Biology lecture phloem

Phloem Transport of photosynthate (sucrose) and ions From source to sink (high to low concentration) Movement through Phloem Solutes higher in phloem Water moves in from xylem Pressure = push Sugars actively unloaded at sink PRESSURE FLOW OR MASS FLOW Phloem is a complex tissue 1) Parenchyma 2) Fibers 3) Conducting cells and associated cells Conducting cells Angiosperms - End walls (sieve plates) contain large pores Sieve Areas in lateral walls Sieve tube element Sieve plate (sieve cells have sieve areas in end walls) Phloem conducting cells – sieve tube elements and companion cells End walls (sieve plates) contain large pores that allow sugars and other organic molecules in a watery solution to pass through easily Plug when injured – p-protein and callose Sieve tube element Sieve plate Primary phloem Zea Primary phloem Helianthus Longitudinal section of stem Primary phloem Forisomes Proteinaceous contractile element found in the phloem of legumes Forisomes contract anisotropically in response to pH variation or the presence of calcium ions Close off sieve tubes in response to injury = aphids CC with plasmodesmata Sieve element with sieve pore Symplastic connections Gymnosperm phloem conducting cells – sieve cells and albuminous cells Albuminous cells (also termed Strasburger cells in earlier literature) in rays No starch and plasmodesmata between them and sieve cells More on secondary phloem in pine Parenchyma axial and ray Resin ducts More on secondary phloem in basswood Fibers Sieve tube members and CCs Ray parenchyma ... element Sieve plate Primary phloem Zea Primary phloem Helianthus Longitudinal section of stem Primary phloem Forisomes Proteinaceous contractile element found in the phloem of legumes Forisomes...Movement through Phloem Solutes higher in phloem Water moves in from xylem Pressure = push Sugars actively unloaded at sink PRESSURE FLOW OR MASS FLOW Phloem is a complex tissue 1)... plasmodesmata between them and sieve cells More on secondary phloem in pine Parenchyma axial and ray Resin ducts More on secondary phloem in basswood Fibers Sieve tube members and CCs Ray parenchyma