烤烟成熟期烟叶GS同工酶活性与氮素运转的关系

为研究不同氮效率烤烟品种成熟期叶片谷氨酰胺合成酶同工酶活性和相关生理指标的动态变化,深入理解烤烟叶片氮素代谢的生理生化机制。以氮效率不同的3个烤烟品种中烟100、K326和NC89为材料进行盆栽试验。在不同叶龄时期取第12片叶(自下向上数),采用Western blot方法,测定叶片的叶肉和主脉谷氨酰胺合成酶同工酶蛋白亚基含量,同时对叶片NH_4~+浓度、总氮、质外体NH_4~+浓度以及氨气挥发量进行测定。结果表明,烤烟叶片叶肉中的GS主要以GS2同工酶为主,其蛋白亚基含量随着叶龄的增长逐渐下降,而叶脉中GS1同工酶占主导地位,其蛋白亚基含量呈先升高后下降的趋势。在叶龄45～65 d,叶肉和主脉的GS同工酶活性均表现为NC89K326中烟100,且品种间差异达显著水平。叶肉和主脉中GS1同工酶活性与总氮和叶片铵浓度呈负相关,与质外体铵浓度和氨气挥发量呈正相关。而叶肉中GS2同工酶活性与总氮和叶片铵浓度呈正相关,与质外体铵浓度和氨气挥发量呈负相关。叶脉GS2活性仅与总氮和氨气挥发量有显著相关性。氮低效烤烟品种成熟期叶片中两种谷氨酰胺合成酶同工酶活性均较低,氮素转移和再利用能力差,导致植株吸收的氮素以氨气形式挥发损失量大,叶片衰老速度较快。而氮高效品种氮素同化和再利用能力较强,氨气挥发量小,易发生贪青晚熟。

Relationship between GS isoenzyme activity and nitrogen transportation in flue-cured tobacco leaves

A pot experiment was conducted to study the dynamic changes of glutamine synthetase isoenzyme activity and the related physiological indexes in leaves of flue-cured tobacco with different nitrogen efficiencies at maturity stage, and understand the physiological and biochemical mechanism of nitrogen metabolism in flue-cured tobacco leaves. Three different flue-cured tobacco varieties Zhongyan 100, K326, and NC89 with different nitrogen efficiencies were used as materials, and the 12th leaves were taken at different leaf ages. Western blot method was used to determine the content of glutamine synthetase isoenzyme isoforms in leaf mesophyll and main veins. At the same time, the concentrations of NH₄ ⁺, total nitrogen, apoplastic NH₄ ⁺ and ammonia volatilization were determined. The results show, GS2 was the main form of GS isoenzyme in mesophyll of flue-cured tobacco leaves, the protein subunit content gradually decreased with the age of the leaf. The GS1 isoenzyme dominated in the veins, and its protein subunits showed a trend of increasing first and then decreasing. From 45 to 65 days of leaf age, the GS isoenzyme activities of leaf mesophyll and main vein were all expressed as NC89 > K326 > Zhongyan 100, and the difference among varieties was significant. The activities of GS1 in mesophyll and main veins were negatively correlated with total nitrogen and leaf ammonium concentrations, and positively correlated with apoplastic ammonium concentration and ammonia volatilization. The GS2 activity in mesophyll was positively correlated with total nitrogen and leaf ammonium, and negatively correlated with apoplastic ammonium concentration and ammonia volatilization. The GS2 activity of leaf veins was only significantly correlated with the total nitrogen and ammonia volatilization. The activity of two glutamine synthetase isoenzymes in leaves of nitrogen-inefficient flue-cured tobacco varieties at the mature period was lower, and the ability of nitrogen transfer and reuse was poor, resulting in most of the nitrogen absorbed by plants evaporated in the form of ammonia, and the leaves had a faster rate of aging. However, nitrogen efficient varieties had strong nitrogen reutilization capacity, so the ammonia volatilization was small and the aging was postponed.