Plant Physiology - Musiyenko, M. M. 2001

Plant Movements
Intracellular Movements

The Cytoplasm, with the exception of a thin outer layer known as the ectoplasm, is in a state of constant motion, as are some of its components, notably METABOLISM/14.html">Chloroplasts. The Cell responds to environmental changes by altering The rate of this movement. It is hypothesized that the driving force behind cyclosis is the interaction between active microfilaments and the microtubules of the ectoplasm. Cyclosis requires ATP energy consumption and the presence of Ca²⁺ ions at specific concentrations. The velocity of cytoplasmic streaming ranges from 2 to 50 µm/s in various Cells.

Cyclosis also facilitates the movement of cell Organelles, although chloroplasts, for instance, are capable of autonomous locomotion. The light receptor that induces chloroplast movement is located in the peripheral region of the cytoplasm. Blue light is effective, whereas long-wave light is inactive, suggesting that flavins or Flavoproteins act as the photoreceptors. The exact role of chlorophylls in these processes remains fully understood.

Chloroplasts are connected to bundles of cytoplasmic microfilaments via Myosin, the molecular heads of which interact with Actin filaments. Chloroplast movement arises from the interaction between Actin and myosin (Fig. 209). This movement is also stimulated by certain Chemical factors, such as CO₂, sugars, and organic acids.

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Fig. 209. Diagram of the mechanism driving chloroplast movement within the cell

Bombardier plants. Certain plants exhibit movements dedicated to the dispersal of seeds, spores, and pollen. For example, well-known species of Touch-me-not (Impatiens L.) possess fruits that burst rapidly upon being touched. The fruit consists of five carpels. As they mature, a layer of large cells situated directly beneath the epidermis swells significantly and maintains turgor pressure. Simultaneously, the connections between the carpels along their suture lines weaken

Fig. 210. Cytology/practical/54.html">Longitudinal section of a mature squirting cucumber fruit (a) and at the moment of ejecting the pulp and seeds (b)

due to The breakdown of pectic substances that cement the cells together. A gentle touch to the touch-me-not fruit disrupts the connections between the carpels, causing them to rapidly coil inward and forcefully scatter the attached seeds. The squirting cucumber (Ecballium elaterium) disperses its seeds in a similar explosive manner (Fig. 210).

Similar movements are characteristic of the sporangia of ascomycetes.