Question

Quiescent centre theory for demonstrating apical organisation in root was proposed by.

Answer 1

Hint:- Seldom found in shoots, the quiescent centre is a universal structure in roots. It is the region containing about 1000 cells in a hemispherical or disc shaped form in the apical meristem of the roots in higher plants. These cells divide either very slowly or not at all, functioning as a stem cell reservoir.

Complete Answer:-
The quiescent centre theory for demonstrating apical organisation in root was proposed by Frederick Albert Lionel Clowes (FAL Clowes). He identified a group of slowly dividing cells at the core of the root apical meristem while studying the organisation of the root apices which he later observed to be the region from which all future cells arose.
The quiescent centre in the root apical meristem is ubiquitous in angiosperms/vascular plants and positioned between the active meristematic region and root cap. The volume and population of cells in this region changes as the root grows. They barely multiply or divide, unless specifically necessary like in the case of damage or injury. Given that they are normally inactive, they contain fewer mitochondria, endoplasmic reticulum, smaller nuclei and a much lower rate of DNA and protein synthesis as compared to the highly active cells surrounding them. During injury, the cells divide rapidly and help in restoration and regeneration of the meristem.

Note:- The quiescent centre is sometimes also referred to as the cytogenerative centre or cytogenetic centre or constructional centre or ontogenetic centre. It may be absent in seedless vascular plants and plants with short or very thin roots.