TiO2 nanomaterial promotes plant growth and disease resistance

Abstract

TiO₂ nanomaterials can promote plant growth and enhance disease resistance. However, the underlying mechanism remains unclear. This study applied TiO₂ to promote the growth of wheat, soybean, tobacco, cucumber, and corn. Genetic analysis using macro-element transporter rice mutants in rice revealed that growth promotion induced by TiO₂ was dependent on potassium transporter (AKT1), nitrate transporter 1.1B (NRT1.1B), ammonium transporter 1 (AMT1), and phosphate transporter 8 (PT8). TiO₂ also enhanced chlorophyll accumulation, and growth promotion was inhibited in the chlorophyll biosynthesis rice mutants, yellow-green leaf 8 (ygl8) and divinyl reductase (dvr), indicating that TiO₂ promoted growth through chlorophyll biosynthesis. In addition to photosynthesis, TiO₂ affected light signaling by inhibiting the translocation of Phytochrome B (PhyB) from the cytosol to the nucleus, thereby improving resistance to rice sheath blight (ShB). TiO₂ application also enhanced resistance to wheat stem rust, tobacco wildfire, angular spot disease, and rice ShB by inhibiting the growth of bacterial and fungal pathogens, suggesting that TiO₂ regulates plant defense signaling and has antibacterial and antifungal effects. Field experiments with wheat, soybeans, and rice confirmed that TiO₂ treatment significantly increased the crop yield. These findings suggest that TiO₂ is a promising nanomaterial for the simultaneous enhancement of plant growth and disease resistance.

Keywords: TiO2; disease resistance; nutrient uptake; plant growth promoting; yield increase.

Figure 1.

Growth-promoting effect of TiO₂ on crops. (a) Rice seedlings were grown in liquid MS solution containing 72, 36, 18, and 9 ppb TiO₂ for 7 d, respectively. (b) Shoot and (c) root lengths of the rice shown in (a). (d) TiO₂ (9 ppb) was sprayed on the wheat to treat them. Seven-day-old wheat was photographed, and (e) the height of the wheat shown in (d) was calculated. (f) TiO₂ (9 ppb) was sprayed on the corn. Seven-day-old corn was photographed, and (g) the height of the corn shown in (f) was calculated. (h) TiO₂ (9 ppb) was sprayed on the soybean. Seven-day-old soybeans were photographed, and (i) the height of the soybeans shown in (g) and the relative leaf area (J) shown in (H) were calculated. (k) TiO₂ (9 ppb) was sprayed on the tobacco. Fourteen-day-old tobacco plants were photographed and (l) the height of the tobacco shown in (k) was calculated. (m) TiO₂ (9 ppb) was sprayed on the cucumber. Seven-day-old cucumbers were photographed, and (n) the height of the cucumbers shown in (M) was calculated. Data are presented as mean ± standard error (SE) (n > 10). Significant differences are denoted by asterisks (*p < 0.05, **p < 0.01, ***p < 0.001). ns: no significant difference. Scale bars = 1 cm.

Figure 2.

The promotion of rice growth by TiO₂ is related to the absorption of nutrient elements. (a) ZH11 and nrt1.1b grown for 7 d in the liquid MS solution with or without 9 ppb TiO₂ were photographed. (b) The growth-promotion rate of the rice shoots shown in (a) was calculated. (c) The growth-promotion rate of the roots in (a). (d) Morphology of Nip and pt8 in MS nutrient solution containing 9 ppb TiO₂ or without TiO₂ for 7 d. (e) The growth-promotion rate of the shoots in (d). (f) The growth-promotion rate of the roots in (d). (g) Morphology of DJ, AMT1 RNAi, and akt1 in MS nutrient solution containing 9 ppb TiO₂ or without TiO₂ for 7 d. (h) The growth-promotion rate of the shoots in (g). (i) The growth-promotion rate of the roots in (g). Data are presented as mean ± standard error (SE) (n > 10). Significant differences are denoted by asterisks (*p < 0.05, **p < 0.01, ***p < 0.001). ns: no significant difference. Scale bars = 1 cm.

Figure 3.

TiO₂ improves disease resistance in plants. Plants were treated with 9 ppb TiO₂ before inoculation. (a) Morphology of wheat leaves after inoculation with Pgt. (b) Lesion area of wheat shown in (a) was calculated. (c) Morphology of rice leaves after inoculation with R. solani AG1-IA. (d) Lesion length of the rice shown in (c) was calculated. (e) Morphology of tobacco leaves inoculated with Pst W11. (f) Relative lesion area of the tobacco shown in (e) was calculated. (g) Morphology of tobacco leaves after inoculation with Psa 1-J. (H) Relative lesion area of tobacco shown in (g) was calculated. (i) Morphology of tobacco leaves after inoculation with Pst ZD. (j) Relative lesion area of the tobacco shown in (i) was calculated. (k) Morphology of tobacco leaves inoculated with Pst D151. (l) Relative lesion area of tobacco shown in (k) was calculated. Data are presented as mean ± standard error (SE) (n > 8). Significant differences are denoted by asterisks (*p < 0.05, **p < 0.01, ***p < 0.001). ns: no significant difference. Scale bars = 1 cm.

Figure 4.

Antifungal activity of TiO₂. (a) Cultures of different fungi grown on PDA plates treated with 9 ppb of TiO₂. (b) Colony diameter of Fusarium verticillioides (a), (c) Exserohilum turcicum, (d) Botryosphaeria dothidea, (e) Sclerotium rolfsii, (f) R. solani AG1-IA, (G) Alternaria alternata shown in (a) were calculated. Different letters above the bars indicate significant differences (p < 0.05). Scale bars = 1 cm.

Figure 5.

Antifungal and antibacterial activities of TiO₂. (a) The OD₆₀₀ growth rate of Pst ZD, (b) Pst D151, (c) Pst W11, (d) Psa 1-J, (e) PXO^99A, and (f) Ustilago maydis was calculated after being inoculated with 72, 36, 18, and 9 ppb TiO₂ for 12 h. (g) The OD₆₀₀ growth rate of Pst ZD, (h) Pst D151, (i) Pst W11, (j) Psa 1-J, (k) PXO^99A, and (l) Ustilago maydis was calculated after being inoculated with 72, 36, 18, and 9 ppb TiO₂ for 24 h. Different letters above the bars indicate significant differences (p < 0.05).

Figure 6.

TiO₂ improves the chlorophyll content of rice and inhibits PhyB translocation from the cytosol to the nucleus. (a) Chlorophyll content was measured after 14 d of 9 ppb TiO₂ treatment. Fig. 6 TiO₂ improves the chlorophyll content of rice and inhibits PhyB translocation from the cytosol to the nucleus. (a) Chlorophyll content was measured after 14 d of treatment with 9 ppb TiO₂. (b) Total chlorophyll content of rice grown in MS liquid medium containing 9 ppb TiO₂ for 14 d. (c) Seven-day-old SH498, dvr, and ygl8 seedlings were grown in MS solution with or without 9 ppb TiO₂. (d) Growth-promotion rate of shoots in (c). (e) Growth-promotion rate of roots in (c). (f) Seven-day-old germinated DJ and gs1;1 seedlings were transferred to MS nutrient solution with or without 9 ppb TiO₂. (g) Growth-promotion rate of shoots in (f). (h) Growth-promotion rate of roots in (f). (i) Distribution of PhyB protein in rice PhyB-OX treated with 9 ppb TiO₂ for 7 d. (j) Total protein content. (k) Grayscale value of (l). Data are presented as mean ± standard error (SE) (n > 8). Significant differences are denoted by asterisks (*p < 0.05, **p < 0.01, ***p < 0.001). ns: no significant difference.

Figure 7.

TiO₂ increases rice, soybean, and wheat yields. (a)–(d) Field-grown wheat, soybean, and rice following TiO₂ treatment were photographed. (e) Height of wheat, (f) spike length, (g) weight per spike, (h) number per spike, and (i) thousand-grain weight of wheat after TiO₂ treatment. (j) Height of soybean, (k) yield per soybean plant, (l) number of pods per soybean, (m) total number of seeds per soybean, and (n) hundred grain weight of soybean after TiO₂ treatment. (o) Tiller number, (p) number of filled grains per panicle, (q) thousand-grain weight number of filled grains per panicle, and (R) yield per plant of rice after TiO₂ treatment. Data are presented as mean ± standard error (SE). Significant differences are denoted by asterisks (*p < 0.05, **p < 0.01). ns: no significant difference.

Figure 8.

Working model of TiO₂ in promoting plant growth and resistance: TiO₂ inhibits the nuclear import of PhyB and promotes the resistance of rice to ShB. TiO₂ mediates the activation of nitrogen, phosphorus, and potassium absorption as well as photosynthesis to enhance plant growth. TiO₂ promotes the growth of wheat, corn, tobacco, soybeans and cucumbers at the seedling stage. TiO₂ directly inhibits growth of pathogenic fungi and bacteria. Furthermore, TiO₂ inhibits PhyB translocation from the cytosol to the nucleus, thereby enhancing the resistance of rice to ShB.