Arsenic Accumulation In Pteris Cretica Var.nervosa Induced By Gibberellin: Effect And (Physiological And Biochemical) Mechanism

Exogenous application of gibberellin 3（GA₃）can effectively promote plant growth and heavy metal uptake,but the related mechanism remains unclear.In this paper,the effects of gibberellin on arsenic（As）uptake,accumulation and translocation in As hyperaccumulator Pteris cretica var.nervosa were determined by pot experiment in a greenhouse.Secondly,in order to analyze how GA₃ affected plants,the plant growth status and physiological and biochemical indicators,including root morphology,photosynthetic pigment content,chlorophyll fluorescence,osmotic regulator and antioxidant enzyme activity,were determined.Finally,the field farmland soil combinedly polluted with P b,Cd and As was directly used to investigate the influence of GA₃ on heavy metal uptake of P.cretica,and the changes of the total and bioavailable heavy metals in soi were also examined.The main results showed that:1.GA₃ promoted the growth of P.cretica,with a significant increase of plant height and the shoot fresh weight.When the As concentration in soil was 53.49±2.52 mg·kg^-1,the plant height was significantly increased by 31.6%and 36.9%at 20 and 40 mg·kg^-1GA₃treatments,respectively.The shoot fresh weight was also significantly increased by 38.8%and 48.7%,respectively,at the two GA₃treatments compared to that of the control.Additionally,GA enhanced the extraction efficiency of As in P.cretica.During the 42-day soil experiment,the maximum As extraction efficiency was achieved at 20 mg·L^-1GA₃ treatment,which was 2.34 times compared to that of the control group.2.The optimum concentration of GA ₃ could significantly promote the growth of P.cretica,with a significant increase of the plant height and fresh weight,which were also significantly affected by culture time（P<0.001）.The contents of chlorophyll a and chlorophyll b were significantly affected by GA₃.The content of chlorophyll a was significantly increased during the first 21 days（P<0.01）,and the content of chlorophyll b was also significantly higher than that of the control during21 to 42 days.The results from chlorophyll fluorescence analysis showed that non-photochemical quenching coefficient（NPQ）at 20 mg·L^-1GA₃treatment was significantly lower than that of the control during 21 to 42days.During the first 28 days,the soluble protein content in plant leaves was significantly increased with 20 mg·L^-1GA₃ addition.The soluble sugar content in leaves was significantly increased during 21 to 42 days,and.the content of malonaldehyde（MDA）was significantly decreased（P<0.01）.The results from stepwise regression analysis showed that the As extraction efficiency of P.cretica was significantly positive correlated with the culture time,activity of superoxide dismutase（SOD）and NPQ,and was significantly negative with the catalase（CAT）activity and projected area of roots.3.In the combined polluted soil,the optimal co ncentration of GA₃significantly promoted the growth of P.cretica compared to the control.After 42-day pot trial,the plant height and shoot fresh weight was significantly increased with GA ₃ addition.In the combined pollution soil containing As,Cd and Pb,the accumulation of As in P.cretica was significantly increased with the optimal GA₃ treatment.At the same time,the cadmium accumulation in shoots（P<0.01）and lead accumulation in roots（P<0.05）of P.cretica were also increased with addition of GA ₃.The parts of heavy metal accumulation in P.cretica were various,and As was mainly accumulated in shoots and lead in roots.No significant difference in Cd accumulation was observed in roots and shoots.However,the total and bioavailable concentrations of As,Cd and Pb in soil were not significantly affected by whether GA₃ was sprayed or not,treatment time and the interaction between them（P>0.05）.In conclusion,the growth status and As accumulation of P.cretica were promoted by GA₃ spraying via plant leaves,and the As extraction efficiency was the highest with addition of 20 mg·L^-1 GA₃.With the induction of GA₃,the physiological and biochemical processes in P.cretica were changed to promote As accumulation,and the As extraction efficiency of plant was significantly positive correlated with the culture time,a ctivity of SOD and NPQ.In the combined polluted soil of Pb,Cd and As,the As and Cd uptake in plant shoots was significantly increased with addition of GA₃.Therefore,it can be considered that the remediation efficiency was improved by GA₃ spraying during the remediation of Cd and As combined pollution soil.