Real-time calcium imaging in living plants

GCaMPs, genetically encoded calcium indicators (GECIs), contain an enhanced GFP (EGFP) sequence with significantly increased luminescence intensity. A hexapeptide GGTGGS connects the amino and carboxyl ends of the EGFP protein to form cpEGFP (circularly mutated EGFP). The C end of cpEGFP is connected to calmodulin (CaM), and the N end of cpEGFP is connected to the Ca2+/CaM-binding 'M13' peptide (M13pep). When the CaM in GCaMP binds to Ca2+, the conformation of CaM changes and it interacts with M13, leading to a conformational change in cpEGFP and enhanced fluorescence of cpEGFP. Therefore, changes in GCaMP fluorescence intensity can be used to indicate changes in cytoplasmic calcium levels. GCaMP can be specifically localized to certain organelles after the addition of various localization peptides, enabling the detection of organelle calcium signals. With GCaMPs, the developmental and defense responses of living plants can be followed visually in real time based on the trajectory of calcium ion oscillations.