Promotive effects of endophytic rhizobacteria on tiller and root growth in creeping bentgrass during drought stress and post-stress recovery involving regulation of hormone and sugar metabolism

Stress-induced accumulation of ethylene exacerbates drought damages in plants and suppressing stress induction of ethylene may promote plant tolerance to drought stress. The objective of this study was to investigate the effects of endophytic bacteria (Paraburkholderia aspalathi) with 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase enzymes in suppressing ethylene production on plant tolerance to drought stress and post-stress recovery and the underlying physiological mechanisms of P. aspalathi-regulation in creeping bentgrass (Agrostis stolonifera L.). A novel strain of P. aspalathi, "WSF23," with ACC deaminase activity was used to inoculate the roots of creeping bentgrass plants (cv. "Penncross") subjected to drought stress for 35 days and rewatered for 15 days (post-stress recovery) in controlled-environment growth chambers. Inoculation with WSF23 bacteria resulted in an increased number of tillers, tillering production rate, root viability, and root growth (quantified in length, surface area, volume, and dry weight) during drought stress or rewatering. Inoculation of plants with WSF23 bacteria increased cytokinin (CK) (c-Zeatin and tZ-riboside) and jasmonate (JA-Ile) content and reduced ACC and abscisic acid (ABA) content in roots during drought or rewatering. Sugar accumulation in crowns was promoted by inoculation during drought stress. The differential changes in ACC, CK, ABA, and JA-Ile and sugar accumulation due to the bacterial inoculation could contribute to ACC deamination bacteria-improved drought tolerance and post-stress recovery in terms of tiller production and root proliferation and elongation in creeping bentgrass.