EARLY SENESCENCE OF CORTICAL CELLS IN THE ROOTS OF CEREALS. HOW GOOD IS THE EVIDENCE?

Abstract

There are numerous reports that cortical cells senesce in young, otherwise healthy main roots of cereals, including corn. These are based on apparent absence of nuclei in root segments or transverse sections after acridine‐orange staining. Senescence is said to progress from the outer to the inner cortex basipetally from the root tip, except cells around branch bases where nuclei always stain. We studied axile roots of soil‐grown cereals using various methods to detect nuclei primarily in longitudinal sections. No senescence marked by nuclear loss was found in healthy‐looking intact cortices. Cortical cells of mature corn roots remained alive except where aerenchyma developed. No cortical death had occurred in barley, wheat, or oat seminal roots in 15‐,17‐, and 20‐day‐old plants, respectively, but cortical cells in older regions of seminal and nodal roots did collapse and slough off, but with no evidence for earlier loss of nuclei. Failure to detect acridine‐orange‐stained nuclei may not indicate that cells are senescent, and can be an artifact caused by sectioning method and wall impermeability. The effectiveness of other methods for evaluation of root cell vitality is discussed.