Phytosiderophore Production in Response to Fe Deficiency in Kentucky Bluegrass.

Some Kentucky bluegrass (Poa pratensis L.) cultivars are susceptible to iron (Fe) deficiency chlorosis when grown on alkaline soils and are routinely treated with Fe fertilizers.  Aesthetics could be improved and this costly practice could potentially be eliminated with the use of cultivars resistant to Fe deficiency.  Grasses are known to release phytosiderophore chelate into the rhizosphere to solublize Fe for plant use, and this characteristic has been used to screen for resistant cultivars with other species.  A chelator-buffer hydroponic study was conducted to stress Baron, Award, Limousine, and Rugby II cultivars at 1 and 10 µM Fe in complete nutrient solution buffered at pH 7.4.  After treatment, plants were oven-dried, ground, digested in nitric-perchloric acid, and analyzed by inductively coupled plasma (ICP).  Average shoot Fe concentration increased from 188 to 249 (shoot) and 223 to 525 (root) mg kg^-1, when solution Fe increased from 1 to 10 µM, respectively. This resulted in a significant increase in chlorosis and a 5% reduction in shoot dry matter yield. Surprisingly, root yield increased significantly by 7% for Fe deficient plants. There was a 16% increase in the amount of phytosiderophore exuded from roots in response to the Fe deficiency stress. Phytosiderophore was increasingly produced and exuded from roots as chlorosis increased and shoot Fe concentrations declined. In general, the cultivars responded similarly, although Baron, which produced the most phytosiderophore, developed the most chlorosis, had the lowest shoot Fe concentration, and had the highest root Fe concentration. These results imply that Fe deficiency susceptibility in Kentucky bluegrass may be related to inefficient uptake mechanisms rather than production and release of phytosiderophore.