Iron source affects iron reduction and re-greening of kiwifruit (Actinidiadeliciosa) leaves

Among deciduous fruit plants, kiwifruit (Actinidia deliciosa) is one of the most susceptible to iron (Fe) chlorosis. To develop effective means for ov ercoming Fe chlorosis, it is of upmost importance to gain information about the reduction of Fe by leaf tissues, especially under conditions that lead to chlorosis. In the present study we have characterised the leaf Fe-chela te reductase (FCR) in Fe sufficient and Fe deficient kiwifruit leaves and f or the first time tested the hypothesis that Fe-III-malate is a suitable so urce of Fe for FCR, in addition to Fe-III-citrate. Under field conditions, we have also tested the re-greening effects caused by the foliar applicatio n of different Fe sources, including Fe-III-malate, Fe-III-citrate, Fe-III- DTPA and an Fe-II source (FeSO4 + aminoacid-polypeptide mixture) on chlorot ic leaves. The results demonstrated that, similarly to other species, mesop hyll tissues of A. deliciosa leaves are able to perform an enzymatic Fe red uction prior to Fe uptake. Plasma membrane enriched material extracted from Fe sufficient leaves reduced Fem-malate and Fem-citrate. The pH optimum wa s 6.0-6.2 for Fe-III-malate and 6.5 for Fem-citrate. The substrate-dependen ce showed higher affinity for malate than for citrate. In contrast to the r oot level, the activity of the FCR of kiwifruit leaves was not enhanced und er Fe deficiency. On the contrary, after two weeks of Fe depletion, the red uction of Fem-citrate was 4.5-fold lower in the Fe deficient plants than in the Fe sufficient ones, while the reduction of Fe-III-malate was not signi ficantly affected. Under field conditions, the Fe solutions caused re-green ing of chlorotic leaves, whose intensity and duration varied according to F e source and Fe concentration. Among the treatments, the highest re-greenin g effect was caused by Fe-III-DTPA and especially by the Fen source. Fem-ci trate and Fem-malate were less effective in stimulating chlorophyll formati on. All treatments increased leaf Fe concentration and content. Although le ss Fe from malate than from citrate penetrated into the leaves, the re-gree ning effect from Fem malate was intermediate between that of Fem-DTPA and t he one caused by Fe-III-citrate. The results suggest that if Fem-malate can reach the plasmamembrane it provides a good source of Fe for leaf Fe uptak e.