Photosynthetic pigments and mineral composition of iron deficient pear leaves

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Abstract
A decrease in the pigment content of pear (Pyrus communis L.) leaves, thought to be related to Fe deficiency, occurs in northeastern Spain where is usually called “pear yellowness”;. A nutritional study has been carried out on a pear orchard affected by this physiological “disease”; and growing in the medium Jalón river valley. Total Fe contents were high both in deficient and control leaves, in good agreement with previous results obtained for Fe deficient crops in the same area. However, K/Ca ratios were low, in sharp contrast with the high K/Ca ratios usually associated with iron chlorosis worldwide. Manganese contents per unit area were significantly lower in the yellow leaves. A new high performance liquid chromatography method confirmed that in Fe deficient leaves most pigments decrease concomitantly with chlorophyll a, in agreement with previous reports from this laboratory. Exceptions to this rule were three carotenoids involved in the violaxanthin cycle, violaxanthin, anteraxanthin and zeaxanthin. The total amount of these pigments actually increased ‐by about 20%‐ when chlorophyll decreased by 60% (mild chlorosis), and decreased only by 25% when chlorophyll decreased by 80% (fully developed chlorosis). In Fe deficient pear leaves and in low light, we found significant amounts of zeaxanthin, suggesting a displacement of the violaxanthin cycle towards this carotenoid.