Abstract
Small succulent halophytic shrubs of the genera Salicornia and Sarcocornia (Salicornioideae, Amaranthaceae) are commonly named sea asparagus and consumed worldwide as green salad in gourmet food, as conserves, and beverages. Their shoots are rich in bioactive compounds and plants show high yields in a wide range of salinities, but little is known about how salt cultivation conditions affect their chemical composition. Two genotypes (BTH1 and BTH2) of the Brazilian sea asparagus Salicornia neei Lag. were evaluated for salt tolerance and changes in shoot concentrations of organic metabolites and antioxidant activity under different salt exposure in both greenhouse and field conditions. All greenhouse plants received full strength modified Hoagland solution in deionized water with a basic electrical conductivity (EC) of 1.7 dS m−1, and with NaCl concentrations (in mM) of ~0.1 (control), 34, 86, 171, 513, and 769. After fifty days of cultivation, both S. neei genotypes showed high salt tolerance and grew better under low salinities (34–86 mM NaCl) than under control salinity. Shoots of BTH1 genotype appeared to be undergoing lignification and used their high carotenoid content to dissipate the oxidative power, and the zeaxanthin content and de-epoxidation state of xanthophylls (DES) were positively affected by salinity. Under increasing salinity, BTH2 genotype had higher relative content of chlorophyll b, which may have lowered the plant photo-oxidation rate, and increased shoot concentration of the flavonoid quercetin (up to 11.6 μg g−1 dw at 769 mM NaCl), leading to higher antioxidant capacity. In the field experiment, after 154 days of irrigation with saline (213 mM NaCl) shrimp farm effluent, BTH2 plants grew taller, produced more metabolites (e.g., total phenolics, total free flavonoids, quercetin, and protocatechuic acid) and had a greater antioxidant capacity of shoots than that of BTH1 plants and that of traditional crops irrigated with fresh water. Yield and bioactive compound composition of S. neei genotypes’ shoots can be enhanced by cultivation under moderate saline conditions.
Highlights
Plants of the genera Salicornia and Sarcocornia (Salicornioideae, Amaranthaceae) are small succulent shrubs with leafless stems and branches commonly named sea asparagus, glasswort or Agriculture 2018, 8, 115; doi:10.3390/agriculture8070115 www.mdpi.com/journal/agricultureAgriculture 2018, 8, 115 samphire [1,2]
After 154 days of irrigation with saline (213 mM NaCl) shrimp farm effluent, BTH2 plants grew taller, produced more metabolites and had a greater antioxidant capacity of shoots than that of BTH1 plants and that of traditional crops irrigated with fresh water
In order to sustain growth under salt stress, S. neei genotypes regulate their physiological mechanisms related to succulence, production of photoprotective pigments, and antioxidant metabolites
Summary
Plants of the genera Salicornia and Sarcocornia (Salicornioideae, Amaranthaceae) are small succulent shrubs with leafless stems and branches commonly named sea asparagus, glasswort or Agriculture 2018, 8, 115; doi:10.3390/agriculture8070115 www.mdpi.com/journal/agricultureAgriculture 2018, 8, 115 samphire [1,2]. The most recently worldwide phylogenetic treatment of Salicornioideae based on molecular markers, according to Piirainen et al [3], proposed merging of perennial species of the genus Sarcocornia in three subgenera under Salicornia These plants are halophytes found worldwide in salt marshes and salt deserts, are consumed as green gourmet salads, preserves, and beverages (nuruk, wine and vinegar) [2,4]. Oxidative stress results from stomatal closure under salt exposure and inability of the plant to reduce electrons generated by photosynthesis in the light-dependent cycle, due to the lack of CO2 molecules. This situation can lead-induce the reducing power (electrons) acts on other molecules generating reactive oxygen species (ROS). Several halophytes showed that their content of phenolic compounds are directly proportional to the intensity of salt stress [6,8,13,22] and the presence of these compounds is frequently linked to the action of scavengers against ROS [12,18]
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