The Effect And Mechanism Of Phosphine On Marine Algae

Phosphine, as a reduced form of phosphorus, is a ubiquitous constituent in themarine environment. It mainly exists as matrix-bound phosphine (MBP) which canhydrolyze to form free phosphine gas. The free phosphine gas can release intoseawater and air to be the probable supplementary form of phosphorus. Phosphine canbe easily oxidized to other forms of P and it could affect marine microalgae andparticipate in the oceanic biogeochemical cycle of phosphorus. It is of greatsignificance for phosphorus cycle. In this article, the effect of phosphine on specificgrowth rates, transcriptional level of high affinity phosphate transporter gene (PHO),alkaline phosphatase activity and antioxidant enzyme activities were studied inThalassiosira pseudonana. Based on these parameters and previous studies, themechanism of phosphine on marine algae was analyzed from the point of phosphateuptake and utilization, and the point of oxidative stress and free radical. We aimed toprovide a basis for future research on the biological and ecological significance ofphosphine in the marine environment. The main results were as follows:The effects of phosphine on the growth of marine microalgae wereexperimentally studied. The results showed that the adaptive amount of phosphinemight stimulate the growth of T. pseudonana, and high levels of phosphine mightinhibit the growth of algae. Generally, phosphine has influence on the growth ofmarine algae, however, phosphine cannot be the sole phosphorus to marine algae.According to variation in the transcriptional level of phosphate transporter gene(TpPHO) and activity of alkaline phosphatase (AKP) in relation to differentconcentrations of phosphine, the effects of phosphine on phosphorus uptake andutilization in T. pseudonana were studied. TpPHO expression and AKP activity werepromoted by phosphine. AKP activity was higher in the phosphine treatment groupsthan that of the control. It increased with increasing phosphine concentration in the range of0to0.056μmol/L, but was inhibited by higher levels of phosphine. What’smore, TpPHO expression was markedly promoted by phosphine in both thephosphate-deficient and phosphate-4μmol/L culture. However, high phosphineconcentrations can inhibit TpPHO transcription in the declining growth phase.Theseresults revealed that phosphine could promote the signal transduction of phosphorusdeficiency. Consequently, it can benefit T. pseudonana to absorb and utilizephosphorus. Comparison of the phosphine treatment with the phosphate treatment ofthe same concentration revealed that the TpPHO transcriptional level of the formerwas much higher than that of the latter. Therefore, phosphine appeared to influencethe algae in a manner other than by being oxidized to phosphate. The increasing AKPactivity with increasing phosphine also supported this point. The effect of phosphineon the transcriptional level of TpPHO and AKP activity would be one influencing wayof phosphine to algae.The activity of superoxide dismutase (SOD) increased with increasing phosphineconcentration when the concentration was below0.11μmol/L. Phosphine induce theproduction of superoxide radical (O2), and stimulate SOD a higher activity todisproportionate O2to hydrogen peroxide (H2O2). And then, the activity of catalase(CAT) was further induced by H2O2. The content of malonyldialdehyde (MDA)decreased with the increasing concentration of phosphine during the early cultureperiod. During the decline phase, high phosphine concentrations had inhibitory effectson SOD and CAT, and the content of MDA increased with increasing phosphineconcentration. The dual effects of phosphine on antioxidant system of T. pseudonanaand the negative correlation between MDA and specific growth rate indicated thatphosphine may affect algae through impacting the ROS level and antioxidant defensesystem.In conclusion, phosphine can both influence algae directly and be oxidized to bephosphate to influence algae. The variations of specific growth rate, antioxidantenzyme activities, AKP activity, and the transcriptional level of TpPHO indicated thedual effect of phosphine on T. pseudonana. Phosphine can stimulate cells to reproduce via promote SOD, CAT, AKP, and TpPHO gene expression at a low concentration,while has inhibitory effect on cell vitality at a high concentration because of itstoxicity.