Abstract
Zinc (Zn) deficiency in major food crops has been considered as an important factor affecting the crop production and subsequently the human health. Rice (Oryza sativa) is sensitive to Zn deficiency and thereby causes malnutrition to most of the rice-eating Asian populations. Application of zinc solubilizing bacteria (ZSB) could be a sustainable agronomic approach to increase the soil available Zn which can mitigate the yield loss and consequently the nutritional quality of rice. Understanding the molecular interactions between rice and unexplored ZSB is useful for overcoming Zn deficiency problems. In the present study, the role of zinc solubilizing bacterial strain Enterobacter cloacae strain ZSB14 on regulation of Zn-regulated transporters and iron (Fe)-regulated transporter-like protein (ZIP) genes in rice under iron sufficient and deficient conditions was assessed by quantitative real-time reverse transcription PCR. The expression patterns of OsZIP1, OsZIP4, and OsZIP5 in root and shoot of rice were altered due to the Zn availability as dictated by Zn sources and ZSB inoculation. Fe sufficiency significantly reduced the root and shoot OsZIP1 expression, but not the OsZIP4 and OsZIP5 levels. Zinc oxide in the growth medium up-regulated all the assessed ZIP genes in root and shoot of rice seedlings. When ZSB was inoculated to rice seedlings grown with insoluble zinc oxide in the growth medium, the expression of root and shoot OsZIP1, OsZIP4, and OsZIP5 was reduced. In the absence of zinc oxide, ZSB inoculation up-regulated OsZIP1 and OsZIP5 expressions. Zinc nutrition provided to the rice seedling through ZSB-bound zinc oxide solubilization was comparable to the soluble zinc sulfate application which was evident through the ZIP genes’ expression and the Zn accumulation in root and shoot of rice seedlings. These results demonstrate that ZSB could play a crucial role in zinc fertilization and fortification of rice.
Highlights
Zinc (Zn) is a critical micronutrient responsible for several cellular functions in plant and its deficiency causes decrease in plant growth and yield
When zinc solubilizing bacteria (ZSB)-inoculated seedlings were assayed for OsZIP1 expression after 7 days (14 days-old seedlings), the expression pattern of root OsZIP1 was different than the earlier (Figure 1B)
Keeping in view the unambiguous benefits of ZSB (Hafeez et al, 2013), through the present investigation, we reported that ZSB inoculation to rice could alter the expression of zinc transporting genes of rice based on the Zn solubilization and thereby regulate the uptake of zinc
Summary
Zinc (Zn) is a critical micronutrient responsible for several cellular functions in plant and its deficiency causes decrease in plant growth and yield. Zn deficiency in major food crops, apart from yield loss, reduced the Zn content of grains and subsequently causes serious problems in human nutrition. 50% of the rice-growing soils are under Zn-deficient and rice grown on these soils generally produce low yield with poor nutritional quality. Zn-sufficient rice had about 40 mg/kg of Zn in its grains, whereas Zn-deficient rice accumulated less than 10 mg/kg of grain-Zn (Wissuwa et al, 2008). Agricultural intensification, imbalanced nutrients and neglected micronutrient application further worsen the Zn-deficiency problem in rice. Zinc deficiency in rice is becoming one of the public health problems through malnutrition in many rice-based food adopting countries of Asia (Cakmak, 2008)
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