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I know humans and other animals start using their own proteins as food when starving. This made me wonder if a plant that is deprived of sunlight, after using up its sugar reserves and other carbs, could break down parts of its own woody structure in order to feed the rest of itself.

Googling yielded no useful results, which leads me to think the answer is no. I've never heard of plants themselves possessing cellulase, only certain animals.

Additionally, I would imagine that cellulose is not easy to transport, so it would have to be decomposed by the region of tissue surrounding it - which obviously couldn't last for long before that region died due to cannibalizing itself.

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  • $\begingroup$ Then deciduous trees would absorb back their leaves rather than losing them in autumn. I think that plants can take back most things from leaves except cellulose. $\endgroup$
    – bandybabboon
    Jun 13, 2020 at 0:55
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    $\begingroup$ breaking down cellulose is very different than breaking it down FOR energy, which are you looking for> it would not surprise me if there are plants that can break down cellulose but do so at a net loss. $\endgroup$
    – John
    Jun 13, 2020 at 3:12

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Plants do not produce extra cellulase to break down cellulose for an energy boost when they are grown in dark conditions (that I know of). But remember, cell walls are the structures maintaining turgor pressure in the cells, so breaking them down would be very costly to plant survival. A couple notes: plant cell walls have more components than just cellulose, and they ARE dynamic. In dark-grown conditions, plants elongate (etiolation) during which time, enzymes (expansions) break down cell wall bonds to allow the cells to elongate the stems of the plants. Elongation is an evolutionary advantage to find light when things get shady.

To read more about what the cell wall is made of, and the function it provides to the cell, try watching the Khan Acadamy video about cell walls. Light signaling is an entire field in Plant Biology (example). Read more, if you are interested in how immobile plants handle shading from other plants or periods of darkness. Plants do break down proteins for reuse! Read more about plant vacuoles if you're interested in how they recycle and break down some molecules and proteins when needed (related to your question's parallel to animal cells; although, not cellulose breakdown to replace photosynthetic sugar output).

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    $\begingroup$ This is a good answer, but it is much more likely to receive a favorable response if you include supporting references (primary literature is best). Without that support, the most directly relevant part of your answer is indistinguishable from opinion and someone with no plant biology background will be unable to judge your assertions. ——— Note that links often break, so we prefer that you also include citation information. This is a good example of how to format references. Thank you! 😊 $\endgroup$
    – tyersome
    Jun 12, 2020 at 23:46
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Plants do not break down cellulose for energy, although it does store energy. Plants store their energy in the form of starch, which is broken down into glucose for the plant to use for energy. Most plants do not survive once the starch is utilized (but they do not breakdown cellulose).

Because cellulose molecules bond strongly to each other, breakdown of cellulose is relatively difficult compared to the breakdown of starch. High temperature is required for breakdown of cellulose, which plants cannot breakdown.

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