Humayra Bashir, Javed Ahmad, Rita Bagheri, M Irfan Qureshi
Proteomics & Bioinformatics Lab, Department of Biotechnology, Jamia Millia Islamia, New Delhi-100 025, India.
The changes induced in leaf proteome and thylakoidal Multi-protein complexes (MPCs) of Arabidopsis thaliana (Col- 0) exposed to cadmium stress and sulphur deficiency were studied. Two different comparative proteomic approaches were used to study leaf proteome (IEF/SDS-PAGE) and thylakoids (BN/SDS- PAGE). Thylakoid preparations showed decline in chlorophyll content in Cadium treated plants both in presence and absence of sulphur. Blue native-PAGE revealed that cadmium disturbs the ratios of main structural proteomic components of thylakoid membranes under S-deficiency by causing significant changes among various photosynthetic pigment-protein complexes. Amount of PSII super complex and cyt b6f were strongly declined when sulphur deficient plants were treated with cadmium. However, sulphur availability aided the plants to recover these complexes. On the contrary, sulphur deficiency lead to monomerization of LHCII and PSI. Cd treatment strongly reduced PSII-M under sulphur deficiency, while as a significant maintenance was observed with sulphur. Sulphur deficient plants when treated with Cd enhanced the LHCII- assembly. Further, Cd stress strongly affected the global leaf proteome in Arabidopsis. In Total, 948 spots were reproducibly detected by PD Quest (Bio-Rad, USA) in 2-D gel maps of leaf. About 230 of which were differentially expressed in response to sulphur deficiency and Cd stress. About 20 of these spots showed potential up regulation and 15 were potentially down regulated. These proteins have pI between 4 and 7 and masses in the range of 22-97 kDa and were analysed by Matrix-assisted laser adsorption ionization time of flight (MALDI-TOF) after digestion with trypsin. These proteins can be functionally grouped into 6 classes: proteins involved in (1) photosynthesis and energy metabolism, (2) sulphur/nitrogen metabolism, (3) oxidative stress response, (4) protein metabolism, (5) gene expression and finally, (6) Proteins with unknown or other functions. The results obtained showed that sulphur assimilation tended to have a significant role in retaining photosynthetic efficiency by stabilizing MCPs and hence the thylakoid membranes under Cd stress. Read More ..