模拟酸雨对‘琯溪蜜柚’叶片抗氧化酶活性和光合作用的影响

Effects of acid rain on the leaves antioxidase activity and photosynthesis of Citrus Grandis(L.) Osbeck. ‘Guanximiyou' seedlings

【目的】探讨酸雨胁迫对‘琯溪蜜柚’叶片抗氧化酶活性和光合作用的影响。【方法】以p H值5.6为对照,采用p H 2.5和p H 4.5模拟酸雨对1 a(年)生‘琯溪蜜柚’进行胁迫,研究酸雨对蜜柚叶片氧化伤害、抗氧化酶系统、气体交换参数和叶片结构的影响。【结果】p H 2.5和p H 4.5模拟酸雨胁迫处理3个月,没有造成叶片可见伤害,叶片上表皮细胞排列整齐紧密,但p H 2.5模拟酸雨胁迫处理显著降低了叶肉中栅栏组织发育;p H 2.5模拟酸雨胁迫处理1 d后,叶片SOD和CAT活性的升高减少O2-和H2O2的积累,降低过氧化伤害,p H 2.5模拟酸雨胁迫处理3 d之后引起叶片膜脂过氧化;p H 4.5模拟酸雨胁迫处理6 d后虽然3种抗氧化系统酶活性显著高于对照,但不足以清除酸雨胁迫引起的活性氧,引起膜脂过氧化;模拟酸雨胁迫处理初期,2种处理均显著抑制光合速率,酸雨处理90 d后,p H 2.5酸雨显著抑制‘琯溪蜜柚’叶片光合速率,推测是由于氧化胁迫、栅栏组织发育等非气孔调节因素引起的,p H 4.5酸雨处理下叶片具有较强自我修复能力,其光合速率没有受到显著抑制。【结论】‘琯溪蜜柚’具有较强的酸雨抗性,p H 4.5中度酸雨胁迫对植株生长影响不显著,p H 2.5重度酸雨胁迫显著抑制叶片光合作用。

【Objective】Acid rain has spread out from Europe beginning in the late 1950 s. The contaminated regions have expanded from North America and Western Europe to developing countries, especially India and China. Acid rain may do harm to plants through changing their p H balance, increasing the leaching loss of nutrient elements, causing the destruction of leaf anatomy, and so on. Citrus grandis（L.） Osbeck.‘Guanximiyou＇is a Rutaceae Citrus evergreen tree fruit whose pomelo is very delicious and nutritious and is an unusual species in Fujian Province. Fujian Province lies in the southeast of the China acid rain area and the pollution by acid rain is the main crisis of the pomelo industry. The majority of research on pomelo focused on the genetic quality, the fresh keeping techniques and the ecological planting mode, and so on. The study of the physiological ecology of the pomelo was given less emphasis. This study focuses on the foliar damage, antioxidant enzyme activity, gas exchange parameters and the leaves anatomical characteristics of Citrus grandis（L.） Osbeck.‘Guanximiyou＇1-year seedlings under acid rain treatment（p H 5.6, p H 4.5 and p H 2.5）.【Methods】Healthy 1-year seedlings of C. grandis（L.） Osbeck.‘Guanximiyou＇were planted in plastic pots with yellowish red soil in a greenhouse,with average day/night temperatures of 25 ℃/20 ℃ and an average relative humidity of 75%. After two months of growing, three levels of acid rain（p H 5.6, p H 4.5 and p H 2.5） were developed. A completelyrandomized design was applied. Each treatment had fifteen replicates, and a 200 m L acid rain solution was watered every two days. The leaves were harvested at 1, 3, 6 and 12 days after acid rain treatment.The malondialdehyde（MDA）, superoxide dismutase（SOD）, catalase（CAT） and peroxidase（POD） of the leaves were measured with kits. The photosynthesis rate（μmol CO2· m-2· s-1）, stomata conductance（mol H2 O·m-2·s-1）, intercellular CO2 concentration（μmol CO2·mol-1） and transpiration rate（mmol H2 O·m-2·s-1）were measured by using a photosynthetic Monitor（Li—6400 XT） at 1, 3, 6, 12 and 90 day after acid rain treatment. The leaf anatomical structures were observed by using the paraffin section method. After 90 days treatment, 5-10 matured leaves in each treatment were selected for a paraffin section. These leaves were made by permanent slicing through fixing, dehydrating, embedding and so on. The leaves anatomical structures were measured by Image-Pro Plus 6.0. The experimental data were sorted out by Excel2007 and analyzed with one-way ANOVA by SPSS19.0.【Results】The leaves treated by p H 2.5 and 4.5 acid rain did not show any visible injury and the surface layer of the cells were arranged in neat rows.And the p H 2.5 acid rain significantly decreased the thickness of the palisade cells and significantly increased the thickness of the sponge tissues compared with the p H 5.6 treatment. p H 4.5 acid rain did not have any significant effect on the thickness of the palisade cells and sponge tissues compared with the p H 5.6 treatment. The leaves did not show any oxidative damage due to the increase in SOD and CAT until after the third day being treated by p H 2.5 acid rain. p H 4.5 acid rain caused oxidative damage after six days of being treated by acid rain and the activities of SOD, CAT and POD were higher than the control treatment（p H 5.6）. The photosynthesis rates were decreased by p H 2.5 and 4.5 acid rain during the initial period of acid rain stress. After three months of acid rain stress, the photosynthesis rate with the p H 2.5 treatment was lower than the control treatment and it was speculated this was because of non-stomas factors（oxidative damage, the decrease of palisade cell and so on）. The photosynthesis rates in the p H 4.5 acid rain treatment were not affected after three months. The stomata conductance and transpiration rates in the p H 2.5 treatment were always significantly lower than the control treatment throughout the treatment process. The results showed that p H 2.5 treatment significantly restrained stomatal conduction and affected water absorption and transport. Stomata conductance in the p H 4.5 treatment was always significantly lower than the control treatment on the first day and the 12 th day. And stomata conductance in the p H 4.5 treatment was not significantly different from the control treatment on the third day, the ninth day and the 90 th day. The transpiration rate in the p H 4.5 treatment was significantly lower than the control treatment most of the time.【Conclusion】During the initial phases of the experimentation, the acid rain treatment did not cause any oxygen issues due to the increasing of the antioxidases activity. With a prolonged treatment time, acid rain treatment induced lipid peroxidation damage. p H 2.5 acid rain treatment did not cause any visible blade damage, but significantly decreased the thickness of the palisade tissues compared with the p H 5.6 treatment. p H 2.5 acid rain treatment significantly decreased the net photosynthetic rate compared with the p H 5.6 treatment. Under the p H 4.5 acid rain treatment, the net photosynthetic rate was not significantly decreased due to the ability to repair itself.