Proteins Related to Stress and Redox State of 'Moncada' Mandarin Leaves with Contrasting Fruit Load

A proteomic study was used to know more about the Citrus redox state and stress response related to fruit load. To this end, we researched for differences in the accumulation of proteins related to these processes between on-crop and off-crop 'Moncada' mandarin leaves. Samples were collected in November, were immediately stored frozen at -80 degrees C, and proteins were extracted in less than two weeks. From 2D DIGE gel of these extracts, 12 related spots were isolated: only 1 showed increased accumulation in the off-crop samples compared to on-crop samples, while the other 11 showed increased accumulation in the on-crop samples against off-crop samples. These spots were identified by MALDI-MS or LC-MS-MS. The only protein with increased expression in the off-crop samples was putative monocopper oxidase precursor, while the up-expressed proteins in on-crop leaves were catalase, monodehydroascorbate reductase, Fe-superoxide dismutase, glutathione peroxidase, and three proteins related to stress response. Thus according to these results, generally, in the off-crop samples, proteins with oxidoreductase activity are down-regulated, while in the on-crop samples the proteins related to stress response and to oxidoreductase activity are up-regulated. Therefore, the redox state is different for off-crop and for on-crop Citrus leaves.