Changes in malic acid concentrations of tobacco leaves and the relative enzyme activities during the curing process | 烘烤过程中烟叶苹果酸含量及相关代谢酶活性的变化

Chinese. 分析烘烤过程中烟叶苹果酸及相关代谢酶活性的变化, 为进一步探明烘烤过程中烟叶内在化学成分的变化及调控机制提供理论依据。以K326、云烟87和豫烟6号为试验材料，研究不同品种烤烟烟叶在烘烤前、烘烤过程中关键温度点（38，42，48，54 ℃）及烘烤结束后苹果酸、总有机酸含量及苹果酸脱氢酶(MDH)、磷酸烯醇式丙酮酸羧化酶(PEPC)及琥珀酸脱氢酶(SDH)活性的变化，并对总有机酸、苹果酸含量与代谢酶活性的相关性进行分析。不同品种烤烟的MDH、PEPC和SDH酶活性变化均表现出一定的规律性。烘烤过程中，MDH活性先升高后降低，并在48 ℃达到最大值； PEPC活性呈先升高后下降再上升的走势变化，但整体呈上升趋势；38 ℃之后SDH活性持续下降，54 ℃降至最低；烘烤过程中，丙二酸含量呈上升趋势，且在54 ℃时达到最大值。K326、云烟87和豫烟6号的苹果酸和总有机酸含量在烘烤过程中均呈先升高后降低的趋势，且分别在54，48和42 ℃达到最大值。相关分析表明，不同品种烤烟MDH活性与苹果酸含量相关性不显著；K326和豫烟6号的PEPC活性与苹果酸、总有机酸含量呈正相关，云烟87的PEPC活性与苹果酸、总有机酸含量呈负相关，相关性均不显著；K326和豫烟6号的SDH活性与苹果酸含量呈显著性负相关，云烟87的SDH活性与苹果酸含量相关性不显著。不同品种烤烟间苹果酸含量差异较大。SDH对苹果酸积累的作用大于MDH和PEPC，相对较高的MDH和PEPC活性与相对较低的SDH活性均能够促进苹果酸的积累。

English. The change mechanism of malic acid concentrations and the relative enzyme activities in tobacco leaves during the curing process were analyzed in order to provide a theoretical basis for intensive study of chemical composition change and control mechanism during flue-curd process. Research was conducted on the contrast of malic acid and total organic acid content and enzyme activities changes of MDH, PEPC and SDH in different flue-cured tobacco varieties such as K326, Yunyan 87 and Yuyan 6 at different stages (before curing, during curing at 38, 42, 48, 54 ℃ and after curing) and the correlation between enzyme activity and malic acid and total organic acid content was analyzed. The MDH, SDH and PEPC enzyme activities of different tobacco varieties showed some regularities. During the flue-cured process, the MDH activity increased first and then decreased and reached its peak at 48 ℃; the PEPC activity first rose and then declined and then rose again, as a whole, the degree of the activity had a ascend trend; the SDH activity steadily declined after 38 ℃ and reached its bottom at 54 ℃. During the curing process, malonic acid content had an up trend and reached its peak at 54℃. Malic acid and total organic acids contents of K326, yunyan 87 and yuyan 6 increased first and then decreased during the flue-cured process and reached its peak at 54, 48 and 42 ℃ respectively. The result of correlation analysis showed that the MDH activity had no significant relation with the malic acid content in different flue-cured tobacco varieties; the PEPC activity had positive relation with the malic acid and total organic acid content in K326 and Yuyan 6 and had negative relation in Yunyan 87, and the correlation was not significant; the SDH activity had significant negative relation with the malic acid content in K326 and Yuyan 6 and not significant in Yunyan 87. The malic acid contents in different flue-cured tobacco varieties were obviously different. The effect on malic acid accumulation of SDH was bigger than that of MDH and PEPC. Relatively high MDH and PEPC activities and relatively low SDH activity could promote the accumulation of malic acid.