Format: ORAL

Pere M. Mir-Rossell, Jaume Flexas, Antoni J. Far, Marc Carriqu

Universitat de les Illes Balears, Palma, Spain

The DNA content in the nucleus, commonly measured as genome size (GS), is considered a strong predictor of minimum cell size in eukaryotic organisms. In tracheophytes, the scaling between GS and cell size determines leaf anatomy and, consequently, plant growth capacity. However, the few studies involving bryophytes, which only considered stomatal guard cells of the diploid phase, suggest that GS-cell size scaling does not apply to this group. We measured leaf area, cell dimensions and cell wall thickness from mid-lamina, largest and smallest cells in phyllidia of 160 moss species with known GS. From these, cell area and volume and different key anatomical traits determining photosynthesis were calculated. We contrasted cell sizes with GS data through Standardized Major Axis (SMA) analyses. GS weakly explained the variability of laminal and maximum cell sizes (width, area and volume), but explained more than half of the variability in minimum cell sizes. While GS positively correlated with moss phyllid area, it did not significantly explain cell wall thickness or other anatomical traits. Notably, SMA slopes for cell sizes were considerably steeper than those reported for tracheophytes. Furthermore, maximum to minimum volume ratios showed greater variability in species with smaller GS. Our findings suggest that GS is a determinant of the minimum cell size in mosses, resembling trends observed in tracheophytes. This similarity holds between tracheophyte sporophytes (diploid leaf and guard cells) and moss gametophytes (haploid leaf cells), but not in moss sporophytes (diploid guard cells), implying a differential impact of GS based on cell and phase function. The relatively steeper SMA slopes and maximum to minimum volume ratios support the hypothesis that smaller GS (as seen in mosses) allow a greater cell size variability. Although not directly determining their physiology, GS could indirectly influence moss productivity and growth capacity by affecting phyllid area.