Construction of red-emitting QD probes and determination of indole-propionic acid binding sites in plant tissues

Plant hormones influence plant growth and development progress, and response to the environment. Therefore, it is highly significant to know the reasons that cause the above phenomena. Research on the signal transduction mechanism of hormones in plants is insufficient due to the lack of an accurate and sensitive method to measure it. The detection of binding sites between hormones and receptors is the first step in studying the signal transduction of plant hormones. The auxin indole-propionic acid (IPA) is an important plant hormone and can promote rooting and fruiting in plants. By conjugating CdTe/ZnS QDs with the IPA moiety, we constructed the CdTe/ZnS–IPA fluorescence probes for the in situ detection of IPA binding sites in plant tissues. By improving the synthesis conditions, we capped ZnS outside the oil bath-obtained CdTe to prepare red-emitting CdTe/ZnS QDs, and the core/shell structure of the CdTe/ZnS QDs was proved by XRD. The success of conjugation was verified by fluorescence spectra, fluorescence decay lifetime, UV-vis spectra, and DLS. The CdTe/ZnS–IPA with a 5.4% coupling rate were selected for the labelling of IPA binding sites, which are concentrated in the endodermis cells of mung bean root tissues. The existence of the competitive relationship of recognition for IPA binding sites between CdTe/ZnS–IPA and IPA declared that CdTe/ZnS–IPA possessed biological activity for IPA. The red-emitting CdTe/ZnS–IPA can contrast with the background of plant tissues compared to green-emitting CdTe–IPA. In sum, the novel probe showed low toxicity, was plant tissue background-resistant, and this new method for the selective detection of IPA binding sites in plant tissues has the advantages of convenience and easy visualization.