Meristem-Specific Suppression of Mitosis and a Global Switch in Gene Expression in the Root Cap of Pea by Endogenous Signals1

Two functionally distinct sets of meristematic cells exist within root tips of pea (Pisum sativum): the root apical meristem, which gives rise to the body of the root; and the root cap meristem, which gives rise to cells that differentiate progressively through the cap and separate ultimately from its periphery as border cells. When a specific number of border cells has accumulated on the root cap periphery, mitosis within the root cap meristem, but not the apical meristem, is suppressed. When border cells are removed by immersion of the root tip in water, a transient induction of mitosis in the root cap meristem can be detected starting within 5 min. A corresponding switch in gene expression throughout the root cap occurs in parallel with the increase in mitosis, and new border cells begin to separate from the root cap periphery within 1 h. The induction of renewed border cell production is inhibited by incubating root tips in extracellular material released from border cells. The results are consistent with the hypothesis that operation of the root cap meristem and consequent turnover of the root cap is self-regulated by a signal from border cells.

Speech and the learning process.

"Reprinted from Quarterly journal of speech education, vol. VI, no. 1, February, 1920."

National strategic research plan for hearing and hearing impairment and voice and voice disorders.

Shipping list no.: 93-0323-P.

Violations of free speech and rights of labor : digest of report of the Committee on Education and Labor pursuant to S. Res. 246 (74th Congress)

At head of title: 76th Congress, 1st session. Senate committee print.

Mental health research and practice in minority communities : development of culturally sensitive training programs /

Item 507-B-5.

Report on Workshop on High Performance Computing and Communications for Grand Challenge Applications : computer vision, speech and natural language processing, and artificial intelligence /

Cover title.