Fig. 4. Stem cross sections of supported (a, c, and e) and unsupported plants (b, d, and f) at different distances from the shoot apex: one meter (a and b), two meters (c and d), and three meters (e and f). Lianescent xylem is produced only in supported plants (white arrows), from 1.5 meters from the apex along the proximal portion of the stem (c and e). In contrast, only self-supporting xylem is produced by unsupported plants (d and f). Note the smaller xylem production in supported plants, measured by the distance between the pith (P, not shown in d and f) and the cambium (C). Scale: 30 µm. Unstained sections.
All plants produced self-supporting xylem near the stem apex (Fig. 5a and b), while the production of lianescent xylem was observed only in plants grown with physical supports. Lianescent xylem formation started from 1.5 – 2 m from the apex and extended through the proximal portion of the stem in supported plants (Fig. 5c and 5e). In contrast, unsupported plants only produced self-supporting xylem along the entire stem (Fig. 5d and 5f).
The production of lianescent xylem was associated with a smaller xylem production, measured as the linear distance between the cambium and the beginning of the secondary xylem (Fig. 5). In contrast, unsupported plants, which only formed the self-supporting xylem, produced more secondary xylem at the same distance from the apex compared to supported plants
These findings indicate that lianescent xylem formation occurs in response to stem attachment to physical supports, leading to reduced cambial activity, increased vessel size, and enhanced xylem conductivity.