鋅逆境下水稻代謝物之變化

Abstract

植物微量營養元素鋅對作物的生長扮演重要的角色，故其在水稻中的調控的分子機制已被廣泛研究。然而，鋅逆境如何改變轉錄體和代謝體，進而影響其生理反應之機制，仍然未知。實驗室過去轉錄體學（RNA定序）的研究結果發現：在鋅逆境下，初級代謝物相關基因會差異性表現。為瞭解轉錄體變化對代謝物的影響，本實驗使用10天大的水稻（Oryza sativa L. cv Kitaake）幼苗進行3、14和21天的不同濃度鋅處理，包括缺鋅（0.002μM ZnSO4），正常鋅（0.2μM ZnSO4）和過量的鋅（300μM ZnSO4），觀察其性狀並進一步分析其代謝產物的變化。研究結果發現，缺鋅和過量鋅處理的水稻幼苗，其根長變短、株高變矮、和葉片白化或黃化。缺鋅處理下的葉片細胞有大量澱粉粒在葉綠體中積累，過量鋅處理則會破壞細胞膜並改變葉綠體的結構。缺鋅期間碳水化合物濃度的變化和澱粉粒的累積，可能是由於澱粉生合成速率增加及澱粉降解受抑制所致。缺鋅處理下的水稻，其氨基酸的累積亦會增加，脂肪酸含量則降低；而在過量的鋅逆境下，碳水化合物，氨基酸和脂肪酸的變化很小。因此，水稻初級代謝的調節與鋅的有效濃度有關。

The molecular mechanism of zinc (Zn) stress in plants have been studied extensively due to its importance to agricultural crop; however, there are still puzzles pertaining to the metabolic regulation in response to both Zn deficiency and phytotoxicity. Preliminary RNA-sequencing results showed that GO-categorized genes for the regulation of primary metabolic process were differentially expressed during Zn stress. To understand the mechanism behind these transcriptional changes, rice (Oryza sativa L. cv. Kitaake) seedlings were treated with different concentration of Zn for 3, 14, and 21 days, inclusive of Zn deficiency (0.002 μM), normal Zn (0.2 μM), and excess Zn (300 μM); and their metabolic profiling were further analyzed. Our results showed noticeable morphological changes such as reduced root length, decreased shoot height and increased leaf chlorosis in the Zn deficient and excess Zn-treated plant, compared to its corresponding normal plants. The Zn deficient leaf cells showed accumulation of starch granules in chloroplast, and excess Zn cells exhibited damages on cell membrane and chloroplast. Altered carbohydrate concentration and starch accumulation during Zn deficiency was likely due to increase in the rate of starch biosynthesis, and inhibition of starch degradation. Zinc deficiency also lead to the increased accumulation of amino acids and decrease fatty acid contents in rice plants, whereas alterations in carbohydrates, amino acids, and fatty acids were minimal under excess Zn stress. Consequently, regulation of primary metabolism in rice is heavily reliant on Zn availability.