Arsenate-induced expression of a class III chitinase in the dwarf sunflower Helianthus annuus

Dwarf sunflower cultivars of Helianthus annuus were exposed to 30 mg/L As alone and in combination with other toxic metals (30 mg/L each of Cd, Cr, and Ni). Total uptake of metals at the end of a 17-day exposure cycle showed variable sequestration of the metals in roots, leaves, and stems with metal concentrations highest in roots and lowest in leaves. The presence of other metals appeared to have little effect on the uptake of As. Proteins were extracted from leaves of plants exposed to arsenic alone or in combination with other metals and size-fractionated by one-dimensional SDS-polyacrylamide gel electrophoresis. Several polypeptides, with molecular masses ranging from less than 10 to over 45 kDa appeared to be unique in extracts obtained from leaves of plants in response to arsenic stress. One polypeptide was induced strongly. It had an approximate molecular mass of 32 kDa and was recovered from gels and analyzed using LC–MS/MS. It was identified as a class III chitinase, whose gene appeared to be induced at the transcription level when As was present.