Abstract
There believed to be around 108-9 of bacteria present per gram of soil. Therefore, it is inevitable for plants to encounter with various soil bacteria during root development. Previous reports demonstrate that plants have evolved systems that sense and respond to environmental stimuli including soil bacteria. Studies on interactions between plants and soil bacteria, however, have been rather limited to elucidation of molecular mechanisms involved in mutualism between plants and either root nodule bacteria or arbuscular mycorrhizal fungi, leaving the possible effect of vast majority of soil bacteria onto plant growth and development mostly uncharacterized. We report here that Bacillus subtilis can inhibit the growth of Arabidopsis and rice without direct contact, possibly by volatile compounds. This inhibitory effect is dependent on the culture condition of the bacteria. Moreover, we found that these two plants also exhibit similar growth retardation when co-cultured with Agrobacterium tumefaciens, suggesting that the plant's response to volatiles of soil bacteria might be regulated by a mechanism that is conserved among plant kingdom.
