Department of Botany, University of Pune, Pune-411 007, India.
National Seminar of Plant Physiology ‘Physiological Basis for Improving Productivity of Agricultural, Horticultural and Medicinal Plants’. December 27–29, 2004. University of Pune, Pune, India. Abstract No. 158, (2004).
Plants defend themselves against pathogens in many ways viz., (i) expression of an oxidative burst, in which H2O2 accumulates, (ii) accumulation of SA and (iii) callose deposition. The non-protein amino acid ß-amino-butyric acid (BABA) protects plants against wide range of pathogens. The mode of action of BABA in the protection of plants against pathogens is not clearly understood. In some plant pathogen systems BABA-induced resistance has been reported to be mediated through induction of salicylic acid, an important signal molecule involved in plant defense responses against pathogens, while in other BABA induced resistance was mediated through callose deposition at the site of infection which prevented spread of pathogen. Experiments were done to study how BABA induces resistance in Brassica juncea against the necrotrophic pathogen Alternaria brassicae. When plants were sprayed with SA or BABA over abroad range of concentrations, 24 h before pathogen application. BABA proved more effective than SA in controlling spread of the pathogen. The effect of SA/BABA in inducing resistance to the pathogen through intensifying the oxidative burst was studied by in situ localization of H2O2 in SA/BABA pretreated leaves to which pathogen was applied. When the leaves were pretreated with SA there was a higher accumulation of H2O2 in response to infection. On the other hand, BABA pretreated leaves did not show any enhancement in H2O2 accumulation at the site of infection. In fact there appeared to be decrease in H2O2 accumulation as compared to the leaves that were not pretreated with BABA indicating that induction of resistance by BABA was not mediated through an enhanced oxidative burst. The levels of free and conjugated SA were estimated using HPLC in plants pretreated with SA or BABA before pathogen application. Application of exogenous SA led to a significant increase in endogenous SA levels with or without pathogen application. BABA on the other hand led to a decrease in the levels of endogenous SA either with or without pathogen application. In situ localization of callose was seen to differ in the infected region of control and BABA pretreated leaves. Our results showed that BABA do not induces resistance through H2O2 or SA pathway.
