不同酸度酸雨对小麦花后氮硫代谢和籽粒蛋白组分的影响

酸雨是中国重要的环境问题,为研究酸雨对小麦籽粒品质的可能影响,以小麦品种扬麦15和汶农17为材料开展盆栽试验,研究了不同酸度(pH2.5、p H4.0和p H5.6)酸雨对小麦花后氮硫代谢关键酶活性和籽粒蛋白质含量及组分的影响。结果显示:酸雨处理抑制叶片硝酸还原酶(NR)活性,提高了扬麦15整个灌浆期及汶农17灌浆中后期叶片谷氨酰胺合成酶(GS)活性,促进了叶片蛋白的降解,降低了叶片可溶性蛋白含量。不同酸度酸雨提高了成熟期籽粒中蛋白质含量,酸度越强,增加幅度越大,籽粒中各蛋白组分含量和大部分氨基酸含量也有明显提高。酸雨提高了扬麦15叶片丝氨酸乙酰转移酶(SAT)和O-乙酰丝氨酸硫裂解酶(OAS-TL)活性,但对汶农17硫代谢关键酶活性影响较小,酸雨处理还提高了籽粒中二硫键和含硫氨基酸含量。可见酸雨对小麦氮硫代谢有不同程度影响,进而影响了小麦籽粒蛋白质含量和组成,酸度越强影响越大,但不同品种对酸雨响应有一定差异。

Effect of different acidities of acid rain on nitrogen and sulfur metabolism and grain protein levels in wheat after anthesis

Recently, acid rain has become a serious environmental problem in China. Acid precipitation has occurred in about 40% of the entire area, especially in the rapidly developing industrial regions, such as the many areas around the Yangtze River. Acid rain is formed when sulfur dioxide (SO₂) and nitrogen oxides (NO_x) react with water in the atmosphere to produce H₂SO₄ and HNO₃ and deposit as acid precipitation. Most studies have focused on the effect of acid rain on seed germination, plant morphology, plant carbon metabolism, and grain yield. However, the impacts of acid rain on plant nitrogen and sulfur metabolisms and grain quality have rarely been investigated, although SO₄^2- and NO₃^-are known to be the main components of acid rain. Wheat (Triticum aestivum L.) is a staple food and plays an important role in food security. It is sensitive to biotic and abiotic stresses from flowering to maturity. In this study, a pot experiment was performed to determine the effects of spraying of acid rain with varying acidities (pH, 2.5, 4.0, and 5.6) after anthesis on the activities of key enzymes related to nitrogen and sulfur metabolisms and amino acid and protein contents in wheat grains. Two winter wheat cultivars (Yangmai 15 and Wennong 17) were used in this study. The results showed that acid rain inhibited nitrate reductase activity and decreased the soluble protein content of leaves. At 10 days after anthesis, the soluble protein content in Wennong 17 and Yangmai 15 subjected to acid rain (pH 2.5) decreased by 26.58% (P < 0.05) and 21.31% (P < 0.05), respectively, compared with that in the control. Glutamine synthetase activity in the leaves was increased in Yangmai 15 during the entire grain filling stage and in Wennong 17 only during the late grain filling stage. Acid rain gradually decreased the free amino acid content from the beginning of grain filling stage up to the later stages. The contents of protein and most essential amino acids in mature gains were increased by acid rain and were the highest after treatment with acid rain of higher pH. Acid rain increased the activities of serine acetyltransferase and O-acetylserine(thiol)lyase in Yangmai 15, but had little effect on the activity of key enzymes related to sulfur metabolism in Wennong 17. Acid rain treatment also increased the contents of disulfide bonds and amino acids containing sulfur in the wheat grains of both the cultivars. Thus, acid rain had different influences on wheat sulfur and nitrogen metabolisms, thereby affecting the protein content and composition of wheat grains, and thus its nutritional quality.