One of the main problems for plants when they colonized terrestrial environments on Earth nearly a half billion years ago was how to survive the dryness.
Today, much of a typical vascular plant’s anatomy, morphology and physiology is dedicated to obtaining and retaining water.
Although most vascular plants can tolerate brief periods (hours to days) of water stress, most plants are killed by long periods (weeks to months) of drought.
Some plants, however, display the remarkable ability to survive near total desiccation (less than 5% relative water content), which causes them to appear dead. But when rehydrated, these plants can be revived. Hence, they are often referred to as “resurrection plants”.
Probably the most well-known “resurrection plant” is the species Selaginella lepidophylla (see photo above). This resurrection plant (a.k.a., Rose of Jericho and Siempre Viva) belong to a group of plants called lycopods.
Other plants sometimes called the “resurrection bushes”, are members of the the genus Myrothamnus, and, in paticular, the resurrection bush Myrothamnus flabellifolia has recently been the object of study by scientists interested in why these plants are so desiccation tolerant.
Bringing Dehydrated Plants “Back To Life”
The nature the desiccation tolerance of resurrection plants has interested plant scientist for many years.
If the cellular mechanisms for such remarkable drought tolerance was understood, and the genes involved identified, then it may be possible to use this information to improve drought tolerance in crop plants. (As previously mentioned here, this may become of increasing concern due to “global weirding”.)
But let’s not get side-tracked with issues regarding global climate change….
…how do resurrection plants work?
When “dead”, these plants exist in a quiescent, desiccated state. That is, their metabolism is at or near zero, along with a significant reduction in cell and tissue volume. (see refs 1 & 2 below, for example).
What has happened at the cellular level to allow these plants to survive such an extreme state, often for a long time?
“Desiccation tolerance in resurrection plants involves a combination of molecular genetic mechanisms, metabolic and antioxidant systems as well as macromolecular and structural stabilizing processes.” (from Ref 3 below)
Briefly, the onset of water loss apparently sets into motion a series of cellular events that can be summarized as follows:
Dehydration –> Activation of “desiccation-related” genes –> (1) Alterations in metabolism and (2) Production of “protective” proteins
(1) Alterations in metabolism: (a) accumulation of protective solutes such as sucrose, trehalose, and proline that stabilize proteins and cellular membranes, (b) production of antioxidant compounds (such as galloylquinic acids), and (c) biochemical alterations in membrane and cell wall composition.
In some ways, responses similar to how plants tolerate sub-freezing cold temperatures (see previous post)
Are All Seed Plants “Resurrection Plants”?
In a way, seeds are vessels for “resurrection plants”.
As we’ve seen above, a “resurrection plant” is a plant that can withstand extreme desiccation without dying and that can be revived with the addition of water.
In each viable, dry seed is an embryonic plant in an extremely desiccated state, but still alive (at least as long as the seed’s food reserves last). This desiccated state allows the seed embryo to withstand periods of cold, drought, heat, etc. Unless the seed is dormant, adding water revives the embryo, and the seed germinates.
Many, if not most, of the cellular mechanisms for desiccation tolerance mentioned above for resurrection plants have also been shown to be relevant to seeds.
So, an interesting question comes to mind: Did the cellular mechanisms for desiccation tolerance that evolved in primitive, spore-producing plants such as the lycopods (think Selaginella) help “pave the way” for the appearance of seed-producing plants?
Bottom line: Some unusual so-called “resurrection plants” have the ability to withstand extreme desiccation using cellular mechanisms not unlike those found in dry seeds.
1. Moore, J.P., et al. (2006) “Response of the Leaf Cell Wall to Desiccation in the Resurrection Plant Myrothamnus flabellifolius.” Plant Physiology Vol. 141, pp. 651–662. (Abstract)
2. Layton, B.E., et al. (2010) “Dehydration-induced expression of a 31-kDa dehydrin in Polypodium polypodioides (Polypodiaceae) may enable large, reversible deformation of cell walls.” American Journal of Botany Vol. 97, pp. 535-544. (Abstract)
3. Moore, J.P., et al. (2009) “Towards a systems-based understanding of plant desiccation tolerance.” Trends in Plant Science Vol. 14, pp. 110-117. (Abstract)
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