Concentrations of Si (as monosilicic acid) and Na in the solutions before and after experiment are presented in Table 1.
Table 1
Concentrations of monosilicic acid and Na in solutions before and after staying barley plants, ppm.
Solution | Before experiment | After experiment |
Si | Na | Si | Na |
Control | 0 | 0 | 8.1 ± 1.1 | 21.0 ± 2.0 |
Si | 150 ± 3 | 65 ± 3 | 112.2 ± 1.3 | 55.3 ± 2.1 |
Na | 0 | 12000 ± 10 | 6.5 ± 0.4 | 11903 ± 125 |
Na + Si | 150 ± 3 | 12000 ± 10 | 101.3 ± 11.5 | 11925 ± 147 |
During 96 h the concentrations of Si and Na in control solution increased from 0 to 8.1 and 21.0 ppm, respectively, as a result of the release from plant tissue. In Si solution, the concentration of monosilicic acid declined from 150 to 112.2 ppm of Si. In Na + Si solution, the concentration of monosilicic acid was reduced up to 101.3 ppm of Si. The Na concentration in Na solution decreased from 12000 ppm to 11903 ppm, while in Na + Si solution a decrease was less, up to 11925 ppm. The amount of Na absorbed from Na solution was statistically larger as compared with that from Na + Si solution.
After 96 h-staying in the solutions, the total Si increased in all tested plant tissues in the Si, Na or Na + Si solutions (Table 2). Higher values of total Si were detected in the roots and stems in Na + Si solution. In the leaves, higher Si was detected in Si solution. Èxposure to Na initiated the Si redistribution from leaves to stems and roots.
The total Na in the roots was maximum in Na + Si solution (1.28%), while in the stems and leaves the maximum total Na was detected in Na solution (1.99 and 1.04%, respectively). The maximum total Si in the roots (2.12%) and stems (0.93%) were determined in Na + Si solution. In the leaves, the maximum total Si (1.42%) was tested in Si solution, while the leaf Si was reduced to 0.82% in Na + Si solution.
The dynamics of monosilicic, polysilicic acids and Na in the apoplast and symplast of roots, stem and leaves is presented in Figs. 1–3.
Table 2
Total Si and Na in barley plants before and after staying in Si, Na and Na + Si solutions, %.
Solution | Before experiment | After experiment |
Si | Na | Si | Na |
Roots |
Control | 0.82 ± 0.04 | 0.041 ± 0.004 | 0.87 ± 0.08 a | 0.36 ± 0.06 a |
Si | 1.25 ± 0.08 b | 0.34 ± 0.06 a |
Na | 1.53 ± 0.08 c | 1.10 ± 0.07 b |
Na + Si | 2.12 ± 0.07 d | 1.28 ± 0.07 c |
Stems |
Control | 0.45 ± 0.07 | 0.032 ± 0.004 | 0.42 ± 0.08 a | 0.30 ± 0.06 a |
Si | 0.87 ± 0.08 c | 0.33 ± 0.06 a |
Na | 0.61 ± 0.07 b | 1.99 ± 0.05 c |
Na + Si | 0.93 ± 0.05 c | 0.82 ± 0.04 b |
Leaves |
Control | 0.68 ± 0.07 | 0.052 ± 0.005 | 0.63 ± 0.08 a | 0.54 ± 0.06 a |
Si | 1.42 ± 0.07 c | 0.65 ± 0.05 a |
Na | 0.52 ± 0.06 a | 1.04 ± 0.05 c |
Na + Si | 0.82 ± 0.06 b | 0.81 ± 0.06 b |
Data express the mean ± S.D. The different letters above the bar indicate significant differences between groups using the Duncan’s multiple range test (p < 0.05).
In DW, the concentrations of monosilicic acid in the apoplast of root, stem and leaf gradually decreased, while its reduction in the symplast was observed only in roots. The monosilicic acid in the symplast of stem and leaf increased.
Exposure to Na initiated reducing monosilicic acid only in the root and leaf apoplast. In the stem apoplast and symplast, monosilicic acid significantly increased. Supplementation with monosilicic acid increased the monosilicic acid content in all organs, except the leaf apoplast. Higher increase was observed in the root apoplast in Na-Si solution.
The dynamics of polysilicic acid in the apoplast and symplast of stem was similar in all solutions: it increased for 96 hours, with smaller changes in DW and larger ones in Na + Si solution. In the root apoplast, considerable continuous increase in polysilicic acid was only in Na + Si solution. In DW, polysilicic acid was reduced in the root and leaf apoplast, whereas it remained stable in the root and leaf symplast. The polysilicic acid concentration increased in the stem and leaf apoplast in Si solution, but did not increase in the root apoplast. However, polysilicic acid increased in the symplast of all organs and in all solutions, except the leaf symplast in DW.
In DW, the Na concentrations decreased during 96 hours from 200 to 135 ppm and from 245 to 119 ppm in the root and stem apoplast, respectively, while the leaf apoplast Na slightly increased (from 50 to 68 ppm). In DW, the Na in the symplast of root, stem and leaf was reduced, but differently. Higher Na reduction was observed in the root (by 47%) and lesser in the leaf (by 6.6%). In Si solution, the root apoplast and symplast Na increased markedly from 200 to 523 and from 480 to 604 ppm, respectively, for 96 h, whereas the leaf symplast Na was reduced from 1500 to 1270 ppm. The fact of increasing Na in the apoplast and symplast of roots may be attributable to the Na plant uptake from Si solution because it contained about 70 ppm of Na.
The dynamics of Na in the apoplast and symplast of all organs of salt-exposed plants represented a parabolic curve. The Na reached equilibrium in the root apoplast within the first 24 h, while in the stem apoplast the equilibrium was observed in 48 h and in the leaf apoplast in 96 h. It is important to emphasize that under salt exposure the penetration of Na into the root and stem symplast was much lower than that into the corresponding apoplast, whereas the dynamics of Na was similar in the leaf apoplast and symplast.
After 96 hours, the Na in the apoplast of root, stem, and leaf decreased from 9320 to 6520 mg kg− 1, from 23600 to 3350 mg kg− 1 and from 30120 to 2945 mg kg− 1, respectively. In symplast, the Na was reduced only in stem (from 2670 to 3450 mg kg− 1), whereas it increased from 557 to 682 mg kg− 1 in root and from 6510 to 10240 mg kg− 1 in leaf.