Uploaded September 2025 | Updated September 2026, 2 weeks ago
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For nearly sixty years, since my PhD work began in Cambridge, I've been investigating a rather different, perhaps even shocking, idea about how plants produce the vital hormone auxin. The conventional wisdom holds that auxin, indole-3-acetic acid, is synthesized in young, living cells. However, my research strongly suggests this is misconceived. I propose instead that auxin is primarily generated as a byproduct when cells die and undergo autolysis – self-digestion.
The biochemical pathway from the amino acid tryptophan, released when cellular proteins break down, involves enzymes like tryptophan amino transferase. Crucially, these enzymes require high tryptophan concentrations to function effectively – levels typically reached only during cell death, not in healthy, living cells. My experiments, and subsequent findings by others, show auxin production correlates strongly with cell death across the plant: in differentiating wood cells, senescing leaves, root caps, parts of flowers, germinating seeds as storage tissues break down, and in response to wounding. Even dying yeast and rat liver cells produce auxin through similar breakdown processes!
I also address the classic case of the coleoptile tip, long thought to be a site of auxin synthesis, arguing the auxin there isn't made there locally but transported up from the dying storage tissues in the seed; it simply accumulates at the tip. The only clear exception to dying cells as a source of auxin is a plant cancer called crown gall, where a bacterium genetically engineers living plant cells causing them to produce different enzymes which do indeed synthesize auxin from low concentrations of tryptophan – the exception highlighting that normal plant cells don't typically do this while alive. This dying cell hypothesis paints a picture where death is intrinsically linked to life and growth in plants, providing a constant source of the hormone that drives growth and development. My 2021 review paper in the Journal of Experimental Botanyprovides the full details and evidence for this perspective.
Reference List:
The Production of Auxin by Dying Cells
Journal of Experimental Botany (2021) Vol. 72, 2288-2300
sheldrake.org/dyingcells
The Production of Hormones in Higher Plants
Biological Reviews (1973) Vol. 48, pp.509-559
sheldrake.org/higherplants
The Production of Auxin by Autolysing Tissues
Planta (1968) Vol. 80, 227-236
sheldrake.org/autolysing
Production of Auxin by Detached Leaves
Nature (1968) Vol. 217, 195
sheldrake.org/detachedleaves
Do Coleoptile Tips Produce Auxin?
New Phytol. (1973) Vol. 72, 433-447
sheldrake.org/coleoptile
Enjoy ad-free viewing, early access, exclusive videos, and Rupert Responds Q&As.
Click Join below to become a YouTube member, or subscribe on Substack: rupertsheldrake.substack.com
For nearly sixty years, since my PhD work began in Cambridge, I've been investigating a rather different, perhaps even shocking, idea about how plants produce the vital hormone auxin. The conventional wisdom holds that auxin, indole-3-acetic acid, is synthesized in young, living cells. However, my research strongly suggests this is misconceived. I propose instead that auxin is primarily generated as a byproduct when cells die and undergo autolysis – self-digestion.
The biochemical pathway from the amino acid tryptophan, released when cellular proteins break down, involves enzymes like tryptophan amino transferase. Crucially, these enzymes require high tryptophan concentrations to function effectively – levels typically reached only during cell death, not in healthy, living cells. My experiments, and subsequent findings by others, show auxin production correlates strongly with cell death across the plant: in differentiating wood cells, senescing leaves, root caps, parts of flowers, germinating seeds as storage tissues break down, and in response to wounding. Even dying yeast and rat liver cells produce auxin through similar breakdown processes!
I also address the classic case of the coleoptile tip, long thought to be a site of auxin synthesis, arguing the auxin there isn't made there locally but transported up from the dying storage tissues in the seed; it simply accumulates at the tip. The only clear exception to dying cells as a source of auxin is a plant cancer called crown gall, where a bacterium genetically engineers living plant cells causing them to produce different enzymes which do indeed synthesize auxin from low concentrations of tryptophan – the exception highlighting that normal plant cells don't typically do this while alive. This dying cell hypothesis paints a picture where death is intrinsically linked to life and growth in plants, providing a constant source of the hormone that drives growth and development. My 2021 review paper in the Journal of Experimental Botanyprovides the full details and evidence for this perspective.
Reference List:
The Production of Auxin by Dying Cells
Journal of Experimental Botany (2021) Vol. 72, 2288-2300
sheldrake.org/dyingcells
The Production of Hormones in Higher Plants
Biological Reviews (1973) Vol. 48, pp.509-559
sheldrake.org/higherplants
The Production of Auxin by Autolysing Tissues
Planta (1968) Vol. 80, 227-236
sheldrake.org/autolysing
Production of Auxin by Detached Leaves
Nature (1968) Vol. 217, 195
sheldrake.org/detachedleaves
Do Coleoptile Tips Produce Auxin?
New Phytol. (1973) Vol. 72, 433-447
sheldrake.org/coleoptile
