苹果褐斑病菌侵染对苹果叶片光合机构功能的影响

为了探究苹果褐斑病菌侵染对苹果叶片光合机构的伤害机制，以‘寒富’苹果为试材，研究苹果褐斑病菌侵染对苹果叶片光合作用和光系统功能的影响。结果表明：随褐斑病菌侵染加重（叶片感病程度分0、1、2、3、4和5级），叶片的叶绿素a含量和总叶绿素含量持续下降，其中2～5级与对照相比差异显著，病菌侵染提高了叶片类胡萝卜素含量，但仅以2级与对照差异显著。苹果褐斑病菌侵染显著降低了叶片的净光合速率（Pn），3～5级病叶的Pn分别较对照下降44．9％、56．6％和70．3％，而胞间CO2浓度（Ci）上升，说明非气孔因素是光合作用的主要限制因子。褐斑病菌侵柒影响了光合电子传递效率，随病菌侵染程度加重，光系统Ⅱ反应中心、供体侧放氧复合体（Wk）和受体侧（Vj）受到的伤害加重，并引起苹果叶片PSII的光合性能指数用PIABS和PSI受体侧末端电子受体的量子产额（φRo）急剧下降。褐斑病菌侵染加重了苹果叶片的膜脂过氧化程度，1～5级感病叶片的丙二醛（MDA）含量均显著高于对照，引发超氧化物歧化酶（SOD）及过氧化物酶（POD）活性的上调。以上结果表明，苹果褐斑病菌侵染引起叶片光合色素降解，对PSII反应中心、受体侧和供体侧造成伤害，进一步影响了PSI的电子传递效率，并导致叶片膜脂过氧化，造成苹果叶片光合能力下降。

Effects of Apple Brown Spot Pathogen Infection on the Function of Photosynthetic Apparatus in Apple Leaves

In order to explore the damage mechanism of apple brown spot pathogen infection on photosynthetic characteristics and photosystem functions of apple leaves, ＇Hanfu＇ apple trees were used as material, and the infected leaves were divided into 5 grades according to the lesion area, namely 0 （CK）, 1, 2, 3, 4, and 5. The results showed that, compared with the control, the content of chlorophyll a and total chlorophyll continued to decline with the infection degree of brown spot pathogen on apple leaves, among which Grade 2-5 infected leaves were significantly different; the infection of pathogen increased carotenoid content in leaves in varying degrees, but only that of Grade 2 infected leaves was significantly increased. Apple brown spot significantly reduced the net photosynthetic rate （P,） of apple leaves, and the decline gradually became more significant with the degree of pathogen infection, the Pn of Grade 3-5 infected leaves fell by 44.9%, 56.6% and 70.3% respectively as compared with the control and intercellular CO2 concentration （Ci） increased, indicating that the decline in photosynthesis was limited by the factor of mesophyll. The infection of brown spot affected the electron transfer efficiency in the photosystem, and the damage of reaction centers, oxygen-evolving complex of donor side and acceptor side of photosystem II gradually increased with the infection degree, resulting in the sharp decline of the performance index （PIABs） and the efficiency with which an electron can move from the reduced intersystem electron acceptors to the PSI end electron acceptors （φRo）. The infection of brown spot pathogen increased the content of membrane lipid peroxidation of apple leaves, and the MDA contents of Grade 1-5 infected leaves were significantly higher than that in control, and increased the activity of SOD and POD. It can be concluded that the infection of apple brown spot caused the degradation of photosynthetic pigments, damaged the acceptor side, donor side, and reaction centers of PSII, and further affected the electron transfer efficiency of PSI, resulting in the membrane lipid peroxidation of leaves, which was one of the important reasons leading to the decrease of photosynthetic ability of apple leaves.