35. Which one of the following root initials gives rise to the root vascular system, including the pericycle?
(1) Columella initials
(2) Epidermal-lateral root cap initials
(3) Cortical-endodermal initials
(4) Stele initials

Introduction

In higher plants, the root vascular system comprising xylem, phloem, and associated pericycle cells develops from specific root initials located in the root apical meristem. These stele initials are critical for establishing the transport network that supports water and nutrient movement, and they serve as the origin of the pericycle, which is key for lateral root initiation.

Function of Stele Initials

• Stele initials are a group of meristematic cells in the root apical meristem that specifically give rise to the central vascular tissues including the xylem and phloem, along with the pericycle surrounding them.​

• The pericycle, derived from stele initials, plays a critical role in forming lateral roots and maintaining vascular continuity.​

• These initials are centrally located underlying the quiescent center and undergo highly regulated divisions to create the organized arrangement of vascular tissues.​

• Genetic factors such as the LONESOME HIGHWAY (LHW) gene regulate the proliferation and patterning of stele initials and vascular development.​

Contrast with Other Root Initials

• Columella initials (Option 1) contribute to the root cap’s central cells but not vascular tissues.​

• Epidermal-lateral root cap initials (Option 2) produce the root epidermis and outer protective layers, unrelated to vascular tissue.​

• Cortical-endodermal initials (Option 3) give rise to cortex and endodermis, ground tissue layers rather than the vascular cylinder.​

Summary Table: Root Initials and Derived Tissues

Conclusion

Stele initials are the primary source of the root vascular system including the pericycle in higher plants, highlighting their essential role in root development and vascular tissue patterning.