Soil secondary salinisation is a problem resulting in a decreased productivity of protected vegetable production in China.In protected greenhouses,salts accumulated in soil are mainly as Ca2+ and NO3-,which are different from those in coast saline soil as Na+ and Cl-.The effects of different types of salts accumulated in soils on plant leaf growth and root morphology have been well documented; however,little has been done on different types of salts affecting root growth and its metabolism.In this research,we used a commercial tomato hybrid Solanum lycopersicum L.cv.Hezuo903 in hydroponic culture to investigate the effects of two types of salts,Ca(NO3)2 and NaCl,on root respiration and metabolism including KCN-resistant respiratory rate (Valt),cytochrome respiratory rate (Vcyt),root production rate of O2·-,H2 O2 concentration and activities of superoxide dismutase (SOD),guaiacol peroxidase (GPX) and catalase (CAT).The seedlings were transplanted into 10 L plastic containers containing aerated full nutrient solution.Fourteen days after being transferred to the hydroponic medium,the salt treatments were applied by adding 80mmol/L Ca(NO3)2 or 120 mmol/L NaCl to the nutrient solution and were maintained for 12 d.Four trays (16 plants) were included in each treatment as well as in the controls.Root respiration was measured as oxygen consumption in a 2-mL closed cuvette using a Clark type oxygen electrode.Salicylhydroxamic acid was used as an inhibitor for alternative respiration and KCN was used as an inhibitor for cytochrome respiration.The results showed that both root and shoot growth of tomato plants were severely inhibited by salt stress.Compared to the control plants,the shoot and root dry masses in Ca(NO3)2-stressed plants were reduced by 42.5％ and 33.5％ respectively,less than in NaCl-stressed plants by 63.2％ and 53.8％ respectively.Salt stress decreased the total respiratory rate (VT) due to the decrease of Vcyt,particularly under NaCl stress,but increased Valt,which was again more pronounced under NaCl stress.After 12 d of treatment,the ratio of Valt to VT increased by 51.2％ in Ca(NO3)2-treated plants and 63.5％ in NaCl-treated plants,respectively,while this ratio remained unchanged at 26.1％ in control plants.The production rate of O2· and H2O2 concentration were increased by salt stress,especially under NaCl stress.This was also the case for the activities of SOD,CAT and GPX during the first 8 d of NaCl treatment,while the activities of these enzymes under Ca(NO3)2 treatment were increased all the time.After 12 d of treatment,the MDA content increased by 48.3％ in Ca(NO3)2-stressed plants and by 122.8％ in NaCl-stressed plants respectively.In conclusion,NaCl stress cause much severer inhibition to plant growth than Ca(NO3)2 stress,which may be resulted from its damage effects with a higher lipid peroxidation level and lower respiratory rate,though its elevated KCN-resistant respiration effect can compensate partly such detrimental effects.It is also interesting to note that in companion with the enhancement of O2·-and H2 O2 production,KCN-resistant respiratory rate and its ratio to total respiratory rate increase significantly in salt-stressed plants,suggesting that the increased KCN-resistant respiration might be able to enhance reactive oxygen species scavenge in salt-stressed plants,especially in NaCl-stressed plants.%以番茄为材料,研究80 mmol/L Ca(NO3)2和120 mmol/L NaCl胁迫对番茄生长、根系呼吸速率、活性氧产生速率和根系抗氧化酶活性的影响；采用氧电极法测定根系呼吸作用,以水杨酸氧肟酸作为抗氰呼吸的抑制剂,以氰化钾作为细胞色素呼吸的抑制剂.结果表明:盐胁迫后番茄地上部和地下部生长受到严重抑制,番茄根系总呼吸速率和细胞色素呼吸速率明显下降,抗氰呼吸速率上升,超氧阴离子自由基产生速率和过氧化氢含量明显增加,其中NaCl处理的作用效果更显著；在NaCl胁迫下,根系超氧化物歧化酶、过氧化氢酶和愈创木酚过氧化物酶活性显著增加,但在处理后期上升幅度下降,而在Ca(NO3)2胁迫下,根系的抗氧化酶活性一直显著上升；NaCl胁迫的根系膜脂过氧化程度显著高于Ca(NO3)2处理.说明NaCl处理对番茄根系的氧化胁迫程度较Ca(NO3)2处理高,其中,NaCl处理对番茄生长抑制作用较强可能与番茄根系呼吸作用下降幅度较大、膜脂过氧化程度较高有关,此外,为了缓解盐胁迫,NaCl处理后番茄根系抗氰呼吸增加幅度较大.
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