Auxin-binding by particulate fractions from tobacco leaf protoplasts

In vitro binding of 1-naphthaleneacetic acid (NAA) to particulate fractions from tobacco leaf protoplasts was studied. In freshly isolated protoplasts no specific binding could be detected, whereas it was present in particulate fractions from tobacco leaves. It is concluded that the NAA-binding-sites are probably located at the external face of the plasma membrane; they are destroyed during protoplast isolation by proteolytic enzymes in the cellulase and macerozyme preparations. After culturing the protoplasts for 3-4 d, the first cell divisions were observed and at the same time specific NAA-binding became detectable. The affinity constant for NAA was approx. 2·10(6) mol(-1) and the number of binding sites increased during further culture.