Abstract
The phytohormones are important in plant adaptation to abiotic and biotic stresses by facilitating a wide range of adaptive responses. Application of gibberellic acid (GA3) and paclobutrazol (PBZ) as GA3 inhibitors have been shown to affect salinity tolerance through modulating phytohormones. The aim of this study was to find out the potential objectives for GA3 and PBZ as affected by salinity through altering the phytohormones and biochemical parameters in sweet sorghum. Following seed germination, seedlings were cultured in Hoagland nutrient solution containing NaCl supplemented with GA3 and PBZ for 12 days. The results were analyzed by principal component analysis to identify the best target(s) for salinity, GA3, and PBZ in sweet sorghum. Paclobutrazol associated with salt improved root/shoot length, carotenoid, and total chlorophyll by modulating cytokinin (CK)/GA3, indole acetic acid (IAA)/GA3, and total polyamines/GA3 ratios. Gibberellic acid-treated plants not exposed to salinity treatments notably improved phytohormones content such as cytokinin, auxin, abscisic acid (ABA), and polyamines resulting in increased stem growth. Moreover, the main objectives of GA3 were ABA, spermidine, and ABA/GA3 ratio in response to salinity. Though GA3 and PBZ have different roles against salt stress, ABA/GA3 ratio was a similar target of GA3 and PBZ. This work suggests that altered levels of GA3 resulting from PBZ- and GA3-treated plants cause different allocation patterns in sweet sorghum by regulation of CK/GA3, IAA/GA3, and total polyamines/GA3 ratio. Also, accumulation chlorophyll pigments, carotenoids, and water soluble carbohydrates of sorghum plants under salinity regulated by total polyamines/GA3 and ABA/GA3 ratios positively correlated with PBZ application.
Highlights
Salinity is a major problem in agriculture and crop production
We found that the SPM, polyamines/GA3, and abscisic acid (ABA)/GA3 were the main objectives of salinity regulating total chlorophyll, carotenoid, and WS contents in sweet sorghum
We found that application of GA3 increased the levels of CK and indole acetic acid (IAA) in leaves, perhaps due to the beneficial effects of hormonal homeostasis of GA3 and its ion uptake and possibly the photosynthesis process in the salt-stressed plants [8]
Summary
Salinity is a major problem in agriculture and crop production. High concentration of toxic ions creates salty soil regions around the world. Sweet sorghum (Sorghum bicolor) has usually been grown in areas with relatively low rainfall, high temperatures, and saline soils This plant, as a moderately salt tolerant crop, has been adapted to water limitation and is more tolerant to salinity at germination stage than in the later stages of growth [4, 5]. A number of methods have been developed for screening salt tolerance in plants because majority of physiological processes (e.g., germination, photosynthesis, biomass production, and chlorophyll content) are highly sensitive to salt stress [3]. Plants can adjust their growth and development in response to salt stress by signaling molecules.
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