Agriculture Reference
In-Depth Information
toxicity. In general inorganic arsenic species are more toxic than organic arsenic
species (Adriano 2001 ).
Arsenic accumulation and speciation in plants are affected by root aeration and
porosity (Wu et al. 2011 ). Behavior of arsenic in soil and also in plants is differ-
ent due to its dynamic and complex chemical species with inter conversable forms
regulated by biotic and abiotic process (Fig. 13.1 ).
This chapter evaluates all the changes in plants at physiological, biochemical and
molecular level to better understand toxicity and resistance mechanisms in plants.
Interaction of Arsenic with Plants
UptakeofArsenicinPlants
Different soil parameters like pH and redox state has a major influence on the toxic-
ity of arsenic species due to altered availability (solubility and mobility). The up-
take of arsenic affected by some factors such as soil type, nutrient supply, pH of the
medium and mugineic acid which is excreted by some graminaceous (grassy) plants
(Sultana and Katsuichiro 2011 ). Among all factors phosphorus and pH are the most
important ones influencing plant growth and As uptake. As(V) has been shown to
be taken up by the high affinity phosphate uptake system (Ullrich-Eberius et al.
1989 ) while As(III) uptake is thought to be through aquaporins in the roots (Meharg
and Jardine 2003 ) while low level uptake of organic As species, such as MMA and
DMA has also been observed in rice but the underlying transport pathways are un-
known (Meharg 2004 ). Recently, Arsenic transformation and volatilization is also
investigated. The uptake of As species into rice roots is in the order of arsenate
[As(V)] > monomethylarsonic acid [MMAs(V)] > dimethylarsinic acid [DMAs(V)]
> trimethylarsine oxide (TMAs(V)O), but the order of the root-to-shoot transport
index (Ti) is reverse. The volatilization of trimethylarsine (TMAs) from rice plants
is also observed when plants were treated with TMAs(V)O but not with As(V),
DMAs(V) and MMAs(V) (Jia et al. 2012 ). Lomax et al. ( 2012 ) has reported a latest
finding on the basis of GeoChip analysis of microbial genes in a Bangladeshi paddy
soil that plants are unable to methylate inorganic As, and instead take up methylated
As produced by microorganisms. Recently, specific accumulation patterns were ob-
served among growth habitat and plant groups, it was found that submerged plants
have a higher accumulation than emergent and terrestrial plants. Whereas (  Oryza
sativa ) grown in multiple sites (Norton et al. 2012 ).
Once arsenic enters inside root cells, As(V) is quickly reduced to As(III) and
become complexed with phytochelatines. Phosphorus nutrition influences As(V)
uptake and toxicity in Gymnosperms had a high [As] (shoot) : [As] (root) ratio (Bergqvist
2012 ). Statistically significant effect of year, location and flooding management
are also reported as an important factors to develop variation in grain arsenic
evaluated in a varied section of rice plants, whilst silicon has similar influences
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