Effects Of BPA On Growth And Photosynthesis Of Soybean Plants At Different Growth Stages

Bisphenol A(BPA), is an emerging environmental endocrine disruptor, and widely exists in the industrial raw materials and manufactured products. BPA is ubiquitous in the environment because of its increasing demand. More and more researchers have paid more attention to BPA due to its potential harm to human health and ecosystem. However, in contrast with the vast literature on the effects of BPA on animals, relevant research on plants, especially terrestrial plants, is little. Photosynthesis, as an indispensable physiological activities in plant, supplies substance and energy required for plant growth. However, how BPA affects plant photosynthesis has been poorly reported. In this study, the effects of BPA on the growth and photosynthesis of soybean during the different growth stages were investigated by using the experiment design of pollution ecology and the test methods,in which soybean(Glycine max, “Zhonghuang 25”) is recommended for the use in the phytotoxicity studies by the U.S. EPA. The major experimental results are shown as follows:(1) Compared with the control, low-dose BPA improved soybean growth, median and high-dose BPA inhibited soybean growth, and the inhibitory effect was more evident as BPA dose increased. Following the withdrawal of BPA exposure, the growth of soybean at different stages restored to varying degrees, and the low-dose BPA groups had a better recovery than the high-dose groups.(2) Low-dose BPA promoted the net photosynthetic rate(Pn) by improving the stomatal factors [stomatal conductance, intercellular CO2 concentration and stomata behaviour]; whereas high-dose BPA decreased the Pn by inhibiting the stomatal factors and non-stomatal factors [Hill reaction rate, apparent quantum yield, carboxylation efficiency, maximum rates of carboxylation, maximum rates of electron transport, ribulose-1,5-bisphosphate activity, chlorophyll content(Chl)] in soybean leaves, and the inhibitory effects were more evident with increasing the BPA dose. Withdrawal of the BPA exposure, all above photosynthetic indices were restored, and the low-dose groups had a better recovery than the high-dose groups.(3) Compared with the control, low-dose BPA exposure decreased the 5-aminolevulinic acid(ALA) content, and increased the contents of main intermediate [porphobilinogen, protoporphyrin IX, magnesium protoporphyrin, protochlorophyll] during chlorophyll synthesis, and the activities of four key enzymes [5-aminolaevulinic acid dehydratase, porphobilinogen deaminase, uroporphyrinogen III synthase, magnesium chelatase]. High-dose BPA exerted the opposite effects on the contents of these five intermediates and the activities of these four enzymes, and the change degrees were decreased with increasing the BPA dose and prolonging the treating time. Following the withdrawal of BPA exposure, the recoveries of above indices were more obvious with lower dose of BPA or longer recovery time.(4) The correlation analysis showed that the Pn in soybean leaves at different stages was positively correlated with the growth, photosynthesis indices(except negatively correlated with the intercellular CO2 concentration) and the Chl content. The Chl content was positively correlated with the contents of main intermediate(porphobilinogen, protoporphyrin IX, magnesium protoporphyrin, protochlorophyll) and the activities of four key enzymes(5-aminolaevulinic acid dehydratase, porphobilinogen deaminase, uroporphyrinogen III synthase, magnesium chelatase), and negatively correlated with the ALA content.(5) After BPA exposure and withdrawal of BPA exposure, the effects of BPA on the growth, photosynthesis, Chl content and Chl synthesis during different growth stages showed the following orders: seedling stage > flowering and pods formation stage > seed filling stage > mature stage(low-dose BPA); seedling stage > mature stage > flowering and pods formation stage > seed filling stage(high-dose BPA).In conclusion, BPA affected the Pn by regulating the stomatal and non-stomatal factors; however, the degree of regulation was dependent on the BPA dose. Low-dose BPA increased the Pn by improving the stomatal factors, whereas high-dose BPA decreased the Pn by inhibiting the stomatal and non-stomatal factors in soybean leaves, and then improved or inhibited the growth of soybean plants. The degree of regulation was various at different growth stages. The results may serve as reference for understanding the effects of BPA on plant photosynthesis from the stomatal and non-stomatal factors, and provide theoretical basis for evaluating the potential risk of BPA on the growth and photosynthesis, as well as offer some references for scientifically evaluating the potential ecological risk of BPA on crop production and food safety.