Fig. 2.

Distribution of homogalacturonans in Quercus suber microgametogenesis. (A) JIM7 labelling of the partially methyl-esterified homogalacturonan at the pre-meiotic stage of pollen development, showing a ubiquitous and constant distribution of epitopes in all pectocellulosic cell walls. (B) JIM7 labelling at the bicellular pollen stage of development shows no distinctive pattern of epitope distribution. (C) Contrasting with JIM7 distribution, the weakly methyl-esterified homogalacturonans labelled by JIM5 showed a more restricted distribution of epitopes at early stages of pollen development, being detected only at the cell walls of the pollen mother cells (M). (D) As meiosis progresses the labelling fades completely. (E) Later only after release of the unicellular microspore, JIM5 labels the vesicles secreted by the tapetum and the tapetum itself. (F) At the mature pollen stage, JIM5 can only be seen in the intin wall next to the pollen pores (arrow). Scale bars = 40 µm. En, endothecium; Ml, middle layer; Tp, tapetum; M, microsporocytes; Tt, tetrad.