豌豆白粉菌侵染对活性氧迸发规律和紫花苜蓿叶片结构的影响

以专性寄生菌豌豆白粉菌接种紫花苜蓿,采用比色法和组织化学法对活性氧^·O2-和H₂O₂迸发的时间、强度及作用位点进行了研究;并就侵染部位的叶片制作了石蜡切片,对叶片结构进行了观察。结果表明,接种后,抗性品种庆阳苜蓿^·O2-和H₂O₂迸发均呈双峰形,^·O2-出现在接菌后4和48 h,H₂O₂出现在接菌后4和24 h,且第一次高峰强度高于第二次;而感病品种德宝苜蓿^·O2-含量未出现明显波动,H₂O₂迸发呈单峰形,仅在接菌后4 h出现一次迸发高峰。对活性氧ROS的作用位点进行研究发现,在叶片表面和内部细胞均未发现蓝色的^·O2-沉积位点;而H₂O₂产生并积累于苜蓿上、下表皮细胞的细胞膜及受侵染处叶肉细胞的细胞质。此外,首次发现病原菌侵染后,苜蓿叶片组织结构也相应发生了改变,表皮细胞下的栅栏组织由一个长柱形细胞变为了多个卵圆形细胞,以致难以区分栅栏组织和海绵组织。本研究结果说明,不同植物种与病原菌互作中,活性氧积累的时间和强度均不相同,启动防御反应的活性氧种类亦不同;苜蓿叶肉细胞结构和形态改变可能是抵御白粉菌侵染的积极反应之一。

The effect of Erysiphe pisi infection on the pattern of oxidative burst and on anatomic structure of leaves in Medicago sativa

Medicago sativa was inoculated with Erysiphe pisi .The colorimetric method was used to study the timing and intensity of · O2 - and H2 O2 bursts in leaves,and histochemical methods were used to study locali-zation of · O2 - and H2 O2 accumulation.In addition,paraffin sections were made from infected leaves to ob-serve structural changes in those leaves.It was found that after inoculation,· O2 - and H2 O2 bursts in Qingy-ang alfalfa (resistant cultivar)were observed as two peaks,appearing 4 and 48 h after inoculation for · O2 - and 4 and 24 h after inoculation for H2 O2 ,respectively,with the intensity of the first peak higher than that of the second peak.By contrast,in Debao alfalfa (susceptible cultivar),no obvious fluctuation in · O2 - content ap-peared and only the one peak for H2 O2 accumulation was seen.Staining to reveal zones of localization of reac-tive oxygen species (ROS)showed that blue-stained · O2 - deposition sites did not occur at the surface of or in-side of leaves,while brown-stained H2 O2 deposition sites were observed in the cell wall of upper and lower epi-dermal cells,and the cytoplasm of infected mesophyll cells.Most importantly,we report here for the first time that the tissue structure of alfalfa leaves was changed after infection with E .pisi.Palisade cells changed from a long-cylindrical cell type to groups of several subrotund cells,so that it was difficult to distinguish the palisade tissue and spongy tissue cells.Our results show that for the different plant species and pathogen resistance combinations investigated,the timing and intensity of ROS accumulation differed,as did the identity of the chemical species generated in activating the defense reaction.The structural and morphological change of meso-phyll cells may be one component of an effective response against powdery mildew infection in M.sativa.