Soils in many agricultural areas have high pH, resulting in low availability of zinc and iron. Plants grown on such soils suffer from either Zn or Fe deficiency or both. The efficient plant genotypes grown normally in calcerous soils were found to evolve some strategies to acquire the iron which is in insoluble form. Iron efficient graminaceous monocots release iron chelating substances, mugineic acid family phytosiderophores (MAs), in response to iron deficiency stress. Several researchers have suggested that phytosiderophores also can play role in grass Zn nutrition and thus it may be possible that it is the uptake mechanism for Zn efficiency. Several possible genes that take role in phytosiderophore synthesis or found to be induced under iron deficient conditions were identified in several organisms but not on wheat. In this study, the efficient barley cultivar Tokak-157, efficient wheat cultivar Kira&ccedil / -66 and relatively less efficient wheat cultivar BDMM-19 were grown in normal growth conditions for 1 week and transfered to zinc deficient, iron deficient and both zinc and iron deficient nutrient solutions. After growing 1 week on these conditions, plants grown on both zinc and iron deficient nutrient solutions were retransfered to zinc and iron sufficient conditions. Degenerate primers were designed for the conserved regions of previously identified genes that take role in phytosiderophore synthesis or induced under iron deficient conditions and RT-PCRs were performed. The complete open reading frame of IDI-1(Iron deficiency induced-1) gene and the putative gene fragment for SAM-s (S-adenosylmethionine synthetase) were identified.

The work presented here focuses on the molecular mechanism of phytosiderophore secretion in graminaceous plants. In maize, yellow stripe3 (ys3) is a mutant that is deficient in its ability to secrete iron-chelating compounds of the mugineic acid family known as phytosiderophores. Phytosiderophores are specific to grasses and are used for the acquisition of iron. Genetic linkage mapping of the ys3 locus lead to a region of interest on chromosome 3 defined by marker UMC1773. The sequence of eleven candidate genes (GRMZM2G390345, GRMZM2G390374, GRMZM2G342821, GRMZM5G800764, GRMZM2G502560, GRMZM5G849435, GRMZM2G105766, GRMZM5G876835, GRMZM2G036976, GRMZM2G502563, miR167g) revealed several small deletions and point mutations within the coding regions of four candidate genes (GRMZM2G390345, GRMZM2G342821, GRMZM2G105766 and GRMZM2G502560). To further investigate these candidate genes, knockout (Mutator) lines were used in an effort to recapitulate the ys3 phenotype. I characterized a GRMZM2G390345 mutant and determined that the mutation in GRMZM2G390345 did not cause the ys3 phenotype. For the three remaining candidate genes, GRMZM2G342821, GRMZM2G105766 and GRMZM2G502560 further analysis is needed. The closest homolog of OsTOM1 (an effluxer of muginieic acid) GRMZM2G603306 which, lies ~7 Mbp outside the linked marker, has also been suggested to be yellow stripe3. Preliminary sequence analysis uncovered a 4 bp insertion within the 9th exon of this gene that shifts the reading frame and leads to a premature stop codon. Three of the genes analyzed remain plausible candidates for yellow stripe3.

When plants are exposed to multiple environmental stress factors, one form of stress can affect the response to another stress. This study used seedlings of a new cultivar of wheat(Triticum aestivum L. cv. 1862), grown under factorial combinations of two levels of ultraviolet-B (UV-B)radiation, two salinity regimes and two levels of iron treatment in chelator-buffered nutrient solutions in a growth chamber. A number of morphological and physiological measurements were made. The accumulation of chlorophyll, UVabsorbing compounds and proline in shoots, as well as phytosiderophores (PSs) in root exudates were measured. Feed value measurements included crude protein, water-soluble carbohydrates, acid detergent fibre and Fe in shoots and roots. After 21 days of stress exposure, results showed that Fe deficiency and NaCl stress generally decreased plant growth and function as well as nutritive value, but increased plant biochemical protection traits such as proline accumulation (16.3 fold under salinity stress) and release of PSs (2.4 fold under Fe deficiency). Interestingly, UV-B radiation affected belowground parameters, inducing a 47% reduction in PS release, together with decreasing root DM by 9% and Fe concentration in roots by 7%. When Fe deficiency and NaCl stress were combined, the results showed a decrease in PS release by 3.5 fold compared to unstressed plants. UV-B radiation synergistically increased UV-absorbing compound levels in combination with Fe deficiency, compared to plants grown under optimal Fe levels. This stress combination also resulted in a cumulative effect by decreasing Fe concentration in shoots and roots. However, salt stress did not interact with UV-B radiation for any of the traits measured. In addition, some three-way interactions were noted, with the Fe x NaCl x UV-B stress combination slightly decreasing PS release and resulting in a cumulative effect by decreasing Fe concentration in roots. In conclusion, this study found that aboveground stress factors such as UV-B can affect important aspects of belowground plant function, and that Fe deficiency can interact with UV-B and salinity stress in modifying plant responses to either stress alone.