Separation and characterization of proteins from green and etiolated shoots of rice (Oryza sativa L.): towards a rice proteome.

Proteins extracted from green and etiolated shoots of rice were separated by two-dimensional polyacrylamide gel electrophoresis and relative molecular weights and isoelectric points were determined. The separated proteins were electroblotted onto a polyvinylidene difluoride membrane and 85 proteins were analyzed by a gas-phase protein sequencer. The N-terminal amino acid sequences of 21 out of 85 proteins were determined in this manner. N-terminal regions of the remaining proteins could not be sequenced. The internal amino acid sequences of proteins were determined by sequence analysis of peptides obtained by the Cleveland peptide mapping method and compared with those of known plant and animal protein sequences to understand the nature of the proteins. Green shoots revealed the presence of photosynthetic proteins as expected; however, as etiolated shoots were not photosynthetic, only precursors of the photosynthetic proteins were identified. Interestingly, the presence of L-ascorbate peroxidase only in etiolated shoots suggests a cellular protectant function for this antioxidant enzyme in the etiolating shoots. Using this experimental approach, we could identify the major proteins involved in growth regulation in photosynthetic green shoots as well as in etiolating rice seedlings.