Underground Storage Swelling Enables Regeneration

Biological Strategy

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Image: Ian Brooker and David Kleinig / CC BY - Creative Commons Attribution alone

Store Chemical Entities

Chemical entities include elements such as carbon and metals, and compounds such as nutrients and proteins. Living systems must often store chemical entities–for example, for food or protection–temporarily or for long periods; the latter is synonymous with sequestration. Because chemical entities can react with other chemicals, living systems must store these entities so that they are stable and out of the way (for long-term storage) or readily available when needed (for temporary storage). An example of temporary storage is found in crustaceans such as crabs, which must shed their external skeletons as they grow. But first, a crab must absorb as much calcium carbonate from its shell as possible, storing the compound in its blood until the crab can use it to grow a new exoskeleton.

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Protect From Animals

Animals–organisms that range from microscopic to larger than a bus–embody a wide variety of harms to living systems, including other animals. They threaten through predation, herbivory, defense, and parasitism, and they compete for resources such as water, nutrients, and space. Any given living organism commonly faces threats from a variety of animals, requiring strategies that effectively defend from each. Trout and other bony fish, for example, escape predators by having scales made of very thin, flake-like pieces of bone covered with slippery mucus. They also have behavioral strategies such as camouflage, fast swimming, and twisting and turning to achieve release from a predator’s grip.

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Protect From Fire

Depending on location, fire can be either predictable or unpredictable. In some areas, fires occur in cycles ranging from annual to hundreds of years. Where fire is cyclic, living systems must be able to not only survive fire, but to quickly recover following it. For example, pine trees that live in areas with periodic fires have thick bark that provides insulation, thereby protecting the tree’s living tissue.

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Physically Assemble Structure

Living systems use physical materials to create structures to serve as protection, insulation, and other purposes. These structures can be internal (within or attached to the system itself), such as cell membranes, shells, and fur. They can also be external (detached), such as nests, burrows, cocoons, or webs. Because physical materials are limited and the energy required to gather and create new structures is costly, living systems must use both conservatively. Therefore, they optimize the structures’ size, weight, and density. For example, weaver birds use two types of vegetation to create their nests: strong, a few stiff fibers and numerous thin fibers. Combined, they make a strong, yet flexible, nest. An example of an internal structure is a bird’s bone. The bone is comprised of a mineral matrix assembled to create strong cross-supports and a tubular outer surface filled with air to minimize weight.

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The lignotuber of Eucalyptus kochii plenissima allows it to regenerate after being destroyed by storing energy reserves and potential bud-forming sites.

When a tree or shrub is cut down or destroyed by either another organism or a destructive natural force, such as fire, the plant itself is usually killed. For Eucalyptus kochii plenissima, however, this is not the case. Due to a special root adaption called a lignotuber, absent in most other plants, this species can regenerate after the aboveground part is destroyed.

A lignotuber is a special swelling at the top of the plant’s root system (which sits mostly submerged below ground). It contains starch, sugars, nutrients, and “meristematic foci” (read on for more about this). These contents enable the plant to regrow its shoots. The key to the process, however, lies in the meristematic foci. Resembling little pimples, meristematic foci are similar to stem cells, with undifferentiated cells and tissue that ultimately grow and change into new shoots.

The meristematic foci, however, cannot act alone, and this is where the starch, sugars, and nutrients within the lignotuber come into play. The nutrients and sugars are broken down and used by the plant to grow and regenerate. The starch is used for respiration, just as it was used by the plant before the leaves were destroyed. Respiration brings in carbon dioxide, which is necessary for the plant to function, just as humans need oxygen.

To increase the energy available to the plant for shoot regeneration, Eucalyptus kochii plenissima sheds most of its root system. By shedding unnecessary roots and leaving only the structural roots needed to anchor the plant, the energy previously used to maintain the extensive root system is made available to regenerate the parts above ground. Thus, the lignotuber of Eucalyptus kochii plenissima acts almost like a plant seed, containing all of the necessary cells, tissue, and energy reserves needed to regrow the damaged plant.

This summary was contributed by Thomas McAuley-Biasi.

Image: Ian Brooker and David Kleinig / CC BY - Creative Commons Attribution alone

Eucalyptus kochii growing west of Dalwallinu, Western Australia

Last Updated July 1, 2020

References

“‘Mallee’ eucalyptus [such as the Eucalyptus kochii plenissima] are characterized by multiple woody stems arising from an underground lignotuber.” (Wildy and Pate, 2002: 185)

“A lignotuber typically contains several thousand of such ‘meristematic foci’ (Noble, 2001), each of which is capable of producing several individual shoots.” (Wildy and Pate, 2002: 185)

“Regardless of life form and sprouting morphology, early growth of shoot sprouts is associated with some degree of mobilization of previously accumulated reserves of nutrients, starch, sugars and other soluble and insoluble energy reserves.” (Wildy and Pate, 2002: 185)

“Lignotubers of E. kochii appear less important as starch storage organs than they are as providers of replacement shoot meristems after decapitation.” (Wildy and Pate, 2002: 193)

“Much of the observed loss of starch from root systems might then be committed to respiration rather than contributing to dry matter gain of new coppice shoots.” (Wildy and Pate, 2002: 195)

Journal article

Quantifying Above- and Below-ground Growth Responses of the Western Australian Oil Mallee, Eucalyptus kochii subsp. plenissima, to Contrasting Decapitation Regimes

Annals of Botany | 30/09/2002 | D. T. WILDY

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Reference

Book

The Nature of Plants: Habitats, Challenges, and Adaptations

01/02/2005 | John Dawson

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