Light Interception

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Science  16 Sep 2011:
Vol. 333, Issue 6049, pp. 1551
DOI: 10.1126/science.333.6049.1551-a

Aside from humankind's special demands, the Sun supplies most of the energy needed by marine and terrestrial organisms. Photosynthesis in leafy plants occurs via chlorophyll pigments, but many aquatic microorganisms can detect and capture sunlight with rhodopsin pigments. The surface of leaves, which is known as the phyllosphere, is an important habitat for pigmented microorganisms. Atamna-Ishmaeel et al. asked whether leaf-colonizing microorganisms, which in the total phyllosphere are estimated to number 1026, compete with or complement their supporting plants' ability to harvest light. In a metagenomic survey of a variety of wild plants, 156 microbial rhodopsin sequences were found, a quarter or more of which seemed to be sensory, and others energy-capturing, proton pumps. Moreover, all of the phyllosphere rhodopsins had the amino acid leucine at position 105 in the protein, indicating that they absorbed green light. In contrast, this position is occupied by glutamine in the marine rhodopsin-bearing microbes, and the pigment consequently absorbs blue light. This means that the phyllosphere microbes are unlikely to compete with their host plant's chlorophyll, but whether this complementarity is a signature of a mutualism is an open question.

Environ. Microbiol. 13, 10.1111/j.1462-2920.2011.02554.x. (2011).

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