Physiological responses of Lonicera japonica container seedlings to plant growth-promoting rhizobacteria inoculation under drought stress
Plant growth-promoting rhizobacteria (PGPR) are rhizosphere inhabitants that promote plant growth and suppress diseases.One of the proposed mechanisms through which PGPR enhance plant growth is the production of plant growth regulators, especially cytokinin.However, little information is available about the effects of cytokinin-producing PGPR inoculation on the drought stress response.Soil water availability is a crucial determining factor of plant yield, because drought stress inhibits stem elongation, leaf expansion, and stomatal movement.Therefore, a strain of rhizobacteria with a high rate of cytokinin production, Bacillus cereus L90, was selected for use in this investigation.The bacteria were obtained from the rhizosphere of a walnut tree, where water is limited and frequent dry periods occur.Serial dilution and a bioassay for the detection of cytokinin production were both used to isolate and screen the bacterial strain from the soil sample.This study investigated how PGPR affects the physiological characteristics of Lonicera japonica Thunb.under different drought stress treatments (light, moderate, severe, and a control).The combined effects of B.cereus L90 inoculation and various levels of drought stress on the photosynthetic characteristics, chlorophyll fluorescence parameters, photosynthetic pigment, cytokinin and ABA(abscisic acid) concentrations, relative water content, and relative electrolyte leakage were studied using the pot method.The results showed that the net photosynthetic rate and stomatal conductance decreased with increasing drought stress.However, B.cereus L90 inoculation was associated with an increase in stomatal conductance and net photosynthetic rate in plants under drought stress.B.cereus L90 inoculation reduced the negative impact of drought stress on the maximum photochemical efficiency of PS Ⅱ, the actual photochemical efficiency of PS Ⅱ, and the photochemical quenching coefficient.B.cereus L90 inoculation also prevented the non-photochemical quenching coefficient from increasing.Although no significant difference was observed under well-watered conditions, the leaves of inoculated drought-stressed L.japonica seedlings had higher photosynthetic pigments contents compared to those of noninoculated seedlings.The roots of inoculated L.japonica seedlings had higher ABA content compared to non-inoculated seedlings.The elevated levels of cytokinins in L.japonica leaves and the higher concentration of ABA are both associated with drought stress.B.cereus L90 inoculation significantly increased the cytokinin content of drought-stressed L.japonica leaves, and improved the rate of transportation of ABA from the roots to the leaves.No significant differences in relative water content and relative electrical conductance were observed between inoculated and non-inoculated seedlings under light drought stress.Compared to the irrigated control, under severe drought stress, the relative water content of non-inoculated seedlings decreased by 20.56％, while that of inoculated seedlings decreased by 10.21％.However, the relative electrical conductance of inoculated and non-inoculated seedlings under severe drought stress increased by 31.42％ and 16.08％, respectively.These results demonstrate that inoculation of B.cereus L90 under drought stress increases the cytokinin content of L.japonica leaves, and interferes with the suppression of photosynthetic pigments and net photosynthetic rate.Thus, B.cereus L90 inoculation could improve the adaptability ability of L.japonica seedlings to drought conditions.In conclusion, inoculation of cytokinin-producing PGPR could be used to alleviate drought stress and interfere with the suppression of physiological processes, showing real potential for practical use in arid environments as a drought stress inhibitor.
国家科技期刊平台
NSTL
万方数据
维普
