Lecture Notes: Structure and Function of FLM

Introduction

• FLM (Phloem)
  • Vascular tissue
  • Contains tube-like structures
  • Transports sucrose and amino acids

Location of Phloem

• Found in:
  • Roots
  • Stem
  • Leaf
• Highlighted in cross-sections:
  • Root, stem, and leaf transfer sections

Structure of Phloem

• Composed of two types of cells:
  1. Companion Cells
  2. Phloem Sieve Tube Elements (SE)
• Connection:
  • Companion cells and SE tube elements are connected by plasmodesma (cytoplasmic connection)

Formation of Phloem

• Companion Cells
  • Black colored cells
• Young Phloem SE Tube Element
  • Orange colored cells
  • Cell walls partially break down (unlike xylem)
  • Some cytoplasm and organelles drain away

Phloem Sieve Tube

• Composed of many SE tube element cells joined together
• Tube for transportation
• Structure:
  • Companion Cells
    • Have organelles like nuclei, vacuole, mitochondria, rough ER, and Golgi apparatus
  • Phloem SE Tube Element
    • Minimal cytoplasm
    • May have few mitochondria
    • Lacks nuclei and large organelles
  • Sieve Plates
    • Parts of cell walls broken down into tiny pieces
    • Resemble a cheese grater with holes for transport

Visual Representations

• Longitudinal and Transverse Section Views:
  • Shows companion cells connected by plasmodesma
  • SE tube with some cytoplasm
• 3D Diagram:
  • Companion cells (black)
  • SE tube elements (elongated orange)
  • Connected by plasmodesmata
  • Sieve plates highlighted

Key Points

• Phloem tissue is made of:
  • Two types of cells:
    • Companion cells
    • Phloem SE tube elements
• Connection:
  • Via plasmodesma
• Function:
  • Transport of sucrose and amino acids in plants