Description

Potassium works in multiple ways to maintain photosynthesis during periods of moisture stress. This allows plants to continue growing, albeit at a slower rate, but at a rate that ultimately explains the improved yields as compared to crops with less potassium. For photosynthesis to continue, the plant needs to be able to maintain and increase water uptake and retention as well as maintain the cellular membranes that protect the chlorophyll structures. This is achieved by increasing the osmotic (salt) concentration of the cells and through the rapid closure of the stomata (pores in the leaf surface). Increasing the osmotic concentration of the cells has the effect of increasing the activity of aquaporins (channels in the membranes of the plant cells) which facilitate the uptake of water. The increase in osmotic concentration also assists the plant in extracting water from the diminishing supply in the soil and helps to keep cells turgid. Potassium plays a crucial role in changing the turgor of the guard cells needed to close the stomata and prevent water loss. When potassium is in short supply, the time taken by the guard cells to close increases from a few minutes to over an hour. As a result the plants continue to lose moisture and are more susceptible to drought. Plants that experience moisture stress produce more oxygen radicals which are very reactive chemical compounds that, if left, unchecked will destroy the cellular membranes thereby disrupting photosynthesis. To counteract this, plants produce NADPH oxidase, an enzyme that reacts with the oxygen radicals and reduces them to neutral compounds. NADPH oxidase activity is regulated by potassium.
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