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Plants, put in the dark, reveal over 100 active peroxisome proteins

A study by the Hu lab has identified 111 peroxisomal proteins in plants, including six newly identified ones. The study is in the Journal of Integrative Plant Biology.

expand iconPeroxisomes work like food processors in plant cells. They break down fatty acids (aka, fats) into smaller pieces that end up in energy compounds to fuel plants. They also play more roles, like breaking down toxins, protecting plants from environmental stresses, and participating in expand iconphotosynthesis.

“We still haven’t fully mapped the functions of plant peroxisomes. To do so, we have to catalogue their body of expand iconproteins,” says Jianping Hu, Professor at the MSU-DOE Plant Research Laboratory.

The new study focused on senescent plants – plants that had aged or that were deteriorating due to some extreme stress. During such times, plants slow down their activity and break down their structures and cellular parts, including proteins and lipids.

“The stage of senescence is one of the lesser investigated areas," says Hu. "Peroxisome shape and function does change, depending on the age of the plant and on where it is located, whether it be the leaf or seed.”

Plants in the dark

Hu and her team grew Arabidopsis plants for four weeks. Then they put them in the dark for two days.

They found 105 proteins that are known to relate to peroxisome activity. They also identified 6 new proteins in both seeds and leaves. Similar studies in non-plant systems, such as humans or fungi, have yielded smaller numbers of proteins. These findings suggest that plant peroxisomes can play more roles compared to their human or fungal counterparts.

"We think the newly identified proteins might help break down compounds and clean up toxic materials," Hu says. “They also might help produce plant defenses against bacteria and assist plants in combatting oxidants (humans drink orange juice and eat leafy greens to fight oxidants).”

“We even found one protein that is localized on the surface of three expand iconorganelles – peroxisomes, chloroplasts and mitochondria. It is possible that this enzyme helps detoxify these three organelles that are metabolically linked,” Hu says.

Hu adds that there is more work to be done. But scientists face major obstacles to establishing an entire catalog of peroxisomal proteins. One, they are difficult to detect. And, two, it is hard to catch transient proteins that are active under specific conditions, like during senescence or under different environmental stresses.

“We still need to compare proteins in different tissues and investigate other plant organs,” Hu says. “Although we looked at plants exposed to the dark, we need to expose them to other conditions, like chemicals and other stresses. These experiments might lead to different observations.”

This research has multiple applications down the road, including breeding crops that are better at generating energy and producing higher yields. There is even a potential benefit to medical science, as some human and plant peroxisomal proteins are closely related. In humans, peroxisomal disorders are very debilitating, with symptoms including poor growth, neurological dysfunctions, hearing/visual problems, liver disease, just to name a few.

This is one instance where plant science might indirectly contribute to human health.


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