Jatropha curcasand Ricinus communisdisplay contrasting photosynthetic mechanisms in response to environmental conditions

Abstract

Higher plants display different adaptive strategies in photosynthesis to cope with abiotic stress. In this study, photosynthetic mechanisms and water relationships displayed by Jatropha curcas L. (physic nuts) and Ricinus communis L. (castor bean), in response to variations in environmental conditions, were assessed. R. communis showed higher CO 2 assimilation, stomatal and mesophyll conductance than J. curcas as light intensity and intercellular CO 2 pressure increased. On the other hand, R. communis was less effective in stomatal control in response to adverse environmental factors such as high temperature, water deficit and vapor pressure deficit, indicating lower water use efficiency. Conversely, J. curcas exhibited higher photosynthetic efficiency (gas exchange and photochemistry) and water use efficiency under these adverse environmental conditions. R. communis displayed higher potential photosynthesis, but exhibited a lower in vivo Rubisco carboxylation rate (Vcmax) and maximum electron transport rate (Jmax). During the course of a typical day, in a semiarid environment, with high irradiation, high temperature and high vapor pressure deficit, but exposed to well-watered conditions, the two studied species presented similar photosynthesis. Losing potential photosynthesis, but maintaining favorable water status and increasing non-photochemical quenching to avoid photoinhibition, are important acclimation mechanisms developed by J. curcas to cope with dry and hot conditions. We suggest that J. curcas is more tolerant to hot and dry environments than R. communis but the latter species displays higher photosynthetic efficiency under well-watered and non-stressful conditions. Keywords: abiotic stress, castor bean, photosynthesis, physic nut, acclimation IntroductionPhotosynthetic performance in higher plants under adverse environmental conditions is largely dependent on plant species, which are able to trigger distinct adaptive mechanisms to deal with specific stressful conditions (Cousins et al., 2014). Plants display a set of acclimation strategies to maintain adequate photosynthesis rates in response to abiotic stress-inducers such as high temperature, drought and high light levels (Liu and Huang 2008;Chaves et al., 2009;Gonzalez-Cruz and Pastenes, 2012). To reach their potential or maximum photosynthesis, plants employ a fine metabolic coordination involving several inter-related processes, especially a close balance between photochemical activity and Calvin cycle reactions (Goh at al., 2012).Abiotic stresses are able to disturb this balance, and affect especially CO 2 assimilation due to stomatal and biochemical limitations (Adams III et al., 2013). The degree of preservation of adequate synchrony between light harvest, energy conversion in photosystems and CO 2 assimilation, under stress conditions, is speciesdependent and important to plant productivity (Athanasiou et al., 2010;Kramer and Evans, 2011;Murchie and Niyogi, 2011;Yamori et al., 2014).In general, native species are able to survive un...

Photosynthetic capacity and water use efficiency in Ricinus communis (L.) under drought stress in semi-humid and semi-arid areas

“…These results suggest that a VPD (leaf-air) increase caused a significant boost in transpiration, while photosynthesis tends to decrease with stomatal closure, a fact confirmed by Lima Neto et al (2015) in castor bean plants under drought stress, where they observed a high transpiration rate linked with low photosynthesis.…”

The regulation of P700 is an important photoprotective mechanism to NaCl‐salinity in Jatropha curcas

“…The amount of blue light was set to 10% of the PPFD to maximize stomatal aperture (Flexas et al ). Measurements conditions were in accordance with the optimum for photosynthesis of J. curcas (Lima Neto et al ). For P N /C i response curves, the rate of CO 2 assimilation was measured at intervals of CO 2 concentration decreasing from 2000 to 30 μl l −1 .…”

Cyclic electron flow, NPQ and photorespiration are crucial for the establishment of young plants of Ricinus communis and Jatropha curcas exposed to drought

“…Measuring conditions were optimal for photosynthesis of both species (Lima Neto et al . ). The P N responses to changes in PPFD and air CO 2 concentration were evaluated and fitted according to the models proposed by Lieth & Reynolds () and Sharkey et al .…”

“…These species are potential crops for non‐edible oil and biofuel production and are well adapted to hot and dry conditions (Lima Neto et al . , ). As both species display reasonable performance under water deficit, and J .…”