Non-climacteric fruits

Non-climacteric fruits do not experience a surge in ethylene production that triggers a respiratory rise. Research in non-climacteric fruit ripening has been traditionally dragging behind its climacteric counterparts and although a large body of information is being accumulated there is not yet a clear picture of the common mechanisms governing the ripening process in this large class of fruits. Numerous ripening-induced genes are being cloned encoding proteins involved in cell wall degradation, sucrose and lipid metabolism, anthocyanin synthesis, cell expansion and flavor development (Civello et al., 1999; Medina-Escobar et al., 1997; Moyano et al., 1998; Nam et al., 1999; Trainotti et al., 1999). DNA microarray techniques have recently been used to identify ripening related genes with the prospect of providing a large amount of data to study the coordination of gene expression during the ripening of strawberry in particular and other nonclimacteric fruit crops in general (Aharoni et al., 2000).

Interestingly, even though ethylene does not play a role in the coordination of ripening, it has been known for some time that it can accelerate senescence of non-climacteric produce (including fruits and vegetables) (Kader, 1985) therefore it is important to avoid the presence of ethylene during transport and storage. Recent evidence (Wills et al., 1999) shows that ethylene can affect the ripening process of 23 different kinds of produce, many of them nonclimacteric, at levels much lower than previously reported. Also recently, genes encoding ACC synthase and ACC oxidase the two key enzymes in the biosynthesis of ethylene, have been cloned in pineapple, a non-climacteric fruit. It has been shown that both genes are induced during ripening in a very similar way to the induction patterns observed in climacteric fruits (Cazzonelli et al., 1998).