Abstract
Key message Effective microspore embryogenesis in triticale is determined by a specific hormonal homeostasis: low value of IAA/cytokinins, IAA/ABA and cytokinins/ABA ratios as well as proper endogenous/exogenous auxin balance, which favours androgenic structure formation and green plant regeneration ability. The concentration of plant growth regulators (PGRs): auxins (Auxs), cytokinins (CKs) and abscisic acid (ABA) was measured in anthers of eight DH lines of triticale (× Triticosecale Wittm.), and associated with microspore embryogenesis (ME) responsiveness. The analysis was conducted on anthers excised from control tillers at the phase optimal for ME induction and then after ME-initiating tillers treatment (21 days at 4 °C). In control, IAA predominated among Auxs (11–39 nmol g−1 DW), with IBA constituting only 1 % of total Auxs content. The prevailing isoforms of CKs were cis isomers of zeatin (121–424 pmol g−1 DW) and zeatin ryboside (cZR, 146–432 pmol g−1 DW). Surprisingly, a relatively high level (10–64 pmol g−1 DW) of kinetin (KIN) was detected. Cold treatment significantly changed the levels of all analysed PGRs. The anthers of ‘responsive’ DH lines contained higher concentrations of IBA, cis and trans zeatin, cZR and ABA, and lower amount of IAA and KIN in comparison with ‘recalcitrant’ genotypes. However, the effects of exogenous ABA, p-chlorophenoxyisobutyric acid (PCIB) and 2,3,5-triiodobenzoic acid treatments suggest that none of the studied PGRs acts alone in the acquisition of embryogenic competency, which seems to be an effect of concerted PGRs crosstalk. The initiation of ME required a certain threshold level of ABA. A crucial prerequisite for high ME effectiveness was a specific PGRs homeostasis: lower Auxs level in comparison with CKs and ABA, and lower CKs/ABA ratio. A proper balance between endogenous Auxs in anthers and exogenous Auxs supplied by culture media was also essential.Electronic supplementary materialThe online version of this article (doi:10.1007/s00299-014-1686-4) contains supplementary material, which is available to authorized users.
Highlights
Under specific circumstances usually occurring in in vitro cultures, plant microspores can enter an alternativePlant Cell Rep (2015) 34:47–62 developmental pathway known as microspore embryogenesis (ME) or androgenesis
Key message Effective microspore embryogenesis in triticale is determined by a specific hormonal homeostasis: low value of indole-3-acetic acid (IAA)/cytokinins, IAA/abscisic acid (ABA) and cytokinins/ABA ratios as well as proper endogenous/ exogenous auxin balance, which favours androgenic structure formation and green plant regeneration ability
A proper balance between endogenous Auxs in anthers and exogenous Auxs supplied by culture media was essential
Summary
Under specific circumstances usually occurring in in vitro cultures, plant microspores can enter an alternativePlant Cell Rep (2015) 34:47–62 developmental pathway known as microspore embryogenesis (ME) or androgenesis. It is known that microspore reprogramming is triggered by a stress treatment, but the effectiveness of the process is controlled by an interaction of genetic and physiological factors. The concerted action of Auxs and CKs controls cell division and morphogenesis (Wedzony et al 2009). These two phytohormone groups usually act antagonistically, but their effect is often modulated by the plant genome and tissue specificity (Moubayidin et al 2009). Besides Auxs and CKs, abscisic acid (ABA), known as the main plant stress hormone, has been claimed to play a role in androgenesis-inducing signal transduction system (Maraschin et al 2005; Z_ ur et al 2012). Some reports suggested the involvement of ABA in androgenesis induction and described its positive influence on the effectiveness of DHs production (Imamura and Harada 1980; Reynolds and Crawford 1996; Van Bergen et al 1999; Wang et al 1999; Guzman and Arias 2000)
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