Editor’s note: ASPB is happy to publish this appreciation of UC-Davis Professor Emeritus, Emanuel Epstein, on the occasion of his 100th birthday.
A single rye plant may possess a root meshwork of more than 600 km total length. Unbelievable, but measured by Howard Dittmer after carefully isolating the main and all side roots of a four months old rye plant (1). Why do plants require such huge root systems, which frequently represent more in mass and surface area than the above-ground part?
Besides anchoring, roots above all withdraw water from the soil as well as the ions dissolved in it like potassium, magnesium, calcium, iron, zinc, phosphorous, selenium and half a dozen more. These elements, which partly exist in minute concentrations in the soil, are essential for plants, but also for animals and humans. We obtain them exclusively via the food chain through plants. Only for the supply of kitchen salt, sodium chloride, we have to care ourselves, since our food plants do not require sodium. For that reason we have a salt shaker on our dining table, however no iron-, magnesium-, calcium, and sulfur shakers. For our cattle salt blocks have to be used.
How plants extract minerals from the soil has been intensively studied by Emanuel Epstein, the father of modern root physiology and biochemistry. On the 5th of November 2016, the emeritus professor of plant biology of the Department of Plant Biology at UC Davis will be hundred years old. Until recently he cycled every day to his office; in the meantime his doctor has forbidden using the bicycle (pers. communication).
Epstein started to investigate how ions are taken up by plant roots already in early fifties of the last century (2). He demonstrated that their transport through the membrane of root cells is a catalyzed process. The postulated catalysts followed the behavior of enzymes (2-4) as described by Michaelis and Menten. This suggested protein-catalyzed mineral uptake, and thus root physiology had caught up with biochemistry. Up to then, the “lipid-filter theory” dominated membrane transport physiology in general, which meant that uptake of a molecule into a cell is dependent solely on its size and its partition coefficient for oil/water and thus is a pure physical process. Proven was the protein-mediated membrane passage finally in the following years, when in the French laboratory of Monod the gene for the bacterial lactose permease was discovered (5) and the American biochemists Fox and Kennedy identified the corresponding protein (6).
Epstein pointed out the tremendous importance of the plant root for the existence of life by stating:
“It may be predicted with some assurance that, if intelligent life on solid land is ever discovered elsewhere in the universe, there as on the earth the world of life will consist of two kingdoms: plant and animal. Only mobile organisms will develop intelligence and only stationary ones can secure from a solid substrate nutrient elements essential for the functioning of living matter”(7).
And indeed we would have to extract 5 to 10 tons of soil to satisfy our daily requirement of phosphate, which amounts to 500 mg. But we could also do with 100 to 200 g of vegetable and a steak, whereby also the steak obtained its phosphate from plants of course. The cells of plant roots are therefore not only equipped to specifically take up ions, but are also able to concentrate them 1000 to 10 000 fold. Once it was shown that Peter Mitchell’s chemo-osmotic theory for active transport of bacteria(8) also holds for eukaryotic cells (9) a huge number of H+/substrate symporters were described in the decades to follow, and the high accumulating potential of root cells was in principle understood.
Epstein’s suggestion that freely movable organisms, wherever existing in the universe on solid ground, require rooted partners to survive seems plausible: the former will develop sensory organs to make optimal use of the possibility to freely move, and a control center to process the signals and to coordinate the locomotor system; the latter will do the mining work as described. Epstein’s prediction will most likely never be proven. When presently, however, daily new exo-planets are discovered (10), which frequently are earthlike, the question whether life exists on other planets is more acute than ever.
Emanuel Epstein has told us about the tremendous importance of the plant’s root more than 40 years ago (7, 11). With his early publications he has established the basis for the work of hundreds of plant biochemists, who in the past 60 years elucidated the molecular mechanisms of membrane transport in plants and at present try to produce crop plants optimized for man and the environment.
This post was submitted by Widmar Tanner , Zellbiologie/Pflanzenphysiologie, Universität Regensburg
- Dittmer H. A quantitative study of the roots and root hairs of a winter rye plant (Secale cereale). Ann. J. Bot.24 (1937) 414–20
- Epstein E. and Hagen C. E. A kinetic study of the absorption of alkali cations by barley roots. Plant Physiol. 27 (1952) 457- 474.
- Epstein E. Mechanism of ion absorption by roots. Nature 171 (1953) 83-84
- Epstein E, Rains D. W. and Schmid W. E.. Course of cation absorption by plant tissue. Science 136 (1962) 1051-1052
- Rickenberg HV, Cohen GN, ButtinG,Monod J. La galactoside-permease d’Escherichia coli. Ann.Inst. Pasteur 91 (1956) 829–57
- Fox CF, Kennedy EP. Specific labeling and partial purification of the M protein, a component of the β-galactoside transport system of Escherichia coli. PNAS 54 (1965) 891–99
- Epstein E. “Roots”, Scientific American, May 1973, pp. 48-58.
- Mitchell P. Molecule group and electron translocation through natural membranes. Biochem. Soc. Symp. 22 (1963) 142–68
- Komor E. Proton-coupled hexose transport in Chlorella vulgaris. FEBS Lett. 38 (1973) 16–18
- Petigura E.A., Howard A. W., Geoffrey W. Marcy G. W. Proc Natl Acad Sci U S A. 110 (2013) 19273-78
- Epstein, E. Mineral nutrition of plants: Principles and perspectives. New York: John Wiley & Sons, Inc., 1972 (412 pages)