Abstract
Elevated CO 2 concentration ( e [CO 2 ]) alleviates the impact of drought stress on plants where abscisic acid (ABA) is involved. To explore the mechanisms by which tomato plants respond to short-term osmotic stress, Solanum lycopersicum cv. Ailsa Craig (AC), a transgenic line overproducing ABA (sp5), and an ABA-deficient mutant ( flacca ) were hydroponically grown under ambient CO 2 (400 ppm) and e [CO 2 ] (800 ppm) and then exposed to 10% or 15% (w/v) polyethylene glycol (PEG) 6000 for 24 h before transferring to PEG-free nutrient solution for 24 h. Under non-stress condition, e [CO 2 ] decreased root hydraulic conductance ( K root ), which was overridden by high endogenous ABA in sp5 through increasing specific leaf area and root branching intensity. Basically, e [CO 2 ] improved stress resistance through enhanced water status. PEG stress decreased stomatal conductance and osmotic potential in AC but these effects were less pronounced in sp5, which exhibited a stronger osmotic adjustment (OA) and improved plant fitness. A greater flexibility of hydraulic system and a reduced sensitivity of K root to ABA might confer sp5 a great ability to recover from PEG stress. On the contrary, high stomatal density, size and pore aperture of flacca rendered plants suffering severe stress. Moreover, the premise that PEG stress could mimic soil water deficit was the sufficient achievement of OA. Our results indicate that e [CO 2 ] and high endogenous ABA level could improve osmotic stress resistance in tomato plants via osmotic and hydraulic adjustments. • High endogenous ABA increased specific leaf area and root branching intensity. • High endogenous ABA overrode the effects of e [CO 2 ] on root hydraulic conductance. • Sufficient osmotic adjustment improved drought resistance. • PEG stress could not mimic soil drought unless it triggered fast osmotic adjustment.
Highlights
Intensified incidence of drought threatens crop growth and produc tivity (McDowell et al, 2008; Trenberth et al, 2014)
Compared with Ailsa Craig (AC) and sp5 plants, flacca had significantly higher stomatal density (SD), stomatal size (SS) and stomatal pore aperture (SA), while there was no difference for these parameters between AC and sp5. e[CO2] decreased SA in all genotypes, whereas it had no influence on SD and SS (Fig. 1)
We investigated the effects of e[CO2] and polyethylene glycol (PEG) stress on physiological processes of tomato genotypes differing in endogenous abscisic acid (ABA) levels
Summary
Intensified incidence of drought threatens crop growth and produc tivity (McDowell et al, 2008; Trenberth et al, 2014). The stomata control leaf gas exchange through a fine-tuned regula tion of stomatal aperture in response to environmental stimuli (Berg mann and Sack, 2007). Both drought stress and e[CO2] induce stomatal closure, decreasing stomatal conductance (gs; Li et al, 2020). In sunflowers and grapevine, a hydraulic signal (leaf turgor) was responsible for the onset of stomatal closure, and foliar ABA only significantly increased after stomata have been fully closed and prevented the recovery of stomatal aperture during re-watering (Huber et al, 2019; Tombesi et al, 2015). In addition to reducing gs, e[CO2] was found to decrease leaf and root hydraulic
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