RESUMEN
In understanding the role of root cell wall mechanisms in plant tolerance to salinity, it is important to elucidate the changes in the pectin composition and physical properties of the cell wall. Two salt-sensitive (Helan 3 and Prius ß) and one salt-tolerant (R7) spinach cultivars were used to investigate the pectin polysaccharides, the characteristics of pectin, including the degree of pectin methy-lesterification, the HG:RG-I ratio, neutral side chains (galactan/arabinangalactan), and elasticity and viscosity parameters in the root elongation zone under salinity. Root growth was inhibited by salinity, whereas the root diameter was thickened in all cultivars. Salinity significantly reduced cell wall extensibility in all cultivars, and increased cell wall viscosity in Helan 3 and R7 relative to Prius ß. Pectin was significantly increased under salinity stress. Cell wall viscosity was affected by pectin due to the molar proportion of uronic acid and/or pectin characteristics (HG:RG-I ratio). The molar proportion of uronic acid in pectin was reduced in Helan 3 and R7 compared with Prius ß. The length and degree of pectin methy-lesterification of neutral side chains were significantly decreased in the R7 cultivar, with no significant changes in the other two cultivars. Demethylation of pectin could alter root growth and boost salt tolerance in the R7 cultivar. In this study, it is shown that cell wall pectin played important roles in regulating the root growth of Spinacia oleracea L. under salinity stress.
RESUMEN
The accumulation of salts within the rhizosphere is a common phenomenon in arid and semi-arid regions where irrigation water is high in salts. A previous study established the ameliorative effect of foliarly applied 24-epibrassinolide (BR) on soybean under salinity stress. As a follow-up to that study, this work evaluated the effects of BR on the electrical conductivity of saturated soil extracts (ECses) under soybean exposed to salt stress. Three salinity levels (3.24, 6.06 and 8.63 dS/m) in a factorial combination with six frequencies of BR application-control, seedling, flowering, podding, seedling + flowering and seedling + flowering + podding-were the treatments, and the rhizospheric ECse was monitored from 3 to 10 weeks after the commencement of irrigation with saline water (WAST). The principal component analysis revealed that samples in saline BR treatments clustered together based on the BR application frequencies. There was a significant increase in ECse with increases in salinity and WAST. The frequent application of BR significantly reduced ECse to 5.07 and 4.83 dS/m relative to the control with 6.91 dS/m, respectively, at week 10. At 8.63 dS/m, the application of BR (seedling + flowering + podding) reduced ECse by 31.96% compared with the control. The underlining mechanism is a subject for further investigation.
RESUMEN
Understanding the role of root cell walls in the mechanism of plant tolerance to salinity requires elucidation of the changes caused by salinity in the interactions between the mechanical properties of the cell walls and root growth, and between the chemical composition of the cell walls and root growth. Here, we investigated cell wall composition and extensibility of roots by growing a halophyte (Suaeda salsa) and a glycophyte (Spinacia oleracea) species under an NaCl concentration gradient. Root growth was inhibited by increased salinity in both species. However, root growth was more strongly reduced in S. oleracea than in S. salsa. Salinity reduced cell wall extensibility in S. oleracea significantly, whereas treatment with up to 200 mM NaCl increased it in S. salsa. Meanwhile, S. salsa root cell walls exhibited relatively high cell wall stiffness under 300 mM NaCl treatment, which resist wall deformation under such stress conditions. There was no decrease in pectin content with salinity treatment in the cell walls of the elongation zone of S. salsa roots. Conversely, a decrease in pectin content was noted with increasing salinity in S. oleracea, which might be due to Na+ accumulation. Cellulose content and uronic acid proportions in pectin increased with salinity in both species. Our results suggest that (1) cell wall pectin plays important roles in cell wall extension in both species under salinity, and that the salt tolerance of glycophyte S. oleracea is affected by the pectin; (2) cellulose limits root elongation under saline conditions in both species, but in halophytes, a high cell wall content and the proportion of cellulose in cell walls may be a salt tolerance mechanism that protects the stability of cell structure under salt stress; and (3) the role of the cell wall in root growth under salinity is more prominent in the glycophyte than in the halophyte.
RESUMEN
Salinity episodes that are common in arid regions, characterized by dryland, are adversely affecting crop production worldwide. This study evaluated the effectiveness of brassinolide (BL) in ameliorating salinity stress imposed on soybean at four levels (control (1.10), 32.40, 60.60 and 86.30 mM/L NaCl) in factorial combination with six BL application frequency (control (BL0), application at seedling (BL1), flowering (BL2), podding (BL3), seedling + flowering (BL4) and seedling + flowering + podding (BL5)) stages. Plant growth attributes, seed yield, and N, P, K, Ca and Mg partitioning to leaves, stems and roots, as well as protein and seed-N concentrations, were significantly (p ≤ 0.05) reduced by salinity stress. These trends were ascribed to considerable impairments in the photosynthetic pigments, photosynthetically active radiation, leaf stomatal conductance and relative water content in the leaves of seedlings under stress. The activity of peroxidase and superoxidase significantly (p ≤ 0.05) increased with salinity. Foliar spray with BL significantly (p ≤ 0.05) improved the photosynthetic attributes, as well as nutrient partitioning, under stress, and alleviated ion toxicity by maintaining a favourable K+/Na+ ratio and decreasing oxidative damage. Foliar spray with brassinolide could sustain soybean growth and seed yield at salt concentrations up to 60.60 mM/L NaCl.
