Iron excess affects rice photosynthesis through stomatal and non-stomatal limitations

Abstract

Iron toxicity is the most important stressor of rice in many lowland environments worldwide. Rice cultivars differ widely in their ability to tolerate excess iron. A physiological evaluation of iron toxicity in rice was performed using non-invasive photosynthesis, photorespiration and chlorophyll a fluorescence imaging measurements and chlorophyll content determination by SPAD. Four rice cultivars (BR IRGA 409; BR IRGA 412; BRA 041171 and BRA 041152) from the Brazilian breeding programs were used. Fe(2+) was supplied in the nutrient solution as Fe-EDTA (0.019, 4, 7 and 9 mM). Increases in shoot iron content due to Fe(2+) treatments led to changes in most of the non-invasive physiological variables assessed. The reduction in rice photosynthesis can be attributed to stomatal limitations at moderate Fe(2+) doses (4mM) and both stomatal and non-stomatal limitations at higher doses. Photorespiration was an important sink for electrons in rice cultivars under iron excess. A decreased chlorophyll content and limited photochemical ability to cope with light excess were characteristic of the more sensitive and iron accumulator cultivars (BRA 041171 and BRA 041152). Chlorophyll fluorescence imaging revealed a spatial heterogeneity of photosynthesis under excessive iron concentrations. The results showed the usefulness of non-invasive physiological measurements to assess differences among cultivars. The contributions toward understanding the rice photosynthetic response to toxic levels of iron in the nutrient solution are also discussed.

Oxidative damage and photosynthetic impairment in tropical rice cultivars upon exposure to excess iron

“…Rice photosynthesis is sensitive to Fe excess through an initial increase in stomatal resistance, lowering the CO 2 mesophyll concentration and through non-stomatal limitation due to biochemical and photochemical impairment after severe stress (Pereira et al, 2013). We propose that light energy partitioning impairment and oxidative damage, which is more severe in cultivars with high sensitivity, may take place before the non-stomatal limitation because of the Fe overload in the roots.…”

“…The measurements were taken in a narrow-leaf chamber (11.35 cm 2 ) by using an integrated light source with saturating irradiance (1000 µmol photon m −2 s −1 ) (Pereira et al, 2013) at a temperature from 26 to 30 °C and an atmospheric CO 2 concentration ranging from 380 to 410 µmol mol −1 . The leaf temperature (Tleaf) was measured with a thermocouple that was placed inside the cuvette.…”

“…The roots become dark brown in color and develop poorly, and exhibit a scanty and coarse aspect (Becker and Asch, 2005;Silveira et al, 2009). Iron toxicity also reduces growth and yield (Dorlodot et al, 2005), causes nutritional disorders (Pereira et al, 2014) and severe impairment in rice photosynthesis (Pereira et al, 2013).…”

Development of High-Yielding Rice Varieties Suitable for Swampy Lands in Indonesia

“…The radicals cause irreversible damage to membrane lipids, proteins and nucleic acids. It could also oxidize chlorophyll and subsequently reduce leaf photosynthesis (Pereira et al 2013), thereby leading to yield reductions. The typical symptoms associated with iron toxicity are leaf discoloration (bronzing) and reddish spots in the leaf blade (Tanaka et al 1966).…”

Double-sided Microfluidic Device for Speciation Analysis of Iron in Water Samples: Towards Greener Analytical Chemistry

“…In countries such as Thailand, where rice agriculture is dependent on natural water conditions, elevated concentrations of toxic Fe 2+ would impair rice harvests. 3 Indeed, there is a clear need for the regular monitoring of iron species in order to examine the equilibrium of iron in natural water. Such assessments would need to be carried out either in fields or immediately after collecting samples, because Fe 2+ tends to rapidly oxidize and become Fe 3+ .…”