Abstract
This study was to investigate the effects of three exogenous substances on chemical constituents of Isatis indigotica leaves and their efficacy in alleviating drought stress, and explore the methods of applying exogenous substances to efficient cultivation of Isatis indigotica. Polyethylene glycol (PEG) was used to simulate drought stress to deal with seeds of Isatis indigotica at the germination stage (concentration: 0, 10％, 15％, and 20％). Simultaneous operation of exogenous growth regulators [microbial inoculum (MI), γ-aminobutyric acid (GABA) and salicylic acid (SA)] and PEG were implemented in seeds of Isatis indigotica. The effects of drought stress and the mitigation of exogenous substances were observed by statistics of seed germination potential, germination rate, hypocotyl length, and radicle length of each treatment. The effects of exogenous substances on the content of alkaloids, crude protein and free amino acids in the leaves of Isatis indigotica grown in a greenhouse were determined after spraying exogenous substances on the plants. The differences of germination potential, germination rate, hypocotyl length, and radicle length among 15％ PEG stress treatment, 10％ PEG stress treatment and the control were significant (P<0.05). According to the predesigned germination standard, the seeds did not germinate under 20％ PEG stress treatment. When the PEG concentration was 15％, the results of seed germination potential and germination rate after adding MI were significantly different from those under stress alone (P<0.05). When exposed to 10％ PEG stress, the supplementation of GABA led to a notable increase in radicle length of Isatis indigotica seeds, showing significant differences compared to other three treatments. The application of MI and GABA under 15％ PEG stress resulted in a significant increase in the radicle and hypocotyl length of Isatis indigotica seeds compared to other two treatments. The content of the total alkaloids in leaves of Isatis indigotica was significantly increased after spraying GABA. Meanwhile, the contents of crude protein and the total free amino acids were kept constant after spraying exogenous substances. Application of MI and GABA could alleviate drought stress of Isatis indigotica. The content of the total alkaloids in leaves of Isatis indigotica could significantly increase after spraying GABA.
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