Hormone Production in Plants
The first problem I investigated in my research career was how the hormone auxin (indole-3-acetic acid) is produced in plants. See scientific papers below. When I started research on this subject, nobody knew how it was made, and years of efforts had failed to clarify the situation. As I reflected on the biochemical mechanisms by which auxin can be produced I realised that it could be a non-specific breakdown product of the amino-acid tryptophan and that it was likely to be produced in dying cells, as proteins break down, releasing tryptophan. When I started this research, in the 1960's, little attention was paid to dying cells in plants or animals. Nevertheless programmed cell death - also known as apoptosis - is now a very fashionable topic of research in cell biology.
I showed dying cells could produce auxin as a by-product of their autolysis or self-digestion. See The Production of Auxin by Autolysing Tissues
There was nothing specific about the way it was produced in plants. Auxin was also produced, for example, by autolysing yeast cells, and also by autolysing rat liver. Many of the places in which auxin is known to be produced in plants are places where cells die, for example in germinating seeds, as storage tissues breakdown. Auxin is known to be produced in developing leaves and buds, and its formation is roughly proportionate to the development of veins within the leaf. Veins contain xylem or wood cells, and when wood cells develop, the walls thicken up and the cell contains break down and are dissolved away, so cell death occurs in all young growing tissues. Perhaps the differentiating xylem cells were a source of auxin, released as they died.
I studied this question in stems in which new xylem cells were being formed as a result of cambial activity, and found that these thickening stems did indeed produce auxin. See The Production of Auxin by Tobacco Internode Tissues
I also looked at auxin production in senescent leaves. As they go yellow, the cells breakdown and sure enough I found the auxin levels increased dramatically. See Production of Auxin by Detached Leaves. There was only one supposed site of auxin production in plants in which dying cells were not present, namely the tips of coleoptiles in cereal seedlings. These sheathing structures around the seedling shoot were some of the first organs in which auxin was studied and were of particular importance in the classical literature on auxin production. However, although auxin was present in coleoptile tips, I found there was no persuasive evidence that it was made there, and found that in fact it was probably accumulating there having been carried up from the seed in the sap. See Do Coleoptile Tips Produce Auxin?
The formation of auxin in developing xylem cells in the trunks of trees as they grow would mean that a gradient of auxin would be set up across the cambium, the region of dividing cells that separates the wood from the bark. I directly measured auxin levels in the xylem cambium and young phloem cells, from the inside of the bark and showed that there was indeed such a gradient. This was one of the first chemical gradients to be characterised in either animals or plants of a chemical known to have morphogenetic effects. See Auxin in the Cambium and its Differentiating Derivatives
Since dying cells produce auxin, and since dying cells occur within all higher plants as a result of xylem differentiation this raised an evolutionary question. Had the responsiveness of plants to this cell-breakdown product, acting as a chemical signal of cell death, evolved only after cell death became an integral part of plant grown with the evolution of a vascular system? Or have plants already become sensitive to auxin before the vascular system evolved? In fact it was already known that non-vascular land plants, like mosses and liverworts are sensitive to low concentrations of auxin in the environment. They react by producing root hairs, or rhizoids. If this sensitivity had developed in response to dying cells, it would enable mosses and liverworts to produce rhizoids which increase the surface area for absorption of nutrients, in places where there was decaying organic matter, in other words when nutrients were most likely to be abundant. Is auxin really present in such situations? I examined the humus on which mosses and liverworts were growing both in the tropics and in temperate countries and found that it did in fact contain auxin in quantities sufficient to produce rhizoid formation. This suggested an evolutionary origin for the auxin responses in higher plants. First, plants evolved sensitivity to auxin as a signal of organic decay in the external environment. Later, as cell death became an integral part of plant growth the evolution of the vascular system, this hormonal-response system became internalised and auxin evolved the wide range of signalling roles that it has today. See The Occurrence and Significance of Auxin in the Substrata of Bryophytes
At the end of my time at Cambridge, I published a comprehensive review of research on production of auxin and other hormones in plants, summarising the dying-cell hypothesis. See The Production of Hormones in Higher Plants
Scientific Papers on Hormone Production In Plants
The Production of Auxin by Dying Cells
Journal of Experimental Botany (2021) 72, 2288-2300
https://doi.org/10.1093/jxb%2Ferab009
by Rupert Sheldrake
The Production of Hormones in Higher Plants
Biological Reviews (1973) 48, pp.509-559
https://doi.org/10.1111/j.1469-185X.1973.tb01568.x
by Rupert Sheldrake
Do Coleoptile Tips Produce Auxin?
New Phytol. (1973), 72, 433-447
https://doi.org/10.1111/J.1469-8137.1973.TB04393.X
by Rupert Sheldrake
Auxin in the Cambium and its Differentiating Derivatives
Journal of Experimental Botany (1971), 22, 735-740
https://doi.org/10.1093/JXB%2F22.3.735
by Rupert Sheldrake
The Occurrence and Significance of Auxin in the Substrata of Bryophytes
New Phytologist (1971) 70, 519-526
https://doi.org/10.1111/J.1469-8137.1971.TB02553.X
by Rupert Sheldrake
The Production of Auxin by Autolysing Tissues
Planta, Berlin (1968), 80, 227-236
https://doi.org/10.1007/BF00392393
by Rupert Sheldrake, D.H. Northcote
Production of Auxin by Detached Leaves
Nature (1968), 217, 195
https://doi.org/10.1038/217195a0
by Rupert Sheldrake
The Production of Auxin by Tobacco Internode Tissues
New Phytologist (1968), 67, 1-13
https://doi.org/10.1111/J.1469-8137.1968.TB05449.X
by Rupert Sheldrake and D. Northcote
Auxin Transport in Plants

In plants auxin is transported from the shoot tips towards the root tips by the polar auxin transport system. I investigated which tissues were most involved in this transport process, and whether the polarity of stems could be reversed: I found it could not be. With my colleague Philip Rubery, I worked out the cellular basis of polar auxin transport. Our hypothesis, the so-called chemiosmotic hypothesis, was subsequently confirmed and is now generally accepted. We predicted the existence of auxin efflux carrier proteins preferentially located at the basal end of cells. These proteins were identified in the twenty-first century, and are now called PIN proteins; they are an important focus for contemporary research on plant development.
Scientific Papers on Auxin Transport In Plants
Effects of Osmotic Stress on Polar Auxin Transport in Avena Mesocotyl Sections
Planta 145, 113-117 (1979)
https://doi.org/10.1007/BF00388706
by Rupert Sheldrake
Carrier-mediated Auxin Transport
Planta (Berl) 118, 101-121 (1974)
https://doi.org/10.1007/BF00388387
by P.H. Rubery and R. Sheldrake
The Polarity of Auxin Transport in Inverted Cuttings
New Phytol (1974) 74, 637-642
https://doi.org/10.1111/J.1469-8137.1974.TB01289.X
by Rupert Sheldrake
Auxin Transport in Secondary Tissues
Journal of Experimental Botany, Vol.24, No.78, pp. 87-96, February 1973
by Rupert Sheldrake
Effect of pH and Surface Charge on Cell Uptake of Auxin
Nature New Biology 244, 285-288 (1973)
https://doi.org/10.1038/NEWBIO244285A0
by P.H. Rubery and A.R. Sheldrake
Polar Auxin Transport in Leaves of Monocotyledons
Nature (1972), 238, 352-353
https://doi.org/10.1038/238352A0
by Rupert Sheldrake
Rupert's research reports as Rosenheim Research Fellow
Royal Society Yearbooks for 1971, 1972 and 1973
Crop Physiology
From 1974 to 1985, I worked at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) in Hyderabad, India, on the physiology of tropical legume crops, first as Principal Plant Physiologist, and later as Consultant Physiologist.
Scientific Papers on Crop Physiology
Effect of harvest methods on the second flush yield of short-duration pigeonpea (Cajanus cajan)
J.agric. Sci., Camb. (1987) 109, 591-593
https://doi.org/10.1017/S0021859600081818
by Y.S. Chauhan, R. Sheldrake, N. Venkataratnam
Factors affecting growth and yield of short-duration pigeonpea and its potential for multiple harvests
J.agric. Sci., Camb. (1987) 109, 519-529
https://doi.org/10.1017/S0021859600081739
by Y.S. Chauhan, N. Venkataratnam, R. Sheldrake
A Perennial Cropping System From Pigeonpea Grown in Post-Rainy Season
Indian Journal of Agricultural Sciences 57, 895-9, 1987
by Rupert Sheldrake
Second Harvest Yields of Medium Duration Pigeonpeas (Cajanus Cajan) in Peninsular India
Field Crops Research (Dec 1985), 10(4), 323-332
by N.Venkataratnam and R. Sheldrake
Pigeonpea Physiology
Chapter 11 of The Physiology of Tropical Field Crops ed. P. H. Goldsworthy and N. M. Fisher, Blackwell, Oxford (1984)
The Anatomy of the Pigeonpea
Research Bulletin No. 5, 1981
International Crop Research Institute for the Semi*Arid Tropics (ICRISAT), Patancheru
by S.S. Bisen and R. Sheldrake
Effect of seed-grading on the yields of chickpea and pigeonpea
Indian Journal of Agricultural Science 1981, 51, 389-393
by R. Sheldrake, N.P. Saxena, A. Narayanan
Varietal Differences in Seed Size and Seedling Growth of Pigionpea and Chickpea
Indian Journal of Agricultural Science, (1981), 51, 389-393
by A. Narayanan, N.P. Saxena and R. Sheldrake
Effects of Pod Exposure on the Yield of Chickpeas
Field Crops Research, (1980), 3, 180-191
https://doi.org/10.1016/0378-4290(80)90024-6
by N.P. Saxena and R. Sheldrake
Iron Chlorosis in Chickpea (Cicer Arietinum L.) Grown on High pH Calcareous Vertisol
Field Crops Research, (1980), 3, 211-214
https://doi.org/10.1016/0378-4290%2880%2990029-5
by N. Saxena and A. Sheldrake
Physiology of Growth, Development and Yield of Chickpeas in India
ICRISAT Publications, (1980), 106-120 ref.25
Proceedings of the International Workshop on Chickpea Improvement, Hyderabad, India, Feb 28 - Mar 2 1979
by R. Sheldrake and N.P. Saxena
Growth and Development of Chickpeas under Progressive Moisture Stress
Stress Physiology in Crop Plants, ed. H.Mussell and R.Staples. Wiley, New York, 1979.
by R. Sheldrake and N.P. Saxena
Comparisons of Earlier- and Later-formed Pods of Chickpeas (Cicer arietinum)
Annals of Botany (1979), 43, 467-473
https://doi.org/10.1093/OXFORDJOURNALS.AOB.A085657
by R. Sheldrake, N.P. Saxena
Comparisons of Earlier- and Later-formed Pods of Pigeonpeas (Cajanus cajan)
Annals of Botany (1979), 43, 459-466
by R. Sheldrake, A. Narayanan
The Effects of Flower Removal on the Seed Yield of Pigeonpeas (Cajanus cajan)
Annals of Applied Biology (1979), 91, 383-390
https://doi.org/10.1111/J.1744-7348.1979.TB06516.X
by Rupert Sheldrake, A. Narayanan, N. Venkataratnam
Growth, development and nutrient uptake in pigeonpeas (Cajanus cajan)
Journal of Agricultural Science (Cambridge) (1979), 92, 513-526
https://doi.org/10.1017/S0021859600053752
by Rupert Sheldrake and A. Narayanan
A Hydrodynamical Model of Pod-Set in Pigeonpea (Cajunus Cajan)
Indian Journal of Plant Physiology, (1979), 22, 137-143
by Rupert Sheldrake
Pigeonpea (Cajanus Cajan) as a Winter Crop in Peninsular India
Experimental Agriculture, (1979), 15, 91-95
https://doi.org/10.1017/S001447970000925X
by Rupert Sheldrake and A. Narayanan
The Expression and Influence on Yield of the 'Double-Podded' Character in Chickpeas
Field Crops Research (1978), 1, 243-253
https://doi.org/10.1016/0378-4290%2878%2990029-1
by R. Sheldrake, N.P. Saxena, L. Krishnamurthy
Some Effects of the Physiological State of Pigeonpeas: on the Incidence of the Wilt Disease
Tropical Grain Legumes Bulletin, (1978), 11, 24-5
by R Sheldrake, A Narayanan, J Kannaiyan
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