Temperature and Water Availability During Maturation Affect the Cytokinins and Auxins Profile of Radiata Pine Somatic Embryos.

Paloma Moncaleán,María D Ugarte,Miroslav Strnad,Olatz García-Mendiguren,Ondrej Novák,Tomás Goicoa,Itziar A Montalbán

doi:10.3389/fpls.2018.01898

Abstract

Somatic embryogenesis (SE) provides us a potent biotechnological tool to manipulate the physical and chemical conditions (water availability) along the process and to study their effect in the final success in terms of quantity of somatic embryos produced. In the last years, our research team has been focused on the study of different aspects of the SE in Pinus spp. One of the main aspects affecting SE is the composition of culture media; in this sense, phytohormones play one of the most crucial roles in this propagation system. Many studies in conifers have shown that different stages of SE and somatic embryo development are correlated with distinct endogenous phytohormone profiles under the stress conditions needed for the process (i.e., cytokinins play a regulatory role in stress signaling, which it is essential for radiata pine SE). Based on this knowledge, the aim of this study was to test the effect of different temperatures (18, 23, and 28°C) and gelling agent concentrations (8, 9, and 10 gL-1) during the maturation stage of Pinus radiata SE in maturation and germination rates. Parallel, phytohormone profile of somatic embryos developed was evaluated. In this sense, the highest gellan gum concentration led to significantly lower water availability. At this gellan gum concentration and 23°C a significantly higher number of somatic embryos was obtained and the overall success of the process increased with respect to other treatments assayed. The somatic embryos produced in these conditions showed the highest concentration of iP-type cytokinins and total ribosides. Although, the different conditions applied during maturation of somatic embryos led to different hormonal profiles, they did not affect the ex vitro survival of the resulting somatic plants, where no significant differences were observed.

Highlights

The use of vegetative propagation in forestry is the fastest, most flexible and effective way to produce enough genetically improved material to meet future wood demands (Lelu-Walter et al, 2013)
Modifying gellan gum concentration in maturation media has been studied in a few species of angiosperms (Márquez-Martín et al, 2011) and gymnosperms (Morel et al, 2014); these authors reported an improvement in the development and maturation of somatic embryos (Se) of P. pinaster by increasing gellan gum concentration, pointing out that the effect of gellan gum concentration on plant response is provoked by changes of water availability in the culture medium
Water relations between the embryo and its environment play a regulatory role in embryo development, during maturation and for this reason, the water availability of maturation media was determined in our experiments

Summary

Introduction

The use of vegetative propagation in forestry is the fastest, most flexible and effective way to produce enough genetically improved material to meet future wood demands (Lelu-Walter et al, 2013). One of the main bottlenecks of the SE in conifers is the progression from immature embryogenic cultures into mature cotyledonary embryos able to develop well-growing plants (Harvengt, 2005). Several external stimuli, such as plant growth regulators (Ayil-Gutiérrez et al, 2013), osmotic agents (Kikuchi et al, 2006), nutritional components (Pencík et al, 2015), amongst others, have been recognized as essential factors in determining both the hormone biosynthesis and the developmental fate of explant cells (Grzyb et al, 2017). As far as we know, the effect of different temperatures in maturation step has not been tested in Pinus spp., only in some angiosperms (Wang et al, 2014)

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