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Biology and Biotechnology of Environmental Stress Tolerance in Plants, Volume 3

avoiding genome destabilization as well as Ni ion mediated disruption of

DNA structure (Gullì et al., 2018). Pine trees (Pinus silvestris) were found

to withstand high ionizing radiation, have much more hypermethylated loci

than less adapted plants (Kovalchuk et al., 2003; Volkova et al., 2018).

Plants exposed to HM have miRNA-directed transcriptional and post-

transcriptional regulation of gene expression through base-pairing with

its focused mRNAs (Min Yang & Chen, 2013). There is an involvement

of mi-RNA in response to Cd which is evidenced by abnormal miRNA

in stressed plant cells and tissue. It is documented when rapeseed (Bras­

sica napus) is treated with Cd exposure there is an up-regulation of the

bna-miR393 gene in foliages, bna-miR156a, bna-miR167a/c in roots and

foliages, bna-miR164b and bna-miR394a/b/c across tissues whereas down-

regulation of miR160 is noticed by Huang et al. (2010). Mercury (Hg) is

an extremely poisonous element, with its ionic type (Hg²⁺) is considerably

common in soil. It is also the most accessible form for plants, as it is rapidly

absorbed by the plant’s root and apical parts. Various toxic responses such

as growth inhibition, an anomalous function of vascular bundle, deformity

of the cell, reduction in chlorophyll amount as well as accumulation of ROS

due to high Hg concentration in the soil. In response to high exposure to

Hg stress, different plant species reveals differential miRNAs expression.

The barrel-clover plants (Medicago truncatula) when exposed to high Hg

stress, conserved miRNAs along with non-conserved miRNAs expressed

differentially. The vast majority of the new candidate miRNAs were shown

to be significantly controlled by the heavy metal mercury Hg (II), including

12 miRNAs showing especially sensitive to Hg treatment (Zhou et al.,

2012). Only next to iron, Mn is the abundant transition element present

on the planet which is widespread in soils, sediment, and water as well as

biological components. Mn is an important co-factor for many enzymes, like

the mitochondrial superoxide dismutase. Excess Mn in plants causes toxicity,

on the other hand, has a variety of morphological consequences, including

chlorosis and necrosis, crinkled leaves, and brown patches, and, eventually,

growth suppression. Valdés‐López et al. in 2010 investigated that the differ­

entially expressed pattern of miRNAs in common bean (Phaselous vulgaris)

in response to Mn stress and found 37 miRNAs. Around 11 miRNAs were

active under Mn stress, whereas another 11 were found to be suppressed.

Mn-responsive miR1508, miR1515, miR1510/2110, and miR1532 have been

discovered, including calcium-dependent protein kinase, heat shock proteins,

nucleotide-binding region leucine-rich repeat resistance-like proteins, and

receptor kinase protein as candidates, correspondingly (Valdés‐López et