Insight into salt tolerance mechanisms of the halophyte Achras sapota: an important fruit tree for agriculture in coastal areas

Abstract

Sapota (Achras sapota), a fruit tree with nutritional and medicinal properties, is known to thrive in salt-affected areas. However, the underlying mechanisms that allow sapota to adapt to saline environment are yet to be explored. Here, we examined various morphological, physiological, and biochemical features of sapota under a gradient of seawater (0, 4, 8, and 12 dS m) to study its adaptive responses against salinity. Our results showed that seawater-induced salinity negatively impacted on growth-related attributes, such as plant height, root length, leaf area, and dry biomass in a dose-dependent manner. This growth reduction was positively correlated with reductions in relative water content, stomatal conductance, xylem exudation rate, and chlorophyll, carbohydrate, and protein contents. However, the salt tolerance index did not decline in proportional to the increasing doses of seawater, indicating a salt tolerance capacity of sapota. Under salt stress, ion analysis revealed that Na mainly retained in roots, whereas K and Ca were more highly accumulated in leaves than in roots, suggesting a potential mechanism in restricting transport of excessive Na to leaves to facilitate the uptake of other essential minerals. Sapota plants also maintained an improved leaf succulence with increasing levels of seawater. Furthermore, increased accumulations of proline, total amino acids, soluble sugars, and reducing sugars suggested an enhanced osmoprotective capacity of sapota to overcome salinity-induced osmotic stress. Our results demonstrate that the salt adaptation strategy of sapota is attributed to increased leaf succulence, selective transport of minerals, efficient Na retention in roots, and accumulation of compatible solutes.

Differential Response of Sugar Beet to Long-Term Mild to Severe Salinity in a Soil–Pot Culture

“…But, under 250 mM salt stress, the RWC of sugar beet plants significantly dropped ( Figure 1B) which might trigger by a sharp accumulation of proline content ( Figure 1A) which inhibited the growth of sugar beet (Table 1). Similar enhancement of proline under decreased RWC was found in Elaeagnus angustifolia [21], Achras sapota [73], and rice (Oryza sativa) [74].…”

“…In our present study, total Chl content of sugar beet plants was significantly increased under 75 mM and 100 mM saline water but showed marked decreased under 150 mM and 250 mM saline water treatment demonstrating that photosynthesis in sugar beet plant was improved under low salinity then declined under high salinity as reflected in the sugar beet's growth, biomass, and yield (Table 1). This finding was supported by the studies on several plants [73,[87][88][89][90][91]. These results led us to speculate that sugar beet plants still retain some halophytic nature of its ancestor see beet [41] and displayed a tolerance mechanism against low and moderate salinity [92].…”

Performance of Medicago sativa Grown in Clay Soil Favored by Compost or Farmyard Manure to Mitigate Salt Stress

“…The irrigation with salty water negatively affected plants due to a reduction in osmosis and increase in ion toxicity [33]. Salt stress and nutritional imbalance affect physiological status and are responsible for harmful effects on plant biomass production [34]. MSW compost increased plant biomass of alfalfa by 40% in soils without salt stress.…”

Transcriptional regulation-mediating ROS homeostasis and physio-biochemical changes in wild tomato (Solanum chilense) and cultivated tomato (Solanum lycopersicum) under high salinity

“…These changes may lead to oxidative damages, perturbation in metabolic pathways and important physiological processes in plants. These changes include reduced photosynthesis (destruction of photosynthetic apparatus), impairment of electron transport, stomatal closure, ion toxicity and decreased cellular growth ( Assaha et al, 2017 , Rahman et al, 2019 ). Further, prolonged exposure to saline conditions might result in hyper ionic and/or hyperosmotic stress, in addition to dehydration response ( Fricke, 2019 ).…”

“…This comprises of ROS homeostasis, increased antioxidant defense mechanism as well as activation of ROS scavenging pathways, compartmentation of toxic ions, osmolyte biosynthesis, ion homeostasis, change in photosynthetic parameters, and hormonal changes ( Flowers and Colmer, 2015 ). Further, ROS scavenging system consists of several non-antioxidant molecules as well as anti-oxidative defense enzymes and/or their isoforms located in different cellular compartments, particularly, isoforms that exist in mitochondria, chloroplast, and peroxisomes ( Assaha et al, 2017 , Rahman et al, 2019 ). Apart from antioxidative defense mechanism, salt stress avoidance is also achieved through accumulation of osmolytes and other non-enzymatic antioxidants that facilitate ROS scavenging and absorption of water, and decrease the osmotic potential of cytoplasm ( Latef and Chaoxing, 2014 , Puniran-Hartley et al, 2014 , Rakhmankulova et al, 2015 ).…”