金银花容器苗对干旱胁迫下接种根际促生细菌的生理响应

Physiological responses of Lonicera japonica container seedlings to plant growthpromoting rhizobacteria inoculation under drought stress

在盆栽试验条件下,以金银花容器苗为试材,研究了不同干旱强度下接种蜡样芽孢杆菌(Bacillus cereus)L90对植物生理特征的影响。结果表明:随着干旱胁迫强度的增加,金银花容器苗的光合速率和气孔导度逐渐降低;而干旱环境下接种L90可显著提高气孔导度,缓解干旱胁迫对净光合速率的抑制;且干旱强度增加,缓解效果增强。接种B.cereus L90可显著抑制干旱胁迫下金银花容器苗PSⅡ最大光化学效率、实际光化学效率和光化学猝灭系数的降低,抑制非光化学猝灭系数的升高。虽然L90并没有提高对照处理中光合色素的绝对含量,但可显著抑制干旱环境下金银花叶片中光合色素的分解。干旱显著降低了金银花叶片中细胞分裂素含量,增加了脱落酸(ABA)的含量;在干旱胁迫下,接种L90可显著提高叶片中细胞分裂素的含量,并可促使根部产生的ABA运输到叶片中。干旱胁迫程度较轻时,L90对金银花容器苗的相对含水量和相对电导率影响不显著;而在重度干旱时,同对照相比,干旱及接种L90处理的相对含水量分别降低20.56%和10.21%,相对电导率分别提高31.42%和16.08%,接种L90处理的变化幅度明显较小。因此,干旱生境下接种B.cereus L90,可增加叶片中细胞分裂素含量,抑制光合色素的分解及光合能力的下降,提高金银花容器苗在干旱环境中的适应能力。

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-produeing 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 rhizobaeteria with a high rate of eytokinin 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 Lg0 inoculation was associated with an increase in stomatal conductance and net photosynthetic rate in plants under drought stress. B. cereus Lg0 inoculation reduced the negative impact of drought stress on the maximum photochemical efficiency of PS I1 , the actual photochemical efficiency of PS 11 , 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 non- inoculated 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.