Apple trees (Malus pumila Mill. var. domestica Fuji/Malus prunifolia rootstock) showed a high susceptibility to bitter pit when supplyed with ammonium salt instead of nitrate (control) in the nutrient solution. When apple fruit was affected by bitter pit, a lower calcium as well as a higher nitrogen and ammonium-nitrogen contents was observed in the fruit flesh near the calyx end. The activity of the mitochondrial Ca2+-uptake of the fruit flesh near the calyx end was higher when the tree was grown with ammonium salt than when grown with nitrate. Both the activities of succinate: cytochrome c oxidoreductase and the mitochondrial Ca2+-uptake per g of tissue were higher in affected fruit than in healthy fruit. Each of chlorpromazine, N-(6-aminohexyl)-5-chloro-l-napthalenesulfonamide (W-7) and N-(6-aminohexyl)-l-naphthalenesulfonamide (W-5), calmodulin antagonists, was infiltrated into the fruit for 20 min under reduced pressure (about 1 × 104 Pa). Few days later, numerous bitter pit-like spots were observed in both fruit treated with W-7 and chlorpromazine, while only a few spots were observed after the infiltration with W-5, a less potent calmodulin antagonist. A possible mechanism for the occurrence of bitter pit is discussed.
[Show abstract][Hide abstract] ABSTRACT: Al present, bitter pit is an unsolved problem despite of the different points of view under which it has been approached. It appears in some orchads in a intermittent way. In this paper, some of the factors that induce or contribute to the development of this disorder are discussed.These factors depend on the soil (high availability of K and/or Mg, hot and dry soils), on the plant (inhibited transpiration, excessive imbalance between leaf mass and fruit, restricted root growth, rootstocks and varieties) and on the management techniques and environmental conditions (excessive nitrogn supply, especially the ammonium forms, intensive pruning, premature harvest, fruits in shady zones, high temperatures). Also, some of the metabolic, functional and structural alterations that cause calcium deficiency, particulary in apple tree are described and some directions for its diagnostic, prevention and treatment, are presented. Peer reviewed
[Show abstract][Hide abstract] ABSTRACT: SUMMARY The seasonal trends of Ca in Fuerte and Hass avocado fruits from vigorous and non-vigorous trees were studied. Non-vigorous trees, with moderate root infection by Phytophthora cinnamomi, produced fruit with significantly higher Ca concentration and Ca content than vigorous trees of the same cultivar. This appeared to be related to less competition from the spring vegetative growth flush. Fuerte fruits had significantly less Ca than Hass fruits throughout the growing season. Management implications are discussed with a view to increasing fruit Ca for better storage ability and reduced post-harvest problems.
[Show abstract][Hide abstract] ABSTRACT: Crude Ca(2+)-activated protein kinase from membranes of apple (Malus domestica L. Borkh., Cox's Orange Pippin) fruit can be partially purified to yield a Ca(2+)-dependent protein kinase whose activity is apparently not regulated by calmodulin. The autophosphorylating catalytic subunit of this protein kinase shows a Ca(2+)-dependent mobility shift of approx. 10 kilodaltons (kDa) on sodium dodecyl sulphate-polyacrylamide gel electrophoresis; in the absence of added Ca(2+) or ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) its apparent molecular mass is approx. 50 kDa. The Ca(2+)-dependent protein kinase is inhibited by the calmodulin antagonists N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide and trifluoperazine with IC50 values of approx. 45 μM and 15 μM, respectively. These similarities between the protein kinase and calmodulin indicate that the kinase may be a calmodulin-like protein.
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