Loline alkaloid

The lolines are insecticidal and insect-deterrent compounds that are produced in grasses infected by endophytic fungal symbionts of the genus Epichloë (anamorph species: Neotyphodium).

Lolines increase resistance of endophyte-infected grasses to insect herbivores, and may also protect the infected plants from environmental stresses such as drought and spatial competition.

Different substituents at the C-1 amine, such as methyl, formyl, and acetyl groups, yield loline species that have variable bioactivity against insects.

)[1] Studies in the 1950s and 1960s by Russian researchers established the name loline and identified the characteristic 2,7 ether bridge in its molecular structure.

Lolines are insecticidal and deterrent to a broad range of insects, including species in the Hemiptera, Coleoptera, Hymenoptera, Lepidoptera, and Blattodea, such as the bird cherry-oat aphid (genus Rhopalosiphum), large milkweed bug (Oncopeltus fasciatus), and American cockroach (Periplaneta americana).

By contrast, the lolines frequently accumulate to very high levels in grass tissues,[1] and were, therefore, initially associated also with toxicity to mammalian herbivores.

[10] Specifically, the lolines were thought to be responsible for toxic symptoms called fescue toxicosis displayed by livestock grazing on grasses infected by N.

[10] However, subsequently it was demonstrated that only the endophyte-produced ergot alkaloids are responsible for the symptoms of fescue toxicosis (or summer syndrome),[11] and not the lolines which, even at high doses, have only very small physiological effects on mammalians feeders.

Unlike the lolines, however, the senecio alkaloids exhibit strong hepatotoxicity,[13] owing to a double bond between C-1 and C-2 in their ring structure.

The lolines have been suggested to inhibit seed germination or growth of other plants (allelopathy),[14] and to increase resistance of infected grasses against drought, but such effects have not been substantiated under more natural conditions of cultivation or in habitats.

[16] Loline concentrations often increase in grass tissues regrown after defoliation and clipping of plants, suggesting an inducible defense response mechanism, involving both symbiotic partners.

[21] However, feeding studies with carbon isotope–labeled amino acids or related molecules in pure cultures of the loline-producing fungus N. uncinatum recently demonstrated that the loline alkaloid pathway is fundamentally different from that of the plant pyrrolizidines.

Figure 1. General structure of the loline alkaloids produced in grasses infected by fungi of the Epichloë/Neotyphodium complex (epichloae endophytes); R' and R'' denote variable substituents that can include methyl , formyl , and acetyl groups giving rise to different loline species.
Figure 2. N -formylloline, one of the most abundant lolines in endophyte-infected grasses.
Figure 3. Neotyphodium coenophialum hyphae in tall fescue leaf tissue. Lolines commonly accumulate in the N. coenophialum –tall fescue symbiosis, providing protection from insects and other environmental stresses. [ 1 ]