ANATOMY OF THE LEGUME NODULE CORTEX - SPECIES SURVEY OF SUBERISATION AND INTERCELLULAR GLYCOPROTEIN

Nodules of 29 species from 23 legume genera were examined for suberisa tion and glycoprotein deposits. Extensive suberisation of the nodule o uter cortex to form a periderm was considered a primitive feature, com mon to non-legume and caesalpinioid nodules. The periderm was less ext ensive in nodules of Mimosoideae and Papilionoideae. Vascular bundles within the nodule were always surrounded by a vascular endodermis, def ined by the presence of suberin on radial walls. Suberisation of the t angential walls of this endodermis was considered to be a primitive fe ature (present in all species examined of Caesalpinioideae and Mimosoi deae, and in 10 out of 21 Papilionoideae) which may limit solute impor t to and export from the nodule. Glycoprotein was observed in the apop last of the cortex in the three papilionoid species examined, but was absent in the caesalpinioid species examined. The common endodermis wa s recognised as an advanced feature, present only in certain species o f the subfamily Papilionoideae (5 of 7, and 11 of 15 species of indete rminate and determinate nodule growth respectively). A membrane imperm eant dye (lucifer yellow-CH), supplied in the rhizosphere under a mild vacuum, was observed to infiltrate through the cortex and into the in fected zone in caesalpinioid nodules, and as far as the inner cortex i n mimosoid and papilionoid nodules. Thus the common endodermis does no t serve as an apoplastic barrier, and is unlikely to serve as a signif icant oxygen 'diffusion barrier'.