Objective Potential of applying an endophyte in plant roots, Piriformospora indica (Pi), to mitigate the ill-effect of excessive usage of plant growth regulators on rice paddies was investigated.
Method Rice seedlings were hydroponically grown in a nutrient solution for 15 d. The height and chlorophyll content of the plants as well as the length, number, and vitality of the roots were monitored. ROS in the leaves was examined by a staining method. Effects of 2,4-D or PP333 treatment with or without Pi addition on the activities of antioxidant enzymes (i.e., SOD, POD, and CAT) in leaves were determined.
Result Excessive applications of plant growth regulator can adversely affect or even retard the growth of rice plants. This study revealed that if a rice plant was inoculated with Pi it could become less vulnerable to the stress. Comparing 2,4-D treatment without Pi addition, the seedlings grew 26.02% taller, the roots 17.27% longer, the root count 30.77% more, the chlorophyll content 64.71% higher, and the root vitality 43.72% greater with the Pi addition. In the Pi+PP333 group, the plants were 36.79% taller and 23.64% higher in root vitality than without the presence of Pi. The leaf ROS of the rice seedlings increased with Pi, 2,4-D or PP333 in the nutrient solution. Either 2,4-D or PP333 treatment enhanced the SOD, POD and CAT activities, but the Pi inoculation did not exert any significant differences on them.
Conclusion It appeared that P. indica could indeed alleviate the stress imposed on rice plants due to overuse of plant growth regulators. By inoculating Pi in the medium, the rice plants could overcome the interference by 2,4-D or PP333, grow well, and develop a robust root system. Restoration of the antioxidant system in rice by Pi might allow the plant to effectively mitigate the ill caused by over-exposure of plant growth regulators.
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