Issue Date: April 9, 2007
Getting to the root of leaf streaks
Plant leaves aren't always uniformly green; some have streaks of white or yellow, a characteristic known as variegation. A new study proposes that a factor influencing variegation is the balance between synthesis and degradation of proteins involved in photosynthesis (to appear in Plant Cell, DOI: 10.1105/tpc.106.049270). Chlorophyll, the green pigment in protein photosystems, uses light energy to initiate electron transfer, but eventually light damages the proteins, says Wataru Sakamoto, a plant biologist at Okayama University in Japan. Variegated mutants of the model plant Arabidopsis do not produce an important protease that breaks down these damaged proteins. Without the housekeeping protease, inactive proteins accumulate, disrupting the membrane where chlorophyll normally resides and inhibiting the production of new photosystem proteins. The result is loss of the green color. But plant cells also have some backup protein housekeepers, so the threshold for photosystem disruption-and color change-is variable. Time and less light also allow the backup housekeepers to restore active photosystems and the green color, Sakamoto notes.
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