The effect of heat stress on the symbiotic interaction between Sinorhizobium sp. and Acacia senegal

Abstract

Sinorhizobium sp. strain HAMBI 2180, marked with the β-glucuronidase (GUS) encoding gusA gene, was used for studying the effect of heat stress on the symbiotic interaction between Acacia senegal seedlings and Sinorhizobium sp. in growth cabinet conditions. The infection process, observed during 18 days after inoculation, was delayed at a root temperature of 40°C compared to a root temperature of ≤38°C, but nodulation was retarded already at 38°C. At 42°C no nodules were formed. At this root temperature the development of lateral roots and root hairs was one week delayed. Although the roots had normally deformed root hairs in addition to abnormally deformed ones, only disintegrated infection threads were present. However, the ability to form symbiosis was reversible. Nitrogen-fixing nodules developed on those parts of the roots which were formed after completion of the thermal stress at 42°C. A root temperature of 42°C did not affect the numbers of culturable rhizobia in the A. senegal rhizosphere.