The Mystery of Photorespiration by panniuniu


									The Mystery of Photorespiration
Yael: Today, we're talking about plants and the mystery of photorespiration.
Don: Photorespiration? Are you sure you don't mean photosynthesis?
Y: Nope, Don. I mean photorespiration, which is actually diametrically opposed
to photosynthesis.
D: You're losing me.
Y: Okay, let's back up. You know what photosynthesis is, right?
D: It's the process by which plants use light to convert carbon dioxide and water into the
sugars that fuel the plant, right?
Y: Right. Well, during photorespiration plants use light energy to consume oxygen and
release carbon dioxide and water.
D: So photorespiration undoes the work of photosynthesis?
Y: At least part of it. So under present atmospheric conditions, plants lose about twenty-
five percent of the energy that they capture through photosynthesis to photorespiration.
D: But why?
Y: Good question. One hypothesis is that photorespiration had a role in early evolution,
when there was more carbon dioxide in the air. Another explanation is that plants use
photorespiration to slow down photosynthesis under certain stressful conditions, like
intense light, so that the photosynthetic apparatus doesn't get damaged. Given all the
mystery surrounding this process, some scientists even began working on genetically
engineering crop plants to minimize photorespiration.
D: So they'd grow better, huh?
Y: Yes. But one study suggests that photorespiration is actually important to plants after
all. Researchers at UC Davis showed that photorespiration enables a plant to convert
inorganic nitrogen into a form of nitrate that's needed for plant growth. This helps explain
why plants have trouble growing in conditions with low oxygen and high carbon dioxide,
which inhibit photorespiration.
D: Hmm! So maybe genetically engineering crops to reduce photorespiration isn't the
way to go after all.

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