Review on the Root, Stem and Leaf Initiations in Plants

The root and shoot apical meristem serve as sources of pluripotent cells and provide new cells for repetitive organ initiation, they are the major meristematic regions on which plant development take place. New meristems are incessantly formed as plants produce new branches or lateral roots thus making the understanding of meristem function central to how plants can establish different growth types, ranging from tiny herbs to huge trees. The sizes and numbers of meristems that are initiated during advanced development control the size and number of fruits and the generation of seeds. The development of a lateral root from a limited number of cells requires compactly coordinated asymmetric cell divisions to generate cell diversity and tissue patterns which characteristically involves the specification of founder cells, followed by a number of cellular changes until the cells divide and give rise to unequally sized daughter cells. Leaf development exemplifies the dynamic nature and flexibility of plant development in response to internal and external cues which is evidenced in the fact that two plants, even if genetically identical, do not look the same, two leaves on the same plant are different, and the final shape of a leaf is not predetermined when it starts to form. Leaves evolved from lateral branches following the acquisition of determinate growth and a flat structure, thus the specification of organ initiation involves a complex network of genetic, hormonal and mechanical factors which has been discussed in this review.