四环素与镉复合污染对水稻根系的影响

为阐明抗生素与重金属复合污染对水稻根系的影响机制，考察了四环素（TC）与镉（Cd）单一和复合污染条件下，水培分蘖期水稻根系生长、污染物积累和根系分泌物的变化特征.结果表明：TC与Cd单一处理时，根部生物量和叶绿素含量下降，表现出毒害作用，低剂量的TC与Cd共同作用能够缓解其毒性效应；TC与Cd单一/复合污染均使根的伸长和植株蒸腾量表现出低促高抑现象.水稻根系对TC和Cd的吸收积累呈现出显著的剂量效应，且两者共存会改变污染物的生物可利用性及在根系的亲和力，从而协同促进TC和Cd在水稻根系的吸收积累，但更多的TC会与Cd络合导致根系Cd吸收减少.TC与Cd单一污染可显著抑制根系分泌物的分泌，复合污染条件下，对根系分泌物的影响随浓度升高存在差异：低浓度时能在一定程度上缓解TC/Cd对光合作用的抑制作用，且伴随蒸腾作用的增加，水稻根系分泌物增多；而高浓度时根系细胞完整性可能受损，进而抑制根系分泌物的分泌.进一步分析发现，高浓度时，根系分泌物中氨基酸及衍生物类、有机酸类和糖醇类物质的分泌显著增加，可能是因为TC与Cd的络合作用使Cd的生物可利用性降低，缓解了高Cd胁迫对水稻的毒性，促进分泌有机酸类、氨基酸及衍生物类和糖醇类物质，增强自我防护作用.本研究结果可为保障水稻安全生产，建立有效控制抗生素-重金属类复合污染的根际调控措施提供参考数据.

Influences of tetracycline and cadmium on rice roots: Growth and root exudates

Hydroponic culture experiments were conducted to find out the changes of rice root morphological characteristics and root exudates after single and combined pollutants treatments of tetracycline (TC) and cadmium (Cd). Pollutants accumulation in rice roots at tillering stage has been studied, so as to elucidate the mechanism of antibiotic and heavy metal combined pollution on rice root system. In single pollutant treatment of TC or Cd, both root biomass and chlorophyll content decreased, which indicated adverse effects on rice growth. However, antagonism effect was observed at low dose TC and Cd combined pollutants treatment. The root elongation and transpiration rate of rice plants showed promotion in low concentration exposure of single or combined pollutants treatments while high concentration exposure environment limited various physiological indexes. The accumulation of TC or Cd in rice root showed observable increase with the increase of the concentration of TC and Cd. Moreover, the coexistence of TC and Cd could increase the bioavailability and affinity of both pollutants, which results in synergistically promotion of pollutants accumulation in rice root. However, high TC concentration might led to Cd accumulation reduction in rice root because of complexation enhancement. The secretion of rice root exudates was significantly inhibited under single pollutant treatment of TC or Cd, but the combined pollution treatment showed different effects. In combined TC and Cd at low concentration treatment, with the remission of toxicity, the increased rice root exudates may result from increased photosynthesis rate and transpiration rate. But, the integrity of rice root cells was damaged under high concentration treatment, which inhibited the secretion of root exudates. Further analysis showed that the secretion of amino acids and derivatives, organic acids and sugar alcohols in root exudates increased significantly under high concentration combined pollutant treatment. The complexation of TC and Cd decreased the bioavailability of Cd, and alleviated the toxicity of Cd under high concentration treatment on rice, which increased the secretion of organic acids, amino acids and derivatives and sugar alcohols for detoxication. The results of this study can provide reference data for ensuring the safe production of rice and establishing effective rhizosphere regulation measurement for the control of antibiotic-heavy metal combined pollution.