Regulation of Chloroplast ATP Synthase Modulates Photoprotection in the CAM Plant Vanilla planifolia.

Generally, regulation of cyclic electron flow (CEF) and chloroplast ATP synthase play key roles in photoprotection for photosystems I and II (PSI and PSII) in C3 and C4 plants, especially when CO2 assimilation is restricted. However, how CAM plants protect PSI and PSII when CO2 assimilation is restricted is largely known. In the present study, we measured PSI, PSII, and electrochromic shift signals in the CAM plant Vanilla planifolia. The quantum yields of PSI and PSII photochemistry largely decreased in the afternoon compared to in the morning, indicating that CO2 assimilation was strongly restricted in the afternoon. Meanwhile, non-photochemical quenching (NPQ) in PSII and the donor side limitation of PSI (Y(ND)) significantly increased to protect PSI and PSII. Under such conditions, proton gradient (∆pH) across the thylakoid membranes largely increased and CEF was slightly stimulated, indicating that the increased ∆pH was not caused by the regulation of CEF. In contrast, the activity of chloroplast ATP synthase (gH+) largely decreased in the afternoon. At a given proton flux, the decreasing gH+ increased ∆pH and thus contributed to the enhancement of NPQ and Y(ND). Therefore, in the CAM plant V. planifolia, the ∆pH-dependent photoprotective mechanism is mainly regulated by the regulation of gH+ rather than CEF when CO2 assimilation is restricted.

[Screening, identification, and biocontrol effect of antagonistic bacteria against Phytophthora capsici].

A total of 98 isolates with antagonistic activity against Phytophthora capsici were isolated from the rhizosphere soil of healthy pepper plants in the fields seriously infected by pepper Phytophthora capsicit, and two strains named as HL-3 and LZ-8 were screened, which had the characteristics of wide-spectrum antagonism and good growth under poor soil condition. The HL-3 and LZ-8 were identified as Paenibacillus polymyxa and Bacillus pumilus, respectively, based on their morphological and biochemical characteristics and 16S rDNA sequences. The two strains could inhibit the mycelium growth of P. capsici, and the inhibitory effect of HL-3 and LZ-8 was 72% and 68%, respectively. The two strains also had antifungal activities toward other plant pathogens such as Verticillium dahliae, Fusarium oxysporum f. sp. cucumerinum, F. oxysporum f. sp. vasinfectum, Rhizoctonia solani, Phtophthora parasitica var. nicotiana, and Ralstonia solanacearum. Pot experiment showed that the biocontrol effects of HL-3 and LZ-8 against P. capsici at the seedling stage of pepper were 72% and 83%, respectively, and both of the strains had significant growth-promoting effect on pepper plants.