Analysis of variance. Analysis of variance in first trial indicated significant differences for all of the measured traits for fungi main effect while stress main effect was significant for all of the traits except root volume (RV), root dry weight (RDW), chlorophyll a (Chl-a), anthocyanin amount (Ant), protein content and Ascorbate peroxidase (APX) (Table 1). The fungi × stress interaction was significant in all of the measured traits except plant height (PH) in first trial. The coefficient of variation (CV) ranged from 3.2 to 14.8% which indicates acceptable magnitude of Error variance (Table 1). In the second trial, analysis of variance showed significant differences for all of the traits for water stress main effect except protein content, APX and GPX (Table 2). The main effect of SiO2 nanoparticles was also significant for all of the traits except root length (RL), RDW, K amount and Phenol while the SiO2 × stress interaction was significant in all of the measured traits exceptChl-a (Table 2). The CV magnitude ranged from 2.2 to 14.4% which shows acceptable magnitude of Error variance in the second trial (Table 2). The significance of interaction effects for most traits in both trials indicated that main effects, water stress, fungi application, SiO2 nanoparticles usage, are not interpretable individually and means of treatment combinations must be compared.
Table 1
Analysis of variance for measured traits of tomato in P. indica trial.
SOV† | DF‡ | Mean squares |
PH | RL | RV | SDW | RDW | Proline |
Stress (S) | 1 | 160.2** | 376.0** | 0.96ns | 0.0442* | 0.0131ns | 0.0004978** |
Fungi (F) | 2 | 62.0** | 257.0** | 56.58** | 1.8395** | 0.1579** | 0.0000878** |
S×F | 2 | 4.7ns | 333.0** | 9.00** | 0.2290** | 0.1825** | 0.0000239** |
Error | 18 | 4.6 | 13.2 | 0.68 | 0.0081 | 0.0057 | 0.0000013 |
CV | | 5.5 | 7.2 | 10.0 | 5.8 | 8.9 | 11.1 |
| | Chl-a | Chl-b | RWC | EL | Ant | Catalase |
Stress (S) | 1 | 0.0088ns | 0.0876* | 311.8** | 461.4** | 0.0045ns | 0.0002100** |
Fungi (F) | 2 | 0.0406** | 0.5958** | 187.3** | 1178.3** | 0.3583** | 0.0000788** |
S×F | 2 | 0.0289* | 2.1687** | 54.9** | 493.6** | 0.3653** | 0.0000863** |
Error | 18 | 0.0049 | 0.0140 | 7.3 | 17.1 | 0.0044 | 0.0000062 |
CV | | 3.2 | 6.0 | 3.6 | 3.4 | 13.4 | 14.8 |
| | Na | K | Phenol | Protein | APX | GPX |
Stress (S) | 1 | 210.0** | 1066.7** | 0.874** | 0.001ns | 3.30E-10ns | 0.0000091** |
Fungi (F) | 2 | 150.0** | 914.3** | 0.588** | 0.064** | 2.30E-08** | 0.0000015** |
S×F | 2 | 30.0* | 267.8** | 3.172** | 0.082** | 8.98E-09** | 0.0000054** |
Error | 18 | 6.9 | 6.7 | 0.041 | 0.002 | 5.27E-10 | 0.0000001 |
CV | | 9.4 | 3.5 | 9.2 | 11.1 | 10.1 | 9.8 |
† SOV, sources of variation; ‡ DF, degrees of freedom;§ CV, coefficient of variation. |
**, * and ns denote statistically significant at 0.01 and 0.05 probability level and non- significant, respectively. |
Abbreviations are: plant height (PH), root length (RL), root volume (RV), shoot dry weight (SDW), root dry weight (RDW), chlorophyll a (Chl a), chlorophyll b (Chl b), relative water content (RWC), electrolyte leakage (EL), Ascorbate peroxidase (APX) and glutathione peroxidase (GPX). |
Table 2
Analysis of variance for measured traits of tomato in nano SiO2 trial.
SOV† | DF‡ | Mean squares |
PH | RL | RV | SDW | RDW | Proline |
Stress (S) | 1 | 29.3* | 839.0** | 76.0** | 11.10** | 0.618** | 0.00002194** |
Silicon (Si) | 2 | 152.0** | 10.3ns | 4.7** | 9.97** | 0.033ns | 0.00024972** |
S×Si | 2 | 43.8** | 205.4** | 20.8** | 1.96** | 0.416** | 0.00004150** |
Error | 18 | 6.1 | 4.6 | 0.7 | 0.14 | 0.014 | 0.00000032 |
CV | | 5.3 | 4.1 | 6.9 | 11.6 | 10.1 | 7.3 |
| | Chl-a | Chl-b | RWC | EL | Ant | Catalase |
Stress (S) | 1 | 2.486** | 0.0643** | 42.1** | 68.6* | 0.10749** | 0.0006212** |
Silicon (Si) | 2 | 1.584** | 0.0758** | 119.7** | 862.0** | 0.01542** | 0.0003973** |
S×Si | 2 | 0.033ns | 0.0922** | 27.5** | 60.6* | 0.01670** | 0.0007599** |
Error | 18 | 0.038 | 0.0023 | 2.9 | 12.8 | 0.00084 | 0.0000022 |
CV | | 8.4 | 2.5 | 2.2 | 3.5 | 7.6 | 11.7 |
| | Na | K | Phenol | Protein | APX | GPX |
Stress (S) | 1 | 486.0** | 1768.2** | 0.790** | 0.00026ns | 6.67E-11ns | 0.00000023ns |
Silicon (Si) | 2 | 14.6* | 36.4ns | 0.041ns | 0.07964** | 1.80E-08** | 0.00000174** |
S×Si | 2 | 205.9** | 4025.3** | 1.527** | 0.04063** | 2.80E-09** | 0.00002595** |
Error | 18 | 3.2 | 18.5 | 0.013 | 0.00083 | 7.07E-10 | 0.00000018 |
CV | | 5.5 | 6.0 | 5.5 | 6.0 | 14.4 | 13.5 |
† SOV, sources of variation; ‡ DF, degrees of freedom;§ CV, coefficient of variation. |
**, * and ns denote statistically significant at 0.01 and 0.05 probability level and non- significant, respectively. |
Abbreviations are: plant height (PH), root length (RL), root volume (RV), shoot dry weight (SDW), root dry weight (RDW), chlorophyll a (Chl a), chlorophyll b (Chl b), relative water content (RWC), electrolyte leakage (EL), Ascorbate peroxidase (APX) and glutathione peroxidase (GPX). |
P. indicatrial. We first investigated the impacts of P. indica on tomato traits under water stress condition. In the first trial, the mean of PH varied from 34.8 to 44.8 cm, whereas S1F2 (non-water stress condition and P. indica spore inoculation) had tallest plant height followed by S1F3 (non-water stress condition and the P. indica mycelium inoculation) (Table 3). The P. indica inoculation significantly increased PH at both stress and non-stress conditions while its positive effect is clearer in non-stress condition. The S1F3 treatment had the tallest root length (RL) while the P. indica mycelium inoculation could relatively decrease the negative effect of water stress (Table 3). The mean of root volume (RV) varied from 5.6 to 11.7 cm− 3, whereas both forms ofP. indica inoculation improved RV magnitudes in stress and non-stress conditions (Table 3). The P. indica inoculation significantly increased RV at both conditions which it seems that its root related nature had remarkable role in this positive performance. The P. indica inoculation significantly improved shoot dry weight (SDW) and root dry weight (RDW) in non-stress condition while such positive impact was clearly observed in RDW due to origin of the P. indica. Thus, our results indicated that both SDW and RDW were significantly decreased under drought stress, neither P. indicainoculation positively improved them. Hosseiniet al.19 reported similar results for both SDW and RDW in drought tolerance of P. indica-inoculated maize plants. It seems that, resistance or tolerance of plants to drought stress by the P. indica inoculation is due to its capability to enhance root properties like RL, RV and RDW. According to Zhang et al.20P. indica had colonized the maize roots via promoting involved genes for root formation microtubule-based movement processes which causes plant growth and development.
Table 3
The means of treatment combinations (P. indica inoculation (control, spore, mycelium) versus water stress) in the measured traits of tomato.
S¶ | F | PH (cm) | | RL (cm) | | RV (cm− 3) | | SDW (g) | | RDW (g) | | Proline (µmol g− 1 FW− 1) |
| 1 | 38.3 ± 1.71 cd | | 44.3 ± 2.99 cd | | 5.6 ± 0.75 c | | 1.05 ± 0.134 e | | 0.55 ± 0.052 c | | 0.0104 ± 0.00048 c |
1 | 2 | 44.8 ± 1.71 a | | 52.5 ± 1.29 b | | 8.0 ± 1.15 b | | 1.27 ± 0.104 d | | 0.79 ± 0.124 b | | 0.0195 ± 0.00228 a |
| 3 | 41.8 ± 3.10 ab | | 66.5 ± 6.56 a | | 11.7 ± 0.79 a | | 2.23 ± 0.088 a | | 1.13 ± 0.076 a | | 0.0150 ± 0.00139 b |
| 1 | 34.8 ± 2.22 e | | 50.5 ± 3.11 b | | 7.5 ± 0.41 b | | 1.48 ± 0.048 c | | 0.89 ± 0.067 b | | 0.0029 ± 0.00027 f |
2 | 2 | 39.3 ± 1.71 bc | | 41.5 ± 1.29 d | | 5.7 ± 0.70 c | | 1.33 ± 0.061 d | | 0.86 ± 0.041 b | | 0.0064 ± 0.00057 e |
| 3 | 35.3 ± 2.06 de | | 47.5 ± 3.79 bc | | 10.9 ± 0.94 a | | 1.99 ± 0.076 b | | 0.86 ± 0.064 b | | 0.0083 ± 0.00062 d |
S | F | Chl-a (mg g− 1 FW− 1) | | Chl-b (mg g− 1 FW− 1) | | RWC (%) | | EL (%) | | Anthocyanin (Abs 530 g− 1 FW− 1) | | Catalase (µmol g− 1 FW− 1 min− 1) |
| 1 | 2.09 ± 0.0409 bc | | 2.09 ± 0.126 b | | 73.3 ± 1.08 b | | 122.1 ± 1.22 c | | 0.565 ± 0.0531 b | | 0.015 ± 0.0024 c |
1 | 2 | 2.15 ± 0.1005 bc | | 1.49 ± 0.080 d | | 66.6 ± 1.87 c | | 105.5 ± 4.67 e | | 0.276 ± 0.0678 c | | 0.012 ± 0.0017 c |
| 3 | 2.30 ± 0.1111 a | | 2.51 ± 0.128 a | | 72.7 ± 3.19 b | | 128.9 ± 1.62 b | | 0.603 ± 0.0871 b | | 0.015 ± 0.0026 c |
| 1 | 2.19 ± 0.0365 b | | 1.26 ± 0.057 e | | 85.9 ± 3.05 a | | 112.8 ± 6.99 d | | 0.099 ± 0.0580 d | | 0.013 ± 0.0022 c |
2 | 2 | 2.05 ± 0.0251 c | | 2.57 ± 0.192 a | | 73.4 ± 3.24 b | | 124.6 ± 1.35 bc | | 0.561 ± 0.0878 b | | 0.021 ± 0.0031 b |
| 3 | 2.18 ± 0.0547 b | | 1.90 ± 0.079 c | | 74.9 ± 3.05 b | | 145.4 ± 5.08 a | | 0.865 ± 0.0210 a | | 0.026 ± 0.0026 a |
S | F | Na (mg Kg− 1) | | K (mg Kg− 1) | | Phenol (mg g− 1 DW− 1) | | Protein (µmol g− 1 FW− 1) | | APX (µmol g− 1 FW− 1 min− 1) | | GPX (µmol g− 1 FW− 1 min− 1) |
| 1 | 23.8 ± 2.22 bc | | 62.3 ± 2.22 d | | 2.28 ± 0.162 c | | 0.278 ± 0.0651 d | | 0.00013 ± 0.000017 d | | 0.0020 ± 0.00026 d |
1 | 2 | 34.3 ± 3.77 a | | 83.8 ± 1.71 b | | 2.52 ± 0.097 bc | | 0.497 ± 0.0608 bc | | 0.00030 ± 0.000022 a | | 0.0034 ± 0.00026 b |
| 3 | 34.8 ± 2.50 a | | 93.3 ± 3.40 a | | 1.25 ± 0.288 e | | 0.533 ± 0.0264 ab | | 0.00025 ± 0.000021 b | | 0.0045 ± 0.00026 a |
| 1 | 22.3 ± 2.63 c | | 62.3 ± 2.22 d | | 2.76 ± 0.104 ab | | 0.447 ± 0.0404 c | | 0.00021 ± 0.000023 c | | 0.0026 ± 0.00021 c |
2 | 2 | 25.5 ± 2.52 bc | | 63.0 ± 2.16 d | | 1.59 ± 0.139 d | | 0.580 ± 0.0240 a | | 0.00025 ± 0.000024 b | | 0.0018 ± 0.00025 d |
| 3 | 27.3 ± 1.71 b | | 74.0 ± 3.37 c | | 2.84 ± 0.307 a | | 0.316 ± 0.0598 d | | 0.00024 ± 0.000029 bc | | 0.0018 ± 0.00031 d |
Means (± SD, n = 4) with the same letter are not different significantly according to LSD test (P < 0.05). |
¶ Treatments are: S1, non-water stress condition; S2, water stress condition; F1, untreated with P. indica; F2, spore treated with P. indica; and F3, mycelium treated with P. indica. |
Abbreviations are: plant height (PH), root length (RL), root volume (RV), shoot dry weight (SDW), root dry weight (RDW), chlorophyll a (Chl a), chlorophyll b (Chl b), relative water content (RWC), electrolyte leakage (EL), Ascorbate peroxidase (APX) and glutathione peroxidase (GPX). |
The P. indica spore inoculation significantly increased proline in both conditions in comparison to non-inoculation (control) and mycelium inoculation (Table 3). Increasing proline under water stress conditions protects plant cells from harmful effect of drought due to de novo synthesis of proteins and inhibits the reactive species of oxygen 21. In most crop species, it has been shown that drought-induced changes in proline are related with the capability of crops to tolerate to drought conditions and can be used as a marker for selecting tolerant individuals 21. In the first trial, the mean of Chl-a varied from 2.05 to 2.30 mg g− 1 FW− 1, whereas S1F3 (non-water stress condition and P. indica mycelium inoculation) had highest magnitudes Chl-a followed by S2F3 (water stress condition and the P. indica mycelium inoculation) (Table 3). Also, the mean of Chl-b varied from 2.57 to 1.49 mg g− 1 FW− 1, whereas S1F3 (non-water stress condition and P. indica mycelium inoculation) had highest magnitudes Chl-b followed by S2F2 (water stress condition and the P. indica spore inoculation) (Table 3). The P. indica inoculation significantly increased Chl-a andChl-b at both stress and non-stress conditions while its positive effect is clearer in non-stress condition. Bonab et al.22 reported a reduction in chlorophyll a and b contents due to drought stress and compensative effect of P. indica application in barley which caused to increase amounts of chlorophyll a and b content under drought stress.
The RWC is one of the important traits used to evaluate the water status in plants under water stress condition and the P. indica application can maintain or even increase its levels in stressful circumstances. However, the P. indica spore inoculated seedlings increased the RWC and mycelium inoculated seedlings maintained RWC in comparison to non-water stress condition. It has been reported that electrolyte leakage (EL) is increased significantly under the water stress condition but the P. indica application can compensate the harmful effects of stress while we cannot find any clear positive effects for the P. indica application in EL (Table 3).Anthocyanins are produced through the phenylpropanoid and the flavonoid line, support chloroplast from harmful impacts of abiotic stress via osmotic adjustment and free radical scavenging23. Application the P. indica fungi enhanced anthocyanins when water stress performed whereas the high amounts of anthocyaninswas observed in S2F3 (water stress condition and the P. indica mycelium inoculation) followed by S2F2 (water stress condition and the P. indica spore inoculation), S1F1 and S1F3 (Table 3).
The catalase antioxidant enzyme (CAT) is involved in plant's adoptive response to water stress, and remarkable differences were observed in tomato seedlings with the P. indicaapplication and thehigher CAT enzymatic activity was found in seedlings grown under water stress and inoculated with the P. indica mycelium followed by stressed plants which inoculated the P. indica spore (Table 3). After superoxide dismutase enzyme, which acts as the first defense factor against any stresses by dismutation of superoxide radical and H2O2, the CAT breakdowns the extra H2O2 and causes the lower H2O2 in fungi inoculated tomato plants under abiotic stresses24. The mean of Na and K contents were high in spore and mycelium inoculated plants under non-water stress while fungi inoculation has improved their contents in water stress condition in comparison with non-inoculated plants (Table 3).Abdelaziz et al.25 reported that the exact mechanism of P. indica positive role in plant’s growth and development under stress is not grasped but it is clear that P. indica improves the Na and K contents as well as the expression of some ion channels which have an important role in ions homeostasis.
The results of Table 3 indicates that water stress increased phenols, as in S2F1 and S2F3treatments contained the highest concentration of phenols (2.84 and 2.76 mg g− 1 DW− 1, respectively). There was a slight increase in phenols when plants inoculated with P. indica; however, the increase was not significant.Crops tissues with higher phenols, show higher potentialagainst reactive oxygen species due to the high activity of hydrogen or electron donor and high amounts of phenols in P. indica inoculatedplants is related with (i)plant protectionresponse to foreign microorganisms, (ii) organization the peltate glandular trichomes, and (iii) enhancement of minerals’absorption23–26.
The mean of APX varied from 0.00013 to 0.00030 µmol g− 1 FW− 1 min− 1, whereas S1F2 (non-water stress condition and P. indica spore inoculation) had high magnitudes ofAPX (Table 3). The P. indica inoculation significantly increased APX at both stress and non-stress conditions. The mean of GPX varied from 0.0018 to 0.0045 µmol g− 1 FW− 1 min− 1, whereas S1F3 (non-water stress condition and P. indicamycelium inoculation) had high magnitudes of GPX (Table 3). Similar to APX, the P. indica inoculation significantly increased GPX at both stress and non-stress conditions.We found, APX and GPX activities in tomato seedlings increased when the P. indica inoculation performed under water stress.The GPX enzyme has a defensive role by elimination of H2O2, thus hold the operational of cell membrane and this finding of our current data relates with the past investigations in finger millet (Eleusinecoracana) by Tyagiet al.7, in Linum albumby Tashackori et al.27, and in grapevine by Karimi et al.28.
Nano SiO2trial. We then studied the effects of SiO2nanoparticles on tomato traits under water stress condition in the second trial.For the mean of PH, S1Si1 (non-water stress condition and 0 mMnano SiO2), S2Si1(water stress condition and 0 mMnano SiO2), and S2Si2(water stress condition and 50 mMnano SiO2), had the tallest plant height and the nano SiO2 application significantly increased PH at water stress condition (Table 4). Similarly, according to Ullahet al.29, tomato plant height was reduced by drought stress but it was improved by 26% with silicon application. Also, drought stress significantly decreases plant height of crops irrigation, but usage of SiO2nanoparticles, significantly improves plant height30. The S1Si1 and S1Si2 treatments had the tallest RL while application of 100 mMnano SiO2 could improve the negative effect of water stress (Table 4). The mean of RV varied from 8.7 to 15.8 cm− 3, whereas application of 50 mMnano SiO2, improved RV in stress condition (Table 4).Ashkavand et al.31 found that seedlings under water stress and non- stress conditions showed an increase in root volume than root length when SiO2nanoparticles were used, and our results are relatively in agreement with such report which proposeameaningful increase in root diameter.
Table 4
The means of treatment combinations (nano SiO2 (0, 50, 100mM) versus water stress in the measured traits of tomato.
S¶ | Si | PH (cm) | | RL (cm) | | RV (cm− 3) | | SDW (g) | | RDW (g) | | Proline (µmol g− 1 FW− 1) |
| 1 | 52.6 ± 1.11 a | | 62.0 ± 2.16 a | | 13.0 ± 0.83 b | | 3.51 ± 0.311 b | | 0.81 ± 0.070 d | | 0.0146 ± 0.00040 a |
1 | 2 | 41.5 ± 1.29 b | | 62.5 ± 3.11 a | | 8.7 ± 0.70 d | | 1.48 ± 0.240 e | | 1.22 ± 0.070 b | | 0.0032 ± 0.00056 d |
| 3 | 43.5 ± 4.04 b | | 52.0 ± 2.94 b | | 10.5 ± 0.71 c | | 2.71 ± 0.440 d | | 1.02 ± 0.074 c | | 0.0027 ± 0.00022 d |
| 1 | 51.3 ± 2.22 a | | 43.4 ± 0.95 c | | 13.8 ± 0.38 b | | 5.52 ± 0.337 a | | 1.50 ± 0.217 a | | 0.0130 ± 0.00043 b |
2 | 2 | 49.0 ± 2.45 a | | 45.8 ± 1.67 c | | 15.8 ± 0.95 a | | 3.34 ± 0.211 bc | | 1.04 ± 0.114 c | | 0.0103 ± 0.00089 c |
| 3 | 44.0 ± 2.58 b | | 51.8 ± 1.08 b | | 13.3 ± 1.33 b | | 2.93 ± 0.587 cd | | 1.48 ± 0.099 a | | 0.0029 ± 0.00065 d |
S | Si | Chl-a (mg g− 1 FW− 1) | | Chl-b (mg g− 1 FW− 1) | | RWC (%) | | EL (%) | | Anthocyanin (Abs 530 g− 1 FW− 1) | | Catalase (µmol g− 1 FW− 1 min− 1) |
| 1 | 2.69 ± 0.092 b | | 2.05 ± 0.019 ab | | 84.3 ± 1.60 a | | 113.4 ± 1.36 a | | 0.359 ± 0.0175 c | | 0.0090 ± 0.00018 c |
1 | 2 | 2.22 ± 0.193 c | | 2.00 ± 0.062 bc | | 82.4 ± 1.22 ab | | 106.0 ± 1.37 b | | 0.524 ± 0.0347 a | | 0.0358 ± 0.00250 a |
| 3 | 3.05 ± 0.396 a | | 2.03 ± 0.066 b | | 73.9 ± 1.82 d | | 105.8 ± 2.69 b | | 0.470 ± 0.0276 b | | 0.0084 ± 0.00064 c |
| 1 | 1.92 ± 0.082 d | | 1.71 ± 0.048 d | | 77.9 ± 1.42 c | | 102.9 ± 2.55 b | | 0.330 ± 0.0440 c | | 0.0030 ± 0.00022 d |
2 | 2 | 1.58 ± 0.043 e | | 1.96 ± 0.038 c | | 79.8 ± 1.24 bc | | 92.5 ± 6.96 c | | 0.338 ± 0.0261 c | | 0.0043 ± 0.00040 d |
| 3 | 2.53 ± 0.139 b | | 2.11 ± 0.041 a | | 74.9 ± 2.59 d | | 86.8 ± 3.29 d | | 0.283 ± 0.0130 d | | 0.0153 ± 0.00250 b |
S | Si | Na (mg Kg− 1) | | K (mg Kg− 1) | | Phenol (mg g− 1 DW− 1) | | Protein (µmol g− 1 FW− 1) | | APX (µmol g− 1 FW− 1 min− 1) | | GPX (µmol g− 1 FW− 1 min− 1) |
| 1 | 28.0 ± 1.41 d | | 54.8 ± 3.10 c | | 2.32 ± 0.135 b | | 0.347 ± 0.0269 d | | 0.00024 ± 0.000026 a | | 0.00551 ± 0.000648 a |
1 | 2 | 31.8 ± 1.71 c | | 87.8 ± 7.41 b | | 1.83 ± 0.072 c | | 0.641 ± 0.0312 a | | 0.00014 ± 0.000026 c | | 0.00273 ± 0.000359 c |
| 3 | 24.3 ± 1.71 e | | 48.5 ± 1.91 c | | 1.59 ± 0.084 d | | 0.445 ± 0.0192 c | | 0.00018 ± 0.000041 b | | 0.00138 ± 0.000213 d |
| 1 | 36.3 ± 2.50 b | | 94.5 ± 4.12 a | | 1.70 ± 0.174 cd | | 0.517 ± 0.0407 b | | 0.00024 ± 0.000022 a | | 0.00168 ± 0.000457 d |
2 | 2 | 31.0 ± 1.83 c | | 53.3 ± 4.27 c | | 2.46 ± 0.115 b | | 0.550 ± 0.0283 b | | 0.00017 ± 0.000021 bc | | 0.00260 ± 0.000141 c |
| 3 | 43.8 ± 1.26 a | | 94.8 ± 2.75 a | | 2.66 ± 0.077 a | | 0.384 ± 0.0214 d | | 0.00014 ± 0.000017 c | | 0.00475 ± 0.000480 b |
Means (± SD, n = 4) with the same letter are not different significantly according to LSD test (P < 0.05). |
¶ Treatments are: S1, non-water stress condition; S2, water stress condition; S1, 0 mMnano SiO2; S2, 50 mMnano SiO2; and S3, 100 mMnano SiO2. |
Abbreviations are: plant height (PH), root length (RL), root volume (RV), shoot dry weight (SDW), root dry weight (RDW), chlorophyll a (Chl a), chlorophyll b (Chl b), relative water content (RWC), electrolyte leakage (EL), Ascorbate peroxidase (APX) and glutathione peroxidase (GPX). |
The SDW and RDW are not affected by water stress and application of SiO2 nanoparticles decreased both shoot and root dry weights at both stress and non-stress conditions (Table 4).The tomato shoots dry weight reduces under drought stress while silicon application can improve SDW up to 36%, and similarly the root dry weight was decreases under water stress but silicon application can improve RDW up to 38%29.The SiO2 nanoparticles application could notincreaseprolinecontents in both conditions (Table 4),while we expectedprolineincreases under stress conditions and protects plant from harmful effect of drought. In most studies, it has been indicated that stress-induced variations in proline are responsible with the capability of plant species to show drought tolerance21, but we cannot find such phenomena in this research.Application of 100 mMnano SiO2 could compensate the adverse effects of water stress in both chlorophyll contents, Chl-a andChl-b(Table 4). According to Ashkavandet al.31, chlorophyll contentsin Prunusmahalebwithout application of SiO2 nanoparticles decreased by 33% under drought stress but using of SiO2 nanoparticlescouldmaintain chlorophyll contents inseedlings subjected to drought.
The SiO2 nanoparticles treated plants decreased the RWC in both non-stress and stressful conditions while EL is decreased by usage of the SiO2 nanoparticles in both non-stress and stressful conditions (Table 4).According to Siddiqui et al.32, xylem water potential is reduced by usage of the SiO2 nanoparticles and RWC has important rolein this capability, thus the SiO2 nanoparticles could not maintain RWC in normal levels because under drought conditions, cell membranes are exposed to changes which can be observedvia electrolyte leakage increase. Similarly, we foundan increase of electrolyte leakage under water stress, which purpose the take place of remarkable harmful to cell membranes and in this research, we foundthat the SiO2 nanoparticles could compensate this adverseimpact.
Application 50mMnano SiO2 enhanced anthocyanins under non-stress condition but treating with the SiO2 nanoparticles could not influence positively, anthocyanins’ magnitudes under drought conditions (Table 4).Plant cells with anthocyanins are tolerant to abiotic stresses which shows its defensive role in plants33, and it is expected that the SiO2 nanoparticles increase the production of such compounds and enhance the plant potential to stress tolerance, but we cannot find such capability in this study.The significant differences for CAT were observed in tomato seedlings with the nano SiO2 application and the higher CAT activity was seen in seedlings grown under water stress and treated with the 100 mMnano SiO2 followed by stressed plants which treated with the 100 mMnano SiO2(Table 4).To compensate the harmful impacts of reactive oxygen species, plants develop antioxidant enzymes such as CATthat scavenge extrareactive oxygen species under stress conditions34, and usage of nano SiO2 cause to more production of such antioxidant enzymes which result in high tolerance to stresses.There are some physiological tools for improving drought tolerance such as classicgenetic improvement program, developing polyploid lines, creation of mutantlines and developing of transgenic cultivars which can be used for cultivation of drought tolerant cultivars under water shortage environments.
Application of 100 mMnano SiO2 enhanced Na and K contents as well as phenols under water-stress condition (Table 4), thus this treatment could eliminate the adverse effect of drought stress.According to Kang et al.35, one of the important mechanisms for drought tolerance of plants is their potential to absorb and stack a large amounts of Na ions as an osmoregulator, and maintain their abilityto absorb and stack silicon dioxide to defense with drought stress.Thus, the exploring that a field crop can restrain Na ion and silicon dioxide to better ensure its performance under drought stress is important and get a novel way for the genetic improvement of crops for economic yield production in arid and semi-arid environments.The S1Si1 (non-water stress condition and application of 100 mMnano SiO2) and S1Si2 (water stress condition and application of 100 mMnano SiO2) had high magnitudes of APX enzyme (Table 4). The application of nano SiO2 significantly decreased APX at both stress and non-stress conditions and could not affect positive effect of APX production in spite of our expectation. In contrast to APX, the nano SiO2 significantly increased GPX at water stress condition butdecreased at non-stress conditions. We found, GPX activity in tomato seedlings increased when the nano SiO2 applied under water stress and regardingthe GPX defensive role by H2O2removing, it seems that GPX can maintain the usable of cell membrane under stress like tostudies of Madanyet al.36in tomato andSutulienė et al.37 in green pea (Pisumsativum L.).
P. indicaversus nano SiO2.Comparison of two trials can be interesting, thus clear differences in some traits two treatments strategies were compared.In catalase enzyme, the P. indica mycelium inoculation enhanced antioxidant response in water stress of tomato greater than the spore form of P. indica inoculation followed by application of 100 mMnano SiO2 (Fig. 1). Both forms of P. indica had significantly greater positive effects in catalase production which accelerate drought tolerance in plants. According to Tahmasebi-Shamansouriet al.38, both silicon and root fungi cause to stress tolerance in plants and production more yield performance but the positive effects of fungi is better than silicon. Using natural fungi instead of artificial chemicals is more acceptable due to environmental concerns and human health issues.The P. indicaspore inoculation had better performance in Chl-b in comparison to the 100 mMnano SiO2, while mycelium form of the P. indica showed relatively the same performance with the 100 mMnano SiO2in phenol concentration (Fig. 2). Increase crop yield could be associated to higher photosynthetic pigments content and high levels of phenol concentration which can be induced stress tolerance in plants39.
Under water stress conditions, application of the 100 mMnano SiO2could produce more root volume and root dry weight while it is expected that root related traits indicate more positive response to the P. indica inoculation as soil and root adapted fungi (Fig. 3).Similar reports about SiO2 nanoparticles were reported by Ivaniet al.40, who indicated that applying nano SiO2 improved dry weight of root and root volume while its application had no toxic effect on growth. Also, the positive impact of the P. indica inoculation on root related characteristics were demonstrated41. The P. indica spore inoculation had better effect in protein content and anthocyanin in comparison to the 50 mMnano SiO2 (Fig. 4), while mycelium form of the P. indica and the 100 mMnano SiO2 did not indicate such positive effects.