玉米不同组织器官谷氨酰胺合成酶同工酶表达差异及聚合方式

摘要

Glutamine synthetase (GS) is a key enzyme in nitrogen assimilation and recycling in cereals. In this study, the expres-sion characteristics of GS isoenzymes in different tissues and organs of maize in grain-filling period were analyzed, and the as-sembly of GS isoenzymes were indentified. The GS isoforms expressed differentially in different organs were shown by West-ern-blot obviously; GS1 with a molecular weight of about 40 kD expressed highly in all tissues, and GS1 with a molecular weight of about 39 kD was merely expressed in the node of ear position and pedical, and GS2 with a molecular weight of about 44 kD was weakly expressed in the photosynthtic tissue such as leaf. With a modified blue naive PAGE (BNE) technique and in-gel ac-tivity analysis, the size of GS holoenzyme was calibrated; combined the 2-D gel with western-blot analysis, the subunits composi-tion of GS isoenzymes were identified. Three GS isoenzymes with different sizes were identified in maize. GS2 holoenzyme was about 460 kD and likely a decamer, GS1 holoenzyme existed two kinds of assembly state, one was about 410 kD and likely a decamer, another was about 240 kD and more likely a pentamer; therefore, the expression of GS isoenzymes exists diversity in maize.%谷氨酰胺合成酶(GS)是作物氮同化及转移利用的关键酶,本试验研究了玉米灌浆期不同组织器官的GS同工酶表达特性,鉴定了玉米GS同工酶的聚合方式.Western blot结果表明,玉米不同组织器官的GS同工酶亚基表达存在明显差异,分子量约40 kD的GS1亚基在所有组织中均大量表达,39 kD的GS1亚基仅在穗位节及穗柄中大量表达,分子量约44 kD的GS2亚基在叶片等光合组织中微量表达.通过改进BNE技术,结合胶内转移酶活性的测定,分析了玉米GS同工酶全酶的大小;利用2-D胶结合Western blot鉴定了GS同工酶相应的亚基组成.结果表明,在玉米组织鉴定出3种分子量不同的GS同工酶,GS2全酶分子量约460 kD,为十聚体;GS1全酶有2种聚合状态,一种是分子量约410 kD的十聚体,另一种是分子量约240 kD的五聚体形式,可见玉米GS同工酶表达存在多种方式.