LIGHT-MEDIATED RELEASE OF PHYTOSIDEROPHORES IN WHEAT AND BARLEY UNDERIRON OR ZINC-DEFICIENCY

The effect of varied light intensity (50 - 600 mu mol m(-2) s(-1)) on the rate of phytosiderophore release was studied under zinc (Zn) defic iency using a bread (Triticum aestivum L. cv. Aroona) and a durum whea t cultivar (Triticum durum Desf. cv. Durati) differing in zinc (Zn) ef ficiency and under iron (Pie) deficiency using a barley cultivar (Hord eum vulgare L. Europe). Plants were grown under controlled environment al conditions in nutrient solution for 15 days (wheat plants) or 11 da ys (barley plants). Phytosiderophore release was determined by measuri ng capacity of root exudates to mobilize copper (Cu) from a Cu-loaded resin. With increasing light intensity visual Zn deficiency symptoms s uch as whitish-brown lesions on leaf blade developed rapidly and sever ely in wheat, particularly in the durum cultivar Durati. In wheat plan ts supplied well with Zn, increases in light intensity from 100 to 600 mu mol m(-2) s(-1) did not clearly affect the rate of phytosiderophor e release. However, under Zn deficiency increases in light intensity m arkedly enhanced release of phytosiderophores in Zn-deficient Aroona, but not in Zn-inefficient Durati. When Fe-deficient barley cultivar Eu rope was grown first at 220 mu mol m(-2) s(-1) and then exposed to 600 mu mol m(-2) s(-1) for 24 and 48 h, the rate of release of phytosider ophores was enhanced about 4-fold and 7-fold, respectively. Transfer o f Fe-deficient plants from 600 to 50 mu mol m(-2) s(-1) for 48 h reduc ed the rate of release of phytosiderophores by a factor of 7. The effe ct of light on phytosiderophore release was similar regardless of whet her the rate of phytosiderophore release was expressed per plant or pe r unit dry weight of roots. The results demonstrate a particular role of light intensity in phytosiderophore release from roots under both Z n and Fe deficiency. It is suggested that in the studies concerning th e role of phytosiderophore release in expression of Zn or Fe efficienc y among and within cereals, a special attention should be given to the light conditions.