Effects of 15% CO2 on the accumulation of the phytoalexin phaseollin in Phaseolus vulgaris in response to mechanical injury and to infection by Colletotrichum lindemuthianum

Abstract

Accumulation of phaseollin at sites of point-freezing injury on etiolated hypocotyls of Phaseolus vulgaris occurred in air but was prevented when seedlings were placed in air containing 15% CO2 immediately after injury. The inhibitory effect was partially overcome when CO2-treated seedlings were returned to air. Phaseollin accumulation in 15% CO2 did occur, however, when injured seedlings were maintained in air for 3–9 h before being transferred to CO2, indicating that the sensitivity to CO2 lies at an early stage of the process leading to phaseollin production. In contrast, phaseollin accumulation at sites of infection of P. vulgaris by an incompatible race of Colletotrichum lindemuthianum was not inhibited by 15% CO2. These results indicate that the processes leading to the accumulation of phaseollin at incompatible infection sites and at injury sites may be regulated differently.