Effects of phosphorus on activities of enzymes related to nitrogen metabolism in flag leaves and protein contents in grains of wheat

Chinese. 选用中筋品种鲁麦22和强筋品种济南17，在大田条件下研究了不同磷素水平（P0，不施磷；P1，每公顷施P2O5 105kg；P2，每公顷施P2O5 210kg）对小麦旗叶氮代谢有关酶活性、籽粒蛋白质积累和蛋白质组分含量的影响。结果表明，磷提高了灌浆前期和中期小麦旗叶硝酸还原酶（NR）和谷氨酰胺合成酶（GS）的活性，以及灌浆中期旗叶内肽酶（EP）的活性，其中对济南17的促进作用大于鲁麦22，而同一品种的P1和P2之间无显著差异；施磷亦提高了开花后14d之前旗叶可溶性蛋白质含量和7d之前游离氨基酸含量，与P0相比，P1有利于旗叶灌浆前期游离氨基酸的积累以及灌浆期间向籽粒的再分配，而过高的磷素水平（P2）对于灌浆后期旗叶游离氨基酸向籽粒再分配的影响较小；磷对籽粒蛋白质合成积累的促进作用在灌浆前期较大，后期较小，表现为前期施磷处理籽粒蛋白质含量显著高于P0，随着灌浆进程，差异逐渐缩小，最终2个品种P1处理成熟籽粒中蛋白质含量最高；不同磷素水平对2个小麦品种蛋白质组分的影响不一，对于2个小麦品种籽粒中清蛋白和球蛋白含量之和P1与P0无显著差异，而P1水平下籽粒谷蛋白和醇溶蛋白含量显著在鲁麦22中提高，在济南17中提高幅度较小，说明P1水平对改善小麦的营养品质意义不大，但能够改善其加工品质；P2水平下，济南17的加工品质有变劣的趋势。磷对小麦籽粒蛋白质各组分含量影响的复杂性要求在生产中，应针对不同品质类型小麦品种制定不同的优化栽培措施。

English. Nitrogen metabolism in leaves has important function on protein accumulation in wheat grains, involving three key enzymes, i.e. nitrate reductase（NR）, glutamine syntbotase（GS）and endopeptidase（EP）. It has been well documented the changes of related enzymes in nitrogen metabolism under different rates of nitrogen and potassium fertilizer. However, little research has been done about the effect of phosphorus（ P）on the contents of protein components in wheat. The objectives of the present research were to investigate the effect of P on the activities of three enzymes concerned with nitrogen metabolism in flag leaves and protein accumulation as well as its component contents in wheat grains. The study was carried out from 2001 to 2002 with two wheat cultivars（ Triticum aestivum L. cv. Lumai 22 and cv. Jinan 17）in field. Three P rates（PO, P1 and P2）were set in the experiment, and the amounts of P application were 0 kg, 105 kg and 210 kg P2O5 per ha, respectively. The results showed that the activities of NR, GS and EP in flag leaves were increased with the increase of P application during the early and middle grain filling stages （ Fig. 1 - 3 ）, and the effect of P application for Jinan 17 was greater than that for Lumai 22, but there was no significant difference between P1 and P2 treatment. The contents of soluble protein and free amino acid in flag leaves were increased by P application before 14 d and 7 d after anthesis respectively （Fig.4 and Fig.5）. And P1 treatment was of benefit to the accumulation of free amino acid during early grain filling stage and the redistribution to grains during the whole grain filling stage, whereas P2 treatment was less effect on the redistribution. It indicated that the synthesis and accumulation of protein in grains were increased by P application during grain filling stage, especially in the early stage. The protein content in P1 and P2 was significantly higher than that in PO during the early grain filling. When maturing,P1 treatment had the highest total protein content in both caltivars（Fig.6）. In P1 treatment, there were little effect on the contents of albumin and globulin, and significant increase for the contents of gliadin and gluten in the two caltivars, which was greater for Lumai 22 than for Jinan 17（Table 1 ）. These results suggested that P1 treatment had little effect on wheat nutritional quality, but could improve its processing quality. However,excessive P application could deteriorate the processing quality as for Jinan 17. Therefore, different cultivation management should be adopted according to the different quality demans of different wheat types.