FIGURE 6.

Possible mechanisms regulating Suaeda salsa dimorphic seed germination under salt stress. GA₄ (red color) is synthesized from precursors GA₁₂, GA₁₅, GA₂₄ and GA₉ (blue color) by GA20ox (20ox) and GA3ox (3ox) enzymes. Bioactive GA₄ is deactivated to inactive form GA₅₁ and GA₃₄ (black color) by GA2ox (2ox) enzyme. Brown seeds are more active in GA biosynthesis and contain higher content of GA precursors and bioactive GA₄ than black seeds. Black seeds are more active in deactivation of GA₄ and contain higher content of inactive GAs than brown seeds. Salt stress inhibits GA biosynthesis and promotes GA deactivation in both brown and black seeds. In addition, salt stress promotes ABA biosynthesis and increase ABA response. Salinity decreases sensitivity to GA₄ probably through affecting the function of DELLA proteins. Brown seeds have better salt tolerance, and faster germination and growth rates than black seeds. On the other hand, dormancy of black seeds might be an adaptation strategy that enables the seeds to avoid adverse environmental conditions. Bars indicate negative regulation, while arrows indicate positive regulation.