Coordination of intertracheid pit traits and climate effects among cycads.

Interconduit pit membranes, which are permeable regions in the primary cell wall that connect to adjacent conduits, play a crucial role in water relations and the movement of nutrients between xylem conduits. However, how pit membrane characteristics might influence water-carbon coupling remains poorly investigated in cycads. We examined pit characteristics, the anatomical and photosynthetic traits of 13 cycads from a common garden, to determine if pit traits and their coordination are related to water relations and carbon economy. We found that the pit traits of cycads were highly variable and that cycads exhibited a similar tradeoff between pit density and pit area as other plant lineages. Unlike other plant lineages (1) pit membranes, pit apertures, and pit shapes of cycads were not coordinated as in angiosperms; (2) cycads exhibited larger pit membrane areas but lower pit densities relative to ferns and angiosperms, but smaller and similar pit membrane densities to non-cycad gymnosperms; (3) cycad pit membrane areas and densities were partially coordinated with anatomical traits, with hydraulic supply of the rachis positively coordinated with photosynthesis, whereas pit aperture areas and fractions were negatively coordinated with photosynthetic traits; (4) cycad pit traits reflected adaptation to wetter habitats for Cycadaceae and drier habitats for Zamiaceae. The large variation in pit traits, the unique pit membrane size and density, and the partial coordination of pit traits with anatomical and physiological traits of the rachis and pinna among cycads may have facilitated their dominance in a variety of ecosystems from the Mesozoic to modern times.

Characterization of the complete chloroplast genome of endangered Cycads Zamia fischeri Miq. ex Lem.

The whole chloroplast (cp) genome sequence of Zamia fischeri has been characterized. The cp genome length was 164,767 bp in length, with a GC content of 39.7%, containing a large single copy (LSC) of 90,226 bp, a small single copy (SSC) of 23,223 bp, and a pair of inverted repeats (IRs) of 25,659 bp. The genome contained 127 genes, including 88 protein-coding genes, 31 tRNA genes, and 8 rRNA genes. A phylogenetic analysis based on complete chloroplast genomes in Cycads indicates that Z. fischeri clustered with another Zamia (Z. furfuracea). This complete chloroplast sequence offers a promising tool for further species identification, population genetic conservation, and evolutionary studies of Zamiaceae, as well as for Cycadales.