Figure 1.
BBS inducing drought tolerance in cucumber plants.
The cell suspension of BBS and sterile water were poured on the soil around cucumber roots in the BBS treatment (BBS) and the control (CK), respectively, and then watering was withheld for 13 days.
Figure 2.
Effects of BBS on physiological indicators of cucumber drought tolerance.
The cell suspension of BBS and sterile water were poured on the soil around cucumber roots in the BBS treatment (BBS) and the control (CK), respectively, and then watering was withheld for 13 days. The leaf MDA content (A), the leaf relative electrical conductivity (B), and the leaf proline content (C), the root recovery intension (D), and the leaf chlorophyll content (E) of cucumber plants under drought stress were determined at 13 dpi. Each treatment was replicated three times; data are presented as means of three replicates ± SD, and error bars represent SD for three replicates. Means with different letters have significant differences (p<0.05; LSD test).
Figure 3.
Effects of BBS on the expression of the rbcS, rbcL, and cAPX genes.
The cell suspension of BBS and sterile water were poured on the soil around cucumber roots in the BBS treatment (BBS) and the control (CK), respectively, and then watering was withheld for 13 days. A, The expression of the genes rbcS, rbcL and cAPX was detected at 0, 5, 7, 9, 11, and 13 dpi by RT-PCR. B, Relative mRNA levels of genes based on Quality One software of Bio-Rad. Each treatment was replicated three times. dpi, day post inoculation; Actin, internal reference.
Figure 4.
Effects of BBS on SOD, POD, and CAT activities.
The cell suspension of BBS and sterile water were poured on the soil around cucumber roots in the BBS treatment (BBS) and the control (CK), respectively, and then watering was withheld for 13 days. The leaf SOD, POD, and CAT activities in cucumber plants under drought stress were determined at 0, 5, 7, 9, 11, and 13 dpi. Each treatment was replicated three times; data are presented as means of three replicates ± SD, and error bars represent SD for three replicates. (p<0.05; LSD test).
Figure 5.
Detection of ACC deaminase activity in three BBS constituent strains and Burkholderia sp. 5BS21.
After grown in MSA medium with ACC (ACC+) or without ACC (ACC−) for 48 h, bacterial cells of Burkholderia sp. 5BS21 (5BS21) and of the three BBS constituent strains Bacillus cereus AR156 (AR156), Bacillus subtilis SM21 (SM21), Serratia sp. XY21 (XY21) were centrifuged at 14000× g for 5 min. Then 5 µL of the supernatant resulting from each culture was spotted on a TLC silica gel plate with 5 µL of MSA medium with ACC (ACC+) and 5 µL of that without ACC (ACC−) as controls. The gel was developed for 2.5 h and then stained with 0.5% ninhydrin for 20 min in an attemperator set at 100°C.
Figure 6.
BBS consortium induced systemic tolerance to drought stress in cucumber plants.
BBS strains colonized the cucumber roots, maintained a high level of root vigor to protect the root from destroy. Solid arrows indicate plant compounds affected by BBS components. The signal mobilized from the roots to the leaves, which kept SOD activity, proline content, chlorophyll content at higher levels, and kept MDA content at a lower level, to protect the integrity of plant cells, and to release oxidative stress and to remain photosynthesis, leading induced drought tolerance.