Response of Olive Shoots to Salinity Stress Suggests the Involvement of Sulfur Metabolism

Abstract

Global warming has two dangerous global consequences for agriculture: drought, due to water scarcity, and salinization, due to the prolonged use of water containing high concentrations of salts. Since the global climate is projected to continue to change over this century and beyond, choosing salt-tolerant plants could represent a potential paramount last resort for exploiting the secondary saline soils. Olive is considered moderately resistant to soil salinity as compared to other fruit trees, and in the present study, we investigated the influence of NaCl solutions (ranging from 0 to 200 mM) in a salt-tolerant (cv Canino) and two of its transgenic lines (Canino AT17-1 and Canino AT17-2), overexpressing tobacco osmotin gene, and in a salt-sensitive (Sirole) olive cultivar. After four weeks, most of the shoots of both Canino and Sirole plants showed stunted growth and ultimate leaf drop by exposure to salt-enriched media, contrary to transgenic lines, that did not show injuries and exhibited a normal growth rate. Malondialdehyde (MDA) content was also measured as an indicator of the lipid peroxidation level. To evaluate the role of the S assimilatory pathway in alleviating the adverse effects of salt stress, thiols levels as well as extractable activities of ATP sulfurylase (ATPS) and O-acetyl serine(thiol)lyase (OASTL), the first and the last enzyme of the S assimilation pathway, respectively, have been estimated. The results have clearly depicted that both transgenic lines overexpressing osmotin gene coped with increasing levels of NaCl by the induction of S metabolism, and particularly increase in OASTL activity closely paralleled changes of NaCl concentration. Linear correlation between salt stress and OASTL activity provides evidence that the S assimilation pathway plays a key role in adaptive response of olive plants under salt stress conditions.

A Review on Plant Responses to Salt Stress and Their Mechanisms of Salt Resistance

“…The same results were observed in soybean plants with overexpression of the tobacco osmotin gene [208]. Bashir et al found that improving salt tolerance by overexpressing tobacco osmotin protein in Olive has something to do with the sulfur metabolism of the transgenic plants [209,210]. Though we have found some evidence for the role of tobacco osmotin protein in enhancing plant stress resistance, the complete mechanism of osmotin activity has not been fully elucidated, and is waiting to be revealed.…”

Exogenous melatonin mitigates salinity‐induced damage in olive seedlings by modulating ion homeostasis, antioxidant defense, and phytohormone balance

“…In this study, moderate and severe salt stresses remarkably reduced the contents of photosynthetic pigments in a concentration‐dependent manner (Figure 2A). Likewise, long‐term exposure to salinity showed a typical negative effect, such as decreased Chl contents in different olive genotypes (Bashir et al 2021). In contrast, MEL application maintained Chl a , Chl b , total Chls, and CARs in the leaves of olive seedlings grown under moderate and severe salt stresses (Figure 2A), implying that MEL might participate in the biosynthesis and/or protection of Chls and CARs, thereby contributing to sustaining the photosynthetic process during salt stress conditions.…”

Mechanism of tobacco osmotin gene in plant responses to biotic and abiotic stress tolerance: A brief history

“…In addition, transgenic C. annum plants showed increased proline, chlorophyll, relative water contents, and antioxidative enzymes (Subramanyam et al, 2011). In a recent report, Bashir et al (2021) demonstrated salt tolerance in transgenic olive (Olea europaea L.) plants over-expressing the tobacco osmotin gene. Salt stress tolerance in transgenic olive plants was associated with the induction of the S assimilatory pathway, especially due to an increase in the activity of O-acetyl serine(thiol)lyase (OASTL) (Bashir et al, 2021).…”

“…In a recent report, Bashir et al (2021) demonstrated salt tolerance in transgenic olive (Olea europaea L.) plants over-expressing the tobacco osmotin gene. Salt stress tolerance in transgenic olive plants was associated with the induction of the S assimilatory pathway, especially due to an increase in the activity of O-acetyl serine(thiol)lyase (OASTL) (Bashir et al, 2021). Under cold treatment (15°C), the over-expression of N. tabacum osmotin gene improved seed germination rate, and the establishment and growth of seedlings in transgenic tomato (Solanum lycopersicum L.) (Patade et al, 2018).…”