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Transport213-page14 - water deficit serves as a signal for...

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Transport in Plants - 14 Nighttime, water deficit or some other harmful conditions* 1. K + leaches out of guard cells passively. 2. H 2 O follows. 3. Guard cells lose turgor and “close”. K + and water movement out of guard cell Things that affect stomatal opening and closing Stomatal Opening As stated, blue light receptors in the guard cells activate the H+/K+ pumps. Photosynthesis maintains a high solute concentration for turgor and also provides a source of ATP for the proton pumps to function. Guard cell chloroplasts respond to red light. Low CO 2 in the mesophyll, which occurs when photosynthesis starts, can trigger stomatal opening. Artificially low CO 2 levels even in the absence of light can trigger stomatal opening. Stomata opening may also be under the influence of circadian rhythms. Stomatal Closing Abscisic acid produced in roots and translocated through xylem monitors water concentration in the plant (root and leaf mesophyll cells) and when there is a
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Unformatted text preview: water deficit, serves as a signal for a transduction pathway (that has a Ca ++ secondary messenger) which results in ion (K + especially, but possibly Cl-and malate) movement from the guard cells, closing stomata within minutes. • High CO 2 levels detected in guard cells will promote stomatal closure • High temperatures also trigger stomatal closure (but may be related to the CO 2 concentrations at higher temperature). • Some chemicals, such as ozone, also promote stomatal closure. • Plants can respond to long-term water deficit by dropping leaves, reducing transpiration, common in many desert plants. • The genetic model plant, Arabidopsis , when grown in high CO 2 concentrations, produces fewer stomata per leaf, validating the observations of the English woodland....
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