Alternating damp plant

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Alternating moisture ( poikilohydre, poikilohydric ) plants do not have any organelles to regulate the uptake and release of water. They are only capable of active life when the relative vapor pressure of their environment is high , as they have no substances in the cell wall that restrict evaporation ( cutin and suberin ). They largely adjust their water content to the moisture level of their surroundings (fog, dew, rain). Your cells do not have a central vacuole . The plasma gradually shrinks when it dries up, and the metabolism is restricted.

Due to the lack of a large central vacuole, plants with varying degrees of moisture do not shrink with greater water loss. The metabolic activity is restricted; but the plants do not die. When the water availability improves, the plants swell up and the life processes start up again. Plants with alternating moisture levels are drought-resistant and therefore very well adapted to constantly changing environmental conditions (such as dry and wet periods).

To periodically wet organisms most include Thallophytes as algae , lichens , fungi and mosses and various bacteria , ferns and a few seed plants . In contrast, naturally moist plants (homoiohydric, homoiohydric plants) can keep the water balance in the cells constant.

Not to be confused with plants with alternating humidity and plants with alternating humidity.

Emergence

In evolution , highly specialized, dehydration-tolerant plants have developed due to very difficult, harsh environmental conditions and severe water shortages. Such plants have to withstand long periods of drought, which are also often short and irregular. The dehydration-tolerant plants have to use phases of moisture as quickly and effectively as possible. Because of this particular need, the possibility has developed that some plants can lose up to 95% of their water content. In doing so, they have to solve some problems within their cells, e.g. B. the detachment of the cell membrane from the cell wall ( embolism ) and the death of chloroplasts . Such plants, which can regenerate their chloroplasts after drying out, are called poikilochlorophyll .

Survival strategies during dehydration

Resurrection plants have developed special strategies so that they can survive longer periods of dehydration.

  • Monocot plants have developed a special abnormal growth in thickness , which allows them to grow in width. You can find this especially with Vellozia .
  • The formation of false stems (pseudostems) in the monocot , i.e. the formation of stems through overlapping leaf bases, can also be advantageous.
  • Vegetative propagation through the formation of runners (stolons) and branches is widespread over the entire plant kingdom. This has the advantage that the plants do not have to go through complicated reproductive cycles.
  • The plant Borya constricta can conserve ATP during dehydration (as long as the water content of the cells is greater than about 30%). However, the ATP level recovers only slowly after water intake. In addition, the Australian plant forms sucrose during dehydration when the turgor pressure inside the cell drops. This is usually found almost exclusively in seeds.
  • The formation of adventitious roots also increases the chances of survival. Such roots are formed directly on the stalk or shoot. This has the advantage that growth is also possible on dead plant parts. In addition, nutrients from old parts of the plant that have already died can be used again.
  • Thanks to special aerial roots (the Velamen radicum , which is mainly known from orchids ), the water can be absorbed extremely quickly when it rains.
  • Many fern plants have developed special xeromorphic leaves whose longitudinal furrows allow the leaves to roll in and out. On the inside of the furrows are protected stomata, which are automatically closed by the rolled up leaf when it is dry. When it rains, reverse hygroscopic movements, which are achieved by the swelling of turgor cells, allow the leaves to roll out
  • A thick layer of roots and overlapping leaves can also protect against fires, which are common in arid areas. This is mainly done through the inclusion of oxygen-impermeable resin layers.
  • Chamaegigas intrepidus , the only known aquatic resurrection plant currently known, can lose up to 80% of its mass. In doing so, she accumulates abscisic acid in her cells.

Representatives in various taxa

Desiccation-tolerant vascular plants occur in 13 families with currently around 330 known species. Most of the representatives can be found among the monocot plants and the fern-like plants . In the three-furrow pollen dicotyledonous plants (Rosopsida) there are only relatively few representatives, which is mainly due to the lack of parallel veins in the leaves and thus their limited ability to curl. The "resurrection plants" also emerged several times independently of one another ( polyphyletic ). One speaks here of convergence .

Desiccation-tolerant plants (or often also called “resurrection plants”) occur more frequently on special locations such as island mountains , rocks, in shallow depressions, in crevices or in rock basins. Her diversity focus lies in Southeast Africa in Madagascar, in South America in Brazil and in Western Australia. The biodiversity is greatest in the tropics, because the seasonal dry seasons predominate there.

Selection of representatives of the Pteridophyta

Among the fern-like plants ( Pteridophyta ) around 50 species are currently known, of which three families are particularly species-rich in drought-tolerant plants.

Selection of representatives of the monocots

The monocotyledonous plants are home to the greatest variety of such species and currently around 250 drought-tolerant representatives are known. Some notable families with such types are:

Selection of representatives of the three-furrow pollen dicotyledonous plants

Of the three-furrow pollen dicotyledonous plants (Rosopsida), only about 30 drought-tolerant species are known.

literature

  • Porembski & Barthlott: Granitic and gneissic outcrops (inselbergs) as centers of diversity for desiccation-tolerant vascular plants (Plant Ecology 151/2000)
  • Black & Pritchard: Desiccation and Survival in Plants - Drying without Dying (CABI Publishing 2002)
  • M. Schaefer: Dictionary of Ecology . Gustav Fischer, Jena, 1992. ISBN 3-8252-0430-8
  • Ludger Rensing , Rüdiger Hardeland , Michael Runge, Gottfried Galling : General Biology. 1984, Ulmer, 420 pages. ISBN 3-8001-2494-7

swell

  1. ↑ Mike F. Quartacci, Olivera Glišić, Branka Stevanović, Flavia Navari ‐ Izzo 2012: Plasma membrane lipids in the resurrection plant Ramonda serbica following dehydration and rehydration . In: Journal of Experimental Botany (2002) 53 (378): 2159-2166. doi : 10.1093 / jxb / erf076 , Oxford.