Abstract Bacterial leaf spot caused by Xanthomonas axonopodis pv. ricini (Xar) is the only important disease of bacterial etiology reported to threaten castor bean production. No cultivars expressing resistance to the pathogen are known. Hence, knowledge of the physiological and biochemical alterations caused by the bacterium to castor bean plants could shed light into alternative approaches to obtain plant resistance. Leaf gas exchange parameters were measured with a portable infrared gas analyzer; Chlorophyll a fluorescence parameters were determined with an Imaging-PAM chlorophyll fluorometer; photosynthetic pigments, malondialdehyde (MDA) and activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), peroxidase (POX) and glutathione reductase (GR) were quantified using standard biochemical assays; and production of hydrogen peroxide (H2O2) and superoxide anion (O2•-) was detected by histochemistry. Inoculated leaves exhibited significant reduction in photosynthetic capacity, accumulation of H2O2, absence of O2•- accumulation, higher concentrations of MDA and higher activities of SOD, APX and POX compared to non-inoculated plants. Bacterial infection of castor bean triggered severe alterations, mainly related to stomatal closure that consequently compromised the CO2 influx into infected tissue. Small increases in SOD activity seemed to be sufficient to remove O2•-, but detoxification of the H2O2 generated during the O2•- dismutation process appeared to be inefficient. Higher concentrations of MDA in inoculated compared to non-inoculated plants indicated membrane damage due to lipid peroxidation. Some of the physiological and biochemical alterations in castor bean plants resulting from Xar infection have not previously been reported for other plants infected by bacteria.

中文翻译：

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细菌性叶斑病对蓖麻光合能力和过氧化氢去除的影响

摘要 由 Xanthomonas axonopodis pv 引起的细菌性叶斑病。ricini (Xar) 是据报道威胁蓖麻豆生产的唯一重要的细菌病原学疾病。没有品种对病原体表达抗性是已知的。因此，了解由细菌对蓖麻子植物引起的生理和生化改变可以为获得植物抗性的替代方法提供启示。用便携式红外气体分析仪测量叶片气体交换参数；叶绿素a荧光参数用Imaging-PAM叶绿素荧光计测定；光合色素、丙二醛 (MDA) 和超氧化物歧化酶 (SOD)、过氧化氢酶 (CAT)、抗坏血酸过氧化物酶 (APX)、过氧化物酶 (POX) 和谷胱甘肽还原酶 (GR) 的活性使用标准生化分析进行量化；通过组织化学检测过氧化氢（H2O2）和超氧阴离子（O2•-）的产生。与未接种的植物相比，接种的叶片表现出光合能力、H2O2 的积累、O2•- 积累的缺乏、更高浓度的MDA 和更高的SOD、APX 和POX 活性的显着降低。蓖麻子的细菌感染引发了严重的改变，主要与气孔关闭有关，从而影响了 CO2 流入受感染组织。SOD 活性的小幅增加似乎足以去除 O2•-，但 O2•- 歧化过程中产生的 H2O2 的解毒似乎效率低下。与未接种植物相比，接种植物中更高浓度的 MDA 表明由于脂质过氧化导致膜损伤。