Zohra Ben Lakhdar

Analysis of in vivo chlorophyll fluorescence spectra to monitor physiological state of tomato plants growing under zinc stress

The effects of zinc (Zn) on plant chlorophyll fluorescence were investigated in 10-day-old tomato (Solanum lycopersicum) seedlings subjected for 7 days to a series of zinc (10, 50, 100 and 150μM) applied via the nutrient solution. The chlorophyll fluorescence spectra of leaves were recorded in the spectral region 650-800nm using the spectroscopic technique of ultraviolet light emitting diode induced fluorescence spectroscopy (UV-LED IFS). These spectra have been used to analyze the effect of several doses of zinc on the photosynthetic activities of tomato plants. The fluorescence intensity ratios (FIR) at the two maxima (F(690)/F(735)) of control as well as treated tomato plants were calculated by evaluating curve-fitted parameters using a Gaussian spectral function. The variable chlorophyll fluorescence decrease ratio (R(Fd)) values were determined from the fluorescence induction kinetics curves recorded at 690nm and 735nm. In addition, Zn accumulation in plants, plant growth, photosynthetic pigments content and malondialdehyde level (MDA, an index of lipid peroxidation) were also estimated. The results indicated that the plants treated with 10μM of zinc exhibited better growth, however, higher concentrations of zinc were harmful for plants. Excess Zn induced a decrease in the R(Fd) values, which was associated with a strong decline of the total chlorophylls content and an increase of MDA level. The total chlorophylls content decline could also be followed via an increase of the chlorophyll fluorescence ratio F(690)/F(735).

Spectroscopic studies of photosynthetic responses of tomato plants to the interaction of zinc and cadmium toxicity.

The in vivo chlorophyll (Chl) fluorescence spectra of Solanum lycopersicum leaves were recorded in the spectral region 650-800nm using a spectroscopic method based on ultraviolet light emitting diode induced fluorescence spectroscopy (UV-LED IFS). These spectra have been used to analyze the interactive functions of cadmium (Cd(2+)) and zinc (Zn(2+)) on photosynthetic activities of S. lycopersicum plants. The fluorescence intensity ratios (F(690)/F(735)) of the chlorophyll bands at 685 and 730nm were calculated by evaluating curve fitted parameters using a Gaussian spectral function, for control as well as treated plants. The fluorescence induction kinetics (Kautsky effect) was also measured on dark adapted intact plant leaves at the chlorophyll bands for determining the variable chlorophyll fluorescence decrease ratio (R(Fd) values) and the stress adaptation index (Ap). In addition, metal accumulation in plants, plant growth and photosynthetic pigments content were estimated. It was found that the R(Fd)(690), R(Fd)(730) and Ap values decreased whereas the F(690)/F(735) ratio increased in the case of 10μM Cd(2+) treated plants, indicating an impairment of the photosynthetic efficiency. Zn(2+) supplementation, at low concentration (10 and 50μM), in combination with Cd(2+) protect the photochemical functions. However, the high Zn(2+) concentration exacerbated the negative effects of Cd(2+) and showed a severe decrease of R(Fd)(690), R(Fd)(730) and Ap values compared to Cd(2+) alone. It is seen that F(690)/F(735) ratios are strongly correlated with chlorophyll contents. The results demonstrate the usefulness of F(690)/F(735), Ap and R(Fd) values in determining the potential photosynthetic activity of an intact attached leaf in a non-destructive way.

THEORETICAL SPECTROSCOPIC DATA FOR THE X2B1 AND A2A1 STATES OF H2S

Abstract Coupled electron pair (CEPA) electronic wave functions have been used to calculate the three-dimensional potential energy functions of the two lowest doublet states X2B1 and A2A1 of H2S+. The near-equilibrium potential for the X2B1 state has been used in variational calculations of the ro-vibrational energy levels up to 10 000 cm−1. Rotationally resolved absorption spectra of the three fundamental transitions have been calculated ab initio using the three-dimensional electric dipole moment functions and the ro-vibrational eigenfunctions. The absolute line strengths are given for the most intense transitions.

Ro-vibronic spectrum of the N2O+ ion in the X 2Π state

Abstract Three-dimensional potential energy functions (PEFs) for the two components of the electronic ground state X 2 Π state of the N 2 O + radical cation have been calculated using multi-configuration self-consistent field approach. The theoretical PEFs and the existing experimental information have been combined to generate empirical PEFs for the beyond Born-Oppenheimer variational calculations of the ro-vibronic energy levels including the couplings of the rotation-vibration, the electron spin and the electronic angular momenta. Band origins ( J = P ) are given for energies up to 4500 cm −1 . The experimentally known vibronic energy levels are reproduced with an accuracy of better than 5 cm −1 for the vibronic states with K ⩽ 2. The anharmonic coupling effects have been investigated.

Optics simulations with Python: diffraction

Python is an easy open source software that can be used to simulate various optical phenomena. We have developed a suite of programs, covering both geometrical and physical optics. These simulations follow the experimental modules used in the ALOP (Active Learning in Optics and Photonics) UNESCO program in the sense that they complement it and help with student prediction of results. We present these programs and the student reactions to these simulations.

Workshop on Active Learning: Two Examples

Optics is an enabling science that has far ranging importance in many diverse fields. However, many students do not find it to be of great interest. A solution to this problem is to train teachers in active learning methodologies so that the subject matter can be presented to generate student interest. We describe a workshop to present an example of an active learning process in Optics developed for training of teachers in developing countries (a UNESCO project) and will focus on 2 two different activities: 1. Interference & diffraction is considered by students as being very hard to understand and is taught in most developing countries as purely theoretical with almost no experiments. Simple experiments to enhance the conceptual understanding of these wave phenomena will be presented and 2. Image formation by the eye. Here we will discuss myopia, hyperopia and astigmatism as well as accommodation. In this module we will discuss image. The objective of the workshop will be to provide an experience of the use of the active learning method in optics including the use of experiments, mind’s on & hands-on exercises, group & class discussions

A simple wavelength division multiplexing system for active learning teaching

The active learning project consists in a series of workshops for educators, researchers and students and promotes an innovative method of teaching physics using simple, inexpensive materials that can be fabricated locally. The objective of the project is to train trainers and inspire students to learn physics. The workshops are based on the use of laboratory work and hands-on activities in the classroom. The interpretation of these experiments is challenging for some students, and the experiments can lead to a significant amount of discussion. The workshops are organized within the framework of the project ‘‘Active Learning in Optics and Photonics” (ALOP) mainly funded by UNESCO, with the support of ICTP (Abdus Salam International Centre for Theoretical Physics) and SPIE. ALOP workshops offer high school, college or university physics teachers the opportunity to improve their conceptual understanding of optics. These workshops usually run for five days and cover several of the topics usually found in any introductory university physics program. Optics and photonics are used as subject matter because it is relevant as well as adaptable to research and educational conditions in many developing countries [1]. In this paper, we will mainly focus on a specific topic of the ALOP workshops, namely optical communications and Wavelength Division Multiplexing technology (WDM). This activity was originally developed by Mazzolini et al [2]. WDM is a technology used in fibre-optic communications for transmitting two or more separate signals over a single fibre optic cable by using a separate wavelength for each signal. Multiple signals are carried together as separate wavelengths of light in a multiplexed signal. Simple and inexpensive WDM system was implemented in our laboratory using light emitting diodes or diode lasers, plastic optical fibres, a set of optical filters and lenses, prism or grating, and photodiodes. Transmission of audio signals using home-made, simple, inexpensive electronic circuits was also demonstrated. The experimental set-up was used during national ALOP workshops. Results are presented and discussed in this paper. Current explorations to further develop these and other closely-related experiments will also be described.

Detection of photosynthetic activity under cadmium stress by measurement of the red and far-red chlorophyll fluorescence

In this work it is shown that, with a new spectroscopic method based on ultraviolet light emitting diode-induced fluorescence spectroscopy (UV-LED IFS), the photosynthetic activity of an intact attached leaf can be measured in a non-destructive way within a few seconds. The effects of cadmium (Cd) toxicity on the photosynthetic activity of tomato plants (Solanum lycopersicum) were studied using various CdCl2 (cadmium chloride) concentrations. The Cd treatment decreases the photosynthetic activity, measured via a decline of the variable chlorophyll (chl) fluorescence decrease ratio (R Fd) values, calculated at 690 and 730 nm. The chl fluorescence ratios of intensity (FIR) and band area were also calculated. It was found that the R Fd(690) and R Fd(730) values decreased whereas the FIR increased from 1 μM Cd treatment and this behaviour is enhanced with the increasing of Cd concentrations. At 10 and 25 μM Cd, the decrease in R Fd values was associated with a strong decline in the chlorophyll-a + chlorophyll-b (chl-a + b). The chl-a + b decline could also be followed via an increase of the chl fluorescence ratio F 690/F 730. Our study demonstrates that the UV-LED IFS is a promising technique for early detection of Cd stress (from 1 μM) in tomato plants, before visual symptoms appear.

Personal Professional Development

Three workshop sessions on personal professional development were held during the Third IUPAP Women in Physics Conference. These were designed to teach participants about planning for career success, “survival skills,” negotiation, and ways to transition into scientific leadership positions in their own countries.

Popularisation of optical phenomena: establishing the first Ibn Al-Haytham workshop on photography

Within the framework of its scientific activities, the Optical Society of Tunisia organized the first photographic workshop called Ibn Al-Haytham session. This activity enabled, through conferences, the evocation of the research done by one of the most distinguished and prolific mathematicians in the medieval tradition of Arabic Islamic science. The camera obscura that he thoroughly studied was the theme of a training where more than twenty participants build and used this basic camera. The adopted training approach based on active teaching and learning made possible the achievements of interesting results in spite of the heterogeneity of the group of trainees.