Concentration of zinc and activity of copper/zinc-superoxide dismutase in leaves of rye and wheat cultivars differing in sensitivity to zinc deficiency

Two bread wheat (Triticum aestivum L. cvs. Bezostaja-1 and BDME-10), two durum wheat (Triticum durum L. cvs. Kunduru-1149 and Kiziltan-91) and one rye (Secale cereale L. cv. Aslim) cultivars differing in sensitivity to zinc (Zn) deficiency were grown under controlled environmental conditions for 21 days in a Zn deficient soil to compare severity of Zn deficiency symptoms with the concentration of total Zn and activities of total superoxide dismutase (SOD), copper (Cu) and Zn containing SOD (Cu/Zn-SOD) and manganese (Mn) containing SOD (Mn-SOD) in leaves. Visual Zn deficiency symptoms such as development of whitish-brown necrotic patches on leaf blades appeared rapidly and were severe in bread wheat cultivar BDME-10 and particularly in both durum wheat cultivars, while Bezostaja-1 was much less affected by Zn deficiency. In the case of rye, the leaf symptoms were either absent or only slightly developed. The effect of Zn deficiency on shoot dry matter production was very similar to the effect on leaf symptoms. Decreases in shoot dry matter production as a result of Zn deficiency were about 16 % in Aslim (rye) and Bezostaja-1, 36 % in BDME-10 and 47% in durum wheats. Despite of such marked differences in sensitivity to Zn deficiency, concentrations of Zn in leaf dry matter were not different between the cultivars under Zn deficiency. However, activities of Cu/Zn-SOD and, in part, total SOD, but not Mn-SOD were very closely related with the sensitivity of cultivars to Zn deficiency. Under Zn deficiency, rye showing a high resistance to Zn deficiency had the greatest activity of Cu/Zn-SOD. Among the wheat cultivars, Bezostaja-1 with less sensivity to Zn deficiency showed higher activity of Cu/Zn-SOD than other wheat cultivars. The results suggested that Zn efficient cereal genotypes possess higher amounts of physiologically active Zn in leaves and that activity of Cu/Zn-SOD is a better indicator of Zn nutritional status of plants than Zn concentration alone. An efficient utilization of Zn at the cellular level seems to be a major factor determining expression of Zn efficiency in cereals growing under deficient supply of Zn.