Effects of a Plant Growth-Promoting Rhizobacterium (Pseudomonas putida GR12-2) on the Early Growth of Canola Seedlings

Abstract

The free-living plant growth-promoting rhizobacterium (PGPR) Pseudomonas putida GR12-2 can enhance plant growth by one or more of several mechanisms including the synthesis of siderophores, the production of phytohormones, and the action of 1-ami- nocyclopropane-1 -carboxylic acid (ACC) deaminase which degrades ACC, the immediate precursor of the phytohormone ethylene (1–6). Following the binding of the PGPR to the seed coat or to the root of a developing seedling, the bacterial deaminase sequesters and then degrades ACC leached from germinating seeds thereby increasing the concentration gradient of ACC from the root. This would lower the level of ACC as well as the level of ethylene in plants, hence promoting plant growth. Plants treated with mutant P. putida GR12-2/acd68, which lacks ACC deaminase activity, produce higher levels of ethylene and have shorter roots than plants treated with wild-type P. putida GR12-2. In the present study, we have examined whether the impact of P. putida GR12-2 on canola plants is affected by the method used to apply the bacterium, i.e. either as a seed coating prior to planting or by direct application to the soil. We have also extended our investigation to determine whether the bacterium moderates plant response to some of the effects of salt stress or cold night temperatures.