Effects of salicylic acid on the development and root nodulation of soybean seedlings

Salicylic acid (SA) is recognized as an endogenous regulator of plant metab olism, mainly involved in induction of systemic acquired resistance (SAR). Exogenous SA can also induce a SAR reaction and SAR gene expression. Excess ive SAR-related activity can be an overall cost to the plant in terms of en ergy and materials expended unnecessarily. Elicitation of plant defence res ponses might also block beneficial plant-microbe interactions and result in negative effects on plant growth. The objective of this study was to inves tigate the effects of SA concentration (5, 1, 0.5, 0.1 and 0 mM) on soybean seedling growth and nodulation by watering of soybean seedling roots or so aking of seedling leaves with SA solutions. It was found that 5 mM SA had n egative effects on soybean seedling development, but other concentrations o f SA did not affect the development of soybean seedlings. In addition, ther e were no negative effects on seedling development due to SA soaking of see dling leaves. Soybean seedling growth in sterile soil was reduced due to re pressed nitrogen uptake following addition of 5 mM SA, indicating that some concentrations of SA can alter the N nutrition of seedlings. A model is pr esented that ties SA to nodule formation and plant growth.