INDUCTION OF SMALL HEAT-SHOCK PROTEINS IN MESOCARP OF CHERIMOYA FRUIT (ANNONA CHERIMOLA MILL.) PRODUCES CHILLING TOLERANCE

Cherimoya is a major crop in the subtropical areas of the Spanish coast. The fruit are perishable because of their rapid climacteric ripening. Storage between 10 and 12C produces some extension of the shelf life of the fruit as a small delay in senescence is produced. A lower storage temperature produces chilling injury. The aim of this work is to find a way to make the fruit more resistant to low temperatures. In several plant species the synthesis of small molecular size heat-shock proteins (sHSPs) prevents and/or repairs stress induced damage; therefore, we investigated the induction of sHSPs in the mesocarp of cherimoya fruit. Heating the fruit at 55C during 5 h produces alleviation of the chilling-injury symptoms when the fruit are stored at 4C. The thermal stress induces proteins recognized by antibodies against sHSPs of different classes from other plant species. This induction is proportional to the temperature in the experimental range of 46-50C. PRACTICAL APPLICATIONS Refrigeration is the only described way to extent shelf life of cherimoya as senescence is delayed by the decreasing temperature. This is true until chilling injury appears. Senescence of this fruit occurs in 4-5 days when stored at 20C, which is a regular temperature in the production area. Storage at 10-12C allows commercialization during one additional week. Different attempts have been made to extend the period of conservation by using controlled atmosphere and lower temperatures. The problem is that cherimoya fruit are very susceptible to chilling injury. If a short heating treatment induces small molecular size heat-shock proteins (sHSPs), which would further protect the fruit from chilling injury, this would probably allow a lower temperature for transportation and conservation, thus increasing the period for commercialization. Exportation could be done in a safer way.