Indole-3-acetic acid and auxin herbicides up-regulate 9-cis-epoxycarotenoid dioxygenase gene expression and abscisic acid accumulation in cleavers (Galium aparine): interaction with ethylene

Abstract

Interaction between auxin and auxin-induced ethylene was suggested in previous work to up-regulate abscisic acid (ABA) biosynthesis in cleavers (Galium aparine) through stimulated cleavage of xanthophylls to xanthoxin, catalysed by 9-cis-epoxycarotenoid dioxygenase (NCED). Here, the effects of auxin on NCED gene expression were studied in relation to changes in ethylene synthesis and ABA levels. A gene from G. aparine shoot tissue was cloned based on sequence similarity to cloned NCED genes from tomato (LeNCED1), potato, Phaseolus, and Arabidopsis. When the roots of G. aparine plants were treated with 0.5 mM indole-3-acetic acid (IAA), IAA concentrations increased from 0.2 microM to 65 microM IAA in the shoot tissue after 3 h. Transient increases in GaNCED1 mRNA levels were detectable as early as 1 h after treatment and reached maximum values of 40-fold, relative to the control, after 3 h. Increases in GaNCED1 mRNA preceded increases in 1-aminocyclopropane-1-carboxylic acid and ethylene. Levels of ABA began to increase more slowly and, significantly, with a lag phase of 2 h, and reached levels 24-fold higher than those in controls after 24 h. GaNCED1 gene expression was also stimulated by auxin herbicides. The ethylene-releasing compound ethephon induced GaNCED1 transcript levels only moderately. In accordance with this, aminoethoxyvinylglycine and cobalt ions, which inhibit ethylene synthesis, only slightly affected the increase in GaNCED1 transcript levels by IAA. However, both ethylene inhibitors decreased IAA-induced ABA accumulation by up to 70%. This suggests that auxin and auxin-induced ethylene are involved in ABA accumulation. While auxin is the primary trigger for NCED gene expression, ethylene appears to enhance ABA biosynthesis, possibly by up-regulation of NCED activity post-transcriptionally.

Factors that determine shoot viability and root development during in vitro adaptation and propagation of silver birch (Betula pendula Roth)

“…The loss of a green shoot apex under the influence of BAP might be associated with auxin-cytokinin crosstalk, since it was found by other authors (Marhavý et al, 2011) that increased amount of cytokinin leads to a decrease of auxin efflux proteins in plant cell membrane. Such interference with auxin transport might have led to an increased auxin concentration in shoot apex of BAP-treated birch explants, resulting in apex browning because of herbicidal action of local auxin excess (auxin ability to act as a herbicide is described in detail by Kraft et al (2007)). It is interesting that those genotypes of birch that remained viable and multiplied shoots in vitro but were unable to form roots (52BPL171 and 43BSM001) developed on the control medium in a pattern similar to that of root-forming genotype 01BPL115 under cytokinin treatment, resulting not only in the absence of roots but also in increased number of shoots per explant.…”

A novel role of ethephon in controlling the noxious weed Ipomoea cairica (Linn.) Sweet

“…Ethylene and ABA are two major factors leading to damage of plant tissues after treatment with auxin herbicides43132. Taking 2, 4-D as an example (see Fig.…”

The High Light Response inArabidopsisInvolves ABA Signaling between Vascular and Bundle Sheath Cells

“…This notion is supported by the observation that two different sized NCED3 isoforms of 64 and 58 kD were detected in dehydration-stressed Arabidopsis leaves (Endo et al, 2008), showing that posttranslational modification of NCED3 can occur. Posttranscriptional activation of foliar NCED by ethylene in cleavers (Gallium aparine) is proposed to occur concomitant with a slower induction of NCED transcription by auxin (Kraft et al, 2007).…”