Ca2+ fluxes in developing Trichoderma viride mycelium

Light-induced conidiation of Trichoderma spp. strains is accompanied by development-dependent changes in the Ca2+ binding to cell walls

The effect of light on the binding of Ca²⁺ to mycelia and to cell walls isolated from aerial mycelia of three strains of Trichoderma spp. was studied. Two independent methods were used to measure the total Ca²⁺ content in mycelia and the Ca²⁺ bound to cell walls isolated from aerial mycelia. The results of these methods showed that the light-induced formation and maturation of conidia in Trichoderma spp. is accompanied by increased Ca²⁺ deposition in mycelia and cell walls. Moreover, the cultivation of Trichoderma atroviride F-534 in the presence of ⁴⁵Ca²⁺ under circadian illumination showed that radioactivity was exclusively localized in the light-induced conidial rings of aerial mycelia. The fluorescence microscopy of chlortetracycline-stained mycelia showed that the major fraction of Ca²⁺ was accumulated in conidia and fructification structures, or some intracellular compartments in T. atroviride F-534 grown under circadian illumination, while only a limited amount of Ca²⁺ was associated with hyphal surfaces. In addition, the study of ⁴⁵Ca²⁺ binding to cell walls revealed that T. atroviride F-534 displays both increased ⁴⁵Ca²⁺ binding capacity and elevated affinity to ⁴⁵Ca²⁺ binding upon illumination. The results indicate that conidia formation and (or) maturation is associated with changes in Ca²⁺ homeostasis.