Plant hormone interactions: how complex are they?

Abstract

Models describing plant hormone interactions are often complex and web-like. Here we assess several suggested interactions within one experimental system, elongating pea internodes. Results from this system indicate that at least some suggested interactions between auxin, gibberellins (GAs), brassinosteroids (BRs), abscisic acid (ABA) and ethylene do not occur in this system or occur in the reverse direction to that suggested. Furthermore, some of the interactions are relatively weak and may be of little physiological relevance. This is especially true if plant hormones are assumed to show a log-linear response curve as many empirical results suggest. Although there is strong evidence to support some interactions between hormones (e.g. auxin stimulating ethylene and bioactive GA levels), at least some of the web-like complexities do not appear to be justified or are overstated. Simpler and more targeted models may be developed by dissecting out key interactions with major physiological effects.

The Transcription Factor ABI4 Is Required for the Ascorbic Acid–Dependent Regulation of Growth and Regulation of Jasmonate-Dependent Defense Signaling Pathways inArabidopsis

“…Seed germination rates were not adversely affected by the higher ABA contents of the vtc mutants compared with Col-0. In agreement with the recent observation that ABA did not affect GA biosynthesis (Ross et al, 2011), the amount and composition of GAs was similar in vtc, abi4, and abi4 vtc2 to that observed in Col-0. These results demonstrate that a 75% decrease in the leaf ascorbate pool (Figure 1) is not sufficient to adversely affect GA metabolism or alter the abundance of bioactive GAs (GA 1 and GA 4 ; Table 4).…”

Mendel’s Genes: Toward a Full Molecular Characterization

“…It turns out also that Mendel's LE gene is regulated by auxin (O'Neill et al 2010;Ross and Reid 2010), another hormone of historical interest, and arguably the most studied of the plant growth substances. Interestingly, even though gibberellins are implicated in a wide range of processes critical for plant yield, including root growth, seed development, and nodulation (e.g., Ferguson et al 2011;Ross et al 2011), Mendel's le-1 mutation has been used in agriculture for many centuries. This appears to have been possible because the LE gene is only one of a family of GA 3-oxidase genes, with at least one other member having greater expression in the roots and seeds and compensating for any loss of 3-oxidase activity in le-1 plants (Weston et al 2009).…”

Gibberellin 3-oxidase Gene Expression Patterns Influence Gibberellin Biosynthesis, Growth, and Development in Pea

“…As internode ABA levels did not vary between any of these lines (Table II), our data provide no evidence for GA 1 regulation of ABA levels in pea internodes. Ross et al (2011) also could find no evidence for the regulation of GA metabolism by ABA in pea internodes.…”