Abstract
The study aimed at distinguishing antioxidant responses conditioning acclimation status to metallic stress in a shoot culture of a woody plant Daphne jasminea. Growth, organogenesis, metal accumulation, oxidative stress level and antioxidant responses were compared in the long-term treated shoots (Lt lines) and short-term treated (St lines) with Cd, Ni and Pb in relation to control shoots. Growth rate and organogenic potential were higher in the long-term treated Lt Cd and Lt Pb lines than in respective short-term treated St lines. Lt Ni line proliferated less effectively than St Ni line, whereas biomass accretion was similar in both Ni lines. All heavy metal (HM)—exposed shoots suffered from oxidative stress, however, it was more severe in St than in Lt lines. In the long-term treated lines three major factors were associated with the acclimation status: activity of peroxidase (POD) and accumulation of anthocyanins and carotenoids. POD activity was 4–1.5-times higher in Lt lines than in the control one. Anthocyanin content nearly tripled, while carotenoid content doubled in Lt lines. Other elements of antioxidant system, CAT and SOD, glutathione, ascorbic acid and proline, complemented the action of the “major players” in long-term treated Lt lines depending on heavy metal type. Short-term treated lines responded by accumulation of proteins and a decline in catalase activity. The study demonstrated that long-term heavy metal treatment can be considered acclimation strategy, during which substantial modulation of the antioxidant system occurs. Due to orchestrated action of cytosolic POD, vacuolar anthocyanins and membrane-bound carotenoids HM toxicity could be counteracted in various cellular compartments.
Highlights
Heavy metal (HM) contamination of the environment is gradually increasing due to natural processes and anthropogenic activities (Wu et al 2015; Tóth et al 2016; Mazurek et al 2017)
In this study we showed that metallic stress affects antioxidant system in the woody plant D. jasminea
We showed that long exposure to HM significantly remodeled antioxidant system in D. jasminea shoots
Summary
Heavy metal (HM) contamination of the environment is gradually increasing due to natural processes and anthropogenic activities (Wu et al 2015; Tóth et al 2016; Mazurek et al 2017). As immobile organisms, are unable to escape from contaminated areas and are forced to adjust their metabolic performance to counteract toxicity of excessive metals and metalloids. Plant Cell, Tissue and Organ Culture (PCTOC) (2019) 139:339–357 especially enzymes, components of cell membranes and DNA (Amari et al 2017; Hasan et al 2017). These direct events have negative consequences at the whole plant level and lead to water and nutrient element imbalances, disruption of photosynthesis and overproduction of radicals that causes oxidative stress (Sytar et al 2013; Amari et al 2017). As a result of metabolism remodeling, HM can be either stabilized in the rhizosphere or accumulated in aboveground organs, in various cellular compartments, contributing to plant tolerance towards their toxicity (Vrbová et al 2013; Rodrigues et al 2017)
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