光照对晒烟变黄期叶绿素荧光及抗氧化指标的影响

  目的  揭示调制变黄期的光照对晒烟叶叶绿素荧光及抗氧化指标的影响。  方法  动态测定了晒烟叶调制变黄期内光照处理与遮光处理(CK)下烟叶叶绿素含量、叶绿素荧光、H₂O₂和MDA含量及抗氧化酶的活力。  结果  ① 光照处理下叶绿素降解速度比遮光对照快。②光照处理下第4 d烟叶的PS Ⅱ实际光化学效率(PhiPS2)和电子传递速率(ETR)较第1 d时分别降了60%和75%，都明显大于它们在遮光对照中的降幅。到第7 d时光照处理的光化学淬灭值(qP)已降至0.28、PSII最大光化学效率(F_v/F_m)降至0.23，较同期遮光对照的qP和F_v/F_m值分别低了38%和43%。③光照处理下烟叶H₂O₂和MDA含量峰值都约为遮光对照下相应峰值的150%，并且都比在遮光对照中提前2 d出现；光照处理中POD和CAT酶活性峰值也比遮光对照中出现得更早、更高；表明光照处理下烟叶的胁迫状况比在遮光对照下严重。④烟叶的被测指标中PhiPS2、MDA和H₂O₂受光照影响最显著。  结论  在调制变黄初期晒烟叶的光能利用效率快速下降，可促进晒烟叶内形成大量过剩光激发能，造成细胞内活性氧激增、氧化胁迫加重，加速烟叶叶绿素、细胞膜膜脂等化学物质的降解转化，损害细胞的结构和功能。 

Effects of light on chlorophyll fluorescence and antioxidant indexes of sun-cured tobacco leaves during yellowing period

This study aims to reveal the effects of light on chlorophyll fluorescence and antioxidant indexes of sun-cured tobacco leaves in yellowing period of curing. Tobacco samples under the light treatment and shading treatment (CK) were collected dynamically during yellowing period. Indexes of chlorophyll fluorescence, activities of antioxidant enzymes and contents of chlorophyll, H₂O₂ and MDA were measured. The results showed: 1) The degradation rate of chlorophyll under light treatment was faster than that under CK. 2) Photochemical efficiency of PS Ⅱ (PhiPS2) and electron transfer rate (ETR) decreased by 60% and 75% respectively in the first 4 days under light treatment, which was significantly greater than that under CK. On the 7th day, photochemical quenching (qP) value and the maximum photochemical efficiency (F_v/F_m) value decreased to 0.28 and 0.23, which were lower than that under CK by 38% and 43%, respectively. 3) The peak values of H₂O₂ and MDA contents under light treatment were 1.5 times of that under CK, and appeared 2 days earlier compared with the situation under CK. The peak values of POD and CAT activities in light treatment were also higher than that under CK. 4) Of all tested indexes, PhiPS2, MDA and H₂O₂ were the most affected by light treatment. In conclusion, this study demonstrates that light energy utilization efficiency of sun-cured tobacco leaves decreased rapidly in the early stage of yellowing. Part of the light energy received by tobacco leaves was converted into excess light excitation-energy, which could proliferate reactive oxygen species, aggravate oxidative stress, accelerate the degradation and transformation of chlorophyll, membrane lipid and other chemical substances in tobacco leaves and damage cell structure and function.