氮素對高溫下水稻穎果充實期蛋白質累積之影響

Abstract

稉型水稻適合生長於溫帶氣候地區，而台灣地處亞熱帶氣候，夏季炎熱的高溫常造成第一期水稻穀粒白堊質產生，以致於品質的下降，全球面臨氣候暖化，此現象可能將更為嚴重。過去對於水稻與高溫的研究多注重於穀粒內的大分子，例如澱粉與蛋白質之改變，鮮少針對高溫下穎果充實期蛋白質累積過程之變化與影響，本試驗希望透過高溫處理加上氮素的添加，觀察高溫下穎果內氮源的利用與蛋白質累積之變化，進而探討高溫對品質影響的原因與改善方法。試驗結果顯示，高溫降低水稻穎果的結實率與充實率，外觀性狀則是呈現嚴重的白堊質，高溫處理下添加氮素則可部分恢復，但是不足以恢復到常溫的結果，不過仍然顯示氮素的添加的確有抵抗高溫逆境之效果，對水稻的產量與品質皆有所助益。生理試驗中，從穀粒鮮重累積與外觀性狀可以看出，高溫使穎果提早且快速累積鮮重，充實後期穎果的種（果）皮與維管束上的葉綠素提早老化消失，等於 提早結束充實期，造成最後糙米乾重比常溫來的低，而提早結束充實期的原因可以從過氧化氫的試驗中發現，高溫處理使穎果內過氧化氫含量提高，尤其充實後期更為顯著，且糙米 pH 值試驗顯示高溫組的 pH 值顯著低於常溫。而氮素處理組則發現，高溫下穎果的過氧化氫含量較少，充實期較為延長。透過 HPLC-FLD 與 SDS-PAGE 分析穎果內氨基酸與儲存性蛋白質的含量，結果顯示高溫處理造成 alanine 的含量顯著提高，而氮素的添加使 alanine 與其他胺基酸含量相較之下，顯著增加，且 ATP 的含量也有所提昇。儲存性蛋白質的結果顯示 glutelins 在充實前期提早累積，充實後期與常溫組無顯著差異，prolamins 也是提早累積，但是在充實後期的含量顯著低於常溫組，albumins 與 globulins 則在充實期皆高於常溫組，唯 Glo-6（19 kA globulins precursor）在充實後期顯著低於常溫組。總體來說，高溫使穎果內儲存性蛋白質的總量下降，進而影響到蛋白質體與澱粉粒之間的堆疊，造成白堊質的發生。氮素添加對儲存性蛋白質中 prolamins 的含量恢復到與常溫組相當，表示高溫處理對穎果之危害，透過添加氮素有所改善。 本試驗之結果顯示高溫對水稻穎果充實期之影響，而添加氮素可能恢復高溫對碳水化合物與氮源相關代謝的損害，並提出高溫下水稻穎果內氮素利用途徑模式圖，未來希望透過其他代謝途徑與基因表現等實驗來加以驗證。

In Taiwan, japonica rice usually exposes to high temperature in summer during grain-filling stage, and frequently causes chalky grain and reducing grain quality. It is expected even worse by global warming in recent years. Previous researches usually focused on starch or protein biosynthetic pathway, their components, or structural changes under high temperature. Few researches have been dealing with the effects on relationship between protein accumulation and grain quality by high temperature during grain-filling stage. The present study focused on effects of nitrogen and storage protein accumulation during grain- filling stage under high temperature of japonica rice ( TK 9 ). The results showed that high temperature caused reducing setting and filling percentage of rice caryopsis. Increase in fresh weight of caryopsis was enhanced but stopped earlier under high temperature, resulting lower grain weight than normal one. Chalky grain percentage was also increased. Nitrogen fertilizer treatment could partially recover the defective effects induced by high temperature. In physiological analysis hydrogen peroxide production was elevated by high temperature during later grain-filling stage. ATP production was also suppressed by high temperature. Through HPLC-FLD and SDS-PAGE analysis, the changes of amino acids and storage proteins were further determined. Results showed that alanine was significantly elevated during early grain-filling stage under high temperature. Amount of glutelins elevated in early grain-filling stage, but there was no differences that of control in later stage. Amount of prolamins also increased at early grain-filling stage, but declined to half of control at later stage. Amount of albumins and globulins elevated during grain-filling stage; nevertheless, the quantity of storage proteins remained decrease than control. The high temperature caused lower amount of storage proteins affect the packing of starch and protein bodies, resulting in a characteristic of chalky grain. Adding nitrogen fertilizer could increase the content of ATP and prolamins. Chalky grains slightly recovered. The present results suggest the existence of a peroxidative condition in caryopsis growing under high temperature, and might cause defective changes in energy, carbohydrate, and nitrogen related metabolisms. Nitrogen application may ameliorate the defective effects induced by high temperature. Studies in metabolic mechanism and gene regulation are certainly needed to elucidate detail pathway in the future.