Objective  Effects of ABA spray on endogenous hormones in Camellia reticulata seedlings under drought stress were studied.

  Methods   An ABA solution in the concentration of 100 mg·L⁻¹ was sprayed on the leaves of 2-year-old C. reticulata Zipao seedlings grown in potting soil under a simulated drought stress using PEG_6000. Osmoregulatory substances and hormone metabolome in the roots and leaves of the plants were measured under the treatment and subsequent rehydration.

  Results  Osmotic regulation of the seedlings took place mainly in the leaves. Under drought stress, ABA, JA , SA ,IAA, and CKs accumulated in the leaves, while ABA, GA , and CKs increased but IAA decreased in the roots. Upon rehydration, ABA, GA, and CKs in the roots gradually declined, while IAA rose, meanwhile, the leaves started regulating with the stored JA, SA, IAA, and CKs. The KEGG enrichment analysis showed that the diterpene biosynthesis pathway in the roots and the hormone signal transduction and zein biosynthesis pathways in the leaves were significantly enhanced. There was a significant correlation between the osmoregulatory substances and endogenous hormones. The ABA spray boosted the contents of soluble protein, soluble sugar, ABA, GA, and CKs in the roots as well as those of free proline, ABA, and JA in the leaves improving the drought tolerance of the plant. With replenished water, CKs in the roots and JA in the leaves were reduced to encourage IAA synthesis, which in turn, aided the recovery of plant functions.

  Conclusion   The responses of the roots and leaves of C. reticulata seedlings to the imposed drought and the subsequent rehydration were different. Application of foliar ABA spray could improve the draught resistance of the plants.