Chemicals to induce plastid signals in Arabidopsis seedlings

Tetrapyrroles and abscisic acid (ABA) were considered as plastid signal molecules for plant cells. However, they attract hot controversies. High levels of sugars also trigger plastid signals to regulate nuclear gene expression. However, the effective concentrations of sugar are extremely high (100-10,000 times of tetrapyrroles). To resolve these controversies and inconsistencies, we investigated which chemicals at what concentrations may work as plastid signal molecules, and summarize their common chemical structures. We found that they can be classified into two categories: (1) tetrapyrroles or other carbon-nitrogen heterocyclic compounds with an adjacent three-membered ring (two of them may be incomplete), with a signaling impact order: Mg-protoporphyrin IX/ABA>Fe-protoporphyrin IX>Zn-protoporphyrin IX>protoporphyrin IX>tryptophan>histidine. The completeness of the rings with a chelated metal ion has a positive effect on the effectiveness of plastid signaling stimulation. (2) Sugar or other carbon-oxygen (sulfur) five- or six-membered ring compounds, such as cyclohexane and thiophene. The effective concentrations of the second category of signal molecules are very high (about 400mM for the monosaccharide). The two types of signal molecules are possibly perceived by different receptors in the plastid.