Multicellular organisms possessing relatively long life spans are "Asexual reproduction in plants regeneration technologies" to diverse, constant, and often intense intrinsic and extrinsic challenges to their survival. Animal and plant tissues wear out as part normal physiological functions and can be lost to predators, disease, and injury.
Both kingdoms survive this wide variety of insults by strategies that include the maintenance of adult stem cells or the induction of stem cell potential in differentiated cells. Repatterning mechanisms often deploy embryonic genes, but the question remains in both plants and animals whether regeneration invokes embryogenesis, generic patterning mechanisms, or unique circuitry comprised of well-established patterning genes. Developmental studies in plants and animals can be thought of as parallel universes.
Each field acknowledges the existence of the other, but rarely do they come in direct contact. Regeneration provided one of those momentous occasions when these parallel universes collided in a stunning discovery that we now take for granted. Over years ago, Abraham Trembley working under the popular scientific belief that only plants and a few microscopic animals could regenerate, decided to test whether a polyp he had discovered in pond water was or was not a plant Figure 1A:.
A Hydra attached to a small twig with its anterior end pointing down. B Regeneration of two pieces of willow suspended in opposite orientations show that polarity is preserved with root and shoot Asexual reproduction in plants regeneration technologies occurring at the respective bases or apices of the fragments.
On the right is a root fragment, also regenerating the corresponding shoots or roots and demonstrating that regenerative capacity is widespread across the anatomy of plants. C Regeneration of whole plants from the leaf of the pansy Achimenes haageana.
The leaf was removed from a flowering plant and regeneration resulted in roots emerging from the base of the leaf-stalk and flowers emerging near stipules.
I speculated anew that perhaps these organisms were plants, and fortunately I did not reject this idea. I say fortunately because, although it was the less natural idea, it made me think of cutting up the polyps. I conjectured that if a polyp were cut in two and if each of the severed parts lived and became a complete polyp, it would be clear that these organisms were plants… On November 25, I sectioned a polyp for the first time…the first polyps I cut were green in color.
The two parts extended the same day that I separated them. I was observing this second half to find out how long it would retain the remnants of life; I had not the least expectation of being a spectator to this marvelous kind of reproduction Lenhoff and Lenhoff, The demonstration that simple animals like the polyp Hydra described by Trembley were capable of regenerating tissue was soon followed by studies from the likes of Bonnet Bonnet, and Spallanzani Spallanzani, They unambiguously demonstrated that regeneration was widely dispersed among the metazoans, including earthworms, snails, and salamanders.
Similarities between animal and plant regeneration intrigued early investigators. Morgan noted in that, as in animals, plant regeneration from a twig involves the formation of specialized tissues near the cut ends giving rise to new organs Figure 1B.
At the same time, clear differences in the kingdoms were also apparent, for example, animals typically replace missing tissues, whereas one mode
Asexual reproduction in plants regeneration technologies regeneration in plants leads to entirely new individuals being formed at the wound sites or from severed organs.
This was demonstrated by Sachs Sachs, and Goebel Goebel,who showed that complete individuals can develop de novo from the severed leaves of pansies and begonias Figure 1C. Animals and plants have almost certainly evolved multicellularity separately.
Thus, the developmental feat of repairing multicellular organs and structures would be expected Asexual reproduction in plants regeneration technologies have critical differences. However, at a fundamental level, regenerating organisms must turn back the clock on differentiation or freeze developmental youth while at the same time inventing or invoking ways to pattern their new tissue Figure 2.
Even though it is likely that the exact pathways used to activate regeneration in plants and animals may be specific to each kingdom, the mechanistic barriers to totipotency are likely to intersect, and basic principles in regeneration could then be distilled from such comparisons.
Do some of the processes called upon during regeneration rely on ancestral functions shared by the two kingdoms, such as nuclear organization and chromatin remodeling? Shared aspects of regeneration, whether ancestral or acquired separately, allow us to focus our attention on those steps that are indispensable during regeneration in multicellular organisms. Descriptions of the known cellular origins, regenerative structures, and patterning mechanisms are indicated.
We include also an experimental method described in animals overexpression of transcription factors and nuclear transplantationwhich allows differentiated cells to assume stem cell attributes.
Whether or not these cells can contribute to regeneration of adult Asexual reproduction in plants regeneration technologies after injury remains untested Takahashi et al. This
Asexual reproduction in plants regeneration technologies aims to compare the knowledge accrued in classic models that show dramatic regenerative capacities in both plants and animals.
Particularly, "Asexual reproduction in plants regeneration technologies" will focus on two separate phenomena that appear to be basic steps in regeneration in the two kingdoms: First, we provide an overview of regeneration in plants and animals, then we canvass the literature preceding the era of molecular biology and use this information as the background against which to examine more recent molecular insights.
Plants grow indeterminately, which the maintenance of meristems that continually give rise to the major axes of the plant, the root and shoot.
Adult plant meristems Figure 3A contain stem cell niches see Essay by J. Benfey, page of this issue with a group of mitotically less active cells, the quiescent center QC in the root and a similar group of cells in the Central Zone CZ in the shoot Mayer et al. However, injury frequently removes the stem cell niche completely, and regeneration entails reformation of the stem cell niche in order to resume the continual production of roots and shoots, and thus indeterminate growth.
Most plants also maintain other means to either activate or dedifferentiate adult cells to resume meristematic growth, such as pericycle cells that give rise to lateral roots, axillary meristems at the base of leaves, and lateral meristems that contribute to girth Steeves and Sussex, In addition, plants can repair damaged tissue by apparent dedifferentiation and respecification of cell types, such as in the repair of severed vascular strands Sinnott, The stem cell niche in the root consists of mitotically less active quiescent center cells greenwhich maintain adjacent stem cells shades of blue in an undifferentiated state.
Cells away from the tip are more differentiated.
Differentiating pericycle cells brown have been found to give rise to callus, which can in turn recreate the entire root or shoot meristem. The structure of the shoot meristem consists of a group of stem cells in the central zone that lie on top of a group of mitotically active cells that are known to signal and maintain the stem cells, similarly as in root.
B A progression series highlighting the cellular processes that take place in the formation of an animal blastema. This structure is assembled by the division progeny of either stem cells residing in the pre-existing tissues planaria or a combination of both stem cells and dedifferentiation salamanders.
Once formed, the blastema differentiates, patterns, and functionally integrates itself with the older tissue. Invertebrates such as Hydra and planarian flatworms have unchanging mortality and reproductive rates after many years of culture Martinez, ; Sonneborn, In mammals, bowhead whales can live more than years George et al. Although the cellular and molecular mechanisms supporting the longevity of vertebrates remain to be elucidated, the long life span observed in many invertebrates is associated with the lifelong maintenance and regulation of stem cells in somatic tissues.
The progeny of these adult stem cells are capable of replacing dying differentiated cells, allowing such organisms to effectively escape death. For instance, animals such as Hydraplanarians, and echinoderms starfish and crinoids maintain cells in their body plans that allow for both growth and injury repair.
In Hydra and planarians, these stem cells are known as interstitial cells and neoblasts, respectively. Both cell types are capable of replacing all differentiated cells lost to physiological turnover Holstein et al.
Cells with similar functions are found in invertebrates that are phylogenetically more closely related to mammals such as the crinoid echinoderms Candia Carnevali and Bonasoro, and the ascidians. Circulating stem cells take part in the regeneration of crinoid arms lost to amputation Candia Carnevali et al. The lack of cell migration Asexual reproduction in plants regeneration technologies plants, which is precluded by rigid cell walls, would prevent movement of dispersed stem cells toward injured sites.
In both plants and animals, injury is a stimulus for the formation of specialized wound tissue that initiates regeneration. A regenerative response from these organisms can be elicited by environmental insults, even predatory or pathogenic attacks.
Other regenerative methods exist in animals, such as the remodeling of pre-existing tissues in planarians to restore both missing body parts and normal scale and proportion see Figure 5 below and the regeneration of a whole Hydra by reaggregation of its dissociated cells Figure 4B Gierer et al. In plants, one frequent but not universal feature of regeneration is the formation of a callus, a mass of growing cells that has lost the differentiated characteristics of the tissue from which it arose.
A callus is typically a disorganized growth that arises on wound stumps and in response to certain pathogens Sinnott, Similar cell masses can be generated in vitro Figure 4Cas will be discussed. One common mode of regeneration is the appearance of new meristems within callus tissue. Thus, the plant callus shares with animal regeneration
Asexual reproduction in plants regeneration technologies the property of being a specialized and undifferentiated structure capable of giving rise to new tissues.
We emphasize that regeneration in both kingdoms entails a diverse array of phenomena Figure 2. Furthermore, there are many possible pathways from early to later stages of regeneration. For example, not all cells that have reactivated stem cell potential must pass through either blastema or callus states to regenerate e.
An interesting point is that, despite the diverse array of regeneration mechanisms within kingdoms, almost all phenomena in one kingdom have a counterpart in the other.
B Head regeneration in Asexual reproduction in plants regeneration technologies after decapitation top and from a cell aggregate of cells obtained after dissociation of a Hydra into individual cells bottom. The signal corresponds to the expression of a Chordin-like gene in this organism. Images reproduced from Rentzsch et al.
USA— C Normally developing Arabidopsis with a basal rosette and a reproductive inflorescence that has arisen Asexual reproduction in plants regeneration technologies the transition of the SAM to a floral meristem left. Middle, dedifferentiated cell masses of callus that formed from auxin treatment of tissue cuttings from Arabidopsis and the regeneration of a complete shoot from one such callus right.
Images of the callus and regenerating shoot are courtesy of S. A trunk fragment of the land planarian Bipalium is shown undergoing remodeling of pre-existing
Asexual reproduction in plants regeneration technologies see text and the regeneration of the missing head and tail. The animal is drawn at the same magnification for each of the days illustrated. Note the progressive increase in length and decrease in width of the fragment.
These changes result in the regeneration of all the missing structures and ultimately reach the appropriate dimensions relative to the sizes of the newly regenerated head and tail.
The table indicates days after amputation and the corresponding change in length to width ratio L: W for each specimen pictured. This was accomplished by digitizing the original, drawn-to-scale image after Morgan and measuring along the midline for length and along the geometric center from lateral edge to lateral edge for width. In the late s, the concept of heredity for multicellular organisms was based on the assumption that each differentiated cell in the adult possessed different genetic information,
Asexual reproduction in plants regeneration technologies restricting their differentiation
Asexual reproduction in plants regeneration technologies. Weismann postulated that only the cells engaged in producing gametes were totipotent, and that such totipotency was at its highest manifestation in the very early embryo soon after fertilization.
As the embryo underwent cleavage, the resulting cells—with the exception of those fated to produce the germline—progressively lost genetic information not needed for the functions of the resulting lineage that is, muscle cells would eliminate genetic information to make neurons and vice versa. Yet, the regeneration experiments of Trembley, Bonnet, and Spallanzani demonstrated that adult differentiated animal tissues have the capacity to undergo remarkable developmental changes not necessarily associated with their differentiated functions.
Weismann noted that the challenge posed to the germ plasm theory by regeneration could be explained by the fact that the tissues being regenerated arose from similar tissues such that limbs only regenerated limbs and tails only regenerated tails Weismann, However, in Wolff demonstrated that a vertebrate cell type believed to be terminally differentiated could undergo a dramatic transformation to produce cell types outside of its normal lineage.
The cells in question are the pigmented retinal epithelial cells of the newt eye. After removal of the newt eye lens, these cells can dedifferentiate, proliferate, and then transdifferentiate from their initial epithelial morphology into cells that eventually will regenerate the lens Wolff, Similar plasticity was uncovered later in the studies of other adult animals, particularly in the planarian flatworms in which pre-existing tissue can remodel itself after amputation to restore lost body parts.
For instance, if the anterior end of a planarian is cut at any level along the anteroposterior axis, a new head is regenerated. The resulting animal, however, is misproportioned, particularly when the amputation was performed at more posterior regions. This is clearly illustrated by the work of T. Morgan on the land planarian Bipalium kewensi Morgan, Asexual reproduction in plants regeneration technologies a trunk fragment is removed, head and tail structures are regenerated that are nevertheless out of proportion too small relative to the size of the fragment Figure 5.
Regeneration is asexual reproduction is the ability of a simple organism to re- grow its lost parts. Simple organisms are more successful with regeneration than complex organisms. For example, some crabs can grow plant reproduction.
Asexual reproduction can be defined as the process by which Some protozoans and many bacteria, plants and fungi reproduce Asexual reproduction in plants regeneration technologies spores. Accumulating evidence suggests that some forms of plant regeneration. Shoot explants of many ornamental plants are used for clonal propagation .
using Pisum sativa suggested that the vegetative-to-reproductive transition is With rapid advances in next-generation sequencing and genome editing technologieswe.