Emily Buxton and Dr. Von D. Jolley, Plant and Wildlife Sciences
Introduction
Fe is an essential nutrient in plants because it is directly involved in chloroplast development and the important reactions of photosynthesis. Although it is the fourth most abundant element in the earth’s crust (Tisdale et al., 1993), its bioavailability in calcareous soils is very low as Fe is rapidly oxidized and immobilized.
Despite iron’s low availability in calcareous soils, many plants have been able to adapt and grow well there. Grasses, including the turfgrass Kentucky bluegrass (KBG), are known to produce phytosiderophores (organic chelates) as a way of taking up Fe from the soil for plant use and these compounds have been identified and characterized (Cesco et al., 2006; Ueno et al., 2007). Quantifying phytosiderophore exudation over time while Fe-deficiency stressed has been used to identify Fe-deficiency resistant genotypes in other monocot and could, potentially, be used as a screening technique for turf.
Often, when turf is chlorotic, Fe is applied and the turf exhibits a greening response, without the negative effects of increased shoot and decreased root growth experienced when correcting chlorosis by application of excess nitrogen. Excess nitrogen application is also a known cause of pollution in air and water. If Fe-deficiency resistant cultivars could be identified, the monetary costs and environmental impacts of excess nitrogen application could be dramatically reduced and the health of the turf improved.
Study Methods
A hydroponic study was conducted with the objective of comparing the phytosiderophore release of four cultivars (‘Award,’ ‘Baron,’ ‘Limousine,’ and ‘Rugby II’) known to differ in their susceptibility to Fe-deficiency chlorosis. After 36 days of germination and growth in an environmental chamber, the groups of KBG were put into deficient (1 µM) or adequate (10 µM) treatments of Fe nutrient solution with a pH of 7.4. After treatment initiation, chlorosis scores were made daily. On days 5-13 of the treatments, phytosiderophore release was measured once daily using an indirect Fe-binding assay. Plant tissue was dried, ground to pass a 1 mm screen, digested in nitric-perchloric acid, and analyzed for nutrient content by inductively coupled plasma (ICP, Thermo Electron Corporation, Franklin, Maryland) spectroscopy.
Physiological Response
As expected, all cultivars showed much greater chlorosis at 1 than at 10 µM Fe. However, the Baron cultivar developed more severe chlorosis than Award, Rugby II, and Limousine at both the high and low levels of Fe. In addition, Baron re-greened after day 9 at the higher level of Fe while all other cultivars’ chlorosis worsened as the treatment progressed. For all four cultivars grown at the low level of Fe, chlorosis increased during the course of the treatment.
Expectedly, the low Fe treatments had 25% less shoot Fe concentration than the adequate Fe treatments. Similarly, the low Fe treatments had 67% less root Fe concentration than the adequate Fe treatments. The Fe deficiency at the 1 µM Fe level resulted in slightly less average shoot yield but a 7% greater root yield than the 10 µM Fe treatment.
All four cultivars produced significantly more phytosiderophore in response to Fe deficiency at the low compared to the high level of Fe. Baron, however, surprisingly produced 12 percent more phytosiderophore than the other cultivars.
Physiology Implications
Based on previous work with other species, we expected susceptibility to Fe-deficiency chlorosis in KBG to be related to a cultivar’s inability to produce adequate phytosiderophore. The unexpected result of our experiment was, however, that the cultivar developing the most chlorosis during the course of the treatment (Baron) also produced the most phytosiderophore and at a significantly higher level than the other cultivars. This finding unique to KBG implies that Fe deficiency susceptibility in KBG may be related to inefficient uptake, transport, or utilization physiology rather than phytosiderophore production and release. This information is valuable for geneticists seeking the development of new cultivars that have very high greenness scores in Fe limiting soils.
Publications
As a result of this grant, I have been able to present my research at the ASA-CSSA National Meetings in Pittsburgh, the Western Nutrient Management Conference in Salt Lake City, and the Utah Conference on Undergraduate Research at Westminster College. I was the primary author of an article, related to this research, which appeared in an industry journal in March 2009. Most importantly, I am working on a manuscript, along with my faculty mentor, to be submitted to a peer-reviewed journal in our field. This ORCA grant has allowed me an experience that has been the highlight of my undergraduate career and has improved nearly every aspect of me, professionally, academically, and personally.