镉胁迫对生菜生长、生理特性及镉富集转运特征的影响

【目的】揭示镉胁迫对生菜生长的影响及毒害机理，为阐明镉的毒理效应提供依据。【方法】以水培生菜品种“四季生菜”为材料，设置镉处理低（25 mg/L）、高（50，100 mg/L）水平，以无镉处理（0 mg/L）为对照（CK），用营养液膜技术（NFT）进行试验，处理7，14，21 d后取样，研究镉处理对生菜的地上部和地下部鲜质量、镉含量、镉富集转运特征、生理指标、抗氧化酶活性、光合色素指标及叶绿素荧光参数的影响。【结果】25 mg/L镉处理前14 d对生菜地上部和地下部鲜质量具有促进作用，21 d时25~100 mg/L镉表现出明显的抑制作用。镉处理生菜的地下部镉含量、富集系数均高于地上部；随着镉质量浓度的升高，富集系数总体呈现下降的趋势；处理7 d后，随着镉质量浓度增加，转运系数下降，14 和21 d则先上升后下降。在25~100 mg/L镉处理后，生菜的可溶性蛋白含量随着镉质量浓度的升高而增加，但随着处理时间延长逐渐下降；MDA含量随着镉质量浓度升高以及处理时间的延长而增加。与CK相比，7 d时镉处理SOD活性显著升高，14 d显著下降；21 d各处理间差异不显著。镉处理7~21 d后POD活性均较CK显著升高（14 d 时25 mg/L处理除外）。随着时间推移，镉处理CAT活性总体表现出先降低后升高的规律。与CK相比，7 d时镉处理生菜光合色素的含量明显增加，14 d时低质量浓度（25 mg/L）镉处理光合色素指标总体增大，高质量浓度（50，100 mg/L）镉抑制了光合色素的合成，21 d时镉处理光合色素指标较CK显著降低。25~100 mg/L镉处理7~21 d后，镉对生菜叶绿素荧光参数有明显影响，其中镉处理21 d后PSⅡ最大光量子效率(F_v/F_m)、PSⅡ有效光量子产量(F_v′/F_m′)、PSⅡ实际光量子效率(ΦPSⅡ)、稳态荧光衰减率(Rfd)较7 d均总体降低，而初始荧光值(F_o)和非光化学淬灭系数(NPQ)则表现为增大。【结论】镉质量浓度越高、处理时间越长，生菜的光能转化效率越低，叶片热量散耗越高，光合作用能力降低，植株生长受抑制程度越严重。

Effects of cadmium stress on growth,physiological characteristics and cadmium enrichment and transport of lettuce

【Objective】This study explored the effects of cadmium stress on lettuce growth and toxicity mechanism to provide basis for elucidating toxicological effect of cadmium.【Method】The hydroponic lettuce variety ‘Si Ji lettuce’ was treated with four cadmium levels of control (CK,0 mg/L),low (25 mg/L),and high (50 and 100 mg/L).The experiment was carried out with nutrient liquid membrane technology (NFT).Samples were taken 7,14 and 21 days after treatment to analyzed the effects of cadmium on aboveground and underground fresh weights,cadmium content,cadmium accumulation and transport characteristics,physiological indexes, antioxidant enzyme activities,photosynthetic pigment indexes and chlorophyll fluorescence parameters of lettuce.【Result】The treatment of 25 mg/L cadmium promoted fresh weight of lettuce in aboveground and underground parts at 14 days,while 25-100 mg/L cadmium showed significant inhibitory effect at 21 days.Cadmium content and enrichment coefficient in the underground part of cadmium treated lettuce were higher than those in the aboveground part.With the increase of cadmium concentration,the enrichment coefficient showed a downward trend.The transport coefficient decreased with the increase of cadmium concentration at 7 days,while it increased first and then decreased at days 14 and 21.For treatments with 25-100 mg/L cadmium,soluble protein content of lettuce increased with the increase of cadmium concentration,but it gradually decreased with the extension of treatment time.MDA content increased with the increase of cadmium concentration and the prolongation of treatment time.Compared with CK,SOD activity of cadmium treatment was significantly increased at 7 days while decreased significantly at 14 days,and there was no significant difference among all treatments at 21 days.POD activity was significantly higher from 7 days to 21 days in cadmium treatments than in control (except 25 mg/L treatment at 14 days).The activity of CAT treated with cadmium decreased first and then increased with the passage of time.Compared with CK,the photosynthetic pigment content of lettuce treated with cadmium increased significantly at 7 days.The photosynthetic pigment index of low concentration (25 mg/L) cadmium treatment increased overall at 14 days,while high concentration (50 and 100 mg/L) cadmium inhibited the synthesis of photosynthetic pigment.The photosynthetic pigment index of cadmium treatment was significantly decreased at 21 days compared with the control.The 25-100 mg/L cadmium treatments for 7 to 21 days had significant effect on chlorophyll fluorescence parameters of lettuce.PSⅡ maximum quantum efficiency (F_v/F_m）,PSⅡ effective quantum yield (F_v′/F_m′),PSⅡ actual quantum efficiency (ΦPSⅡ) and steady state fluorescence decay rate (Rfd) decreased overall from 7 days to 21 days,while initial fluorescence value (F_o) and non-photochemical quenching coefficient (NPQ) increased.【Conclusion】Higher cadmium concentration and longer treatment time led to lower light energy conversion efficiency of lettuce,higher heat dissipation of leaves,lower photosynthesis ability and more serious inhibition of plant growth.