Photosynthesis and antioxidant activity in Jatropha curcas L. under salt stress

Abstract

Biodiesel is an alternative to petroleum diesel fuel. It is a renewable, biodegradable, and nontoxic biofuel. Interest in the production of biodiesel from Jatropha curcas L. seeds has increased in recent years, but the ability of J. curcas to grow in salt-prone areas, such as the Caatinga semiarid region, has received considerably meager attention. The aim of this study was to identify the main physiological processes that can elucidate the pattern of responses of J. curcas irrigated with saline water, which commonly occurs in the semiarid Caatinga region. This study measured the activity of the antioxidant enzymes involved in the scavenging of reactive oxygen species, which include catalase (CAT) and ascorbate peroxidase (APX), as well as malondialdehyde (MDA) levels. The levels of chlorophyll (Chl), carotenoids, amino acids, proline, and soluble proteins were also analyzed. The net carbon assimilation rate (P N ), stomata conductance (g s ), and transpiration rate (E) decreased with salt stress. The activities of CAT and APX were decreased, while H 2 O 2 and MDA levels as well as electrolyte leakage were significantly increased in salt-stressed plants compared to the untreated ones. These observations suggest that the ability of J. curcas plants resist to salt stress is associated with the activities of protective enzymes and their defensive functions. However, our results indicate that the reactive oxygen species scavenging system is not sufficient to protect J. curcas leaves against oxidative damage caused by salt stress, and, therefore, it cannot be treated as a salt tolerant plant species.

Morpho-physiological adaptation of Jatropha curcas L. to salinity stress

“…Kumar et al (2008) also found decreased protein content in J. curcas callus under 100 mM of NaCl; their findings corroborate the results in the present study. These results also corroborate other studies, such as that by Campos et al (2012), who found decreased protein levels in J. curcas plants grown under saline conditions.…”

“…Our study showed that moderate salinity levels (EC 1.76 dS.m -1 ) did not affect the amino acid, proline and carbohydrate; they were only affected by higher salt concentrations. However, Campos et al (2012) found increased osmolyte levels in J. curcas plants cultivated in higher salt concentration (EC, 3.5 dS m -1 ) in the irrigation water. Contradictory results about J. curcas seedlings were recorded by Díaz-López et al (2012), who did not find any contribution from the osmotic adjustment resulting from osmolytes accumulation when plants were under salt stress.…”

“…Campos et al (2012) also showed decreased total chlorophyll content in J. curcas grown under salinity conditions, but no such effect was observed in the carotenoid content. Overall, there is strong evidence that salt stress can reduce chlorophyll concentration, fact that has been attributed either to the decreased recovery ability of the photosynthetic apparatus or to lower chlorophyll synthesis caused by the decreased number of specific enzymes involved in pigment synthesis (Sharma and Hall, 1991;Vajpayee et al, 2000;Meeta et al, 2013).…”

“…Many studies have reported different plant sensitivity depending on the salt application method (Campos et al, 2012;Díaz-López et al, 2012). Pinheiro et al (2008) showed decreased leaf dry weight (by 43.7%) and stem dry weight (by 53.5%) in castor bean (Ricinus communis L.) grown in soil presenting electrical conductivity (EC) 8.54 dS m -1…”

“…De Lima et al (2015) also found decreased leaf dry weight (by 47.3%) and stem dry weight (by 43.2%) in castor bean 120 days after planting at irrigation water EC 3.9 dS m -1 . The most commonly used method to set the sensitivity to salinity of J. curcas is the saline irrigation water (Campos et al, 2012;Díaz-López et al, 2012;Silva et al, 2013;Hishida et al, 2014;Zhang et al, 2014); however, studies about the physiological responses of J. curcas to salinity under natural environment conditions remain scarce. Therefore, the present study was carried out in natural saline soil in order to better understand how J. curcas can tolerate saline soils.…”