Iron excess affects rice photosynthesis through stomatal and non-stomatal limitations.
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.
Universidade Federal de Viçosa (UFV), Minas Gerais, Brazil. egpereira@ufv.br
Eduardo Gusmão
EG
Pereira
Marco Antonio
MA
Oliva
Laíse
L
Rosado-Souza
Giselle Camargo
GC
Mendes
Denise Santos
DS
Colares
Carlos Henrique
CH
Stopato
Andréa Miyasaka
AM
Almeida
D000222:Adaptation, Physiological; D019069:Cell Respiration; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D004492:Edetic Acid / Q000494:pharmacology; D004579:Electron Transport; D005453:Fluorescence; D007501:Iron / Q000378:metabolism / Q000494:pharmacology*; D012275:Oryza / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D055668:Photochemical Processes; D010788:Photosynthesis; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D054046:Plant Stomata / Q000378:metabolism* / Q000502:physiology; D018526:Plant Transpiration; D017382:Reactive Oxygen Species / Q000378:metabolism; D013312:Stress, Physiological
D017382:Reactive Oxygen Species; D002734:Chlorophyll; D004492:Edetic Acid; D007501:Iron; D000077194:Chlorophyll A