Bitter pit is a physiological disorder of apple fruits apparently caused by a localised calcium deficiency or imbalance in fruits associated with low levels of calcium in the flesh. A new, highly selective method using glyoxal bis(2-hydroxyanil, GBHA) was tested to reveal the presence of calcium within the fruit as a red stain. Water-soluble and insoluble calcium was analysed by capillary electrophoresis and atomic absorption spectroscopy in pitted regions, adjacent sound areas and pulp from sound apples. Both methods, selective calcium staining and mineral analysis, showed that calcium accumulates in the pitted areas of apples affected by bitter pit. However, in mechanically inflicted wounds, the pulp of the apple was heavily stained but not the corresponding fingerprint, indicating a similar mechanism of insoluble calcium accumulation but a different distribution of soluble calcium compared to the pits.Keywords: apple, bitter pit, calcium staining, glyoxal bis(2-hydroxyanil) INTRODUCTIONThe browning of plant tissues is a manifestation of mechanical damage, certain diseases and physiological disorders, senescence and a hypersensitive reaction induced by pathogenic microorganisms. It is generally believed that the process of browning is due to the loss of cell compartmentalisation and involves the oxidation of polyphenolic compounds by polyphenol oxidase, resulting in the production of polymerised melanin-like pigments (Vaughn and Duke, 1984). Calciumrelated physiological disorders in apples and other fruits also induce corky brown tissues in the fruit pulp. Bitter pit is a physiological disorder of apples (Malus x domestica Borkh) that has been related to calcium deficiency in the fruit (Ferguson and Watkins, 1989). The symptoms generally arise in stored fruit after harvest. Economic losses can be quite substantial since the affected apples cannot be sold as a fresh commodity and must be removed by hand. Many studies have shown that the calcium nutrition of horticultural crops has an important influence on fruit quality (Neilsen and Neilsen, 2003). Indeed, several physiological disorders in the storage organs of fruits and vegetables are related to inadequate calcium supply (Shear, 1975).The translocation of calcium in higher plants is mainly restricted to xylem sap, following the unidirectional transpiration stream (Kirkby and Pilbeam, 1984), unlike K + and Mg 2+ (and N and P), which are easily transported throughout the phloem (Bergmann, 1992;Tagliavini et al., 2000). Once * To whom correspondence should be sent J. Val et al2 incorporated within the leaf, calcium does not recycle, even under conditions of deficiency (Hanger, 1979). Calcium moves into the plant in ionic form or is complexed with malic or citric acids (Bradfield, 1976;Vang-Petersen, 1980). As pointed out by Zocchi and Mignami (1995), calcium is only slightly mobile in the xylem. Thus, it can reach high concentrations in transpiring tissues (leaves) through water mass flow, but is relatively scarce in low transpiring tissues such as fruit, seed...

Polypeptides from the apple pulp of Smoothee Golden Delicious and White Renete apples were resolved by 1-D denaturing sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). According to the electropherograms, there were lower concentrations of 88, 74, 70.6 and 47.5-42 kDa proteins in bitter pit spots. Proteins weighing 30 and 26 kDa were rare in sound pulp but frequently appeared in pits and adjacent tissue. Finally, a novel 18 kDa protein was found in bitter pit spots in both varieties, and also in chemically induced corky lesions either by magnesium infiltration or ammonium oxalate cortical injections. The available data suggested that the novel protein might be an inhibitor of pectinmethylesterase, a small heat stress protein (smHSP) or a product of the Ypr-10 gene family identified with 'Mal d 1', the main allergen of apples. To elucidate the possible smHSP nature of the 18 kDa, a set of apples were heated at 40 ºC for 20 h, developing this protein in both the oxidised tissue and in the adjacent.

No abstract