施氮量和采收时期对油蔬两用型油菜菜薹维生素合成的影响

为明确施氮量和采收时期对油蔬两用型油菜薹维生素含量的影响,以富硒1号为材料,采用裂区试验设计,设置3个施氮量(120、180和240 kg·hm^-2)和4个采收时期(以株高20、30、40和50 cm表示),分析了油菜薹维生素C、维生素E、维生素B₁和维生素B₆含量的变化;比较了半乳糖内酯脱氢酶(GalLDH)、抗坏血酸氧化酶(AAO)、抗坏血酸过氧化物酶(APX)、脱氢抗坏血酸还原酶(DHAR)和单脱氢抗坏血酸还原酶(MDHAR)活性,并分析了维生素家族基因在菜薹中的表达量。结果表明,随着施氮量的增加,油菜薹还原型维生素C(AsA)含量降低;氧化型维生素C(DHA)含量在株高20 cm采收时增加,但在30 cm及以上株高采收时则降低;维生素E和维生素B₆含量先增加后降低;维生素B₁含量增加;维生素C合成关键酶GalLDH活性先略增加后降低;AAO和DHAR活性增加,APX和MDHAR活性则整体表现为先增加后降低。且施氮量增加后,维生素家族各基因在株高30和40 cm采收的菜薹中主要表现为正向调控,而在株高20和50 cm采收的菜薹中主要表现为负向调控。就采收时期而言,菜薹中的维生素含量在株高30~40 cm时高于其他时期;在同一施氮量下,随着菜薹采收株高的增加,维生素家族基因的表达量主要呈上调模式。综合分析可知,GalLDH活性的降低以及AAO/DHAR和APX/MDHAR代谢平衡是增施氮肥导致菜薹维生素C含量降低的重要原因。本研究结果为油蔬两用型油菜薹优质栽培技术提供了理论依据。

Effect of Nitrogen Application Rate and Harvesting Time on Vitamin Biosynthesis in Young Stem of Oil-Vegetable Double Usage Type Rapeseed

In order to elucidate the effect of nitrogen rate and harvesting time on the vitamin content in young stem of oil-vegetable double usage type rapeseed, a field experiment was conducted using Fuxi 1 as plant material with a split plot design that was composed of three nitrogen rates as main plot, 120, 180, and 240 kg·hm^-2, and four harvesting times, using plant height of 20, 30, 40, and 50 cm as sub plot. Change of vitamin family compound contents in young stem was analyzed; activities of key enzymes including GalLDH, AAO, APX, DHAR, and MDHAR in vitamin C biosynthesis and metabolism were compared; expression levels of vitamin family genes under nitrogen rates and plant height treatments were also assayed. Results showed that ascorbic acid content in the young stem of rapeseed decreased as nitrogen rate increased. Content of dehydroascorbic acid increased as nitrogen rate increased when the young stem was harvested at 20 cm of plant height while that was decreased when it was harvested above 30 cm of plant height. Contents of vitamin E and vitamin B₆ were increased and then decreased and content of vitamin B₁ in young rapeseed stem increased as nitrogen application rate increased. The activity of key enzyme, GalLDH, for vitamin C biosynthesis in young rapeseed stem slightly increased and then decreased as nitrogen application rate increased. The activities of vitamin C metabolic key enzymes AAO and DHAR increased as nitrogen application rate increased while APX and MDHAR increased firstly and then decreased. The vitamin family genes were positive regulated in the young rapeseed stem by increased nitrogen application at 30 and 40 cm plant height while that were negative regulated at 20 and 50 cm plant height. As for the harvesting time, vitamin content in young rapeseed stem at 30 to 40 cm was in generally higher than that at 20 and 50 cm plant height. The vitamin family genes up-regulated as the harvesting plant height increased in the young rapeseed stem under the same nitrogen application rate. In conclusion, the reduction of GalLDH activity and the equilibrium of enzymatic systems between AAO/DHAR and APX/MDHAR resulted in the decrease of vitamin C content in young rapeseed stem. The results provide the information for the high quality cultivation of oil-vegetable double usage type rapeseed.