Hormonal and environmental regulation of seed germination in salt cress (Thellungiella halophila)

Abstract

Thellungiella halophila (salt cress) is a salt tolerant species with high genetic and morphological similarity to model plant Arabidopsis thaliana. The role of growth regulators in imposing seed dormancy and a release from it while responding to environmental signals has been examined. Seeds of salt cress possess a deep dormancy at maturity which decreased during after-ripening and cold stratification. After-ripened seeds of salt cress failed to germinate in dark and in strong light (134 µmol m −2 s −1) while best seed germination was obtained in weak white light (1–10 µmol m −2 s −1) at 22 °C. The germination of non-dormant salt cress seeds was also regulated by red and far-red light. Light enhanced the sensitivity to gibberellin in dark-imbibed salt cress seeds and strong light inhibited biosynthesis of gibberellins. The endogenous abscisic acid was not affected by strong light implying that inhibition of seed germination is not mediated through ABA signals. Higher seed germination was recorded at a constant temperature of 20 °C and a thermoperiod of 15/25 °C (12 h strong light/12 h dark). Seeds of salt cress when exposed to 400 mM NaCl for 10 days maintain their viability however there was a heavy mortality among Arbidopsis seeds under similar conditions. Our data indicates that seed germination in salt cress is highly regulated by environmental and hormonal signals to provide opportunities to germinate under natural conditions.