Transport in plants

  • 0_1550145564367_IMG_20190214_172911.jpg
    Is the given information correct?

    According to the modern theory of opening of stomata, potassium malate has a big role to play. There is no involvement of glycolate anywhere. Please explain.

  • administrators


    Theory of Glycolate Metabolism:
    Zelitch (1963) proposed that production of glycolic acid in the guard cells is an important factor in stomatal opening. Glycolate is produced under low concentration of CO2. He suggested that glycolate gives rise to carbohydrate, thus raising the osmotic pressure and also that it could participate in the production of ATP. Which might provide energy required for the opening of stomata.


    1. It fails to explain the opening of slomata in dark (e.g., – in succulent plants).

    2. In some plants slomata have been found to remain closed even during daytime.

    3. It fails to explain the effect of blue light on stomatal opening.

    Malate anions + K+ →Potassium malate:

    Potassium malate enters the cell sap of the guard cells thereby reducing the water potential while increasing the osmotic concentration (and the O.P.) of the cell sap. Hence, endosmosis occurs, guard cells become turgid and kidney-shaped and the stomata opens.

    Role of K+, Cl- and Malate in Increasing Osmotic Concentration

    It is also observed that the CO2 concentration is low in and around guard ceils during day time. This is due to high photosynthetic utilization of CO2. It helps in opening of stomata.

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