Plant stem cells
Encyclopedia
Plant stem cells are innately undifferentiated cells located in the meristem
Meristem
A meristem is the tissue in most plants consisting of undifferentiated cells , found in zones of the plant where growth can take place....

s of plant. Plant stem cell
Stem cell
This article is about the cell type. For the medical therapy, see Stem Cell TreatmentsStem cells are biological cells found in all multicellular organisms, that can divide and differentiate into diverse specialized cell types and can self-renew to produce more stem cells...

s serve as the origin of plant vitality, as they maintain themselves while providing a steady supply of precursor cell
Precursor cell
In cytology, a precursor cell, also called a blast cell or simply blast, is a type of partially differentiated, usually unipotent cellthat has lost most or all of the stem cell multipotency....

s to form differentiated tissues and organs in plant.

Characteristics

Plant stem cells are characterized by two distinctive properties: the ability to create all differentiated cell types and the ability to self-renew such that the number of stem cells is maintained. Plant stem cells never undergo aging process but immortally give rise to new specialized and unspecialized cells, and they have the potential to grow into any organ, tissue, or cell in the body. Thus they are totipotent cells equipped with wondrous regenerative powers that facilitate plant growth and production of new organs throughout lifetime.

Unlike animals, plants are immobile. As plants cannot escape from danger by taking motion, they need a special mechanism to withstand various and sometimes unforeseen environmental stress. Here, what empowers them to withstand harsh external influence and preserve life is stem cell. In fact, plants comprise the oldest and the largest living organisms on earth, including Bristlecone Pines
Bristlecone pine
The bristlecone pines are a small group of pine trees that are thought to reach an age far greater than that of any other single living organism known, up to nearly 5,000 years....

 in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

, U.S. (4,842 years old), and the Giant Sequoia in mountainous regions of California, U.S. (87 meters in height and 2,000 tons in weight). This is possible because they have a modular body plan that enables them to survive substantial damage by initiating continuous and repetitive formation of new structures and organs such as leaves
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....

 and flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...

s.

Plant stem cells are also characterized by their location in specialized structures called meristematic tissues, which are located in root apical meristem (RAM), shoot apical meristem (SAM), and vascular system ((pro)cambium or vascular meristem.)

Research and Development

Traditionally, plant stem cells were thought to only exist in SAM and RAM and studies were conducted based on this assumption. However, recent studies have indicated that (pro)cambium also serves as a niche for plant stem cells: “Procambium cells fulfill the criteria for being stem cells since they have the capacity for long-term self renewal and being able to differentiate into one or more specialized cell types.”

Cambium is a type of meristem with thin walls which minutely exist in small populations within a plant. Due to this structural characteristic, once physical force is applied to it, it is easily damaged in the very process of isolation, losing its stem cell characteristics. Despite 160 years of biological effort to isolate and retrieve plant stem cells, none succeeded in the isolation due to the distinct structural characteristics of plant stem cell: “[t]he cambium consists of a few layers of narrow elongated, thin-walled cells, easily damaged during sampling.” This highly vulnerable feature has made studies on cambial structure and ultrastructure
Ultrastructure
Ultrastructure is the detailed structure of a biological specimen, such as a cell, tissue, or organ, that can be observed by electron microscopy...

 difficult to achieve with conventional methods. Thus failure to isolate plant stem cells from meristematic tissues prompted scientists to administer plant cell culture by using callus
Callus (cell biology)
Plant callus is a mass of undifferentiated cells derived from plant tissue for use in biological research and biotechnology. In plant biology, callus cells are those cells that cover a plant wound. To induce callus formation, plant tissues are surface sterilized and then plated onto in vitro...

 (dedifferentiated cells) as an alternative to plant stem cells.

Callus, or dedifferentiated cells, is somatic cell
Somatic cell
A somatic cell is any biological cell forming the body of an organism; that is, in a multicellular organism, any cell other than a gamete, germ cell, gametocyte or undifferentiated stem cell...

s that undergo dedifferentiation to give rise to totipotent embryogenic
Embryogenesis
Embryogenesis is the process by which the embryo is formed and develops, until it develops into a fetus.Embryogenesis starts with the fertilization of the ovum by sperm. The fertilized ovum is referred to as a zygote...

 cells, which temporarily gains the ability to proliferate and/or regenerate an embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

. Since embryogenic cells were considered totipotent cells based on their ability to regenerate or develop into an embryo under given conditions, dedifferentiated cells were generally regarded as stem cells of plant: “…we propose to extend the concept of stem cells to include embryogenic stem cells that arise from plant somatic cells. We examine the cellular, physiological and molecular similarities and differences between plant meristematic stem cells and embryogenic stem cells originating directly from single somatic cells.”

Plant Stem Cell vs. Callus

Despite that callus exhibits a number of stem cell-like properties for a temporary period and that it has been cultured for useful plant compounds as an alternative source of plant stem cell, callus and plant stem cell are fundamentally different from each other. Callus is similar to plant stem cell in its ability to differentiate, but the two are different in their origin. While plant stem cell exists in the meristematic tissues of plant, callus is obtained as a temporary response to cure wound in somatic cell.

Moreover callus undergoes dedifferentiation as differentiated cells acquire ability to differentiate; but genetic variation
Genetic variation
Genetic variation, variation in alleles of genes, occurs both within and among populations. Genetic variation is important because it provides the “raw material” for natural selection. Genetic variation is brought about by mutation, a change in a chemical structure of a gene. Polyploidy is an...

 is inevitable in the process because the cells consist of somatic undifferentiated cells from an adult subject plant. Unlike true stem cells, callus is heterogeneous. Due to this reason, continuous and stable cell division of callus is difficult. Hence plant stem cell originated from cambium is an immortal cell while callus is a temporary cell obtained from stimulating the cell.

Furthermore, the ability to differentiate and proliferate is different that differences between plant stem cell and callus are prevalent in culture and research. Only plant stem cells embedded in meristems can divide and give rise to cells that differentiate while giving rise to new stem cells. These immortal cells divide infinitely.

Bioprocess Innovation

Plant cells are cultured to acquire plant useful compounds. However cell culture
Cell culture
Cell culture is the complex process by which cells are grown under controlled conditions. In practice, the term "cell culture" has come to refer to the culturing of cells derived from singlecellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi and microbes,...

s are often hindered by various factors especially if cell culture continues long-term. However, strong vitality and structural characteristics of plant stem cell overcome previous drawbacks to plant cell culture. Thus plant stem cell culture is the most ideal and productive method of cell culture and phytochemical production as cells are successfully mass cultured while maintaining quality.

Further Applications

Numerous medicine
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....

s, perfume
Perfume
Perfume is a mixture of fragrant essential oils and/or aroma compounds, fixatives, and solvents used to give the human body, animals, objects, and living spaces "a pleasant scent"...

s, pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...

s, antimicrobial
Antimicrobial
An anti-microbial is a substance that kills or inhibits the growth of microorganisms such as bacteria, fungi, or protozoans. Antimicrobial drugs either kill microbes or prevent the growth of microbes...

s, and insecticide
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...

s are derived from plant natural products. Cultured cambial meristematic cells may provide a cost-effective, environmentally friendly, and sustainable source of important natural products, including paclitaxel
Paclitaxel
Paclitaxel is a mitotic inhibitor used in cancer chemotherapy. It was discovered in a U.S. National Cancer Institute program at the Research Triangle Institute in 1967 when Monroe E. Wall and Mansukh C. Wani isolated it from the bark of the Pacific yew tree, Taxus brevifolia and named it taxol...

. Unlike plant cultivation, this approach is not subject to the unpredictability caused by variation in climatic conditions or political instability in certain part of the world. Also, CMCs from reference specifies may also provide an important biological tool to explore plant stem cell function.

In 2010, researchers from the Plant Stem Cell Institute (formerly Unhwa Institute of Science and Technology) presented their data to the world via Nature Biotechnology. Their research demonstrated the world's first cambial meristematic cell (CMC) isolation. Due to the valuable and beneficial compounds for human health (ie. paclitaxel) which are secreted by the CMC's, this technology is considered a serious breakthrought in plant biotechnology.

http://www.nature.com/nbt/journal/v28/n11/full/nbt.1693.html
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