Effects of two microplastics on the growth and physiological characteristics in lettuce
As a new category of pollutant,the impact of microplastics on the environment is still unclear.Exploring the effects of polyethylene(PE)and polypropylene(PP)on the growth and physiological characteristics of lettuce contributes to our comprehension of the toxic effect of microplastics on lettuce.This research provides a theoretical foundation for elucidating the toxic mechanism associated with microplastics.Lettuce(Italian lettuce 333)was used as the material for the hydroponic experiment.A total of seven treatments,including control(CK),three PE supply levels(0.1,0.5 g·L-1,and 1.0 g·L-1),and three PP supply levels(0.1,0.5 g·L-1,and 1.0 g·L-1),were employed.The particle sizes of both PE and PP were 13 μm.Various parameters such as lettuce biomass,root morphological parameters,photosynthetic parameters,ultrastructure of leaves and roots,and antioxidant capacity were measured.Under conditions involving microplastic stress,the dry weight of the lettuce and root volume decreased significantly.The photosynthetic parameters and chlorophyll a and carotene levels were reduced.In the ultrastructure of the blade and root system,the chloroplasts and the membrane and the cell walls of the root system were destroyed by different types of microplastics.Compared with CK,superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),and ascorbate peroxidase(APX)levels increased by 3.0-15.0-fold,2.8%-164.0%,2.8-12.0-fold,and 3.5-8.1-fold,respectively.Malondialdehyde(MDA)and ascorbic acid(ASA)levels increased by 1.2-18.9-fold and 7.2%-10.1%.Microplastics exert toxic effects on lettuce leaf and root cells,damage cell chloroplasts in mesophyll,reduce photosynthetic parameters and pigment concentrations in leaves,and inhibit root growth,thereby reducing the biomass in lettuce.In addition,the antioxidant system of lettuce responded to the two kinds of microplastics.
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