Uptake and transport of foliar applied zinc (65Zn) in bread and durum wheat cultivars differing in zinc efficiency

Using two bread wheat (Triticum aestivum) and two durum wheat (Triticum durum) cultivars differing in zinc (Zn) efficiency, uptake and translocation of foliar-applied Zn-65 were studied to characterize the role of Zn nutritional status of plants on the extent of phloem mobility of Zn and to determine the relationship between phloem mobility of Zn and Zn efficiency of the used wheat cultivars. Irrespective of leaf age and Zn nutritional status of plants, all cultivars showed similar Zn uptake rates with application of (ZnSO4)-Zn-65 to leaf strips in a short-term experiment. Also with supply of (ZnSO4)-Zn-65 by immersing the tip (3 cm) of the oldest leaf of intact plants, no differences in Zn uptake were observed among and within both wheat species. Further, Zn nutritional status did not affect total uptake of foliar applied Zn. However, Zn-deficient plants translocated more Zn-65 from the treated leaf to the roots and remainder parts of shoots. In Zn-deficient plants about 40% of the total absorbed Zn-65 was translocated from the treated leaf to the roots and remainder parts of shoots within 8 days while in Zn-sufficient plants the proportion of the translocated Zn-65 of the total absorbed Zn-65 was about 25%. Although differences in Zn efficiency existed between the cultivars did not affect the translocation and distribution of Zn-65 between roots and shoots. Bread wheats compared to durum wheats, tended to accumulate more Zn-65 in shoots and less Zn-65 in roots, particularly under Zn-deficient conditions. The results indicate that differences in expression of Zn efficiency between and within durum and bread wheats are not related to translocation or distribution of foliar-applied Zn-65 within plants. Differential compartementation of Zn at the cellular levels is discussed as a possible factor determining genotypic variation in Zn efficiency within wheat.