Miracle molecule: Salicylic acid

Salicylic acid, a naturally occurring plant hormone acting as an important signalling molecule adds to tolerance against abiotic stresses. It plays a vital role in plant growth, ion uptake, and transport. Salicylic acid is also involved in endogenous signalling to trigger plant defense against pathogens. This positive effect of SA could be attributed to an increased CO2 assimilation and photosynthetic rate and increased mineral uptake by the stressed plant under SA treatment. The application of salicylic acid, acetylsalicylic acid, or other analogues of SA, to leaves of plants accelerated their leaf area and dry mass production, but plant height and root length remained unaffected. SA reduced the Na uptake of plants and/or increased the uptake of N, P, K, Ca, Mg, and the other minerals as compared to control treatment under salt stress. Salicylic acid (SA) plays many roles in plant physiology. Besides pathogenesis-related resistance, SA is involved in the response to abiotic stress. However, the effects of SA on plant resistance to abiotic stress were found in contra dictionary, and the actual role of SA in abiotic stress remains unresolved. Generally, a deficiency of SA or a very high level of SA increases the plant susceptibility to abiotic stress. The optimal levels for the highest stress tolerance range from 0.1 mm to 0.5 mm for most plants. But the role of SA at a certain level in moderate and severe abiotic stress may be different. This can be attributed to redox regulations in plant cells. In this paper, we discuss the relationship between reactive oxygen species (ROS) and SA, and propose a subsequent intracellular signal transduction network of SA and ROS under abiotic stress. Anti-stress substances besides antioxidant enzymes induced by SA are also summarized.