Page Banner

United States Department of Agriculture

Agricultural Research Service

Title: When There Is Too Much Light

Author
item Ort, Donald

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 1, 2000
Publication Date: N/A

Interpretive Summary: Emerging directly from recent discoveries about the regulated thermal dissipation of excess light is a current view of the regulation of crop photosynthesis as a balancing act in which photoprotection is traded for photosynthetic efficiency. It appears that evolution has refined the photosynthetic apparatus with an emphasis on high efficiency at limiting light with regulatory features to ensure that high light levels can be endured without the accumulation of photodamage. While this view is somewhat over simplified, it is clearly true that when light levels are high, factors such as maintenance of water status take physiological precedence over maximizing photosynthesis. Although the trade-off between efficiency and photoprotection is clear, from an agricultural prospective the potential impact of this concept is in determining how well this evoluntionarily determined trade-off is suited for agricultural environments and productivity goals. That is, the forfeiture of photosynthetic efficiency under many agriculturally relevant circumstances may exceed that required to prevent photodamage thus reducing photosynthetic productivity more than necessary. It is important for crop breeders and plant engineers to realize that genetic or induced variation in the ability of crop plant varieties to maintain photosynthetic efficiency at higher light levels may prove to be an important factor in the search for improved photosynthetic productivity of crops.

Technical Abstract: While photodamage has been documented in crops grown outside of their ancestral geographic range, the vast majority of plants in native habitats and even most crops under cultivation deal successfully with excess light avoiding photodamage even under daunting environmental challenges. Photoprotection is a complex process that includes an array of alternative electron acceptors to utilize excess absorbed light when CO2 is limiting, intricate pathways to detoxify photosynthetically produced reactive molecules, as well as a variety of repair processes to prevent the accumulation of photodamage. However, the regulated thermal dissipation of absorbed light is without question the keystone of photoprotection. There is a great deal of importance that is not yet understood about the mechanism and regulation of thermal dissipation but the recent emergence of molecular genetic approaches portend rapid and exciting progress.

Last Modified: 9/20/2014
Footer Content Back to Top of Page