Photoinhibition and recovery in a herbicide-resistant mutant from Glycine max (L.) Merr. cell cultures deficient in fatty acid unsaturation

Biointeractions of Herbicide Atrazine with Human Serum Albumin: UV-Vis, Fluorescence and Circular Dichroism Approaches

The herbicide atrazine is widely used across the globe, which is a great concern. To investigate its potential toxicity in the human body, human serum albumin (HSA) was selected as a model protein. The interaction between atrazine and HSA was investigated using steady-state fluorescence spectroscopy, synchronous fluorescence spectroscopy, UV-Vis spectroscopy, three-dimensional (3D) fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The intrinsic fluorescence of HSA was quenched by the atrazine through a static quenching mechanism. Fluorescence spectra at two excitation wavelengths (280 and 295 nm) showed that the fluorescence quenched in HSA was mainly contributed to by tryptophan residues. In addition, the atrazine bound to HSA, which induced changes in the conformation and secondary structure of HSA and caused an energy transfer. Thermodynamic parameters revealed that this binding is spontaneous. Moreover, electrostatic interactions play a major role in the combination of atrazine and HSA. One atrazine molecule can only bind to one HSA molecule to form a complex, and the atrazine molecule is bound at site II (subdomain IIIA) of HSA. This study furthers the understanding of the potential effects posed by atrazine on humans at the molecular level.

A temporal regulatory mechanism controls the different contribution of endoplasmic reticulum and plastidial ω-3 desaturases to trienoic fatty acid content during leaf development in soybean (Glycine max cv Volania)

We analyzed the molecular mechanism controlling ω-3 fatty acid desaturases during seed germination and leaf development in soybean. During germination, soybean seeds were characterized by a high 18:2(Δ9,12) level (more than 50%) and reduced 18:3(Δ9,12,15) content (10%). Interestingly, transcripts from all endoplasmic reticulum (GmFAD3A and GmFAD3B) and plastidial (GmFAD7-1/GmFAD7-2 or GmFAD8-1/GmFAD8-2) desaturase genes were detected during seed germination. Upon germination, soybean trifoliate leaf development was accompanied by an increase in linolenic acid (18:3(Δ9,12,15)). Our data showed that transcripts corresponding to the endoplasmic reticulum ω-3 desaturases GmFAD3A and GmFAD3B decreased with leaf development. No changes in the expression profile of the plastidial ω-3 desaturases GmFAD7-1 and GmFAD7-2 genes were detected. On the contrary, GmFAD8-2 transcript levels increased while GmFAD8-1 transcripts decreased during leaf development. Given this expression profile, our data suggested the existence of a temporal regulatory mechanism controlling ω-3 desaturases during leaf development in which the endoplasmic reticulum ω-3 desaturases would be more important in young leaves while plastidial ω-3 desaturases might contribute to 18:3(Δ9,12,15) production in mature leaves. Photosynthetic cell cultures showed 18:3(Δ9,12,15) levels similar to those from leaves. No changes in the 18:3(Δ9,12,15) content or expression of the ω-3 desaturase genes were detected along the cell culture cycle. A comparison of our data with those available in Arabidopsis or wheat suggested that the regulatory mechanism controlling the expression and activity of both endoplasmic reticulum and plastidial desaturases during leaf development might differ among plant species.

Malondialdehyde generated from peroxidized linolenic acid causes protein modification in heat-stressed plants

When polyunsaturated fatty acids (PUFAs) in biomembrane are peroxidized, a great diversity of aldehydes is formed, and some of which are highly reactive. Thus they are thought to have biological impacts in stressed plants; however, the detailed mechanism of generation and biochemical effects are unknown. In this study, we show that chloroplasts are major organelles in which malondialdehyde (MDA) generated from peroxidized linolenic acid modifies proteins in heat-stressed plants. First, to clarify the biochemical process of MDA generation from PUFAs and its attachment to proteins, we carried out in vitro experiments using model proteins (BSA and Rubisco) and methylesters of C18 PUFAs that are major components of plant biomembrane. Protein modification was detected by Western blotting using monoclonal antibodies that recognize MDA binding to proteins. Results showed that peroxidation of linolenic acid methylester by reactive oxygen species was essential for protein modification by MDA, and the MDA modification was highly dependent on temperature, leading to a loss of Rubisco activity. When isolated spinach thylakoid membrane was peroxidized at 37 degrees C, oxygen-evolving complex 33kDa protein (OEC33) was modified by MDA. These model experiments suggest that protein modification by MDA preferentially occurs under higher temperatures and oxidative conditions, thus we examined protein modification in heat-stressed plants. Spinach plants were heat-stressed at 40 degrees C under illumination, and modification of OEC33 protein by MDA was detected. In heat-stressed Arabidopsis plants, light-harvesting complex protein was modified by MDA under illumination. This modification was not observed in linolenic acid-deficient mutants (fad3fad7fad8 triple mutant), suggesting that linolenic acid is a major source of protein modification by MDA in heat-stressed plants.

Changes in photosynthetic electron transfer and state transitions in an herbicide-resistant D1 mutant from soybean cell cultures

Anomalies in photosynthetic activity of the soybean cell line STR7, carrying a single mutation (S268P) in the chloroplastic gene psbA that codes for the D1 protein of the photosystem II, have been examined using different spectroscopic techniques. Thermoluminescence emission experiments have shown important differences between STR7 mutant and wild type cells. The afterglow band induced by both white light flashes and far-red continuous illumination was downshifted by about 4 degrees C and the Q band was upshifted by 5 degrees C. High temperature thermoluminescence measurements suggested a higher level of lipid peroxidation in mutant thylakoid membranes. In addition, the reduction rate of P700(+) was significantly accelerated in STR7 suggesting that the mutation led to an activation of the photosystem I cyclic electron flow. Modulated fluorescence measurements performed at room temperature as well as fluorescence emission spectra at 77 K revealed that the STR7 mutant is defective in state transitions. Here, we discuss the hypothesis that activation of the cyclic electron flow in STR7 cells may be a mechanism to compensate the reduced activity of photosystem II caused by the mutation. We also propose that the impaired state transitions in the STR7 cells may be due to alterations in thylakoid membrane properties induced by a low content of unsaturated lipids.