Emergences at Drosera
The species of the genus sundew ( Drosera ) are characterized by different types of emergences , some of which occur individually, some in combination with one another on the plants and mostly support the capture of prey. A distinction must be made between tentacles and non-glandular emergences in the strict sense.
Glue tentacles
Whatever their form, all characterized by their Sonnentaue with sticky secretions occupied tentacles on the leaves of which are movable in a majority of the species of the genus. These are stalked glands that secrete a sticky, sugary secretion. Their shimmer attracts insects, which then stick to the secretion. The tentacles in the immediate vicinity of the prey may then incline in the direction of the catch and thus increase adhesion and subsequent digestion.
The captured animals either die from exhaustion or choke on the viscous secretion that seeps into their trachea and blocks them. Meanwhile, the tentacles secrete enzymes such as esterase , peroxidase , phosphatase and protease , which now slowly decompose the prey and dissolve the nutrients it contains. These are then taken up by the sedentary glands on the leaf surface and used for the growth process. The latter can also be missing in some species, for example in Drosera erythrorhiza .
Quick tentacles
Charles Darwin reported in his book "Insectivorous Plants" in 1875 of relatively fast moving, marginal tentacles in Drosera rotundifolia . Because of the dimorphism of the outer marginal tentacles in this species, mostly glue tentacles, but at times also partially or completely dry quick tentacles, which bend about equally quickly when touched, Darwin's work does not reveal which of the two morphologically different structures he observed. In his detailed drawings of the leaves, no quick tales are shown, only glue tentacles.
The secretion-free structures now known as rapid tentacles have long been known from Drosera burmannii and Drosera sessilifolia . A construction that is unique in the genus are the quick tentacles of the Australian Drosera glanduligera , which only function once, and which fold in only 75 milliseconds and thus even exceed the speed of the Venus flytrap (100 ms). However, the resulting hydraulic pressure destroys the joint zone. The force (acceleration 7.98 ms -2) ) of the prey hitting the inner glue tentacles triggers a moderate bending of the glue tentacles that have been struck, whereby the catch is placed in a digestive trough in the center of the plant in 1–2 minutes. This two-stage trapping mechanism was proposed by Poppinga et al. (2012) named the catapult glue trap. Other sundew with catapult glue traps, the quick tentacles of which close in a tenth of a second and function several times, were also described in 2015 in the section Bryastrum (dwarf sundew ).
Further investigations were able to show that quick tentacles, as at times also in D. rotundifolia, occur in numerous species worldwide. These tentacles, which can only be moved up or down, are only found at the edge of the leaf blade and have a significantly wider base than the glue tentacles on the leaf surface, which can move in all directions. They are significantly elongated, with the shape of the tentacle stem varying. The head is predominantly round to shovel-shaped, flat on the underside, while on the top there are cells arranged in a pillow shape, which neither secrete drops of glue nor enzymes. In D. glanduligera the head, which functions as a step switch, is lifted off like a hook, which is not the case with the catapults of the dwarf drosera. All quick tentacles widespread in the genus have a kind of joint, mostly in the lower third of the petiole, in which the quick movement takes place. However, there are clear differences in different sections in terms of joint morphology and speed, which is between 75 ms and about 120 seconds for a movement to the center of the leaf.
Non-glandular emergences
With the first description of Drosera hartmeyerorum in 2000, discussions arose about the structure and function of the conspicuous, secretion-free emergences, which are a diagnostic feature of the species and have evidently formed from normal glue tentacles. Various, much smaller emergences could later be found on the catch leaves of the Indian sundew Drosera indica .
In Drosera hartmeyerorum , the clearly visible, 3–4 mm large, bright yellow emergences are concentrated on the base of the dark red catch leaves, as well as above the dark red crescent-shaped bracts of the inflorescence. The secretion-free emergences on the catch leaves and the inflorescence are identical and show a complex structure, the function of which is not immediately apparent. A lens-like structure made up of honeycomb-shaped, transparent giant cells, which focuses incident light on a compact, bright yellow center, sits as the head on a transparent tentacle stem. The bright yellow color does not come from the surface of the tentacle head, but is reflected from the inside through the transparent lenses.
If you shine a flashlight on these emergences, they light up bright yellow. In particular, the 1–3 “lens tentacles” sitting in a row on the red bracts of the inflorescence create a real yellow “chain of lights” when illuminated - or in nature by sunlight - which is very attractive to insects. Since their color perception is shifted into the short-wave range, the dark red bracts and catch leaves are a high-contrast, almost black background for them, against which the light yellow emergences shine intensely.
A further specialization is waiting for insects attracted by this, because the lower 8–10 cm of the flower stem are completely smooth and free of glands and bracts. So when an insect reaches the first bract with emergence (seen from the plant center), it has the very smooth stretch in front of it, at the end of which the bundles of emergence shine out of the dark red plant center, densely covered with glue tentacles. Flying or jumping there effectively traps smaller insects.
When observing the site, most of the prey consisted of young grasshoppers, which are very common in the region at the end of the rainy season. However, this still has to be confirmed by statistically usable counts. It stands to reason that the interplay of the emergences and the construction of the conspicuously perpendicular flower stalk has developed a specialization that significantly increases the effectiveness of prey capture compared to the glue traps of the rainbow plants ( Byblis ) and other sundew species that compete at the location .
Non-glandular emergence as a "chain of lights" on the inflorescence of Drosera hartmeyerorum
Non-glandular emergence of Drosera hartmeyerorum on the bracts
Non-glandular emergence of Drosera hartmeyerorum on the bracts
The non-secreting emergences observed on the catch leaves of Drosera indica are between 0.1 and 1.0 mm small, mostly distributed over the entire leaf surface, mushroom-shaped and have a hemispherical yellow head in Australian varieties, while African varieties have a colorless, translucent, wavy head have a plate-shaped head (see pictures). These are usually so small that they are barely noticeable with the naked eye, so they are unlikely to be visually attractive to insects. The function is therefore still unclear.
Non-glandular emergence of Drosera indica (Australian form)
Non-glandular emergence of Drosera indica (Australian form)
Non-glandular emergence of Drosera indica (African form)
literature
- Jan Schlauer: Drosera hartmeyerorum spec. nov. (Droseraceae), a New Sundew in sect. Arachnopus from Northern Australia. In: Carnivorous Plant Newsletter. Vol. 30, No. 4, 2001, ISSN 0190-9215 , pp. 104-106, ( online version ).
- Irmgard Hartmeyer, Siegfried Hartmeyer: A new sundew from the Ord River area (Northern Australia). In: The Taublatt. No. 42 = 1, 2002, ISSN 0942-959X , pp. 25-28, ( online version ).
- Siegfried Hartmeyer: News from the sundew: The arachnopus section under the microscope. In: The Taublatt. No. 47 = 3, 2003, pp. 4-8, ( online version ).
- Irmgard Hartmeyer, Siegfried Hartmeyer: Drosera hartmeyerorum - The sundew with light reflectors. In: The Taublatt. No. 56 = 3, 2006, pp. 4-9, ( online version ).
- Irmgard Hartmeyer, Siegfried Hartmeyer: Drosera: quick tentacles and landing lights. DVD, 2006.
Individual evidence
- ^ Wilhelm Barthlott , Stefan Porembski, Rüdiger Seine, Inge Theisen: Carnivores. Biology and culture of carnivorous plants. Eugen Ulmer GmbH & Co., Stuttgart 2004, ISBN 3-8001-4144-2 , p. 41.
- ↑ Irmgard Hartmeyer, Siegfried Hartmeyer: Drosera glanduligera - The sundew with "snap tentacles". In: The Taublatt. No. 52 = 2, 2005, pp. 34-38, ( online version ).
- ↑ a b c Simon Poppinga, Siegfried Richard Heinrich Hartmeyer, Robin Seidel, Tom Masselter, Irmgard Hartmeyer, Thomas Speck .: Catapulting Tentacles in a Sticky Carnivorous Plant . In: PLOS ONE . September 26, 2012, doi : 10.1371 / journal.pone.0045735 .
- ↑ Siegfried RH Hartmeyer and Irmgard Hartmeyer: Several pygmy Sundew species catapult-flypaper traps with repetitive function possess, indicating a possible evolutionary change into aquatic snap traps similar to Aldrovanda. In: Carnivorous Plant Newsletter . tape 44 , no. 4 , December 1, 2015, p. 172-184 .
- ↑ Irmgard Hartmeyer, Siegfried Hartmeyer: Hidden diversity: The quick tentacles of the genus Drosera. In: The Taublatt. No. 54 = 1, 2006, pp. 38-50, ( online version ).