Plant Growth-Promoting Activity of Herbaspirillum aquaticum ZXN111 on the Zijuan Tea Plant ( Camellia sinensis var. assamica ).

Herbaspirillum aquaticum ZXN111 which was isolated from the tea plant Zijuan can produce indole-3-acetic acid (IAA) and contain abiotic-stress tolerance gene 1-aminocyclopropane-1-carboxylate deaminase ( accd ). In this study, ZXN111 PGP activity and the molecular mechanism were investigated. The result showed that ACCD activity of wild-type ZXN111 was 0.4505 mM α-KB/mg·Pro·h, but mutants Δ acc and Δ acc - tyrb did not showed ACCD activity. IAA production by ZXN111 within 48 hrs was 20.4 μg/mL, while mutants of Δ tyrb and Δ acc - tyrb were lower than 3.6 μg/mL, indicating that indole-3-pyruvic acid is the primary IAA synthesis pathway. Potting tests found that ZXN111 displayed significant PGP activity to the tea plant Zijuan, but Δ tyrb and Δ acc - tyrb did not show PGP activity, indicating that IAA is critical to PGP activity. In a salt-stress test, ZXN111 did not enhance the tea plant NaCl tolerance by gene accd . The results of this study indicated that strain ZXN111 has potential for biofertilizer development on tea plantation.