How plants uptake heavy metals?? Mass flow is the principal mechanism or other mechanism also involved in this?? and why the plants adopt a specific phenomena to absorb heavy metals??
The plant uptake of heavy metals by mass flow, diffusion and root interception. Mass flow definitely the principal mechanism. The amount of heavy metal enter to plants by mass flow are based on its concentration in the soil solution which is driven by transpiration.The contribution by diffusion based on the amount supplied by root interception together with mass flow.The amount of heavy metal uptake by root interception depends on the amount of available metal in the soil volume occupied by the root. In general, only a small portion can be entered by root interception. The mechanism differs because of the differences in concentration of heavy metal in the soil solution as well as depends on the buffer power of the soil and bio-availability.
J. C. Tarafdar Sir many thanks for your detailed explanation.
As I understand,the cations and anions which occur in high amounts in soil solution like Ca and NO3 etc are taken up/absorbed by plant roots by mass flow mechanism.Ions like H2PO4 which occur in small amounts in soil solution are taken up by diffusion.Probably, the heavy metal ions which occur in small amounts in soil solution(because of specific adsorption by soil colloids) are taken up by diffusion (as per concentration gradient in soil solution created by active uptake).Both passive (diffusion) and active (involving energy expenditure) mechanisms are involved in metal ion uptake by plants.
Mr.Rizwan,the following two references may provide good information pertaining to your question.
Soil and plant factors influencing the accumulation of heavy metals by plants by Cataldo,DA and Wildung,RF Environmental Health Perspectives 27:149-159( 1978) pdf is available online
https://www.ncbi.nlm.nih.gov/pmc/article/PMC1637297/pdf/envhper00484-0146
A review on heavy metals(As,Pb,Hg) uptake by plants through phytoremediation. International Journal of Chemical Engineering 2011(2011) article ID939161 pdf available online
http//:dx.doi.org.10.1155/2011/939161
https://www.hindawi.com/journals/ijce/2011/939161
Annangi Subba Rao and Ketil Haarstad for your detail explanation and recommendations.
Article A Review on Heavy Metals (As, Pb, and Hg) Uptake by Plants T...
This is helpful in understanding uptake and also relevance to phytoremediation.
Really BIG question~_~! There are a plenty of review papers talking about various mechanisms.
2000-Emerging mechanisms for heavy metal transport in plants.
2003-Phytoremediation of heavy metal-contaminated land by trees - a review.
2003-The hyperaccumulation of metals by plants.
2006-Physiological changes and defense mechanisms induced by cadmium stress in maize.
2006-Put the metal to the petal-- metal uptake and transport throughout plants.
2006-Reactive oxygen species as signals that modulate plant stress responses and programmed cell death.
2007-Nitric oxide as a bioactive signalling olecule in plant stress responses.
2007-Phytoremediation Technology-- Hyper-accumulation Metals in Plants.
2009-Molecular mechanisms of metal hyperaccumulation in plants.
2009-Regulation of macronutrient transport.
2010-Understanding molecular mechanisms for improving phytoremediation of heavy metal-contaminated soils.
......
May others add some recent ones.
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