Kudzu speed limits
September 13, 2022 9:58 AM   Subscribe

Kudzu famously grows up to a foot a day. Why doesn’t it grow a foot an hour, or a foot a second? I’m guessing some kind of nutrient limits it before it becomes a risk of bursting into flame from waste heat, but I don’t know. Biologists with a mad science streak: what kind of mutation or environment would make kudzu grow even faster?
posted by BeeDo to Science & Nature (4 answers total) 6 users marked this as a favorite
Best answer: Growth rates are limited by the availability of nutrients, water, and sunlight. A mad scientist might come up with some bonkers chimera involving bamboo, which can grow 3' a day in ideal circumstances.
posted by jquinby at 10:54 AM on September 13, 2022

Best answer: I think the limitation is at least partially due to DNA replication. Plant genomes tend to be very very big (very duplicated). Polymerases (enzymes that make copies of genomic DNA) can only go so fast before they suffer from infidelity (copying errors). Also due to the large genome size, there are limitations on how fast the DNA can "open up" (for copying) and condense back so they can get appropriately assorted into the mother and daughter cells.

A way to get around this is to have really really big cells, so less cells = less nuclei. But then you run into surface-to-volume ratio issues.

Some multicellular fungi do this, some even have cells with no nucleus.

On the face of it, I think these are higher order limitations than waste heat from high metabolic rates, but metabolic rate is definitely a factor (and transportation of nutrients from the roots to the shoot tips to provide the raw materials for cell growth/ DNA replication) as well as local energy synthesis (and catabolization of stored energy).
posted by porpoise at 11:44 AM on September 13, 2022 [3 favorites]

Best answer: There's probably an interface limit to how quickly its roots can take up nutrients from the soil, as well as how much energy it can absorb from the sun, though these scale with size. I think a more fundamental thing to improve would be the speed of the nutrients in the plant itself, which travel through relatively slow channels (xylem and phloam IIRC) that aren't actively pumped. If there were some kind of upgraded kinesin that could accelerate the distribution of useful molecules along the plant's stalks from where it was produced (old growth) to where it's needed (new growth) it may speed things up.

But there's also limits on the speeds of cell division and creation that may be more to the point. Too fast and there isn't time for the usual processes of error correction, the production of the proper amounts of various proteins and active biomolecules etc. It would probably mutate or grow in janky fashion.

On preview: As porpoise says, DNA replication is a fundamental limit in that realm as well.
posted by BlackLeotardFront at 11:47 AM on September 13, 2022

Parasites often have little DNA compared to their independent ancestors. Maybe a kudzu in its perfect environment could, hm, become parasitic too?

posted by clew at 1:45 PM on September 13, 2022

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