Ultrastructural characterization of yellow shoulder disorder in a uniform ripening tomato genotype

Yellow shoulder disorder (YSD) is characterized by sectors of yellow or gre en tissue under the peel of uniform ripening tomato (Lycopersicon esculentu m Mill.) fruit. Tissues excised from sectors of fruit expressing YSD, from adjacent red sectors, and from mature green fruit were used to compare the ultrastructural alterations in cells and tissue affected by YSD and to dete rmine whether the disorder is caused by delayed fruit maturation or by aber rant development. Cells from YSD sectors were smaller than those from both adjacent red-ripe tissue and mature green fruit, The smaller cells from the YSD sectors were at a different developmental stage than cells of the adja cent red-ripe tissue, Chromoplasts in red-ripe tissue were more advanced in development than those in YSD sectors or mature green fruit. Using the tra nsition from chloroplast to chromoplast and the degradation of the middle l amella between adjacent cells as developmental markers, the maturity of tis sue from YSD sectors appeared to be equal or greater than that of tissue fr om mature green fruit. However, cell enlargement, which takes place early i n fruit development, was retarded in YSD sectors, Therefore, the ultrastruc tural features of YSD are not compatible with a delayed ripening model for this blotchy ripening disorder, These observations provide a basis for comp aring YSD in uniformly ripening tomatoes with other blotchy ripening disord ers.