<P> 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 cells . In fact, plants comprise the oldest and the largest living organisms on earth, including Bristlecone Pines in California, 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 and flowers . </P> <P> 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 .) </P> <P> 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 ." </P> <P> 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 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 . </P>

Where do we get stem cells in plants and animals