Magazine: Is there a role for Salicylic Acid in Turf?
By Jerry Spencer in Consultancy on 1st Nov 2007 10:35
Even when conditions for plant growth such as temperature, light and moisture are ideal there exist inefficiencies which result in what are termed free radicals in chloroplast photosystems. Similar to a car engine, there are a number of toxic chemical emissions or byproducts of photosystem function that the plant must deal with to remain healthy. Under less than optimal temperature, light and moisture conditions, the inefficiencies will be greater.
Two stress-related dynamics in plant physiology are the production of free radicals and antioxidants. Free radicals disrupt key plant functions, and one of the key roles of antioxidants is to "deactivate" or "neutralize" these free radicals.
Production of free radicals occurs even under optimum conditions, but it is significantly higher when conditions for photosynthesis are suboptimal such as under stress or in shade. Production of antioxidants is natural, but it can be hindered when carbohydrate reserves are low or rootzone conditions are unfavorable. This is also related to how efficient photosynthesis has been. It is clear that rootzone conditions affect both stress occurrence and turf's ability to defend itself against that stress.
For example optimized turfgrass canopies have photochemical efficiencies of about 0.7, while those under stress are at 0.55 or below.
Free radicals, if not quickly converted to water and ground-state oxygen by antioxidants, damage proteins and DNA, bleach chlorophyll, and disrupt membrane integrity.
To address these inefficiencies, the plant has various natural coping and defense mechanisms. To deal with the free radicals, healthy plants have a robust defense system that produces antioxidants to "deactivate" or "neutralize" the damaging free radicals. Three of the most common (and important) antioxidants that make up this defense system are the enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase.
This defense system also requires favourable conditions to operate efficiently and can be overwhelmed by stress. Stresses such as drought
and heat increase the production of free radicals and if turf has low energy reserves, is under moisture stress or possesses a damaged root systems, then it will often lack the ability to increase production of enough antioxidants (which are nitrogen and carbon-rich proteins) to offset the increase in free radicals. The result is called oxidative stress — a primary factor in summer bentgrass decline.
Plants make salicylic acid to trigger natural defenses against bacteria, fungi, and viruses. This is termed an activator of ‘Systemic Acquired Resistance’ (SAR). However, plants often don’t produce the acid quickly enough to prevent injury when attacked by a microbe. Spraying this on the plants speeds up the SAR response.
Research has shown that spraying this naturally occurring compound onto some plants triggers natural defenses that keep harmful fungi, bacteria, and viruses at bay.
Plants have always had some means to defend themselves; it's just that some don't recognize their microbial attackers in time. Spraying salicylic acid snaps them to attention and puts their defenses on high-alert against future attacks.
Plant scientists first encountered the phenomenon, called systemic acquired resistance (SAR), in the 1930s. but only recently have companies begun marketing salicylic acid as a way to activate SAR.
Research has found:
· Exogenous application of SA improved plant tolerance to heat (Dat et al., 1998) and specifically to creeping bentgrass (Larkindale and Huang, 2004) and tall fescue seedlings (He et al., 2002).
· Chilling (Janda et al., 1999)
· Salt stress (Borsani et al., 2001).
For more contact or view:
e-mail: jerry.spencer@etpturf.com.au
web: www.etpturf.com.au
References:
Schmidt, R.E..; Ervin, E.H.; and Xunzhong Zhang Questions and answers about Biostimulants Superintendents are often in the dark about the best ways to use biostimulants and what types of results to expect. 30/6/03
He, Y.L., Y.L. Liu, Q. Chen, and A.H. Bian. 2002. Thermotolerance related to antioxidation induced by salicylic acid and heat acclimation in tall fescue seedlings. (In Chinese, with English abstract.) J. Plant Physiol. Mol. Biol. 28:89–95.
Janda, T., G. Szalai, I. Tari, and E. Paldi. 1999. Hydroponic treatment with salicylic acid decreases the effects of chilling injury in maize (Zea mays L.) plants. Planta 208:175–180
Borsani, O., V. Valpuesta, and M.A. Botella. 2001. Evidence for a role of salicylic acid in the oxidative damage generated by NaCl and osmotic stress in Arabidopsis seedlings. Plant Physiol. 126:1024–1030.
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Even when conditions for plant growth such as temperature, light and moisture are ideal there exist inefficiencies which result in what are termed free radicals in chloroplast photosystems. Similar to a car engine, there are a number of toxic chemical emissions or byproducts of photosystem function that the plant must deal with to remain healthy. Under less than optimal temperature, light and moisture conditions, the inefficiencies will be greater.
