Germination responses in Zephyranthes tubispatha seeds exposed to different thermal conditions and the role of antioxidant metabolism and several phytohormones in their control

Zephyranthes tubispatha is an ornamental species distributed along several countries of South America. Although it can be multiplied through bulbs or scales, seed germination is a simpler and more cost-effective process. Temperature plays a major role in the control of germination; however, its effect has been scarcely investigated in this species. In the present work, we characterized the germination responses of Z. tubispatha seeds to different temperatures and analyzed the role of key components of the antioxidant metabolism and phytohormones in their control. Seeds showed an optimal temperature range for germination between 14 and 20 degrees C, with higher temperatures (HTs) being progressively inhibitory. While germination was almost nil above 28 degrees C, it could be recovered after transferring the seeds to 20 degrees C, suggesting that thermoinhibition was the underlying phenomenon. The duration of the HT incubation period affected both the time to germination onset and the germination rate at 20 degrees C. Similarly, the activity of antioxidant enzymes, the production of reactive oxygen species in the embryo and the sensitivity to some germination promoters varied depending on the duration of the HT treatment. The addition of 20 mu M fluridone was sufficient to recover germination dynamics as in the control treatment when given after a long-term incubation period (25 d) at HT. Ethephon supply was more effective than gibberellins to suppress thermoinhibition, suggesting that changes in the balance and/or sensitivity to ethylene and abscisic acid over time play an important role in the regulation of germination responses to thermal cues in this species.

Automated summary

Zephyranthes tubispatha seeds have optimal germination temperature range between 14 and 20 degrees C, with higher temperatures progressively inhibiting germination. Thermoinhibition is the underlying phenomenon and can be reversed by transferring seeds to 20 degrees C. Duration of high temperature incubation affects germination onset, germination rate, antioxidant enzyme activity, reactive oxygen species production, and sensitivity to germination promoters. Ethephon supply is more effective than gibberellins in suppressing thermoinhibition, suggesting the importance of changes in ethylene and abscisic acid balance/sensitivity in regulating germination responses to thermal cues in this species.