Ad. Rombola et al., Iron source affects iron reduction and re-greening of kiwifruit (Actinidiadeliciosa) leaves, J PLANT NUT, 23(11-12), 2000, pp. 1751-1765
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.