Role of calcium in tomato (<i>Lycopersicon esculentum</i> Mill.) resistance to <i>Botrytis cinerea</i>

Abstract

Tomato (Lycopersicon esculentum Mill.) was cultured in Hoagland’s solution containing 0, 3 or 8 mM Ca²⁺, to investigate the responses against Botrytis cinerea infection and the effects of Ca²⁺ on salicylic acid (SA) biosynthesis and signal transduction. The disease index was significantly lower in 8 mM Ca²⁺ treatment compared to the lower Ca²⁺ treatment groups. Gene expression studies exhibited that the expression level of chorismate mutase (CM), phenylalanine ammonia lyase (PAL) and activity of benzoic acid 2-hydroxylase (BA2H), which are involved in SA biosynthesis, were greater in the 8 mM Ca²⁺ group compared with the other treatments. This in turn, results in SA constitutive accumulation. Conversely, another SA biosynthesis pathway operates via isochorismate (ICS); the transcription of ICS-pathway related genes were hardly or only partly induced by the three treatment groups. The expression levels of SA-dependent signaling pathway genes (NPR1, PR1, TGA2.2 and TGA1a) increased significantly in the 8 mM Ca²⁺ treatment group after application of 2 mM SA, compared with the low Ca²⁺ treatments. Overall, all the changes were Ca²⁺ dose-dependent. The results suggest that Ca²⁺ had the ability to enhance SA accumulation and pathogen resistance with high concentration Ca²⁺ treatment; 8 mM Ca²⁺ also had a positive effect on SA-dependent signaling pathway in tomato seedlings.

Keywords: Salicylic acid, Ca²⁺, tomato, synthesis, signaling