Cell Wall Microdomains Analysis in the Quadrifids of Utricularia dichotoma

Carnivorous plants have fascinated botanists and ecologists with their various unusual adaptations in organ structure, physiology, and complex interactions with other organisms since the time of Charles Darwin. Species of the genus Utricularia (bladderworts, family Lentibulariaceae) are carnivorous plants that prey mainly on invertebrates using traps (bladders) of leaf origin. In the traps, there are glandular trichomes called quadrifids, which produce digestive enzymes and absorb the products of prey digestion. These quadrifids are unique due to their highly complex glandular cell structure; hence, they are an excellent model for studying the cell wall and its specialization. The main aim of the study was to investigate the presence and distribution of homogalacturonans (HGs) and hemicelluloses in the cell walls of trichome cells and especially in cell wall ingrowths in the quadrifid cells. The following antibodies were used against the wall components: anti-HGs (homogalacturonans) -JIM5 (low methylesterified HGs), JIM7 (highly esterified HGs), LM19 (low methylesterified HGs), CCRC-M38 (a fully de-esterified HG), LM5 (galactan); anti-hemicelluloses-LM25 (galactoxyloglucan; XXLLG, XXLG, XXXG modules of xyloglucans), LM15 (xyloglucan), CCRC-M138 (xylan), LM11 (heteroxylan); and anti-mannans: LM20 (heteromannan) and LM22 (heteromannan). The localization of the examined compounds was determined using immunohistochemistry techniques and immunogold labeling. In quadrifid cells, we found differences in the presence of the epitope detected by the LM5 antibody in the cell walls. In addition, cell wall ingrowths represented distinct microdomains of the cell wall in terms of the occurrence of wall components (they were methylesterified and demethylesterified homogalacturonan-poor). Hemicelluloses (galactoxyloglucan and xyloglucan) and arabinogalactans co-occur in cell wall ingrowths. Also, a part of the cell wall of the pedestal cell, which forms a Casparian strip, represented a distinct microdomain. We did not detect epitopes recognized by LM11, LM20 and LM22 antibodies. Our research shows that several cell wall microdomains occur in the cell walls of quadrifid cells. They differ depending on the presence and distribution of low methylesterified HGs, highly esterified HGs, fully de-esterified HGs, galactan (the epitope detected by the LM5 antibody), xyloglucan, galactoxyloglucan, and xylan (the epitope detected by the CCRC-M138 antibody).