Using GCaMP6 as a Genetically Encoded Ca²⁺ Indicator in Tomatoes

Abstract

Ca²⁺ indicators, such as GCaMP6, have been primarily developed for animal research, and with limited applications in plants, they mainly target the vegetative organs of Arabidopsis and tobacco. Therefore, we focused on utilizing GCaMP6 in tomato fruit. Our observations revealed changes in fluorescence intensity upon cutting, as well as exposure to glutamate and EGTA, indicating that is possible to effectively measure the cellular Ca²⁺ concentration of GCaMP6-transformed tomato plants. The enhanced fluorescence intensity patterns under cold and salt stress imply that Ca²⁺ signals trigger responses to abiotic stress in fruit, with the salt stress response being organ-specific. Investigating the relationship between Ca²⁺ signaling and sugars, we found that glucose and fructose induce Ca²⁺ signaling in tomato fruit, with a response pattern dependent on sugar concentration. Moreover, a comparison of Ca²⁺ levels using corrected fluorescence intensity values during early fruit development, which is a critical stage for fruit physiology and the occurrence of disorders, revealed lower levels in the blossom end compared to the stem end 15 days after flowering. Using Ca²⁺ indicators in fruit has the potential elucidate the connection between Ca²⁺ and horticulturally important traits in fruits.