Abstract
Ceylon leadwort (Plumbago zeylanica) is ornamental plant known for its pharmacological properties arising from the abundant production of various secondary metabolites. It often grows in lead polluted areas. The aim of presented study was to evaluate the survival strategy of P. zeylanica to lead toxicity via photosynthetic apparatus acclimatization. Shoots of P. zeylanica were cultivated on media with different Pb concentrations (0.0, 0.05, and 0.1 g Pb∙l−1). After a four-week culture, the efficiency of the photosynthetic apparatus of plants was evaluated by Chl a fluorescence measurement, photosynthetic pigment, and Lhcb1, PsbA, PsbO, and RuBisCo protein accumulation, antioxidant enzymes activity, and chloroplast ultrastructure observation. Plants from lower Pb concentration revealed no changes in photosynthetic pigments content and light-harvesting complex (LHCII) size, as well as no limitation on the donor side of Photosystem II Reaction Centre (PSII RC). However, the activity and content of antioxidant enzymes indicated a high risk of limitation on the acceptor side of Photosystem I. In turn, plants from 0.1 g Pb∙l−1 showed a significant decrease in pigments content, LHCII size, the amount of active PSII RC, oxygen-evolving complex activity, and significant remodeling of chloroplast ultrastructure indicated limitation of PSII RC donor side. Obtained results indicate that P. zeylanica plants acclimate to lead toxicity by Pb accumulation in roots and, depending on Pb concentration, by adjusting their photosynthetic apparatus via the activation of alternative (cyclic and pseudocyclic) electron transport pathways.
Highlights
The intensive development of metallurgy, ore mining, chemical and fertilizer industry, municipal services, and other industries involves the production of various waste types that increase environmental pollution
The photosynthetic apparatus of Plumbago plants cultivated on media with lower Pb concentration was characterized by no changes in both the content of photosynthetic pigments and the size of light harvesting complex (LHC) II antennas, as well as the lack of limitation on the reaction center (RC) Photosystem II (PSII) donor side
No changes in the efficiency and performance of the PSII compared to the control plants were observed
Summary
The intensive development of metallurgy, ore mining, chemical and fertilizer industry, municipal services, and other industries involves the production of various waste types that increase environmental pollution. Visible symptoms of lead toxicity to plants are manifested by retardation of the growth and development of plant organs and the reduction of plant yield [5,6,7,8]. These reductions result mainly from oxidative stress, photosynthesis inhibition, and damage to DNA and its consequences caused by Pb ions [9]. Lead decreases activity of antioxidant enzymes by interference with the effective accumulation of K, P, Fe, Zn, Cu, Mg and Ca elements [12]. Disruptions of mitosis may result from Pb interference with the cytoskeleton, which leads to chromosome aberrations [18]
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