Differential inhibition of photosynthesis under drought stress in Flaveria species with different degrees of development of the C₄ syndrome

Abstract

The effect of drought stress (DS) on photosynthesis and photosynthesis-related enzyme activities was investigated in F. pringlei (C 3 ), F. floridana (C 3 -C 4 ), F. brownii (C 4 -like), and F. trinervia (C 4 ) species. Stomatal closure was observed in all species, probably being the main cause for the decline in photosynthesis in the C 3 species under ambient conditions. In vitro ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and stromal fructose 1,6-bisphosphatase (sFBP) activities were sufficient to interpret the net photosynthetic rates (P N ), but, from the decreases in P N values under high CO 2 (C a = 700 µmol mol -1 ) it is concluded that a decrease in the in vivo rate of the RuBPCO reaction may be an additional limiting factor under DS in the C 3 species. The observed decline in the photosynthesis capacity of the C 3 -C 4 species is suggested to be associated both to in vivo decreases of RuBPCO activity and of the RuBP regeneration rate. The decline of the maximum P N observed in the C 4 -like species under DS was probably attributed to a decrease in maximum RuBPCO activity and/or to decrease of enzyme substrate (RuBP or PEP) regeneration rates. In the C 4 species, the decline of both in vivo photosynthesis and photosynthetic capacity could be due to in vivo inhibition of the phosphoenolpyruvate carboxylase (PEPC) by a twofold increase of the malate concentration observed in mesophyll cell extracts from DS plants.Additional key words: bundle sheath cells; C 3 /C 4 metabolism; CO 2 compensation concentration; malic enzyme; NADP-malate dehydrogenase; phosphoenolpyruvate carboxylase; pyruvate-orthophosphate dikinase; RuBP; RuBPCO; stromal fructose 1,6-bisphosphatase; water potential.

Improvement ofex vitroacclimatization of mulberry plantlets by supplement of abscisic acid to the last subculture medium

“…However, ABA application strongly reduced water loss even when stomata did not function normally (Pospisilova et al 2007), which decreased water stress during acclimatization of Ulmus minor, indicating a faster and efficient improvement of the water control mechanisms. Stomatal closure is considered as one of the first defense strategy against drought damage under water stress conditions, protecting the plants from dehydration and eventually from sudden death (Chaves et al 2003;Dias and Bruggemann 2007). But stomatal closure unavoidably limits the CO 2 availability in the intercellular spaces of the mesophyll cells.…”

Limitations of photosynthesis in Phaseolus vulgaris under drought stress: gas exchange, chlorophyll fluorescence and Calvin cycle enzymes

“…Decreased Rubisco activity (Castrillo et al 2001, Parry et al 2002, Tezara et al 2002 or impaired capacity for RuBP regeneration , Dias and Brüggemann 2007 have been suggested as the main limitations to photosynthesis under drought conditions. Our results match with the conclusions of the data analysis reported in the literature in P. vulgaris and also for other species.…”

“…Rubisco (EC 4.1.1.39) was extracted and the activity assayed as described by Lilley and Walker (1974) and Dias and Brüggemann (2007). This assay follows NADPH oxidation measured spectrophotometrically at 340 nm.…”

“…Recent studies have shown that the reduced CO 2 diffusion from the atmosphere to the site of carboxylation as a result of stomatal closure and reduced mesophyll conductance is the main cause for decreased photosynthesis under drought stress conditions (Correia et al 1999, Cornic 2000, Chaves and Oliveira 2004, Ennahli and Earl 2005, Grassi and Magnani 2005, Flexas et al 2006. Nevertheless, other studies have shown that drought stress also induces metabolic impairment, particularly decreases in Rubisco activity/ RuBP regeneration (Gunasekera and Berkowitz 1993, Flexas and Medrano 2002, Lawlor and Cornic 2002, Dias and Brüggemann 2007 and reduction of ATP production (Lawlor 1995, Tezara et al 1999. Differences among species and variations of the rates of DS imposition, as well as other environmental stresses, may also play a role in the relative importance of stomatal vs. nonstomatal limitations under DS conditions (Chaves 1991).…”

Aspectos produtivos e fisiológicos de cultivares de feijão irrigado

“…A principal consequência dessas respostas à supressão hídrica afeta diretamente o aparato fotossintético da cultura em maior ou menor intensidade (CASTRILHO et al, 2001;PARRY et al, 2002;DIAS et al, 2007). Médias seguidas pela mesma letra minúscula na coluna e maiúscula na linha não diferem entre si pelo teste de Tukey a 5% de probabilidade.…”