水稻葉綠素缺失突變株之葉綠素新陳代謝之研究

Abstract

nonePhotosynthesis is a vital biological process in higher plants, which contributes to approximately 90% of biomass production in crops. Therefore, enhancing photosynthesis is considered as an effective strategy for increasing crop yield. In addition, photosynthesis take place in chloroplasts where chlorophylls (Chl) biosynthesis and degradation occur. Chloroplast pigments are extremely important during photosynthesis since they play an essential role in light absorption and energy transfer. Therefore, understanding and enhancing the efficiency of Chl biosynthesis are a potential way to increase accumulation of pigments and crop yield.Chl-deficient mutants is valuable approach for studying pigment synthesis. Generally, Chl-deficient mutants can be classified into two main types, namely, Chl b-lacking mutants (with undetectable Chl b) and Chl b-deficient mutants (containing reduced levels of Chl b). Next-generation sequencing (NGS) for transcriptome profiling was used to determine the transcription profiles and photosynthetic characteristics underlying different Chl a/b ratio of Chl b-lacking rice (Chl a/b ratio of ch1); Chl b-deficient rice (Chl a/b ratio of 11.25, ch11) and type 2b (Chl a/b ratio of 15.7, ch14).In the first chapter, the literature on the characteristic of chlorophyll-deficient mutants and the function and metabolism of Chl in higher plant.In the second, third and fourth chapter, the photosynthetic properties and transcriptomic profiles of wildtype and Chl b-lacking (ch11), 2 types of Chl b deficient mutants (ch11, ch14) of rice were investigated. Those mutants exhibited dwarf phenotype, light green leaves, and abnormal chloroplast structure (i.e., loss or small of starch granules, abundant vesicles, and abundant plastoglobuli), indicating abnormal plastid development with amplifier Chl a/b ratio. Changes in the expression of genes related to Chl metabolism, chloroplast development, cell division, and photosynthesis were found to be associated with abnormal chloroplast development and reduced Chl accumulation in the mutants. qPCR analysis was used to validate the DEGs. The data indicated that an increase in the Chl a/b may attribute to both a reduction in Chl content, owing to abnormal chloroplast development, and the involvement of an alternative degradation pathway.In the fifth chapter, the effect of temperature on the Chl biosynthesis and characteristic of ch1 rice was further investigated. The data indicated that ch1 was sensitive to low temperature at beginning of incubation and may adapt to temperatures ranging from 15 °C to 35 °C.In the sixth chapter, the effect of shade conditions on Chl biosynthesis in ch1 and wt was evaluated. Pigment contents, ultrastructure analysis, and RT-qPCR was evaluated in ch1 under 2 shade conditions. The data revealed that Chl b was unable to be generated in ch1 rice whereas Chl a remained unchanged. The results suggested that Chl b in ch1 rice was degraded or unable to generated rather than rapidly converted to Chl a during shade conditions.The final chapter discussed the finding and future works on Chl-deficient mutants.