Endophytic Neotyphodium lolii induced tolerance to Zn stress in Lolium perenne

The effect of Zn on growth, chlorophyll a fluorescence, net photosynthetic rate, gas exchange, water content and mineral concentrations (Zn, Mn and Mg) in ryegrass infected with or free from Neotyphodium lolii was studied by addition of ZnSO₄ (0–20 m M ) to the nutrient solution. Zn induced a decrease in growth of plants at 1, 5 and 10 m M and cessation of growth at 20 m M ZnSO₄. From 1 to 10 m M , the decrease was less pronounced in the presence of the endophytic fungus than in its absence. The growth limitation was due to an accumulation of Zn in leaves. From 8 to 15 days, the presence of the fungus in the plant led to a limitation of the Zn concentration in the leaves (24–32% lower with N. lolii than without). This restriction of Zn concentrations in leaves also had a beneficial effect on photosystem II (PSII) activities, net photosynthetic rate and internal CO₂ concentration. Particularly at 1 and 5 m M , the quantum yield of electron flow throughout PSII was greater in the presence of the fungus than in its absence and at 5 and 10 m M , the internal CO₂ concentration was maintained at a normal level. Compared with the endophyte-free ryegrass, the symbiotic plants showed higher values of total dry weight and tiller number, indicating a tolerance to environmental Zn stress.