Temperature response of photosynthesis and its interaction with light intensity in sweet orange leaf discs under non-photorespiratory condition

Abstract

This study aimed to evaluate the response of photosynthesis (A), given by photosynthetic O 2 evolution, to increasing temperature from 25 to 50ºC in sweet orange (Citrus sinensis (L.) Osbeck) leaf discs under non-photorespiring conditions. In order to evaluate the response of gross photosynthesis to temperature and the balance between photosynthetic and respiratory activities, respiration (R d ) rates were also measured, i.e. the O 2 uptake in each temperature. In addition, light response curves of photosynthesis were performed by varying the photosynthetic photon flux density (PPFD) from 0 to 1160 mol m -2 s -1 at 25 and 40 o C. The highest A values were observed at 35 and 40 o C, whereas the highest R d values were noticed at 50ºC. A higher relationship A/R d was found at 30 and 35ºC, suggesting an optimum temperature of 35ºC when considering the balance between photosynthesis and respiration under non-photorespiring condition. Overall, heat effects on plant metabolism were more evident when evaluating the relationship A/ R d . In light response curves, higher A values were also found at 40ºC under PPFD higher than 300 mol m -2 s -1 . Light saturation point of photosynthesis was increased at 40ºC, without significant change of quantum efficiency under low PPFD. Respiration was also enhanced at 40ºC, and as a consequence, the light compensation point increased. The better photosynthetic performance at 35-40ºC was supported by higher photochemical efficiency in both light and temperature response curves. The temperature-dependence of photosynthesis was affected by growth temperature, i.e. a high air temperature during plant growth is a probable factor leading to a higher photosynthetic tolerance to heat stress. Index terms:Citrus sinensis, heat stress, high temperature, O 2 evolution. RESUMOEste estudo foi conduzido para avaliar a resposta da fotossíntese (A), dada pela evolução fotossintética de O 2 , ao aumento da temperatura de 25 para 50ºC em discos foliares de laranjeira doce (Citrus sinensis (L.) Osbeck) sob condição de não-fotorrespiração. Visando avaliar a resposta da fotossíntese bruta à temperatura e o balanço entre as atividades fotossintética e respiratória, a taxa de respiração (R d . O ponto de saturação luminosa da fotossíntese foi aumentado a 40ºC, sem alterações significativas na eficiência quântica sob baixa DFFF. A respiração também foi estimulada a 40ºC, e como conseqüência, houve aumento do ponto de compensação luminoso. O melhor desempenho fotossintético a 35-40ºC foi relacionado com uma maior eficiência fotoquímica, tanto na curva de resposta à temperatura como à luz. A dependência da fotossíntese em relação à temperatura foi afetada pela temperatura de crescimento, i.e. maior temperatura do ar durante o crescimento das plantas é um provável fator determinante da maior tolerância fotossintética ao estresse térmico. Termos de indexação:Alta temperatura, Citrus sinensis, estresse térmico, evolução de O 2 .

When it is too hot for photosynthesis: heat‐induced instability of photosynthesis in relation to respiratory burst, cell permeability changes and H2O2 formation

“…2004). Ribeiro, Machado & de Oliveira (2006) observed a steep increase in respiration under high temperatures in steady‐state conditions, but did not observe a break‐point. As an excess of reductants may be generated under high temperature (Bukhov et al .…”

Moderate warm temperature improves shoot growth, affects carbohydrate status and stimulates photosynthesis of sweet orange plants

“…Considering high temperatures, Guo et al (2006) found a significant reduction in citrus photosynthesis, with impairment of primary photochemistry under 38ºC. Citrus respiration is also affected by temperature, being stimulated in leaf temperatures higher than 35ºC (Ribeiro et al, 2006a). As exposed leaves of field-grown trees commonly face temperatures higher than 35ºC under subtropical conditions , citrus plants have to deal with both low and high temperatures during their life span.…”

“…Although high and low temperature effects on citrus physiology have been reported, it is difficult to establish the importance of such physiological responses for plant growth, as most studies have not addressed the morphological or biometric changes caused by sub or supraoptimal temperatures (Guo et al, 2006;Machado et al, 2005;Ribeiro et al, 2006a;2009a;Santos et al, 2011). In addition, most of the available literature reports the physiological responses of tree species to extreme temperature conditions, for instance near to heat damage or freezing (Ahrens and Ingram, 1988;Hoch and Körner, 2009).…”

Efeitos das condições ambientais sobre o teor e variabilidade dos óleos voláteis de dalbergia frutescens (Vell.) Britton (Fabaceae)

“…Segundo Ribeiro et al, 10 a temperatura é um dos mais importantes fatores ambientais que influenciam a fisiologia das plantas, sendo a atividade fotossintética especialmente sensível a mudanças de temperatura. A fotossíntese, não somente determina o crescimento e desenvolvimento das plantas através da incorporação de carbono, mas também consiste no passo inicial para a síntese de metabólitos secundários, incluindo os óleos essenciais.…”