Cytological differentiation and cell wall involvement in the growth mechanisms of articulated laticifers in Tabernaemontana catharinensis A.DC. (Apocynaceae)

Abstract

The cellular mechanisms of laticifer growth are of particular interest in plant biology but are commonly neglected. Using transmission electron microscopy and immunocytochemical methods, we recorded cytological differentiation and evaluated the cell wall involvement in the growth of articulated laticifers with intrusive growth in the mature embryo and plant shoot apex of Tabernaemontana catharinensis. The incorporation of adjacent meristematic cells into the laticifer system occurred in the embryo and plant shoot apex, and the incorporated cells acquired features of laticifer, confirming the laticifers' action-inducing mechanism. In the embryo, this was the main growth mechanism, and began with enlargement of the plasmodesmata and the formation of pores between laticifers and meristematic cells. In the plant shoot apex, it began with loose and disassembled walls and the reorientation of the cortical microtubules of the incorporated cell. Plasmodesmata were absent in these laticifers. There was stronger evidence of intrusive growth in undifferentiated portions of the plant shoot apex than in the embryo. The numerous plasmodesmata in laticifers of the embryo may have been related to the lower frequency of intrusive growth. Intrusive growth was associated with presence of arabinan (increasing wall flexibility and fluidity), and absence of galactan (avoiding wall stiffness), and callose (as a consequence of reduction in symplastic connections) in the laticifer walls. The abundance of low de-methyl-esterified homogalacturonan in the middle lamella and corners may reestablish cell-cell bonding in the laticifers. The cell wall features differed between embryo and plant shoot apex and are directly associated to laticifer growth mechanisms.

Laticifer growth pattern is guided by cytoskeleton organization

“…Two concurrent hypotheses based on observations from anatomical and developmental studies have been debated to explain their mode of growth in the plant body: (1) Laticifers grow through apical intrusive growth in meristematic regions, dissolving the middle lamella through enzymatic activity and growing intrusively between cells ( Mahlberg, 1993 ; Canaveze and Machado, 2016 ; Castelblanque et al, 2016 ; Canaveze et al, 2019 ). In this case laticifers might combine two types of cell expansion, diffuse growth followed by polarized growth, as described for some fibers ( Snegireva et al, 2010 ; Gorshkova et al, 2012 ; Majda et al, 2021 ); (2) Laticifers may grow through the addition of new cells in the laticifer system followed by cell expansion, thus not through apical growth.…”

New Aspects of Secretory Structures in Five Alismataceae Species: Laticifers or Ducts?

“…Leaves, flowers and floral apices were dehydrated with an ethanol series (10%, 30%, 50%, 70%, 80%, 90% and 95%), embedded in histological resin using a preinfiltration solution (95% alcohol: pure resin, 1:1) and a pure resin solution (Historesin, Leica Microsystems Inc., Heidelberg, Germany), and cut into longitudinal and transverse 5 µm sections using a rotary microtome (Leica RM 2145, Leica Microsystems Inc., Heidelberg, Germany). The sections were stained with 0.1% toluidine blue in phosphate buffer, pH 6.5 [68][69][70][71], washed under running water, dried in the open air, mounted in Entellan ® (Merck KGaA, Darmstadt, Germany) and observed under a Nikon Eclipse Ci light microscope (Tokyo, Japan) with a Motic ® Cam Pro 252B digital camera (Beijing, China).…”

“…Petiole samples were also free-hand sectioned using fresh material, with five fragments and more than 20 sections for each, and the main compounds of the exudate were analyzed using the following reagents: Sudan Black B and Sudan IV for total lipids [72], oil red for rubber [73], Lugol for starch [66,73], ferric chloride for phenolic compounds [66], and Wagner's reagent for alkaloids [73,74]. Material embedded in historesin was stained with toluidine blue for the detection of phenolic compounds and pectin [67], with periodic acid-Schiff (PAS) for neutral polysaccharides [73,75] and Ruthenium red for acidic mucilage [76], and with Coomassie blue [73,77] and xylidine Ponceau [73,78] for proteins (see [68,70,71]). Photomicrographs were obtained with a Leica DFC 495 digital camera coupled to a Leica DM 5500 B light microscope and a Nikon Eclipse Ci photomicroscope (Tokyo, Japan) with a Motic ® (Beijing, China) Cam Pro 252B digital camera.…”

Laticifers in vascular plants

“…Several papers support the theory of intrusive apical growth in non-articulated laticifers (Snyder 1955, Wilson and Mahlberg 1977, Mahlberg 1993) and in some articulated laticifers (Rudall 1994, Canaveze and Machado 2016, Canaveze et al 2019. According to this theory, laticifers would develop in the intercellular spaces of plant tissues (Mahlberg 1993).…”

“…According to this theory, laticifers would develop in the intercellular spaces of plant tissues (Mahlberg 1993). Although this theory is hard to explain, many authors still support it (Canaveze and Machado 2016, Canaveze et al 2019, Marinho and Teixeira 2018.…”