| Abutilon theophrasti Medicus,which was an important industrial material and traditional medicine,was widely grown in China.The study of adding exogenous compounds was one of the hot spots in the field of soil plants safety and economic utilization.It could enhance plant tolerance to Cd and reduce Cd accumulation in edible parts to increase plant biomass and produce green drugs.Although there had been many studies on the use of exogenous Melatonin to improve plant tolerance to abiotic stresses such as salt and drought,there were few studies on its enhancement of the economic benefits of Abutilon tolerant to Cd pollution.Abutilon naturally grown in in the Ningqiang mining area of Qinling Mountains where was seriously polluted by Cd.Therefore,this article studied the tolerance of Abutilon theophrasti Medicus seeds and seedlings collected from mining areas to Cd pollution under laboratory conditions,and the mechanism of melatonin on the accumulation and tolerance of cadmium in hydroponic Abutilon,which could provide scientific basis of safe and economic use of cadmium-contaminated soil in mining areas.The main findings were as follows:（1）The effects of different concentrations of Cd stress on the germination rate and germination vigor of Abutilon seeds showed"low promotion and high suppression".When the Cd concentration was higher than 400μmol·L-1,the germination rate and germination potential of Abutilon seeds were significantly reduced.However,the germination rate could still reach more than 70%under the Cd stress of 2000μmol·L-1,indicating that the Abutilon seeds were more resistant to Cd stress,and high concentration of Cd could still germinate.（2）Cd stress caused the green loss of Abutilon leaves and inhibited the formation of lateral roots.Under Cd stress of 200μmol·L-1,the root dry weight of Abutilon was not decreased in short and long term,and the root growth was not affected.The severity degree of Cd stress above 200μmol·L-1on the root dry weight was in turn:2000μmol·L-1>1000μmol·L-1>800μmol·L-1>400μmol·L-1,showing obvious dose effect.The effects of Cd above 200μmol·L-1on the root dry weight of Abutilon were 5 d>3d>24 h>12 h>6 h,showing obvious time effect.The dry weight in the upper part of root decreased significantly with the increase of the stress concentration and time.Therefore,the stress concentration of 200μmol·L-1,400μmol·L-1and 800μmol·L-1（low,middle and high）,stress time of 3 d and 5 d were selected as the stress dose and action time of melatonin regulation test.（3）The malondialdehyde（MDA）content of Abutilon seedlings increased in degrees under different concentrations of Cd,and reached the maximum at 5 days and2000μmol·L-1.The soluble protein content of Abutilon first increased and then decreased with the increase of Cd concentration and the extension of stress time,and reached the minimum at 5 d and 2000μmol·L-1.The chlorophyll content of Abutilon significantly decreased with the increase of Cd concentration and the extension of stress time,and reached the minimum at 3 d and 2000μmol·L-1.（4）Compared with control,0.1 mmol·L-1melatonin treatment significantly increased root activity,chlorophyll content,Peroxidase activity and soluble protein level of Abutilon seedlings（p<0.05）,and significantly decreased MDA content.The results showed that the damage of Cd to Abutilon was reduced.In contrast,0.1 mmol·L-1melatonin had the most significant effect on other physiological indexes besides chlorophyll under 400μmol·L-1,3 d and 5 d Cd stress.The effect of 0.1 mmol·L-1melatonin on the chlorophyll content of Abutilon was the most obvious at 3 d,800μmol·L-1and 5 d,200μmol·L-1.The results showed that melatonin could effectively alleviate the toxic effect of Cd on Abutilon and improve its tolerance to cadmium pollution.（5）Compared with the control,0.1 mmol·L-1melatonin significantly decreased the accumulation coefficient of Abutilon seedlings,but increased the transfer coefficient;while the accumulation coefficient of Abutilon seedlings increased with the time of cd-stressed,it was still significantly lower than the control group with the same concentration.Under 200μmol·L-1Cd stress,the transfer coefficient of 0.1 mmol·L-1melatonin in the experimental group was significantly lower than the control group,which decreased 31.92%of Cd transfer to the upper part of the root,suggesting that melatonin could effectively alleviate the accumulation of Cd in the upper part of the root--stem and leaf of Abutilon.Because the Cd accumulation coefficient of Abutilon was much higher than the transfer coefficient,although the transfer coefficient increased significantly,the Cd accumulation concentration of Abutilon decreased significantly with the addition of melatonin,the tolerance of the Abutilon to cadmium pollution was increased. |
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