Abstract
Highly evolved carnivorous plants secrete digestive enzymes for degradation of trapped animals and absorb whole macromolecules from their prey by means of endocytosis. (1) Background: In the pitcher-plant family Sarraceniaceae, the production of enzymes is dubious and no evidence for endocytosis is known so far. (2) Methods: Heliamphora nutans, Darlingtonia californica, and nine taxa of Sarracenia are tested for cuticular pores, and for protease and endocytosis of the fluorescent protein analogue FITC-BSA, after 10–48 h of stimulation. (3) Results: Cuticular pores as a prerequisite for enzyme secretion and nutrient uptake are present in all tested species. Permeable cells form clusters in the inner epidermis of the pitchers, but are only little differentiated from impermeable epidermis cells. Proteases are found in S. psittacina, S. leucophylla, S. minor, S. oreophila, S. alabamensis, H. nutans, D. californica lacking only in S. flava and in S. purpurea ssp. purpurea, S. purpurea ssp. venosa, S. rosea, where enzyme production is possibly replaced by degradation via the extraordinary diverse inquiline fauna. S. leucophylla, S. minor, S. oreophila exhibit both protease production and endocytosis; S. psittacina, S. alabamensis, H. nutans, D. californica produce proteases only; no single species shows endocytosis without protease production. (4) Conclusions: Protease secretion seems to be a prerequisite for endocytotic nutrient uptake. Transport of FITC-BSA absorbed by endocytosis towards the vascular tissue of the trap leaves suggests that endocytosis of nutrients is more than a side effect of enzyme secretion.
Highlights
The American pitcher plant family Sarraceniaceae comprises three genera of pitcher plants with at least 35 species: Darlingtonia, Heliamphora, and Sarracenia
Pores were restricted to the absorptive zone for uptake which is, following the terminology of Juniper et al [20], zone 4 for Sarracenia and Heliamphora, and zone 5 for Darlingtonia (Supplementary Figure S2)
Though no morphologically differentiated glands are developed in the absorptive zones of the pitchers in Sarraceniaceae, three types of epidermal cells can be distinguished: (1) Trichoblasts protruding into retentive hairs never absorb methylene blue, neither to the cell wall, nor to the cytoplasm
Summary
The American pitcher plant family Sarraceniaceae comprises three genera of pitcher plants with at least 35 species: Darlingtonia, Heliamphora, and Sarracenia. Heliamphora comprises 23 species, which grow in northern South America, whereas Darlingtonia is a monotypic genus that appears only in the northwestern United States [1,2,3]. Within the family of Sarraceniaceae, prey capture is performed by cone shape leaves, which are superficially similar to the pitcher traps of Nepenthes and Cephalotus, but less sophisticated. This is true on the morphological level, but possibly for the physiology. Since the first studies on Sarracenia, Plants 2019, 8, 367; doi:10.3390/plants8100367 www.mdpi.com/journal/plants
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