GREAT SUNDEW

Drosera anglica

Sundew Family [Droseraceae]

month8jul month8july month8aug

status
statusZnative
flower
flower8white
inner
inner8yellow
morph
morph8actino
petals
petalsZ5
stem
stem8round

16th June 2011, Glascarnoch Loch, Wester Ross Photo: © John Brailsford
Taller (to 6 inches) and more robust than the similar Oblong-leaved Sundew


16th June 2011, Glascarnoch Loch, Wester Ross Photo: © John Brailsford
Un-like Oblong-Leaved Sundew which has sticky hairs in an oval shaped area near the tip, Great Sundew has leaves that gradually taper to a hairless similar in outline to a lacrosse stick.


16th June 2011, Glascarnoch Loch, Wester Ross Photo: © John Brailsford
The hairs are red with sticky transparent blobs on the ends and occupy one side of the flattened yellowish-green 'leaf', more reminiscent of a cat brush. The other side is nominally free of hairs.


16th June 2011, Glascarnoch Loch, Wester Ross Photo: © John Brailsford
When an insect lands on the hairy side, it triggers the release of chemicals responsible for closing the 'leaf' up onto the insect, whereupon the plant slowly digests the insect with enzymes, absorbing the released nutrients for its own purposes. The leaf will curl over starting at the top in about a minute from being triggered.


Easily mistaken for : Oblong-leaved Sundew

Hybridizes only with : The commoner Round-Leaved Sundew (Drosera rotundifolia) to produce Obovate Sundew, but unlike Round-leaved Sundew, it grows over a much smaller area, occupying mainly the North of Scotland.

No relation to : Sunflower, Perennial Sunflower, Sun Spurge or Dewberry [plants with similar names]. Nor to Purple Sundew (Disphyma crassifolium) a serpentine rock speciality in the Dewplant Family [Aizoaceae].

The clear liquid mucilage at the end of each hair is viscous, and traps the insect, which is attracted to the plant by the sugary scent coming from the glands. When small prey land on the hairs, the hairs are triggered into moving towards the insect, physically trapping it to prevent escape from the stick mucilage. This takes place over a few minutes. When the insect is thus trapped, the leaf blade bends over upon itself in order to secrete additional mucilage on the insect to first liquidise it and then absorb the nitrogenous fluids for the plants own use. Only the indigestible chitin exoskeleton of the insect is left over, when the plant un-furls ready to catch the next un-wary insect. Nitrogenous compounds are in short supply in the boggy peaty uplands that the plant grows upon. Digesting insects are not the only way the plant survives, it does actually also have roots with which it feeds itself. The insects are supplementary, but necessary. However, not all insects are trapped by Sundews: ants are able to plunder Sundews with impunity, making off with 2/3rds of the sticky spoils.

The plant is normally lime-green, but some parts redden under strong sunlight as a protection from the suns rays.

The flowers are white, actinomorphic, with five petals, five sepals and five stamens. The flowers are seemingly shy to appear, your author has not seen any despite traipsing through miles of upland bogs over the decades he has been walking the mountains. But then bogs are not something walkers like to linger on for long for fear of sinking too far.

In the World there are more than 194 species of Sundew (only 3 in the uk plus two hybrids). The sticky transparent mucilage consists of polysaccharides mixed with the ions of calcium, magnesium, potassium and sodium producing an acidic mixture with a pH of 5. These sweet polysaccharides attract insects. Sundews also produce enzymes called chitinases which are able to break down the chitin exo-skeleton of insects which the plant then absorbs as part of its diet. Sundews also contain enzymes called proteases which are able to break down proteins. Sundews contain two types of glands: secretory glands which secrete a sweet attractive mucilage, and sessile glands which absorb the soup of digested chitins, proteins and fatty acids once contained in the insects it has trapped.

The sequence of events is thus outlined:
An insect is attracted to the sundew leaf by the odour of sweet-smelling polysaccharhides. The insect lands on the leaf. The leaves are highly sensitive to touch and slowly start curling over so as not to alarm the insect into trying to escape. This traps the insect both mechanically and by the sticky polysaccharide goo. The insects die within 15 minutes either through the exhaustion of trying to escape or by being asphyxiated by sticky mucilage. The enzymes (protease, peroxidase, phosphatase, esterase and others) contained within the sticky mucilage start to break down the chitin exo-skeleton and proteins and fatty acids within the insect into a soup which is absorbed by the sessile glands of the sundew into the plant for use by the plants metabolic machinery.

THIGMONASTY

Thigmonasty is one of the phenomena exhibited plants called nastic movements, whereby some part of a plant moves in response to some form of stimulus. Mastic movements are initiated by various stimuli, thus Chemonasty (whereby the plant moves in response to soil chemicals / nutrients), Epinasty (by gravity), Geonasty (by gravity), Hydronasty (by water), Hyponasty (by the growth hormone Ethylene), Nyctonasty (by circadian clock and light), Photonasty (by light), Thermonasty (by heat) and Thigmonasty (by touch); all initiated by differing stimuli.

The rapid curling up of the leaves to touch is called Thigmonasty. Thigmonasty occurs in several plant families, each by probably differing mechanisms.

The mechanism by which Sundews react to touch involves an action potential (an electrical voltage generated by some specialist cells) which changes the leaf turgor. The cells of the outer part of the leaf rapidly elongate in response to the rapid lowering of the pH (caused by the action potential associated with the movement of Calcium, Potassium and Chlorine ions across a membrane). The resulting elongation of the cells on just one of the surfaces of the leaf forces the leaf to curl inwards. However, the exact modus operandi has not yet been fully elucidated; as always, biology is more intricate than what it at first appears.

Thigmonasty, the movement of plant parts in response to touch, is also to be found in some species of Thistles, where the anthers first shrink in response to touch and then rapidly fling back showering the insect with pollen. The leaves of the Wood-Sorrels also exhibit thigmonasty which fold downwards in response to touch.

The non-native Venus Flytrap (Dionaea muscipula), another carnivorous plant, also snaps its two open jaws shut in response to being touched inside.

But probably the most well-known plant exhibiting thigmonasty is the non-native Sensitive Plant (Mimosa pudica) which belongs to the Pea Family (Fabaceae). This plant folds its bipinnate leaves almost instantly in response to touch (thigmonasty).

There are several other similar terms to denote plants moving in response to some stimulus or other; these are Tropism, Nastism, Kinesis and Taxis...

Kinesis is the movement (or activity) of a cell or organism in response to a stimulus, such as light, temperature-variation or a gaseous substance, but un-like Taxis, the movement is non-directional in relation to that stimulus. Orthokinesis is where the speed of the movement is dependent upon the intensity of the stimulus, whereas in Klinokinesis the rate of response is proportional to the intensity of the stimulus (it could be inversely proportional, or just a binary on or off with Orthokinesis).

Taxis is where the movement in response to the stimulus is directional in relation to the stimulus, it could be either negative (away from the stimulus) or positive (towards the stimulus). There are many forms the stimulus can take, in chemotaxis the organism responds to chemicals (either gaseous or liquid), aerotaxis (to oxygen), anemontaxis (to wind), barotaxis (to pressure), electrotaxis (to electrical currents or voltages), gravitaxis (to gravity), hydrotaxis (to water or moisture), magnetotaxis (to magnetic field), phototaxis (to light), rheotaxis (to fluid flow), thermotacis (to temperature), and thigmotaxis (to physical contact). Not all these '-taxis' are relevant to plants, although your Author suspects that some plant somewhere will be found to respond to magnetic fields yet, if they have not already found a plant behaving so.

Tropism is where the plant, like Taxis, responds to the direction the stimulus came from whereas Nastism, like Kinesis, is non-directional. Exactly what the difference is between these paired terms is fairly esoteric. Tropism and Nastism are more associated with plants than the other two terms.

TURGORINS and AUXINS


Turgorins or so-called 'Leaf Movement Factors' are derivatives of organic acids such as Gallic Acid and Catechuic Acid and they affect leaf movement by altering the turgor pressure in a wide range of plants.

Turgorins are auxins, plant hormones (phytohormones), which are involved in the thigmonastic response of plants. Turgorin itself is one such Turgorin, being the Sulfate of the Glucoside of Gallic Acid. The sulfate group makes Turgorin strongly acidic. This acidity seems to be the reason for the leaf-movements - the same leaf movements can be induced by using dilute sulfuric acid. In Mimosa pudica the Glucoside of Gallic Acid is sulfated by the enzyme Sulfotransferase (ST) which transfers a sulfate moiety from 3'-PhosphoAdenoside-5'-PhosphoSulfate (PAPS) to the Glucoside of Gallic Acid.



Another Turgorin is Turgorin LMF1 (Turgorin Leaf Movement Factor 1) which is the double Glycoside of Gentisic Acid (rather than of Gallic Acid as for Turgorin itself). One of the glycosides (the pentose) is related to DeoxyRibose. Both Turgorins are involved in the leaf movements in Sensitive Plant (Mimosa pudica). These same phytohormones are involved both in the tactile and the diurnal closing of its leaves.

The Turgorins are very likely also involved in the mechanism for opening and closing the stomata whereby plants are able to transpire. Thus they are probably involved not only in the regulation of temperature of the plant but also for the transportation of themselves throughout the plant via the sap.

Turgorin LMF1 is also present in False Acacia (Robinia pseudoacacia) and effects leaf movement by stomatal closure.


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Drosera
(Sundews)

GREAT SUNDEW

Drosera anglica

Sundew Family [Droseraceae]

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