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As an essential process in the life of a plant, natural leaf senescence is necessary for adaptation to environmental diversity, whereas early leaf senescence can reduce per-unit yield and cause inferior harvest quality during crop production. To explore the molecular mechanism of leaf senescence in rice (Oryza sativa L.), we studied an early senescence leaf (esl11) mutant obtained by ethyl methane sulfonate (EMS) mutagenesis. The leaves of the esl11 mutant showed normal growth and leaf coloration prior to the three-leaf stage, but after this stage, all fully expanded leaves underwent yellowing and senescence from the edges of the leaf blade and tips, apart from the emerging leaves, which showed gradual growth. The net photosynthetic rate and photosynthetic pigment content of the tip and leaf base of the mutant esl11 were significantly lower than those of the wild type. The role of active oxygen species O2 -, H2O2, and ×OH in the mutant increased, whereas the activities of MDA, peroxidase, superoxide dismutase, and catalase decreased compared with the wild type. The results of trypan blue staining on the senescent part of the leaf tip of the mutant esl11 indicated procedural death in part of the cell, whereas the wild type showed no change. The early leaf senescence trait in the mutant was controlled by of recessive nuclear gene, which was mapped to chromosome 7, with a physical range of 143.0 kb. The results of this study provide the foundation for important progress in gene cloning and functional analysis of the esl11 gene. [ABSTRACT FROM AUTHOR]

A novel starch accumulation and early senescent leaf mutant esl10 was identified among progenies of the rice (Oryza sativa L.) indica maintainer line Xinong 1B raised from seeds treated with ethyl methane sulfonate (EMS). Under paddy field conditions, leaf starch accumulation commenced at the three-leaf stage in the mutant esl10 and the leaves began to yellow at the four-leaf stage, gradually extending from the tip to the middle of the leaf. The yellowing phenotype was most obvious at the tillering stage and persisted until maturity. Compared with the wild type, photosynthetic pigment concentrations and net photosynthetic rate of esl10 were significantly lower, whereas the concentrations of reactive oxygen species and malondialdehyde (MDA) were higher. Moreover, catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activities decreased in leaves at the tillering stage. Quantitative real-time polymerase chain reaction showed that the expression of genes associated with starch metabolism pathway changed. Excessive accumulation of leaf starch may have caused the leaf premature senescence, finally influencing grain yield and quality of esl10. Genetic analysis showed that esl10 was controlled by a dominant nuclear gene (tentatively called ESL10). ESL10 was mapped between the single-nucleotide polymorphism markers SNP585 and SNP498 on chromosome 7 with a physical distance of 416.29 kb including 56 annotated genes. The results provide a foundation for gene cloning and functional analysis of ESL10. [ABSTRACT FROM AUTHOR]

A novel rice (Oryza sativa L.) mutant derived from the ethyl methane sulfonate-treated restorer line Jinhui10 was identified that exhibited stable inheritance and was tentatively named yellowgreen leaf 6 (ygl6). Leaves of ygl6 were yellowgreen at the seedling stage and pale green at the jointing stage. The contents of chlorophyll a, chlorophyll b, and carotenoids were significantly lower in the mutant than those in the wildtype (WT) at the seedling and heading stages. Leaf mesophyll cells of the ygl6 mutant and WT showed no obvious differences in ultrastructure. However, ygl6 chloroplasts developed abnormally with poorly developed thylakoids and fewer grana stacks. Genetic analysis demonstrated that the mutation was controlled by a single recessive gene. Genetic mapping of the mutant gene was conducted using 1997 recessive individuals from the F2 segregating population. YGL6 was mapped to the centromeric region of chromosome 12 between the insertion/deletion primers Ind23 and Ind37, with an interval of 143 kb. Sequence analysis of the candidate genes within the delimited region showed a single base-pair change in Os12 g23180 that corresponded to a codon transition from leucine to a stop codon. Results of RNA interference knockdown of YGL6 suggested that Os12 g23180 is the candidate gene. Further characterization of YGL6 will provide insights into the molecular mechanisms of chloroplast development. [ABSTRACT FROM AUTHOR]

An 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. [ABSTRACT FROM AUTHOR]