Influence of exogenous abscisic acid on germination and plantlet conversion frequencies of hybrid larch somatic embryos (Larix � leptoeuropaea)

Abstract

The effect of exogenous abscisic acid, provided to somatic embryos during the maturation step, on endogenous abscisic acid and its main conjugated form (abscisic acid glucose ester), germination and conversion frequencies is presented in this paper . Abscisic acid measurements were obtained after a methanolic extraction, a fractionation through high performance liquid chromatography, quantitation with an immunoassay and identification of the quantitated compound using gas chromatography-mass spectrometry . Results show that endogenous abscisic acid and abscisic acid glucose ester levels are clearly correlated with the exogenous abscisic acid concentration provided to the embryos . Maturation was clearly enhanced by exogenous abscisic acid, but no correlation was found between abscisic acid concentration and germination frequency . Conversely, development of the aerial part of the germinated somatic embryos was dependent upon the abscisic acid concentration in the culture medium and results suggest that this dependence could be related to the endogenous abscisic acid content . . IntroductionHybrid larch, a fast growing conifer, has good wood quality and is an interesting species for reafforestation programmes [20] . Since the first communication on somatic embryogenesis in Daucus carota, the method of its induction has been widely used in angiosperm tissues [2,31] . By contrast, in gymnosperms, especially in coniferous trees, somatic embryogenesis is a recent phenomenon [7,26] . In the Larix genus, somatic embryogenesis has been achieved in L. decidua [4,15], L. leptolepis [29], L. occidentalis [27], L. x eurolepis [12] and L. x leptoeuropaea [14,15], using immature zygotic embryos . In other conifer genera (Picea sp ., Pinus sp .) it has been shown that factors like abscisic acid (ABA) [23] greatly improved the efficiency of the maturation step and most importantly the 175 quality' of the somatic embryos .`High quality' somatic embryos are those which resemble a mature zygotic embryo and produce plants phenotypically similar to the parent [22] . In our case, ABA is required to promote and synchronize maturation of hybrid larch somatic embryos . However, many selected lines still reflect the difficulty of optimizing culture conditions for every genotype. To control the maturation of such genotypes we need to improve our knowledge of ABA physiology in larch somatic embryos . The first question we address is : how does exogenous ABA control maturation? Hence, we studied the effect of exogenous ABA on the endogenous ABA level and on its main metabolite abscisic acid glucose ester (ABAGE) . The aim was to determine the optimal exogenous ABA concentration to be supplied to embryonal mass in order to promote the best maturation . We also measured the

Ethylene and abscisic acid in the control of development of the rhizome of Kohleria eriantha (Benth.) Hanst. (Gesneriaceae)

“…In the analysis, the most abundant components co-purified with the isomer standards of ABA and thus are likely ABA derivatives. Ions at m/z 190 have also been found in the purified extract of ABA from other species, in Zea mays (Rivier et al, 1977), Malus domestica (Subbaiah and Powell, 1987), Citrus sinensis (Cowan and Richardson, 1993) and Larix decidua (Label and Lelu, 1994). In K. eriantha the putative ABA ion at m/z 190 was more abundant in the sections kept on substrate with low water availability than that from sections with sufficient water.…”

Somatic embryogenesis in Larix: the state of art and perspectives

“…At the maturation of somatic embryos, abscisic acid becomes the most important component of the nutrient medium (Lelu et al, 1994b(Lelu et al, , 1995. The optimal content of this phytohormone (0.01-32.0 mg/L) and the cultivation time of somatic embryos in its presence (1-4 weeks) vary significantly in different larch species (Label, Lelu, 1994von Aderkas et al, , 2002von Aderkas et al, , 2015Gutmann et al, 1996;Klimaszewska et al, 1997;Ogita et al, 1999b;Kim, Moon, 2007;Song et al, 2018). Sometimes, indolebutyric acid at 1.0 mg/L (Tret'yakova et al, 2012), 5.0 mg/L of auxin transport inhibitor 2-(p-chlorophenoxy)-2-methylpropionic acid (PCIB), 5.0 mg/L phloroglucinol (auxin synergist) (Kim, Moon, 2009) or silver nitrate (2.0-5.5 mg/L) (Saly et al, 2002;Song et al, 2018) are used together with abscisic acid to improve the process of maturation of somatic embryos.…”