original parental variety, ‘Dhawal’. The 14 double-mutant recombinant lines showed 20 – 36% and 5 – 19% higher concentrations of total leaf alkaloids than the ‘nerium leaf’ and ‘necrotic leaf’ mutants, respectively, and 34 – 52% higher concentrations of total leaf alkaloids than ‘Dhawal’. Their fresh leaf yields were equivalent to those in the ‘nerium leaf’ mutant, but were significantly lower than those in the ‘necrotic leaf’ mutant and in ‘Dhawal’.

Identification and Gene Fine Mapping of Early Senescent Leaf Mutant esl5 in Oryza sativa

Identification and Gene Fine Mapping of Early Senescent Leaf Mutant <i>esl5</i> in <i>Oryza sativa</i>

Genetic Analysis and Gene Fine Mapping of Yellow-Green Leaf Mutant ygl80 in Rice

A yellow-green leaf mutant ygl80 was isolated by chemical mutagenesis.Compared with the wild-type parent 10079,chlorophyll content of the ygl80 mutant decreased by 76.64% and 54.59%,and the carotenoid content decreased by 53.85% and 41.18% at the seedling and booting stages,respectively.In addition,plant height,number of productive panicles per plant,number of spikelets per panicle,panicle length and 1000-grain weight reduced by 14.8%,16.5%,21.3%,9.1%,and 7.4%,respectively,at the maturity.Genetic analysis showed that the yellow-green leaf trait of the ygl80 mutant was controlled by one pair of recessive nuclear genes.Genetic mapping of the mutant gene was conducted by using 627 yellow-green leaf individuals from the F2 mapping population of ygl80/Zhefu 802.Finally,the mutant gene was mapped between InDel markers C2 and C3 on the long arm of chromosome 5,with genetic distances of 0.24 cM and 0.39 cM,respectively,and with physical distance of 90 kb,in this region eleven predicted genes had been annotated.Sequencing analysis of these candidate genes between the mutant and its wild-type parent revealed a single base change(C5027T)of YGL1(LOC_Os05g28200)gene for chlorophyll synthase resulted in a missense mutation(P348L)in the encoded product,suggesting that the ygl80 mutant gene is allelic to the ygl1 gene.The ygl80 mutant exhibited yellow-green trait throughout the growing period.But the ygl1 mutant showed yellow-green trait at seedling stage,then turned into green slowly,and its leaf color and chlorophyll and carotenoid contents almost closed to those of the wild-type parent during the later stage of growth.Different phenotypes of the two mutants may be caused by different mutational sites of genomic sequence of YGL1 gene encoding chlorophyll synthase.

Genetic Analysis and Gene Mapping of a Marginal Albino Leaf Mutant mal in Rice

The research on the color change of plant leaf is very important to clarify the structure and mechanism of photosynthetic system,such as chloroplast development and chlorophyll biosynthesis.A novel rice mutant mal(marginal albino leaf)with marginal albino leaf,was derived from the EMS-treated restorer line Jinhui 10.The mutant trait inherited steadily after several generations' self-crossing.The mal leaf displayed albino margin and narrow blade in the whole life.Compared with the wild type,mal decreased contents of photosynthetic pigments very significantly in the whole third leaf blade,margin parts of the second and third leaves at heading stage.The observation by that transmission electronic microscopy showed cells and chloroplasts in the green part of mal leaf developed normally,while in the albino part,the mesophyll cells were nearly hollow without obvious intact organelles and the chloroplast were fully degraded.Genetic analysis showed that the mutant trait was controlled by single recessive nuclear gene.MAL was finally mapped between SSR marker M22 and InDel marker ID27 with an interval of 171 kb on chromosome 8.These results provide a foundation for cloning and function analysis of MAL.

Genetic Analysis and Fine Mapping of a Premature Leaf Senescence Mutant in Rice ( Orzya sativa L.)

Leaf senescence induces degradation of chlorophyll and other macromolecules, reducing leaf photosynthetic capacity. This process is accompanied by the accumulation of reactive oxygen species(ROS), the decreasing of cell antioxidant enzyme(SOD, CAT, and APX) activity, and the increasing of aging related gene(SAG) expression, leading in early maturity and yield reduction. Therefore, studies on the genetic mechanism and gene function of premature senescence in rice, has the important effect and significance in genetic improvement of rice. PLS2 from space radiation mutation breeding project showed leaf senility, at booting stage. Compared with the wild type, in PLS2 the photosynthetic capacity decreased, the plant height, internode and panicle length shortened, tiller and effective tiller number reduced, number of grains per ear and seed setting rate were significantly lower, 1000-grain weight decreased, main panicle was stunted and grain-filling was not full. CAT activity decreased significantly in leaves, H2O2 accumulated, and the number of dead cell increased, chloroplast structures in leaves were worse, with more starches grains and osmiophilic granules. Dark treatment accelerated mutant leaf senescence, chloroplast ultrastructure was spheroidized. Using implicit localization population derived from PLS2/Shuhui 527 and PLS2/02428 the pls2 was located between markers RM14704(8 674 283 bp) and SL-I-5(8 758 394 bp) on chromosome 3, with physical distance of 84.11 kb, including 14 genes in the interval. Sequencing result showed that C was replaced with T in the position of 41 base pair of the ninth extron of LOC_Os03g15840 leading to an exchange of Arg(R) is replaced by Cys(C). LOC_Os03g15840 coding a glycosyl transferase(GTs) may be the candidate gene of pls2. These results provide a foundation for the further gene cloning and functional analysis of pls2.

Genotypic-dependent alteration in transcriptional expression of various CAT isoenzyme genes in esl mutant rice and its relation to H2O2-induced leaf senescence

To clarify the intricate relationship of H2O2-induced leaf senescence with distinct CAT gene expression, the genotypic-dependent alteration in the temporal patterns of H2O2 content, malondialdehyde (MDA) accumulation, relative conductivity, and the transcript expression of three CAT isoform genes during leaf senescence was investigated using two rice genotypes, namely, the early senescence leaf (esl) mutant and its wild type. Detached leaf segments were used to examine the effects of different exogenous H2O2 and ABA treatments on the expression of three CAT genes and other senescence-related physiological parameters. The results showed that the esl mutant had higher H2O2 level than its wild type at the initial phase of leaf senescence, which was followed by a sharp increase in MDA accumulation. Then, membrane integrity was severely destroyed and chlorophyll content decreased rapidly, which accelerated the senescence symptoms and significantly decreased the seed-setting rate in the esl mutant. The association of expression of the three CAT genes with rice leaf senescence lesions induced by H2O2 was isoform dependent, and the CATA and CATB expression exhibited remarkable genotype-dependent variation in the amount of transcript and their temporal pattern during leaf senescence. CATA and CATB also showed more sensitive response to exogenous H2O2 treatment compared with CATC, which suggests that CATA and CATB genes have a more important role than CATC in H2O2 inactivation of rice leaf senescence. The contribution of CATA expression to H2O2 scavenging in senescing rice leaves was most prominent at the initial stage of leaf senescence, with higher levels observed at the onset of leaf senescence, whereas CATB expression in esl flag leaf peaked later compared with CATA and was also responsible for the execution and acceleration of H2O2 inactivation particularly after the initiation of leaf senescence. CATB expression partially overlapped with CATA expression during H2O2 scavenging. For the CATC expression in rice leaves, its temporal pattern was poorly associated with H2O2-induced leaf senescence, but CATC was expressed preferentially in rice leaves and sheath and was involved in organ/tissue specificity. Exogenous ABA treatment can cause senescence-related increase in MDA accumulation and relative conductivity in the detached leaf segments, concomitant with a remarkable increase in H2O2 level. However, the expression of the three CAT isoforms under exogenous ABA treatment differed from those induced directly by H2O2 treatment, indicating the different ways for scavenging H2O2 accumulation during leaf senescence despite the increase in H2O2 level in senescing leaves induced by ABA.