Abstract
Mn toxicity inhibits both primary root (PR) growth and lateral root development. However, the mechanism underlying Mn-mediated root growth inhibition remains to be further elucidated. Here, we investigated the role of auxin in Mn-mediated inhibition of PR growth in Arabidopsis using physiological and genetic approaches. Mn toxicity inhibits PR elongation by reducing meristematic cell division potential. Mn toxicity also reduced auxin levels in root tips by reducing IAA biosynthesis and down-regulating the expression of auxin efflux carriers PIN4 and PIN7. Loss of function pin4 and pin7 mutants showed less inhibition of root growth than col-0 seedlings. These results indicated that this inhibitory effect of Mn toxicity on PR growth was mediated by affecting auxin biosynthesis and the expression of auxin efflux transporters PIN4 and PIN7.
Highlights
Manganese (Mn) is one of the essential micronutrient elements that constitutes the Mn-SOD and Mn-cluster of the oxygen-evolving complex in photosystem II and is involved in the biosynthesis of acyl lipids, flavonoids, and lignin (Lidon et al, 2004)
Our results indicated that Mn toxicity reduced auxin levels in root tips by reducing IAA biosynthesis and down-regulating the expression of auxin efflux carriers PIN4 and PIN7 in Arabidopsis
These data indicated that Mn toxicity inhibited root growth by reducing the meristematic cell division potential in root tips
Summary
Manganese (Mn) is one of the essential micronutrient elements that constitutes the Mn-SOD and Mn-cluster of the oxygen-evolving complex in photosystem II and is involved in the biosynthesis of acyl lipids, flavonoids, and lignin (Lidon et al, 2004). Mn is necessary for plant growth and development (Chen et al, 2015). Manganese (Mn) toxicity is probably the most important growth-limiting factor after aluminum (Al) for plants in acidic soils in some subtropical and tropical areas. Mn toxicity induced oxidative damage and thereby disrupting photosynthesis system in leaves. Excess Mn results in a rapid accumulation of reactive oxygen species (ROS) in plants and causes chlorosis and necrosis in leaves (Le Bot et al, 1990). Excess Mn (0.5 or 1.5 mM MnCl2) inhibited photosynthetic efficiency in the long term hydroponic-cultured Arabidopsis plants (Millaleo et al, 2012). Mn toxicity disrupted thylakoid structure and the photosynthetic electron transport chain, it is possible that chloroplast is the primary target of Mn toxicity (Lidon et al, 2004; Chen et al, 2015)
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