Probing the interactions between iron nutrition, salinity and ultraviolet-B radiation on the physiological responses of wheat (Triticum aestivum L.)

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.