Light and High Temperature Negatively Regulate Germination Dynamics of Zephyranthes tubispatha Seeds

Zephyranthes tubispatha is an Amaryllidaceae species with high ornamental potential, whose seed dispersal coincides with periods of high temperatures (HTs) and long photoperiods. While supraoptimal temperatures (>28 °C) have been shown to induce thermoinhibition, the effect of light on germination dynamics has not yet been explored. The aim was to study the effect of different exposure times to white light (WL) and different light qualities, as well as the interaction with HT, on seed germination. Changes in the endogenous levels of several phytohormones, responses to pharmacological treatments, and O2.− production in the embryo were analyzed to gain an understanding of the underlying physiological mechanisms. Our results suggest the presence of a negative photoblastic response of the high-irradiance (HIR) type. Fluridone (an ABA synthesis inhibitor) restored germination in light-exposed seeds to levels close to the dark control, highlighting the importance of ABA content for photoinhibition. The preincubation period at HT (33 °C) significantly influenced germination behavior and photosensitivity at optimal temperature (20 °C). Thermoinhibition depends on changes in phytohormone balance and/or sensitivity, rather than on their absolute concentration. Unlike thermoinhibition, photoinhibition was not associated with the suppression of O2.− production in the embryonic root pole, confirming that these environmental signals utilize different regulatory pathways.