Profiles of endogenous ABA, bioactive GAs, IAA and their metabolites in Medicago truncatula Gaertn. non-embryogenic and embryogenic tissues during induction phase in relation to somatic embryo formation

Ewa Kępczyńska,Anna Orłowska

doi:10.1007/s00425-021-03582-8

Abstract

Main conclusionDuring the 3-week-long induction phase, when M. truncatula cells leaf explants from non-embryogenic genotype (M9) and embryogenic variant (M9-10a) were forming the callus, biosynthesis and degradation of ABA, Gas and IAA proceeded at different levels. Induction of embryo formation is related to a lower ABA content, compared to the content of IAA and that of total bioactive GAs.Endogenous phytohormones are involved in the regulation of zygotic embryogenesis, but their role, especially of ABA, a plant growth inhibitor, in inducing somatic embryogenesis (SE) in angiosperms is still incompletely known. To arrive a better understanding of the ABA role in the process, we analyzed simultaneously and in detail changes in the contents of both ABA and five bioactive GAs (GA4, GA7, GA1, GA3, GA6) and IAA in M. truncatula non-embryogenic M9 (NE) and embryogenic M9-10a (E) genotypes. The initial leaf explants of both genotypes, and particularly NE, contained many times more ABA compared to the total bioactive GAs or IAA. In tissues during the entire 21-day induction all the hormones mentioned and their metabolites or conjugates were present; however, their contents were found to differ between the lines tested. The ABA level in primary explants of NE genotype was more than two times higher than that in E genotype. An even larger difference in the ABA content was found on the last day (day 21) of the induction phase (IP); the ABA content in E callus was over six times lower than in NE callus. In contrast, the IAA and GAs contents in primary explants of both genotypes in relation to ABA were low, but the contents of IAA and GAs exceeded that of ABA in the M9-10a tissues on the last day of IP. It is shown for the first time that endogenous ABA together with endogenous bioactive GAs and IAA is involved in acquisition of embryogenic competence in Medicago truncatula leaf somatic cells. These findings have a strong functional implication as they allow to improve the SE induction protocol.

Highlights

Somatic embryogenesis (SE), a nonsexual process, is the developmental restructuring of different somatic cell types along different embryogenic pathways that lead to regeneration of embryos capable of germinating to form complete1 3 Vol.:(0123456789) 67 Page 2 of 13Planta (2021) 253:67 plants (Zimmerman 1993; Pasternak et al 2002; Fehér et al 2003; Imin et al 2004; Rose et al 2013; Rose 2019; Fehér 2015)
Nolan et al (2014) stated that the synergism they observed between abscisic acid (ABA) and GAs as a result of their exogenous application to the medium at the beginning of the induction phase in M. truncatula, requires confirmation by analyzing their endogenous contents in explants
The present study was conducted to determine the levels of endogenous ABA and its catabolites in tissues of embryogenic (M9-10a) and non-embryogenic (M9) M. truncatula genotypes during the induction phase, and to compare it to the content of the classical growth stimulants such as bioactive GAs and indole-3-acetic acid (IAA) and their metabolites

Summary

Introduction

Somatic embryogenesis (SE), a nonsexual process, is the developmental restructuring of different somatic cell types along different embryogenic pathways that lead to regeneration of embryos capable of germinating to form complete1 3 Vol.:(0123456789) 67 Page 2 of 13Planta (2021) 253:67 plants (Zimmerman 1993; Pasternak et al 2002; Fehér et al 2003; Imin et al 2004; Rose et al 2013; Rose 2019; Fehér 2015). Its fundamental phases are characterized, at the morphological level, by the induction of proembryogenic structures followed by the somatic embryo formation and maturation leading to plant regeneration Each of these phases is regulated by various physical and chemical factors the most critical of which is considered to be the exogenous application of plant growth regulators. Knowledge on the role of endogenous classical plant growth phytohormones such as abscisic acid (ABA), a growth inhibitor, and growth stimulators: gibberellins (GAs) and indole-3-acetic acid (IAA) during induction of the somatic embryogenesis is far from satisfactory These phytohormones play important roles during many phases of the plant life cycle and have a pleiotropic range of physiological effects. Their biosynthetic pathways start in plastids and end, just like their catabolism, in the cytoplasm

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Conclusion