Arsenic Stress in Plants: An Inside Story - Crop Improvement: New Approaches and Modern Techniques - page 380

et al. 1993 ; Meharg and Hartley-Whitaker 2002 ; Quaghebeur and Rengel 2003 ).
Exposure of plants to inorganic As leads to the synthesis of phytochelatins that
complex with As(III), those complexes or as alone, being transported across the
tonoplast by ABC-type transporters or can be efflux from the cytoplasm by As(III)
efflux transporters. Once arsenic enters in plant cell it causes various changes in
normal metabolic activities. The changes occur due to arsenic toxicity and also in
process to cope up from arsenic toxicity to some extent. But at higher concentration
of arsenic toxicity plants fails to counterbalance between toxicity and resistance.
AnatomicalChangesinPlantsExposedtoArsenic
Arsenic causes many physiological changes and damages in plants (Wells and
Gilmor 1997 ). There are several anatomical parameters, in which reduction in
growth is the earliest As toxicity response. Arsenic affects root growth more se-
verely than shoot growth possibly due to the retention of As in the roots in higher
amount than in the stem. Stoeva et al. ( 2005 ) also reported that arsenic accumulated
mainly in the root system and to a lesser extent in the overgrown organs. This also
confirmed from the study of mung bean and Anadenanthera Peregrina (Pal et al.
2006 ; Gomes et al. 2012 ). There is however, contrasting reports showing that the
effect of arsenic on stem and root growth varies depending on the plant species,
level of contamination and plant tissue ability to As. Arsenic also inhibits fresh and
dry biomass accumulation (Wells and Gilmor 1997 ) which may be possibly due to
plant growth inhibition. From the study of mung bean it is also observed that reduc-
tion in root elongation is accompanied by the anatomical changes, which occurs on
exposure to arsenic toxicity (Pal et al. 2006 ). The anatomical changes are severe
decrease or completely loss of root hairs, damage to epidermal cells and the cortex,
with those cells losing their shape and showing signs of shriveling and disintegra-
tion while the untreated epidermal root cells are intact and the root hairs are turgid.
Further compared to the control roots, where the stele is in a tetrarch condition,
there is a lack of complete differentiation and pith formation in arsenic treated root
cells. Also, arsenic cause necrosis and reduction of the number of raminification in
root system (Stoeva et al. 2005 ). According to a study by Kopittke et al. ( 2012 ) the
accumulation of As causes permanent damage to the meristem but root border cells
accumulates high levels of As and limiting its movement into the root. When roots
are counteract with arsenic in soil environment a greater diffusion of oxygen from
the roots indicates increased root oxidizability (RO). This is considering as avoid-
ance from the toxicity. The TIC, salt used to measure RO, which absorbs electrons
from the mitochondrial transport chain and correlates positively with the respiratory
activity, in term associated with enhanced RO is also an indicator of higher reactive
oxygen species generation (Singh et al. 2007 ).
Besides roots, above ground part of plant is also affected by arsenic toxicity.
There is reduction in leaf area, necrosis and chlorosis of leaf tips are occurred on
arsenic toxicity (Stoeva et al. 2005 ). Arsenic also changes the osmotic adjustment