Objectives]Chloroplasts are plant organelles that produce reactive oxygen species (ROS). Chloroplasts are extremely sensitive to salt stress. In order to investigate the mechanism of chitosan on regulating photosynthesis under NaCl stress, the improvement of antioxidant system in the chloroplasts by applying exogenous chitosan on soybean [Glycine max(L.) Merr.] was studied.[Methods]A pot experiment was conducted inside greenhouse of the Experimental Base of Inner Mongolia University from April to June 2014. Vermiculite was used as culture substrate, salt sensitive soybean cultivar of ‘Lixiang gaochan 95-1’ (LX) and not tolerant one of ‘Lvling’ (LL) were used as test materials. Four treatments were designed: 1) Soybean leaves were sprayed with water, and roots fed with the nutrient solution (CK); 2) Only the leaves were sprayed with chitosan solution, and the roots fed with nutrient solution; 3) Leaves were sprayed with water, and the roots were fed with nutrient solution containing NaCl; 4) The leaves were sprayed with chitosan solution, and the roots were fed with nutrient solution with NaCl.[Results]Under NaCl stress and exogenous chitosan, the chloroplast H2O2content of two varieties was significantly decreased, while the activities of peroxidase (POD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydro ascorbic acid reductase (DHAR), glutathione reductase (GR) and glutathione peroxidase (GPX) were increased markedly, meanwhile the dehydroascorbic acid (AsA) and dehydroascorbic glutathione (GSH) contents during the mid-term of NaCl stress were also increased. Salt-resistant cultivar LL maintained lower H2O2content, and higher DHAR activity and AsA content in the mid and late period (6–15 d) of NaCl stress, maintained higher APX, GR and GPX activities in the whole period, and maintained higher GSH content in the late period (12 d, 15 d) of the stress, as compared with those of salt-sensitive cultivar LX.[Conclusions]Exogenous chitosan supply significantly induces POD activity and AsA-GSH cycle in the chloroplast under NaCl stress. The AsA-GSH cycle in salt tolerant cultivar LL maintain relatively stronger activity than that in salt sensitive cultivar in reactive oxygen scavenging, which might explain a reason for salt tolerant cultivar to maintain strong photosynthetic capacity, and be capable of maintaining active growth of soybean.%【目的】叶绿体是植物体产生活性氧(ROS)、且对盐最敏感的细胞器，本试验研究了外源壳聚糖对 NaCl胁迫下菜用大豆[Glycine max(L.) Merr.]叶绿体内抗氧化系统的影响，以期探讨壳聚糖对 NaCl胁迫下光合作用的调节机制。【方法】试验于2014年4月至6月在内蒙古民族大学试验基地日光温室内进行。采用蛭石栽培，选用菜用大豆盐敏感品种‘理想高产95-1’(LX)、耐盐品种‘绿领特早’(LL)为试材。试验设4个处理：1)叶面喷洒清水，根部浇灌营养液(对照)；2)叶面喷洒壳聚糖溶液，根部浇灌营养液；3)叶面喷洒清水，根部浇灌溶有NaCl的营养液；4)叶面喷洒壳聚糖溶液，根部浇灌溶有 NaCl的营养液。【结果】外源壳聚糖显著降低了 NaCl胁迫下两品种菜用大豆叶绿体 H2O2的含量，显著提高了过氧化物酶(POD)、抗坏血酸过氧化物酶(APX）、单脱氢抗坏血酸还原酶(MDHAR)、脱氢抗坏血酸还原酶(DHAR)、谷胱甘肽还原酶(GR)、谷胱甘肽过氧化物酶(GPX)活性以及胁迫中期还原型抗坏血酸(AsA)、还原型谷胱甘肽(GSH)含量；与盐敏感品种 LX相比，耐盐品种 LL在胁迫6～15 d期间维持了相对较低的 H2O2含量，相对较高的 DHAR活性及 AsA含量，在整个胁迫期间维持了相对较高的 APX、GR、GPX活性，在胁迫后期(12 d、15 d)维持了相对较高的 GSH含量。【结论】外源壳聚糖对 NaCl胁迫下菜用大豆叶绿体内 POD活性及 AsA-GSH循环产生了显著诱导作用，但对不同品种的诱导效果不同，耐盐品种 LL的 AsA-GSH循环维持了相对较强的活性氧清除能力，这可能是其维持较强光合能力，进而维持较旺盛生长的重要原因之一。
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