About the Cover
On the Cover: The interveinal chlorotic sunflower leaves shown in the photograph suffer from Fe chlorosis. Fe chlorosis occurs mainly on calcareous soils with nitrate as the exclusive N form, and leaves are frequently chlorotic in spite of abundant Fe concentrations. Kosegarten et al. (pp. 1069-1079) have shown that leaf apoplast pH regulates Fe3+ reduction and thus Fe2+ transport across the plasmalemma. Microscope imaging combined with the fluorescence ratio technique revealed high apoplastic pH at cellular sites in the interveinal area of young leaves due to nitrate nutrition (see inset of the interveinal area). Insets show the fluorescence intensity from which apoplast pH was calculated. In the interveinal area, Fe3+ reduction was depressed at sites of high apoplastic pH, thus inducing leaf yellowing. In contrast, apoplastic pH in the xylem vessels (see related inset) was low even with nitrate nutrition, and, due to high rates of Fe3+ reduction at low apoplastic pH, the tissue around the leaf xylem remained green.
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Copyright © 2007 by the American Society of Plant Biologists
