Cyto-architecture of Byblis glands and leaf cells based on freeze-substitution and conventional TEM.

Background And Aims: Byblis liniflora (Byblidaceae) is a carnivorous plant that has developed sticky flypaper traps with two types of glandular trichomes producing digestive enzymes and sticky mucilage. This study aimed to analyse the ultrastructure of these glandular leaf trichomes based on rapid freeze-fixation and conventional chemical fixation in the attempt to understand their functional contribution to the carnivorous performance of the plants.

Methods: The Byblis cells were studied in transmission electron microscopy, scanning electron microscopy and scanning transmission electron microscopy using cryo-techniques for fixation and substitution in addition to conventional chemical fixation.

Key Results: We show in detail the architecture of both the digestive glands and the mucilage glands with their relevant sets of organelles. Both mitochondria and plastids have a conspicuous plasticity, with branches and constrictions, and they associate to form clusters. The glandular cells appear to be transfer cells with cell wall ingrowths. Digestive glands occur in different states of development. Their cuticle forms discontinuities that are unique among glands of carnivorous plants. They look like cuticular holes - the cuticle separates from the cell wall in only one spot and then ruptures. Cuticular discontinuities thus differ from the cuticular gaps and cuticular pores so far described in carnivorous plants. We therefore propose for them the term 'cuticular holes'.

Conclusions: Application of cryo-techniques made it possible to show the true structure of the cell wall and the relationship between cell wall ingrowths and organelles, as well as the morphology and structure of organelles and their associations.