The role of auxins in somatic embryogenesis of Abies alba

Abstract

The somatic embryogenesis of conifers is a process susceptible to exogenous phytohormonal treatments. We report the effects of the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) and the auxin inhibitor p-chlorophenoxyisobutyric acid (PCIB) on the endogenous level of the auxin indole-3-acetic acid (IAA) and on the anatomical composition of early somatic embryos of Abies alba (European silver fir). The embryogenic suspensor mass (ESM) of Abies alba proliferated on a medium supplemented by 2,4-D as well as on an auxin-free medium. The endogenous level of IAA was significantly higher in the ESM cultivated on a medium supplemented by 2,4-D. The decrease in the endogenous level of IAA in the first week of maturation is one of the most important stimuli responsible for the subsequent development of embryos. However, suppression of IAA synthesis by an auxin inhibitor did not stimulate the development of embryos. The maturation of somatic embryos from the globular to the cotyledonary stage occurs when the concentration of endogenous auxin in the ESM (including the embryos) increases. Early somatic embryos proliferating on a medium supplemented by auxin had an increased probability of maturing successfully. Exogenous auxin treatment during maturation did not compensate for the auxin deficiency during proliferation.

Dynamics of the concentration of IAA and some of its conjugates during the induction of somatic embryogenesis inCoffea canephora

“…For several years, it has been known that the presence of an exogenous auxin can induce the endogenous biosynthesis of IAA. 1,5,6,13 However, it is also possible that the exogenous auxin promotes the inhibition of IAA degradation by reversible conjugating reactions. 52,53 Thus, the homeostasis of the auxins is critical for the induction of the SE process.…”

“…In D. carota, the level of IAA decreased 10-fold from that of the initial cell clusters, 1 as well as in Abies alba somatic embryos. 13 It has been suggested that in the continuous presence of auxin, carrot cell lines are able to develop into the globular stage, but not beyond. 61 In addition, recently it has been suggested that the removal of exogenous auxin from the medium triggers both auxin polar transport and auxin gradient establishment for SE induction.…”

“…of Abies alba (European silver fir). 13 Other plants, such as Coffea canephora, 14 Medicago spp., 15,16 and Manihot esculenta Crantz 17 also require the addition of an auxin to induce SE. The increase in IAA conjugates is related to the presence of enzymes with acyl-amidosynthetase activity; they are codified by genes belonging to the GRETCHEN HAGEN 3 (GH3) family.…”

The Role of the Auxins During Somatic Embryogenesis

“…However, during the first week of maturation, this Ax decreases suggesting that the increase in the level of endogenous IAA is important to start the differentiation process. Later, the IAA levels increase again according to the embryo growth, which can be seen as an important mechanism for the correct establishment of cells division patterns and the organization of both shoot and root meristems (Vondráková et al 2011).…”

Molecular analysis of somatic embryogenesis through proteomic approach and optimization of protocol in recalcitrant Musa spp.

“…The overexpression of auxin related proteins in matured somatic embryos of cv. Rasthali revealed that higher concentration of endogenous auxin is required for the maturation of somatic embryos from the globular to the cotyledon stage as also reported in Abies alba (Vondrakova et al ). The embryo development process and pattern are influenced by auxin biosynthesis and polar auxin transport (Moller and Weijers ).…”