Nondestructive and Rapid Probing of Biochemical Response of Arsenic Stress on the Leaves of Wheat Seedlings Using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy

ABSTRACT

The goal of the current study is to characterize the changes in the biochemical composition of the leaves of wheat seedlings stressed by arsenic at concentrations of 0.2, 0.3, 0.4, and 0.5 mM using laser induced chlorophyll fluorescence and attenuated total reflectance Fourier transform infrared spectroscopy. The chlorophyll fluorescence spectra of the leaves of control and arsenic treated wheat seedlings showed increase in the intensity and intensity ratios of chlorophyll fluorescence bands indicating decrease in the photosynthesis performance and chlorophyll content of the leaves of wheat seedlings treated with arsenic. The infrared spectra of the leaves of control and arsenic treated wheat seedlings were obtained from 4000 to 485 cm⁻¹ at a resolution of 4 cm⁻¹. Multivariate principle component analysis of the preprocessed spectra suggest significant biochemical discrimination between the control and arsenic treated seedlings. Arsenic treatment decreased the concentration of cellulose while increasing the pectin, hemicellulose, xyloglucan, and lignin levels in the wheat seedling leaves. The exposure to arsenic also increased the spectral signatures of α-helix, β-sheet, amino acids, glutathione, lipids, and carboxyl compounds. These changes in the biochemicals indicate their physiological roles in mediating arsenic stress in wheat seedlings. The study also demonstrates the applicability of spectroscopic techniques for the non-invasive and rapid monitoring of the metabolism and physiology of the vegetation stressed by metals and metalloids before visual signs of toxicity appear.

KEYWORDS:

• Arsenic
• attenuated total reflectance Fourier transform infrared spectroscopy
• laser induced chlorophyll fluorescence
• wheat seedlings

Acknowledgments

The authors are thankful to UGC, New Delhi for providing financial assistance to create attenuated total reflectance Fourier transform infrared spectroscopy facility under the UGC–CAS program to the Department of Physics, University of Allahabad, Allahabad. We are 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.