Abstract
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.
Highlights
Flooding severely impedes gas exchange between plants and the environment owing to the 104-fold slower diffusion of gases in water compared with in air (Armstrong, 1979)
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 SUB1 QTL confers submergence tolerance in rice, assessed as survival and recovery of growth and/or yield following transient complete submergence (Jagadish et al, 2012). This tolerance is associated with less elongation during submergence, higher soluble carbohydrates in shoots, and less oxidative damage post-submergence (Fukao et al, 2009; Xu and Mackill, 1996; Xu et al, 2006). These traits are well studied in FR13A and SUB1 genotypes, whereas the known ability of FR13A to retain chlorophyll when submerged (Ella et al, 2003b) and its influence on underwater PN had not previously been evaluated
Summary
Flooding severely impedes gas exchange between plants and the environment owing to the 104-fold slower diffusion of gases in water compared with in air (Armstrong, 1979). Rice genotypes with SUB1 show better survival and recovery post-submergence than those lacking this QTL SUB1A-1 is an ERF transcriptional regulator that blocks ethylene responsiveness during submergence and downstream targets It maintains the expression of the gibberellic acid (GA) signalling repressors SLENDER RICE1 (SLR1) and SLR1-like-1 (SLRL1) and their proteins during submergence. Schmitz et al (2013) reported that SUB1 differentially regulates genes associated with brassinosteroids (BR) synthesis, and BR induces a GA catabolic gene, GA2ox, under submergence Together these processes lead to suppression of GA-induced underwater elongation growth and conserve carbohydrates for maintenance metabolism and survival
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