Quantum dot-mediated detection of gamma-aminobutyric acid binding sites on the surface of living pollen protoplasts in tobacco.

gamma-Aminobutyric acid (GABA) is an inhibitory transmitter in the central nervous system of mammals. Recent investigations showed that it also plays an important role in regulating pollen tube growth and orientation in plants. To determine whether GABA receptors are also present on the membrane of pollen protoplasts, a fluorescence probe of quantum dots (QDs) was constructed and applied. The water-soluble CdSe-ZnS (core-shell) QDs were first synthesized and verified to possess good optical properties. GABA was then bioconjugated to the QDs in the presence of 1-ethyl-3-(3)-dimethylaminopropyl carbodiimide (EDC) and N-hydroxysuccinimide (NHS) to make the fluorescence probe. Using the probe, GABA binding sites were detected on the protoplast membrane of both pollen and somatic cells. Both the fluorescent signals on the surface of the protoplasts and the Ca(2+) oscillation assayed via the Ca(2+) probe Fluo-3/AM inside the protoplasts provided evidence that the potential GABA(B) receptors are present on the plant protoplast membrane.