Abstract
Exogenous abscisic acid (ABA) is known to either stimulate or inhibit root growth, depending on its concentration. In this study, the roles of ethylene and auxin in this biphasic effect of ABA on root elongation were investigated using chemical inhibitors and mutants. Inhibitors of ethylene perception and biosynthesis and an auxin influx inhibitor were all found to block the inhibitory effect of high ABA concentrations, but not the stimulatory effect of low ABA concentrations. In addition, three ethylene-insensitive mutants (etr1-1, ein2-1, and ein3-1), two auxin influx mutants (aux1-7, aux1-T) and an auxin-insensitive mutant (iaa7/axr2-1) were all insensitive to the inhibitory effect of high ABA concentrations. In the case of the stimulatory effect of low ABA concentrations, it was blocked by two different auxin efflux inhibitors and was less pronounced in an auxin efflux mutant (pin2/eir1-1) and in the iaa7/axr2-1 auxin-insensitive mutant. Thus it appears that the stimulatory effect seen at low ABA concentrations is via an ethylene-independent pathway requiring auxin signalling and auxin efflux through PIN2/EIR1, while the inhibitory effect at high ABA concentrations is via an ethylene-dependent pathway requiring auxin signalling and auxin influx through AUX1.
Highlights
Plant growth and yield production are often limited by a variety of abiotic stresses in agricultural systems (Cramer et al, 2011)
The results showed that 10 μM abscisic acid (ABA) inhibited root growth by about 40% while 0.1 μM ABA stimulated growth by almost 20% when measured over the 6-day period (Figure 1A)
The stimulatory effect of 0.1 μM ABA persisted over the duration of the treatment and by the 6th day the roots were growing at a rate which was more than 30% faster than the control (Figure 1B)
Summary
Plant growth and yield production are often limited by a variety of abiotic stresses in agricultural systems (Cramer et al, 2011). A root system that is able to efficiently take up water and nutrient from the soil is crucial for plant growth and functioning, if the plant is to accumulate any yield when water and nutrients are in short supply (Hammer et al, 2009; Hodge et al, 2009; Hodge, 2010). There is no consensus on the mechanisms underlying these root responses. An improved understanding of the mechanistic basis of root growth and development will be useful. Abscisic Acid and Root Growth both for novel crop management and breeding aimed at plant improvement to at least maintain yield in different environments under a changing climate
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