Endophytic mediation of reactive oxygen species and antioxidant activity in plants:a review

Reactive oxygen species are in all types of organisms from microbes to higher plants and animals.They are by-products of normal metabolism,such as photosynthesis and respiration,and are responsive to abiotic and biotic stress.Accumulating evidence suggests reactive oxygen species play a vital role in programmed cell death,stress responses,plant defense against pathogens and systemic stress signaling in conjunction with antioxidant production.Here,we propose that reactive oxygen species and antioxidants,as both universal and evolutionarily conserved,are likely to play important role(s)in symbiotic interactions.To support this hypothesis we review the root and foliar fungal endophyte literature specific to fungal-plant symbiotum production of reactive oxygen species and antioxidants in response to stress.These asymptomatic fungi can produce antioxidants in response to both biotic and abiotic stress when grown in culture as well as in planta.In addition,there is a growing but nascent literature reporting a significant impact of endophyte colonization on the antioxidant activity of colonized(E+)hosts when compared to uncolonized(E-)hosts,especially when exposed to stress.Here we summarize general patterns emerging from the growing literature specific to antioxidant activity of endophytes in colonized hosts and bring up possible future research questions and approaches.The consequences of changes in reactive oxygen species production and increased antioxidant activity in the symbiotum appear to be beneficial in many instances;but costs are also indicated.Unexplored questions are:1)to what extent do antioxidants originating from the fungal endophyte mediate host metabolism,and thereby control host responses to endophyte colonization;(2)what role do fungal,plant,or symbiotum produced reactive oxygen species and antioxidants have in determining symbiotic outcome between extremes of pathogenicity and mutualism;and(3)what role if any,do the production of reactive oxygen species and their antioxidant counterparts play in the symbiotum’s ability to respond to changing selection pressures?If as the literature suggests,such endophyte imposed mediation can be utilized to foster increases in plant production in resource limited habitats then the utilization of fungal endophytes may prove useful in agronomic and conservation settings.

Fungal endophyte mediated occurrence of seminiferous and pseudoviviparous panicles in Festuca rubra

Fungal endophytes are suggested to manipulate host grass reproduction.Using different grass-endophyte combinations in a four year common garden experiment,we show that endophyte can retain control over the reproductive functions of the host.Plants were collected as seeds from two different environments,meadows and riverbanks.Natural endophyte infection(E+)increased reproductive effort of plants;13 and 15%higher proportion of E+plants produced panicles compared to naturally uninfected(E-)and manipulatively endophyte-infected(ME+)plants,respectively.Meadoworigin E+plants produced also higher number of panicles compared to E-in the last two years,and both meadow-and riverbank-origin ME+plants produced higher number of panicles compared to ME-plants in most of the years.Pseudovivipary was recorded in 5%of the plants each year.Pollen limitation appears not to induce pseudovivipary.Both E+and ME+plants produced higher number of seminiferous panicles compared to E-and ME-plants.The higher proportion of pseudoviviparism in ME+plants compared to E+,Eand ME-plants from meadows suggests specific genotypegenotype cross-talk between endophyte and grass.Pseudovivipary was affected by year and primarily explained by plant reproductive effort since most vigorous plants produced more pseudoviviparous panicles.We propose that endophytes can promote host grass reproduction in a habitatspecific manner and depending on genetic compatibility between partners.However,reproductive behavior depended on maternal habitat and the annual environmental conditions highlighting the importance of long-term experiments to estimate the effects of endophytes on host plant ecology.