摘要或動機

全球暖化造成水災頻繁，嚴重威脅植物生存。看似耐淹水的水稻，在完全淹水下亦有其生存危機。水稻FR13A 因耐水性極佳而常用於分子育種，IR64 產量高卻不耐水。是那些特質使稻種間有不同耐水機制？我們觀察其幼苗淹水24 小時後生長情形、通氣組織 (aerenchyma) 變化及應用即時反轉錄聚合?鏈反應 (real time RT-PCR)，研究酒精醱酵的主要蛋白質：乙醇脫氫? (alcohol dehydrogenase, ADH1, 2) 及丙酮酸脫羧? (pyruvate decarboxylase, PDC2) 基因之表現量。兩種水稻的胚鞘及根都因淹水減緩生長，以FR13A 減緩最明顯。通氣組織在淹水期間都有增加，FR13A 中的形成近似於對照組，IR64 則明顯較差。FR13A 中ADH1 及ADH2 在淹水一小時後迅速增加60 至100 倍，IR64 僅增加10 至20 倍。PDC2 在IR64 中表現量的增加幅度較大，但最大值仍小於FR13A 之基礎表現量。由此可知，FR13A 在完全淹水時成長減緩而原有通氣組織則持續生長，且酒精醱酵中的基因有獨特誘導反應，因此耐水性較佳。藉由此研究揭開水稻細胞及分子生物學上的耐水反應策略，將可更精準地改良稻作使其對抗淹水逆境，解決未來因環境造成的糧食危機。Global warming increases the frequency of flooding, which drastically reduces the growth and survival of plants. Although rice (Oryza sativa) appears well-adapted to flooding of roots as it is often farmed in paddies, problems arise when the whole plant is submerged in water. I am interested in the structural and molecular responses that result in different submergence tolerances in rice cultivars. Indica rice FR13A is submergence-tolerant and frequently used in molecular breeding for this trait, while IR64 is a high-yield but submergence-intolerant cultivar. In this study, I monitored the growth rate, aerenchyma formation, and gene expressions of the carbohydrate metabolism in FR13A and IR64 seedlings subjected to submergence for 24 hours, by means of real time RT-PCR and microarray. FR13A had prominently inhibited coleoptile growth and sustained levels of aerenchyma formation whereas IR64 did not. The mRNA levels of alcohol dehydrogenase 1 (ADH1) in FR13A was induced prominently, while ADH2 was induced in IR64 during early hours of submergence. The induction of pyruvate decarboxylase 2 in FR13A was stronger than IR64. The expression of sucrose synthase was similar in both strains. Expressions of the genes involved in anaerobic carbohydrate metabolism were also studied by analyses of microarray data. My findings demonstrate that elongation quiescence, persistent aerenchyma formation and shifts in anaerobic carbohydrate metabolism gene expressions are beneficial strategies of FR13A towards submergence. Through elucidating the molecular basis of coordinating submergence tolerance genes as this study provided, it will be possible to discover multiple traits associated; hence crop improvement for flooding tolerance could be achieved.