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Abstract
With mounting pressure of heavy metal pollution on agriculture, the demand of practical tools and protocols for nondestructive, pre-visual detection of plant response towards heavy metals has received great impetus. Advances in modern spectroscopic techniques such as synchrotron radiation X-ray fluorescence and attenuated total reflectance Fourier transform infrared spectroscopy have the capability of providing a complete picture of the metabolic events taking place in plants stressed with heavy metals without subjecting the sample to pre-processing. The present study explores the utility of synchrotron radiation X-ray fluorescence and attenuated total reflectance Fourier transform infrared spectroscopy along with multivariate analysis for the detection of the response as spectral indices of wheat seedlings towards chromium treatment. For this, wheat has been grown under optimized growth conditions and exposed to chromium at concentrations from 20 to 100 µM. The synchrotron radiation X-ray fluorescence spectra of control and chromium exposed seedlings show that exposure to chromium leads to its accumulation in the leaves of wheat seedlings which results in a reduction of the uptake of calcium, potassium, manganese iron, copper and zinc by the seedlings. The alterations in the biochemicals of wheat seedlings as a result of chromium exposure have been assessed by attenuated total reflectance Fourier transform infrared spectroscopy. Analysis of the infrared data reveals that chromium significantly alters the spectral signatures of cellulose, pectin, hemicelluloses, lignin, amide II, amide I and lipid in the leaves of wheat seedlings. The observed changes are dependent on the dose of chromium. The spectral signatures obtained in this study serve as important monitoring indices for observing alterations in the physiological, biochemical and metabolic status of plants under heavy metal stress.
Acknowledgements
The authors are thankful to UGC, New Delhi for providing financial assistance to create the ATR-FTIR facility under UGC–CAS program to the Department of Physics, University of Allahabad, Allahabad. RRCAT, Indore for providing SR-μXRF facility (BL-16), Indus-2 for carrying out XRF measurements is greatly acknowledged. We are also grateful to Prof. M. M. Joshi and Prof. R. Gopal, former Head, Department of Physics, University of Allahabad, Allahabad for their keen interest in this problem. One of us (Sweta Sharma) is also grateful to UGC, New Delhi for the financial assistance in form of SRF (NET, UGC) scholarship.