Cover of JXB with leaf gas films on submerged rice

Gas film retention and underwater photosynthesis during field submergence of four contrasting rice genotypes

Floods can completely submerge some rice (Oryza sativa L.) fields. Leaves of rice have gas films that aid O2 and CO2 exchange under water. The present study explored the relationship between gas film persistence and underwater net photosynthesis (PN) as influenced by genotype and submergence duration. Four contrasting genotypes (FR13A, IR42, Swarna, and Swarna-Sub1) were submerged for 13 days in the field and leaf gas films, chlorophyll, and the capacity for underwater PN at near ambient and high CO2 were assessed with time of submergence. At high CO2 during the PN assay, all genotypes initially showed high rates of underwater PN, and this rate was not affected by time of submergence in FR13A. This superior photosynthetic performance of FR13A was not evident in Swarna-Sub1 (carrying the SUB1 QTL) and the declines in underwater PN in both Swarna-Sub1 and Swarna were equal to that in IR42. At near ambient CO2 concentration, underwater PN declined in all four genotypes and this corresponded with loss of leaf gas films with time of submergence. FR13A retained leaf gas films moderately longer than the other genotypes, but gas film retention was not linked to SUB1. Diverse rice germplasm should be screened for gas film persistence during submergence, as this trait could potentially increase carbohydrate status and internal aeration owing to increased underwater PN, which contributes to submergence tolerance in rice.

The study is published in: 
Winkel A, Pedersen O, Ella ES, Ismail AM, Colmer TD (2014) Gas film retention and underwater photosynthesis during field submergence of four contrasting rice genotypes. Journal of Experimental Botany 65: 3225-3233 

Exciting collaboration between UCPH, UWA and Nagoya University
Much of the recent work of rice is done in collaboration with the University of Western Australia (Prof Colmer) and Nagoya University in Japan (Prof Ashikari). We have recently identified a gene that regulates wax synthesis in rice so that the leaf cuticle becomes superhydrophobic and retains a thin leaf gas films during submergence. The gas film enhances gas exchange with the floodwater so that CO2 for underwater photosynthesis is taken up during the day (and O2 excreted) whilst O2 is taken up from the floodwater during the night to sustain dark respiration. The identification of the gene Leaf Gas Films 1 (LGF1) opens up for possibilities to breed rice varieties that better tolerate floods in a future climate change scenario.

Colmer, Nagai, Kurokawa, myself and Mori