Response mechanisms of antioxidants in bryophyte (Hypnum plumaeforme) under the stress of single or combined Pb and/or Ni

Abstract

The short-term responses and mechanisms of antioxidants in moss Hypnum plumaeforme subjected to single or combined Pb and/or Ni stress has been revealed in this study, in order to clarify (1) the relationship between the stress intensity and antioxidant fluctuation, (2) the difference between single and combined stress, and (3) the possibility of biomonitoring by the application of antioxidant fluctuation under stress. The results showed that the stress induced dose dependent formation of reactive oxygen species (ROS) and subsequent lipid peroxidation. Total chlorophyll (Chl) content and superoxide dismutase (SOD) activity were initiated under lower stress but were inhibited under higher stress. Both single and combined stress decreased catalase (CAT) activity but increased peroxidase (POD) activity, indicating POD in the moss played an important role in resisting the oxidative stress induced by Pb and Ni. The accumulation of (.)O2(-) and H2O2 in H. plumaeforme was respectively related to the low activity of SOD and the decreased activity of CAT. The study indicated that Pb and Ni had synergistic effect in inducing the oxidative stress in moss H. plumaeforme, especially under the combination of high concentration of Ni (0.1, 1.0 mM) and Pb. POD and CAT activity, as well as H2O2 and MDA content, which increased or decreased regularly with a dose dependent under Pb and Ni stress, could be used as an effective indicator in moss biomonitoring, especially in the case of light pollution caused by heavy metals without the changes in the appearance of mosses.

Bryophytes and heavy metals: a review

“…Additionally, in all three species under heavy metal stress, the amount of chlorophyll b was greater than that of the chlorophyll a, indicating that in these bryophytes heavy metals could induce the conversion of chlorophyll-a to chlorophyll-b (Shakya et al 2008). Another study, involving he moss Hypnum plumaeforme Wilson, showed that Pb and Ni, single or combined, at higher concentrations, can also lead to a strong decline in total chlorophyll concentration (Sun et al 2009). The highly negative effect of Pb on total chlorophyll content was also demonstrated in the moss Taxithelium nepalense (Schwaegr.)…”

“…The absence of a root system indicates the ability of these plants to absorb heavy metals over the entire surface (Berg andSteinnes 1997, Degola et al 2014). The lack of the cuticle layer, which makes their cell walls easy accessible for metal ions (Choudhury andPanda 2005, Koz andCevik 2014), pronounced ion-exchange properties (Little and Martin 1974) and a large surface-to-weight ratio also significantly contribute to this ability (Sun et al 2009). Consequently, they can react to and reflect the changes in the heavy metal concentrations faster than most vascular plants (Zvereva and Kozlov 2011).…”

“…To obtain that information, it is essential to establish and maintain the linear correlation between the concentrations in bryophyte tissue and the concentrations of metals to which it is exposed, accounting for all the factors that could disturb this relationship (Boquete et al 2014). In this sense, the toxicity of heavy metals could also cause the alternation of the metal accumulation characteristics of the bryophytes, which could affect their reliability as biomonitoring systems (Wolterbeek 2002) or result in an effective physiological markers of heavy metal pollution (Sun et al 2009). Investigations on bryophytes' relation with heavy metals in strictly controlled condition like in vitro culture are still in very short supply (e.g.…”

“…These effects include ultrastructural changes as well as the changes in the plant physiological processes and characteristics (Sun et al 2009, Canivet et al 2015. Ultrastructural changes seen in bryophytes under heavy metal stress may include alternations of the chloroplast shape and thylakoid organization (Choudhury and Panda, 2005) as well as the appearance of the stromal plastoglobules in them (Basile et al 2009).…”

“…Additionally, comparable results are limited to laboratory experiments (Varela et al 2013). Nevertheless, most of these studies have revealed the reduction in total chlorophyll content as a specific response to heavy metal stress, though the degree of it may vary between the species and the metals tested (Choudhury and Panda 2005, Shakya et al 2008, Sun et al 2009). In the study of Tremper et al (2004) on Rhytidiadelphus squarrosus, of the three metals investigated (Cu, Zn, and Pb) only copper caused a significant decline in the total chlorophyll.…”