Environmental effects on photosynthetic capacity of bean genotypes

Abstract

-Photosynthetic responses to daily environmental changes were studied in bean (Phaseolus vulgaris L.) genotypes 'Carioca', 'Ouro Negro', and Guarumbé. Light response curves of CO 2 assimilation and stomatal conductance (g s ) were also evaluated under controlled (optimum) environmental condition. Under this condition, CO 2 assimilation of 'Carioca' was not saturated at 2,000 1mol m -2 s -1 , whereas Guarumbé and 'Ouro Negro' exhibited different levels of light saturation. All genotypes showed dynamic photoinhibition and reversible increase in the minimum chlorophyll fluorescence yield under natural condition, as well as lower photosynthetic capacity when compared with optimum environmental condition. Since differences in g s were not observed between natural and controlled conditions for Guarumbé and 'Ouro Negro', the lower photosynthetic capacity of these genotypes under natural condition seems to be caused by high temperature effects on biochemical reactions, as suggested by increased alternative electron sinks. The highest g s values of 'Carioca' were observed at controlled condition, providing evidences that reduction of photosynthetic capacity at natural condition was due to low g s in addition to the high temperature effects on the photosynthetic apparatus. 'Carioca' exhibited the highest photosynthetic rates under optimum environmental condition, and was more affected by daily changes of air temperature and leaf-to-air vapor pressure difference.Index terms: Phaseolus vulgaris, chlorophyll fluorescence, gas exchange, photosynthesis. Efeitos ambientais na capacidade fotossintética de genótipos de feijoeiroResumo -Foram avaliadas as respostas fotossintéticas às variações diárias do ambiente nos genótipos de feijoeiro (Phaseolus vulgaris L.) 'Carioca', 'Ouro Negro' e Guarumbé. Curvas de resposta da assimilação de CO 2 e condutância estomática (g s ) à luz foram realizadas em condição ambiental controlada (ótima). Nessa condição a assimilação de CO 2 de 'Carioca' não foi saturada mesmo a 2.000 1mol m -2 s -1 , enquanto Guarumbé e 'Ouro Negro' apresentaram diferentes níveis de saturação lumínica. Os genótipos mostraram fotoinibição dinâmica e aumento reversível da fluorescência mínima da clorofila em condição natural, assim como menor capacidade fotosintética quando comparada à sob condição controlada. Uma vez que Guarumbé e 'Ouro Negro' apresentaram valores similares de g s em ambas condições ambientais, a menor capacidade fotossintética desses genótipos sob condição natural parece ser causada pelos efeitos da alta temperatura nas reações bioquímicas, como sugerido pelo aumento dos drenos alternativos de elétrons. Os maiores valores de g s em 'Carioca' foram observados em condição controlada, podendo a redução da capacidade fotossintética em condição natural ser atribuída aos baixos valores de g s em adição aos efeitos da alta temperatura no aparato fotossintético. 'Carioca' exibiu as maiores taxas fotossintéticas em condições ambientais ótimas, sendo mais afetado pelas mudanças diárias de temperatura...

Leaf Photosynthetic Metabolism and N2 Fixation at the Flowering Stage in Three Genotypes of Cowpea [Vigna unguiculata (L.) Walp.]

“…1). These values measured between 09:00 and 11:00 h for healthy plants without stress were similar when compared to studies with bean plants (Lippi et al, 1999;Ribeiro et al, 2004;Santos et al, 2006). Despite the smaller amount of mineral nitrogen in the leaves BNF treatment showed similar photoprotective capacity of the control treatment, which is confirmed by the content of photosynthetic pigments (Table 1) (Schreiber et al, 1994) and resulting in photochemical efficiency (Fig.…”

Identification of cowpea genotypes for drought tolerance

“…Such situation was also observed by Ribeiro et al (2004), Matsui and Singh (2003) in cowpea researches. According to Netto et al (2005), the indirect determination of chlorophyll content in leaves can be used as a tool to diagnose the integrity of the photosynthetic apparatus when the plants are subjected to environmental adversity.…”

Drought-induced changes in chlorophyll fluorescence, photosynthetic pigments, and thylakoid membrane proteins of Vigna radiata

“…Bean plants are commonly exposed to high irradiance during the diurnal period (Ribeiro et al 2004), which may cause additional disturbances in the photosynthetic apparatus under water deficit. Some experiments show that Vigna radiata var.…”