AGE-DEPENDENT MODIFICATIONS AND FURTHER LOCALIZATION OF THE CX 26-LIKE PROTEIN FROM VICIA-FABA L

A strong age dependency together with alterations in the cellular dist ribution of CX 26 immunorelated protein(s) was found for differently d eveloped leaves of Vicia faba L. With increasing age, an immunoreactiv e 40 kD band was observed in the soluble and microsomal fraction. In t he cell wall protein preparation of young and fully differentiated lea ves the 40 kD band was the minor constituent. A 33 kD polypeptide was dominantly localized in the microsomal fractions of all developmental stages and in SDS-extracts of total cell proteins of young leaves. A 2 1 kD protein together with a 16 kD polypeptide was associated with the cell wall fraction. The 21 kD protein, assumed to represent a plasmod esmatal constituent, was reduced with age. In SDS extracts, prepared f rom the different developmental stages of the leaves and of mesophyll protoplasts, the age-dependent appearance of the several immunostained bands was most obvious. A correlation of the 16, 33, and 40 kD bands to a turnover of the 21 kD protein is suggested. The reduced amount of the 21 kD protein with increasing age may be contemplated as an indic ation for a relative decrease of symplastic connections between cells of maturing leaves. This is in agreement with the results obtained by immunofluorescence studies using guard cell protoplasts. Here, observa tions pointed also to a reduction and final loss of CX 26-related prot ein at the protoplast surfaces.