Salicylic acid beyond defence: its role in plant growth and development

Abstract

In recent years salicylic acid (SA) has been the focus of intensive research due to its function as an endogenous signal mediating local and systemic plant defence responses against pathogens. It has also been found that SA plays a role during the plant response to abiotic stresses such as drought, chilling, heavy metal toxicity, heat, and osmotic stress. In this sense, SA appears to be, just like in mammals, an 'effective therapeutic agent' for plants. Besides this function during biotic and abiotic stress, SA plays a crucial role in the regulation of physiological and biochemical processes during the entire lifespan of the plant. The discovery of its targets and the understanding of its molecular modes of action in physiological processes could help in the dissection of the complex SA signalling network, confirming its important role in both plant health and disease. Here, the evidence that supports the role of SA during plant growth and development is reviewed by comparing experiments performed by exogenous application of SA with analysis of genotypes affected by SA levels and/or perception.

Plant immunity triggered by engineered in vivo release of oligogalacturonides, damage-associated molecular patterns

“…In particular, it is known that the phytohormone SA, which plays a key role in the response to biotic stress (38), also has significant effects on growth (39). Arabidopsis mutants that have constitutively high levels of SA, such as cpr5 (constitutive expressor of PR5) (40) and acd6-1 (accelerated cell death 6-1) (41), are dwarfs, whereas NahG (naphthalene-degrading salicylate 1-hydroxylase) transgenic plants, which accumulate lower than normal levels of SA as a consequence of NahG-mediated degradation of SA, have a higher growth rate and leaf biomass, compared with untransformed plants (42).…”

Hormone-regulated defense and stress response networks contribute to heterosis inArabidopsisF1 hybrids

“…8F). Although we cannot exclude potential effects of the catechol by-product of NahG-mediated SA degradation, the phenotypic effects seen in the NahG transgenic plants of increased rosette biomass through greater cell expansion and increased seed yields are known to be directly associated with reduced SA levels in Arabidopsis (39)(40)(41)(42). NahG-generated catechol may not accumulate to high levels (43), which in any case would cause growth inhibition (44) and not the growth enhancement observed.…”

Salicylic acid mediates the reduced growth of lignin down-regulated plants

“…Our data do not support an alternative model in which reduced growth is largely a result of the diversion of energy into defense responses (e.g., PR protein expression). Although SA is increasingly being shown to impact plant growth (15), there has been little study of its potential involvement in elongation growth. Our work therefore provides a unique system for studying the poorly understood cross-talk between plant defense and growth control mechanisms (31,32).…”

“…PR gene expression can be induced by cell-wall pectic fragments via processes involving SA (12,13), and SA can impact plant growth and development through largely unknown mechanisms (14,15). A previous report that lignin reduction in HCT-down-regulated plants results from flavonoid-mediated inhibition of auxin transport has recently been refuted (4).…”