Endophytic infection modifies organic acid and mineral element accumulation by rice under NaCO stress

Background and aims: Saline and alkali soils severely impact plant growth. Endophyte and plant associations are known to significantly modify plant metabolism. This study reports the effects of a type of endophyte on organic acid (OA) accumulation and ionic balance in rice under NaCO stress. Methods: Rice seedlings with (E+) and without (E-) endophytic infection were subjected to different levels of NaCO stress (0, 5, 10, 15, and 20 mM) for two weeks. Organic acids and mineral elements in the leaves and roots were determined. Results: Seedlings with endophytic infection accumulated mainly citrate and fumarate, with some malate and succinate in the leaves. In the roots, accumulation of malate and fumarate was enhanced significantly by endophytic infection, while less citrate and succinate was accumulated under NaCO stress, which suggested that leaves and roots use different mechanisms to control OA metabolism. Endophytes reduced the total Na and Na:K ratios, but increased ST values, the percent changes of other measured nutrients, Chl content, and dry weight per plant under NaCO stress. Conclusions: Endophytic infection plays a key role in maintaining plant growth by improving nutrient uptake and adjusting OA accumulation under NaCO stress. The application of endophytes can enhance the resistance of rice to salinity.