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Salicylic Acid in Rice (Biosynthesis, Conjugation, and Possible Role)
P. Silverman1, M. Seskar, D. Kanter
1AgBiotech Center, Cook College, P.O. Box 231, Rutgers University, New Brunswick, New Jersey, 08903-0231 (P. Silverman, M.S., I.R.).
Plant Physiology
|June 1, 1995
Summary
Salicylic acid (SA) is abundant in rice and may act as a constitutive defense compound, though it doesn't increase after pathogen exposure. Rice metabolizes SA similarly to tobacco, with an inducible enzyme enhancing its activity.
Area of Science:
- Plant science
- Biochemistry
- Plant pathology
Background:
- Salicylic acid (SA) is a known inducer of disease resistance in dicotyledonous plants.
- Rice (Oryza sativa L.) exhibits high endogenous SA levels, with the highest concentrations found in seedlings.
- Previous research has not fully elucidated SA's role in rice disease resistance.
Purpose of the Study:
- To investigate the role of salicylic acid (SA) in rice disease resistance.
- To examine SA levels in rice following inoculation with bacterial and fungal pathogens.
- To compare SA biosynthesis and metabolism in rice with that of tobacco.
Main Methods:
- Quantified SA levels in rice seedlings and leaves.
- Inoculated rice with avirulent and virulent pathogens (Pseudomonas syringae D20, Magnaporthe grisea, Rhizoctonia solani).
- Studied SA biosynthesis and metabolism using radiolabeled precursors ([14C]cinnamic acid, [14C]benzoic acid) and measured glucosyltransferase (SA-GTase) activity.
Main Results:
- SA levels did not increase in rice after inoculation with tested pathogens.
- Leaf SA levels across 28 rice varieties correlated with generalized blast resistance, suggesting a constitutive defense role.
- Rice demonstrated SA biosynthesis from cinnamic acid via benzoic acid, similar to tobacco.
- Exogenously supplied SA induced a 7-fold increase in SA-glucosyltransferase (SA-GTase) activity in both rice shoots and roots.
Conclusions:
- Salicylic acid (SA) may function as a constitutive defense compound in rice, rather than being induced by pathogen attack.
- Rice shares a similar SA biosynthesis pathway with tobacco, involving cinnamic and benzoic acids.
- SA-inducible glucosyltransferase (SA-GTase) plays a role in SA metabolism in rice, with significant induction observed after exogenous SA application.