Quercetin and gamma-aminobutyric acid content and in vitro germination in pollen grains of Citrus species at different temperatures

Environmental factors such as temperature have negative effects on the reproductive phase and can cause yield loss in Citrus species. Pollen grains play a key and essential role in the fertility of plants. Quercetin and gamma-aminobutyric acid (GABA) are involved in certain biochemical functions to regulate growth and increase tolerance to biotic and abiotic stresses. The purpose of this study was to evaluate the effect of different temperatures on pollen germination and also on the levels of quercetin and GABA. The branches containing flowers of Cirus reticulata, C. sinensis, and C. paradisi were exposed to 5, 10, 15, 20, and 25 °C for six hours and then pollen grains were collected. Levels of quercetin and GABA were quantified by HPLC. The amount of quercetin was highest at 5 °C and then decreased by increasing the temperature in all species. Also, with increasing temperature, the amount of GABA decreased in all species. The highest and lowest pollen germination was observed at 25 °C and 5 °C, respectively.