PL SC221 Lecture Notes - Lecture 9: Vessel Element, Phytochrome, Auxin
Document Summary
Directed movements resulting from external stimuli (tropism): Tropism directed movements in response to a stimulus. Random movements caused by changes in turgor pressure. Studies how an organism grows and how its cells and tissues differentiate. Phytochrome etc. that sense light, other ones that sense gravity, etc. Signaling via hormones, action potentials, and hydraulic signals. Hydraulic signals that travel in the xylem (pressure pulses) Cambium initial forms a new vessel element or fiber. This new cell grows bigger and differentiates (cell walls are modified, pits are formed, etc. ) In the case of vessel elements, the cytoplasm is dissolved and the cell undergoes programmed cell death. A few undifferentiated cells grow and differentiate into many different cell types. Plants often grow toward a light source (the leaves do it, makes sense) Primary plant roots respond positively, while young shoots respond negatively to gravity. Growth movements are often in response to changes in auxin flow.
