氮素對水稻穀粒蛋白質表現及品質形成之影響

Abstract

稻米品質的優劣，雖以品種特性為基礎，但其品質卻亦受外界的栽培環境所影響，如：氣候、栽培管理、氮肥施用等。本研究之主要目的為探討氮肥施用對水稻穀粒蛋白質表現之影響與其稻米品質的關係。 本研究將氮肥處理分為37.5 kg/ha、75 kg/ha、150 kg/ha三個處理等級，施用於三個良質米品種，臺稉9號、越光、及臺中秈10號，探討葉片中葉綠素含量、生長所需積溫、發育葉數、稻米澱粉性質、稻米總蛋白質含量、稻米貯藏性蛋白質含量及蛋白質體之表現等是否受氮肥處理之影響。結果顯示施氮量的增加會延長水稻生育期，提高成熟所需積溫、植株高度與分蘗數。但水稻發育葉數不會因氮肥的增加而改變。水稻葉片在施加追肥後會延緩老化，且葉綠素含量（SPAD值）會隨氮肥增加而提高。氮肥增加造成越光、臺稉9號榖粒內的Amylose含量下降，臺中秈10號的Amylose含量上升。近一步藉由Rapid Viscosity Analysis〈RVA〉發現稻米粉的breakdown與final viscosity隨著施氮量增加而下降，其中breakdown可代表稻米的黏流性（thixotropy）且與蛋白質含量呈負相關，而final viscosity則與烹煮後米飯食味品質的粘著性（stickness）相關。故推論breakdown與final viscosity的下降會造成食味品質的降低。透過直鏈性澱粉與蛋白質含量之綜合分析，發現氮素增施造成稻米RVA性質下降的主因可能為榖粒中蛋白質含量的增加，而非Amylose含量的改變。蛋白質方面，本研究發現稻米蛋白質含量隨著氮肥增加而增加，更近一步分析其貯藏性蛋白質的改變，發現在增加氮肥的情況下prolamins與glutelins量會增加，而albumins會減少，其中以prolamin的變化最顯著。在2-D gel中發現glutelins大部分的subunits是隨氮肥增加其表現量也增加，而prolamins的各subunits則是因品種的不同其表現量增加或減少。此結果顯示氮肥對稻米各類貯藏性蛋白質基因群的調節並非同步地。此外，本試驗也建立了albumins 蛋白質群的SDS-PAGE圖譜之各蛋白質鑑定，可供後續研究使用。又氮肥對其他功能性蛋白質表現的影響，如GBSS、SSII、elongation factor、及allergen like proteins等也可能影響稻米品質的形成。綜合現有的試驗結果，本論文提出一模式說明氮素影響稻米品質形成的可能途徑。

Although the quality of the rice grains are mainly based on the genotype background, the culture environments, including climate, management, and nitrogen fertilizer, can still significantly cause quality change. This study aimed to explore the effects of nitrogen fertilizer on the expression of proteins of rice grains and the relationship with the grain quality formation. Rice plants of three quality rice cultivars (Taikeng 9, Koshihikari、and Taichung sen 10）were treated with three levels of nitrogen fertilizer: 37.5 kg/ha、75 kg/ha、150 kg/ha in this study to estimate the responses of chlorophyll content in leaves, effective accumulated temperature, leaf number, grain physicalchemical properties, total protein content and storage protein content in rice grains, as well as to check the effects of nitrogen fertilizer on proteins expression by proteomics approach. Results showed that increase of nitrogen fertilizer level has positive effect on growth duration, plant height, and tiller number, while the nitrogen fertilizer level has no effect on leaf number. Applying of additional fertilizer can delay leaf ageing, but increase the chlorophyll content (SPDA value). Higher level of nitrogen fertilizer decreased amylose content in the grains of Koshihikari、Taikeng 9, but increased amylose content in grains of Taichung sen 10. Through rapid viscosity analysis 〈RVA〉,values of breakdown and final viscosity were decreased with the increase of nitrogen fertilizer rate, suggesting that thixotropy of the rice flour, stickness were also decreased by the increase of nitrogen rate. In chemical composition, grain protein content was increased by the higher nitrogen application, but change of amylose was not consistent with nitrogen application rate. The nitrogen induced high protein content may be the major factor conferring the changes of physical-chemical characteristics of rice grains. More detailed analysis of the change of storage proteins revealed that the increase of the level of nitrogen fertilizer has positive effect on the content of prolamins and glutelins, especially the prolamins. Nevertheless, albumin content was decreased with the increase of the nitrogen rate. Through 2-D gel analysis, amount of most of the subunits of glutelins and prolamins could be elevated by increase of nitrogen rate, while the fluctuations of the expression amount of subunits was not synchronized among cultivars. Effects on the expressions of other important proteins, including GBSS, SSII, elongation factor and allergen like proteins, were also determined and discussed in the present study. In addition a basic proteomic profile was established for albumins of rice grains, and can be a useful tool for related studies. Conclusively, a schematic model has been proposed to rationalize the pathway of the influence of nitrogen on rice quality formation.