| Plant senescence, as the last stage of plant development, plays important roles in development and environmental responses. Leaf-senescence progresses in an age-dependent manner and is affected by complex interaction of developmental age with other internal and external factors. Reproduce development also is a vital process for plants and also affected by several factors. Male sterility make the plant itself not normally produce the progeny, which attract many scientists to take research on this field. To date, the molecular basis of plant senescence and male sterility has been known to a certain extent, and there are still more unknown facts needed to study in future. In this paper, a newly discovered spontaneous mutant, smsl (senescence and male sterility 1), with the early senescence and male sterility in rice was used to observe the physiological characters and fine map the mutant gene. The main conclusions are as follows:1. When the smsl mutant grew up to three-or four-leaf stage, the long-spot like rust started to come up. At the tillering stage, the smsl mutant was dwarf with less tillering capacity, and many lesions appeared on the leaves except the leaf veins. Until the heading stage, the mutant tends to dying, developed about 20% panicles compared with the wild type parent, and the few spikelets can have ablity of seed setting and expressed the severe male-sterility. In addition, the temperture did not affect duration of the occurrence of spot like rust.2. The anthers of smsl plants were abnormally developed with a shrunk brown color shape in comparison with the wild type under the stereoscope. Moreover, the pollens of the mutant were not stained by the I2-KI solution and had weak livelily. Further investigation of transverse sections of anthers at mature pollen stage and leaves showed that the cells around the lesion mimic leaf, sterile pollens and the anther wall in the mutant was distorted or even died. The Scan electroscopic observation on leaf surface demonstrated that the mutant cells were distorted and non-aligned. 3. The leaf chlorophyll contents (SPAD values) measured by a portable fluorometer (SPAD-502, Minolta) in the mutant was much lower than that of the wild type parent. In experiment of trypan blue staining, the cell death spots, even without obvious lesion, displayed blue-black points in the mutant leaves, which demonstrated that form of larger cell-death-lesions was caused by continuingly dying cells. Thus it can be inferred that massive cell death causes the initiation and expanding of early senescence of the smsl leaves. In experiment of diamino benzidine (DAB) staining, compared with the wild type leaf, the mutant leave had the obvious spots of H2O2 accumulation, possible indicating that the cell death/early senescence was associated with the oxidative burst.4. The genetic analysis indicated that the smsl phenotype was controlled by a single recessive gene. With help of the F2 population derived from a cross between the self-pollinated mutant smsl and the indica variety Zhanshan 97, the gene smsl gene was located on the short arm of chromosome 8 in rice by the map-based cloning approach. Then through further enlarge the mapping population and the new markers developed, the smsl gene was fine-mapped in a 67kb region. By the mean of the bioinformatics, the SMS1 gene is a novel functional gene that hasn't been reported.In this research, the smsl gene has been fine mapped to the7kb region on the short arm of chromosome 8 in rice in rice, and the some results on physiological and biochemical characters were obtained, all which may lay the indispensable foundation for SMS1 gene clone and functional research. The further research will help us to know the regulation pathways and mechanisms relevant to the plant senescence and male sterility. |
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