Abstract
Soil salinity is one of the main barriers to increasing global food production as it reduces crop growth and productivity. While irrigated lands in arid climates (about 20% of total affected) are more prone to salinization, many other natural and anthropogenic factors contribute to an increase in salinity in arable lands that currently affects over 100 countries and more than one billion ha. Management of agro-ecosystems at every level, including soil, water, and the plant itself, is important in mitigating the effects of salinity. Plant hormones control cellular metabolism, and mediate plant defense response mechanisms against abiotic and biotic stresses. Foliar fertigation with plant growth regulators has been shown to improve growth and metabolism under stress conditions. Strigolactones (SLs) have emerged as a group of novel phytohormones with several functions in plant interactions with microorganisms, plant metabolism, development, and in responding to many environmental cues. The present research addressed SL (GR24) effects on growth, photosynthetic parameters, and oxidative stress in Solanum lycopersicum under salinity stress. Growth indices, photosynthesis and related attributes, antioxidant enzyme activity, and malondialdehyde (a product of lipid peroxidation) and hydrogen peroxide concentrations were compared in unstressed and salt-stressed (NaCl; 150 mM) S. lycopersicum seedlings untreated or treated with GR24 (2 mu M). Improved antioxidant enzyme activity, proline (8%) and protein (14%) contents, and photosynthetic (33%) and transpiration (34%) parameters under GR24 treatment result in a significant increase in plant growth parameters, viz., shoot length (29%), root length (21%), shoot fresh weight (31%), root fresh weight (23%), shoot dry weight (26%), and root dry weight (19%). Increased chlorophyll index (14%) and stomatal conductance (16%) in GR24-applied plants under salinity stress results in improved growth and photosynthetic efficiency of S. lycopersicum. Our results add to the existing knowledge of the relatively new function of SLs in mitigating abiotic stress, particularly that of salinity stress in crop plants.