Isidia ontogeny and its effect on the CO₂ gas exchanges of the epiphytic lichen Pseudevernia furfuracea (L.) Zopf

Abstract

The development of isidia in thalli of Pseudevernia furfuracea from the Carnic Alps (North-eastern Italy), and the effects of these structures on CO 2 gas exchanges were investigated. The ontogenetic events were studied by comparison of sections stained with different histochemical tests and SEM observations. A high cell turnover rate in both symbiotic partners is the first sign of isidium development, followed by an increased aplanosporogenesis of algae and growth of neighbouring medullary hyphae which become oriented upwards. Large nuclei and an intense cytoplasm activity characterize the mycobiont cells. The surface of very young isidia shows an irregular structure of spherical to ovoid protruding tips of perpendicular cortical hyphae, that are later organised in a pseudomeristematic area similar to that observed in the apex of growing lobes. CO 2 gas exchange measurements carried out in the laboratory confirmed the high metabolic activity of isidia. At optimal water content and favourable light conditions, isolated isidia had rates of gross photosynthesis and dark respiration that were twice those of non-isidiate lobes. Isolated isidia also had a very low CO 2 saturation point, probably because of their favourable surface/volume ratio, and a high light saturation, probably linked to their high content of photosynthetic pigments. The different roles played by isidia in the biology of Pseudevernia furfuracea, and particularly their rejuvenating effect on aged lobes, are discussed, and the presence of thalloconidia is briefly mentioned.

Comparative thallus anatomy of two Parmotrema (Parmeliaceae, lichenized Ascomycetes) with reticulate maculae

“…The upper cortex organization in both species also seems to be associated with thallus water uptake and CO 2 diffusion capacity, as pointed out by several authors (Hale 1981;Elix 1993;Tretiach et al 2005;Crespo et al 2006;Barbosa et al 2009b). High cortex thickness may work as a barrier to water diffusion, lengthening thallus saturation time, as observed by Hale (1981) in other Parmeliaceae species.…”

Water availability modifies tolerance to photo-oxidative pollutants in transplants of the lichen Flavoparmelia caperata

“…CO 2 gas exchange was measured with an Infrared Gas Analyzer (IRGA) LICOR-6250, operating in a closed system (for technical details, see Tretiach et al 2005). Nearly natural spectrum light was provided by a FL-400 Lighting Unit (Walz), powered by an Osram HLX 250 W lamp.…”

Thallus structure and isidium development in two Parmeliaceae species (lichenized Ascomycota)

“…However, as pointed by Hale (1983), the major question in using these characteristics is the lack of studies and understanding of their origin and ontogeny. The most recent studies on isidia have focused on their dispersion pattern, settling and survival (Gilbert, 1988;Scheidegger et al, 1995;Zoller et al, 2000), but their anatomical structure and ontogenesis are scarcely reported (Tretiach et al, 2005).…”