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: "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 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 (dedifferentiated cells) as an alternative to plant stem cells.
Callus, or dedifferentiated cells, are somatic cells that undergo dedifferentiation to give rise to totipotent embryogenic cells, which temporarily gains the ability to proliferate and/or regenerate an embryo. 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."
Read more about this topic: Plant Stem Cell
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