Flood tolerance of wheat – the importance of leaf gas films during complete submergence

Abstract

Submergence invokes a range of stressors to plants with impeded gas exchange between tissues and floodwater being the greatest challenge. Many terrestrial plants including wheat (Triticum aestivum L.), possess superhydrophobic leaf cuticles that retain a thin gas film when submerged, and the gas films enhance gas exchange with the floodwater. However, leaf hydrophobicity is lost during submergence and the gas films disappear accordingly. Here, we completely submerged wheat (with or without gas films) for up to 14 days and found that plants with gas films survived significantly longer (13 days) than plants without (10 days). Plants with gas films also had less dead tissue following a period of recovery. However, this study also revealed that reflections by gas films resulted in a higher light compensation point for underwater net photosynthesis for leaves with gas films compared with leaves without (IC = 52 vs 35 µmol photons m–2 s–1 with or without gas films, respectively). Still, already at ~5% of full sunlight the beneficial effect of gas films overcame the negative under ecologically relevant CO2 concentrations. Our study showed that dryland crops also benefit from leaf gas films during submergence and that this trait should be incorporated to improve flood tolerance of wheat.

Physiology, gene expression, and metabolome of two wheat cultivars with contrasting submergence tolerance

“…Superhydrophobic wheat leaves retain a gas film when submerged (Konnerup et al, ; Raskin & Kende, ), and leaf gas films enhance wheat submergence tolerance (Winkel et al, ). We therefore assessed if leaf gas film thickness during submergence differed between cultivars Frument and Jackson (Figure a).…”

“…Wheat shoot biomass was reduced to 29–31% of controls following 14 days of waterlogging (Malik, Colmer, Lambers, & Schortemeyer, ; Robertson, Zhang, Palta, Colmer, & Turner, ) and to 2–6% of controls following 14 days submergence in this study. The larger growth penalty due to submergence resulted from negative shoot RGR during submergence (−0.03 day −1 during 8 days, Figure S1) compared with positive shoot RGR of 0.09 days −1 during 14 days of waterlogging (Malik et al, ) and would also have been aggravated by senesced shoot material (Winkel et al, ) impeding recovery growth. It should be noted that complete submergence of winter wheat at low temperatures during winter dormancy is likely to result in less detrimental effects as shown for waterlogging (Luxmoore, Fischer, & Stolzy, ; Trought & Drew, ).…”

“…Each pot received 1 g of Osmocote slow release fertilizer (Osmocote Bloom, Everris, Geldermalsen, The Netherlands). In a recent study using identical pots and substrate, O 2 disappeared from the soil matrix within 6–22 hr of soil flooding (Winkel et al, ). To control powdery mildew, shoots were sprayed with a 2‐g/L sulfur solution (ECOstyle Svampefri, ECOstyle A/S, Odense, Denmark) 9, 19, and 39 days after imbibition and Flexity (Metratenon; 0.15 g/L) 15 and 41 days after imbibition.…”

“…For R D , the incubation medium was initially adjusted to air equilibrium by purging with air to obtain R D at nonlimiting external O 2 concentrations (Colmer & Pedersen, ), whereas the dissolved O 2 concentration in the P N incubation medium was initially set at approximately 50% of air equilibrium (Pedersen et al, ). Initial concentrations of 200 μM CO 2 in both solutions ( P N and R D ) was obtained by adjusting pH to 7.35 after adding 2.2 mmol KHCO 3 /L solution; 200 μM CO 2 is considered an environmentally relevant CO 2 concentration (Colmer, Winkel, & Pedersen, ) and allowed direct comparison with other wheat studies (Konnerup, Winkel, Herzog, & Pedersen, ; Winkel et al, ).…”

“…Chlorophyll concentrations of the lamina of the third leaf at the time of submergence (consisting of homogenized, freeze‐dried leaf segments from gas film thickness, tissue porosity, and gas exchange measurements) were measured following Winkel et al () after 24‐hr extraction in 96% ethanol.…”