干旱胁迫对3种苹果砧木叶片光合、叶绿体超微结构和抗氧化系统的影响

以新疆野苹果（Malus sieversii Roem.（XJ））、垂丝海棠（Malus halliana Koehne（CS））和山定子（Malus baccata Borkh.（SDZ））3种一年生苹果砧木实生苗为材料，采用盆栽控水的方法设置正常供水（75%~80% RWC）和干旱胁迫（45%~50% RWC）2种水分处理，研究干旱胁迫下叶片光合特性、叶绿体超微结构、丙二醛（MDA）含量、超氧阴离子（O^—[KG-1][JX*3]·[JX-*3]₂）产生速率以及抗氧化酶活性的变化规律，并利用主成分分析（PCA）对3种砧木进行抗旱性综合评价。结果表明：干旱胁迫抑制了3种苹果砧木的光合作用，但干旱胁迫下CS的净光合速率（Pn）、气孔导度（Gs）、蒸腾速率（Tr）、PSII最大光能转化效率（Fv/Fm）、潜在光化学活性（Fv/Fo）及光化学猝灭系数（qP）的降幅均显著小于其他两种砧木，胞间CO₂浓度（Ci）和非光化学猝灭系数（NPQ）的增幅显著高于其他两种砧木；干旱胁迫下，3种砧木超微结构受到不同程度的伤害，其中CS叶片的超微结构损伤较小，能较好地保持细胞结构的完整性；干旱胁迫下3种砧木的SOD和CAT活性先升高后降低，POD活性逐渐增加至21 d趋于稳定，MDA含量和O^—[KG-1][JX*3]·[JX-*3]₂产生速率持续升高。PCA结果显示：2个主成分的方差贡献率达到98.502%，干旱胁迫下CS的综合得分最高。因此，干旱胁迫下，垂丝海棠能保持叶绿体结构的完整性，激活抗氧化酶系统，清除氧化产物而保持较高的光合能力。

Effect of drought stress on the photosynthesis, chloroplast ultrastructure and antioxidant system in leaves of three apple rootstocks

One-year-old seedlings of three apple rootstocks, Malus sieversii Roem. (XJ), Malus halliana Koehne (CS), and Malus baccata Borkh. (SDZ), were used as test materials. The pot experiment with artificial water control was carried out with two water treatments including normal irrigation (75%~80% of the field moisture capacity) and drought stress (45%~50% of the field moisture capacity). Photosynthetic characteristics, chloroplast ultrastructure, malondialdehyde (MDA) content, superoxide anion (O_-2) production rate, and antioxidant enzyme activities in leaves were determined under drought stress. These indices were analyzed by principal component analysis (PCA) to compare the drought tolerance of three apple rootstocks. The results showed that drought stress inhibited photosynthesis of three apple rootstocks. The decrease in net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), PSII maximum light conversion efficiency (Fv/Fm), potential photochemical activity (Fv/Fo), and photochemical quenching coefficient (qP) in CS was remarkably lower than those of the other two rootstocks, while the intercellular CO₂ concentration (Ci) and non-photochemical quenching coefficient (NPQ) were enhanced to a greater extent in CS than that in the others. The chloroplast ultrastructure of three rootstocks were subjected to different degrees of damage when they were exposed to the same level of drought stress. The CS maintained integrity of cell structure better than did the other two rootstocks, and had less ultrastructure damage in leaves. The activities of SOD and CAT of three apple rootstocks increased firstly and then decreased, while POD activity increased gradually until the 21 day stress. In addition, MDA content and O_-2 production rate of three apple rootstocks increased. Based on the PCA, the cumulative contribution rate of the 2 principal components totaled at 98.502%, and the PCA score of CS was the optimum under drought stress. Therefore, CS could maintain the integrity of chloroplast structure, activate the antioxidant enzyme system, and scavenge the oxidation products to maintain high photosynthetic capacity under drought stress.