Gibberellins and light synergistically promote somatic embryogenesis from the in vitro apical root sections of spinach

Abstract

Gibberellins (GAs) play a pivotal role in the induction of somatic embryogenesis from in vitro root apices of spinach plants. With the aim to understand the role of GAs in this process and to improve somatic embryo (SE) regeneration efficiency, the impact of light and GAs on SE initiation from the in vitro root apices was studied. The root sections were isolated from in vitro-grown SE-derived plants and placed on medium containing 20 µM α-naphthaleneacetic acid (NAA) and 0–10 µM GA3 or GA1, and cultivated under light conditions or in darkness. The most efficient SE regeneration response (100% regenerating SEs and 40.73 SEs per root apices) was achieved only in the presence of both light and GAs, with GA3 always exhibiting much stronger effect than GA1. Considering that light enhances GAs biosynthesis and the necessity of GAs for SE initiation, the expression levels of genes encoding the key enzymes involved in the final steps of GAs synthesis (SoGA20-ox1 and SoGA3-ox1) and deactivation (SoGA2-ox1, SoGA2-ox2 and SoGA2-ox3) were analyzed. Light enhanced the expression of all five GA-ox genes, while exogenously supplied NAA + GA3 provoked downregulation of SoGA20-ox1 and SoGA3-ox1 and upregulation of SoGA2ox-2 and SoGA2ox-3 expression. The expression of SoGA2ox-1 only slightly decreased. The results indicated the capability of isolated spinach roots to perceive the light and autonomously produce GAs. The expression levels of genes encoding key enzymes involved in GA biosynthesis suggest that lower levels of GAs favor SE initiation.