Crassulacean acid metabolism species differ in the contribution of C₃ and C₄ carboxylation to end of day CO₂ fixation

Abstract

Crassulacean acid metabolism (CAM) is a photosynthetic pathway that temporally separates the nocturnal CO 2 uptake, via phosphoenolpyruvate carboxylase (PEPC, C 4 carboxylation), from the diurnal refixation by Rubisco (C 3 carboxylation). At the end of the day (CAM-Phase IV), when nocturnally stored CO 2 has depleted, stomata reopen and allow additional CO 2 uptake, which can be fixed by Rubisco or by PEPC. This work examined the CO 2 uptake via C 3 and C 4 carboxylation in phase IV in the CAM species Phalaenopsis "Sacramento" and Kalanchoe blossfeldiana "Saja." Short blackout periods during phase IV caused a sharp drop in CO 2 uptake in K. blossfeldiana but not in Phalaenopsis, indicating strong Rubisco activity only in K. blossfeldiana. Chlorophyll fluorescence revealed a progressive decrease in ΦPSII in Phalaenopsis, implying decreasing Rubisco activity, while ΦPSII remained constant in phase IV in K. blossfeldiana. However, short switching to 2% O 2 indicated the presence of photorespiration and thus Rubisco activity in both species throughout phase IV. Lastly, in Phalaenopsis, accumulation of starch in phase IV occurred.These results indicate that in Phalaenopsis, PEPC was the main carboxylase in phase IV, although Rubisco remained active throughout the whole phase. This will lead to double carboxylation (futile cycling) but may help to avoid photoinhibition.

Seasonal changes in photosynthesis for the epiphytic bromeliad Tillandsia brachycaulos in a tropical dry deciduous forest

“…Moreover, the observed reduction of tissue acidity during the dry season is more likely to occur because of higher nocturnal temperatures than during the rainy season (Nobel et al 1991, Cervera et al 2007, Andrade et al 2009). Additionally, increased light incidence without a proportional increase in the malate supply would predispose this epiphytic species to photoinhibition, which, along with drought stress, would increase the negative effects of the high radiation (Skillman & Winter 1997, van Tongerlo et al 2021. In fact, studies show that stress caused by drought or extreme temperatures increases the risk and severity of photoinhibition in plants in arid regions and in tropical epiphytes (Athar & Ashraf 2005, Hasanuzzaman et al 2013, Chaves et al 2018, Arroyo-Pérez et al 2017.…”

Sensitivity and Regulation of Diel Photosynthesis in Red-Fleshed Pitaya (Hylocereus polyrhizus) Micropropagules under Mannitol-Induced Water Stress/Rehydration Cycle In Vitro

“…Compared to the CO 2 uptake of control with a trend of increase (not significant) by weekly −0.5 MPa solution replacements, plants under MWS treatment exhibited relatively stable carbon assimilation after a 5-week incubation, despite a calculated peak on week 2. There was a significant decrease in the relative INCU in IWS after 5 weeks of incubation, with 46.03% (t(2) = 1.69, P upper-tailed = 0.1167), 59.92% (t(2) = 1.5, P upper-tailed = 0.1357), 39.34% (t(2) = 6.56, P upper-tailed = 0.0112), and 32.27% (t(2) = 16.18, P upper-tailed = 0.019) from weeks 2 to 5 compared to week 1, respectively.…”

“…The detected CO 2 values from each vessel were recorded every 30 s for 5 consecutive weeks. The CAM photosynthesis phases were shifted after signs of three successive positive/negative Pn [58,59].…”

“…This study showed a diel pattern of CO 2 uptake change on day 4 after mannitolinduced MS solution replacement. The offset performance of the gas exchange pattern might respond to the circadian clock, which is modulated by PEPC kinase [68] and light quality [59,69]. PEPC kinase is upregulated by phosphoenolpyruvate and downregulated by cytosolic malate abundance, where the nighttime accumulation of malate decreases the activities of PEPC kinase and PEPC, affecting CO 2 uptake [68,70].…”

Role of carboxysomes in cyanobacterial CO2 assimilation: CO2 concentrating mechanisms and metabolon implications

“…During the day, stomata are closed to prevent water loss via transpiration, malate is transported out of the vacuoles and converted back to CO 2 in chloroplasts, where it is fixed by RuBisCO. This temporal separation suppresses O 2 fixation and photorespiration by limiting O 2 diffusion through closed stomata when RuBisCO is active (van Tongerlo et al, 2020). Unlike C 4 carbon fixation, CAM can be an inducible phenotype in C 3 plants (Schiller & Bräutigam, 2021) as the enzymes in C 3 and CAM plants are identical and differ mainly in temporal regulation.…”