Study of Laser-induced Fluorescence Signa- Tures from Leaves of Wheat Seedlings Growing under Cadmium Stress

Steady state LIF spectra using 488 nm of cw Ar + laser and 355 nm of pulsed Nd:YAG laser, fluorescence induction kinetics using 488 nm laser light were studied in wheat seedlings exposed to increasing cadmium (Cd) concentrations (0.01, 0.1, 1.0 and 2.0 mM). In addition, some growth parameters and pigment content were also measured. The LIF spectra of the leaves exhibited two characteristic bands at 685 nm and 730 nm registered at 488 nm excitation wave length and four bands at around 450 nm, 520 nm, 685 nm and 735 nm at 355 nm excitation wave length. The peak parameters of the bands were calculated by Gaussian curve fitting of the LIF spectra. The result showed higher intensity of the red band (685 nm) as compared to the far-red band (730 nm) in the case of 488 nm excited spectra, however, 355 nm excited chlorophyll (Chl) fluorescence spectra exhibited a higher value in the far-red intensity. The plant vitality index (Rfd) of the plants was also calculated for both Chl fluorescence bands using the fluorescence induction kinetics curve. The decrease in plant growth parameters as well as Rfd values at 685 nm and 735 nm in response to increasing Cd concentrations could be considered as symptoms of Cd toxicity. Variations in the Chl FIR and other fluorescence ratios of intensities, bandwidth and band area were also observed. Thus, we demonstrate the use of the LIF spectra for rapid detection of Cd stress in wheat plants.