Abstract
Glomalin is a glycoprotein produced by arbuscular mycorrhizal (AM) fungi, and the soil fraction containing glomalin is correlated with soil aggregation. Thus, factors potentially influencing glomalin production could be of relevance for this ecosystem process and for understanding AM fungal physiology. Previous work indicated that glomalin production in AM fungi may be a stress response, or related to suboptimal mycelium growth. We show here that environmental stress can enhance glomalin production in the mycelium of the AM fungus Glomus intraradices. We applied NaCl and glycerol in different intensities to the medium in which the fungus was grown in vitro, causing salinity stress and osmotic stress, respectively. As a third stress type, we simulated grazing on the extraradical hyphae of the fungus by mechanically injuring the mycelium by clipping. NaCl caused a strong increase, while the clipping treatment led to a marginally significant increase in glomalin production. Even though salinity stress includes osmotic stress, we found substantially different responses in glomalin production due to the NaCl and the glycerol treatment, as glycerol addition did not cause any response. Thus, our results indicate that glomalin is involved in inducible stress responses in AM fungi for salinity, and possibly grazing stress.
Highlights
Glomalin is a glycoprotein produced by arbuscular mycorrhizal fungi (AMF)
Glomalin has been characterized as a putative homolog of heat shock protein 60 [3], but little is known about the ecophysiology of glomalin production so far, and it is not clear why AMF produce this compound
The biomass of the mycelium exposed to the clipping treatment was not significantly different from the control, since the clipping was performed after development of the mycelium
Summary
Glomalin is a glycoprotein produced by arbuscular mycorrhizal fungi (AMF). The soil organic matter fraction called glomalinrelated soil protein Glomalin levels in soil and in vitro cultures were negatively correlated with hyphal length [6,7], suggesting that its production might be a stress response. A common stress in soils is grazing by soil biota, and AMF were found to have lower palatability than other fungi to soil mesofauna [8], and if the only food source, reduced collembolan fecundity significantly [9]. This led to the hypothesis that glomalin might be involved in grazing stress avoidance or grazing defence [10]
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