Cooling effect of fungal stromata in the Dactylis-Epichloë-Botanophila symbiosis.

Abstract

The stromata of Epichloë fungi are structures covering part of the stem of grasses. Under the fungal layer, still green tissues of the plant survive, although the development of the new leaves is inhibited. Stromata are the places where conidia and ascospores develop. Also, here Botanophila flies dine on mycelium, lay the eggs, defecate, and the larvae develop. The interaction of the three symbionts was analyzed concerning the organisms' adaptation to understand the differences in physiology and ecology of this microenvironment that support stable symbiosis spreading presently in Europe since the beginning of the XXI century. For analysis of the infrared radiation emitted by stromata, a high-resolution infrared camera FLIR E50 was used. The visualization of stromata temperature profiles was shown in the form of pseudo-colored (false) infrared images. The ¹³C discrimination was used to characterize photosynthesis of the plant tissue enclosed within the stromata. The stromata had a substantially lower temperature than the green plant tissues. The difference reached ~5.6°C during midday hours, whereas it was smaller in the evening, reaching only ~3.6°C. The mycelium of Epichloë cultivated on agar showed about 2°C lower temperature in comparison to the surrounding. The plant tissues enclosed within the stroma were photosynthetically active, although this activity was of phosphoenolpyruvate carboxylase (PEPC) type and less involved in heat dissipation during the day. The stromata, built by fungal hyphae, on which fungal reproductive structures develop, form a cool shelter. This shelter provides a place for the larvae of Botanophila flies.