Most biology students are more interested in animals than in plants or algae, and among the general public, it is fair to say that “Plant Blindness” is widespread. Sessile green organisms are regarded as a kind of background-vegetation, with little value to humans, except, probably ornaments and crops. They may be ancient living beings, but clearly not “higher organisms”, so the popular argument goes. Accordingly, during the first half of the 19th century, even many biologists believed in the occurrence of “vital forces” in plants. It was the German biologist Julius Sachs (1832–1897), who rejected this metaphysical idea and replaced it by a purely naturalistic concept based on chemistry and physics. Moreover, Sachs fully elucidated the “aliveness” of plants.
In a new textbook, the German biologist Ulrich Kutschera traces the roots of all branches of the experimental plant sciences to the work of Julius Sachs.
In Chapter 1, the history of plant physiology is summarized, with reference to the “vital force-concept”, as proposed by German philosophers (Schelling, Hegel, Schopenhauer); it was soon incorporated into plant biology by leading pre-Sachsian botanists (Meyen, Treviranus, Schacht, de Candolle). Then, the author describes the “Sachs-Pfeffer-revolution” in the botanical sciences, and defines plant physiology, with reference to a Kutschera-paper published 2015 in Nature Plants, as “systems biology of photoautotrophic organisms (embryophytes, algae, cyanobacteria)”. The position of plants in the Five-Kingdom-System of Life is described, and the role of bacteria for the development of embryophytes addressed, with reference to gnotobiology.
All the 19 subsequent Chapters begin with a brief description of the research that Sachs had carried out and published in the respective area of plant science. These introductory remarks are supplemented by the pertinent woodcuttings Sachs had created, reproduced from his original papers and textbooks.
In Chapter 2, the principles of experimentation and deduction of hypotheses vs. theories, with reference to the Sachsian principle of Factor-analysis, are described. Basic and applied research using crop plants is summarized, and the pro- and cons of Arabidopsis as a model organism juxtaposed.
In Chapter 3, plant cell biology is treated in some detail, with reference to tissue tension (as described/discovered by Sachs), cell wall architecture, aquaporins, as well as the organism concept of plant development and the significance of stem cells, inclusive a comparison between embryonic stem cells in humans vs. plants.
In Chapter 4, cell-water relationships are summarized, with illustrations of the water potential concept and resurrection plants. In this context, climate change, which leads to warming of the atmosphere and dryer soils, is discussed.
In Chapter 5, water transport in seedlings, shrubs and trees is described. The cohesion-theory is introduced, and the author describes, possibly for the first time in a textbook, experiments with “synthetic trees”, which corroborated the purely physical mechanism of the ascent of water. In addition, the ascent of sap before the emergence of leaves is described, with reference to little-known work published by forest scientists in Germany.
In Chapter 6, translocation of organic substances (sucrose etc.), and the newly discovered “heart of the plant”, is described. To transfer and concentrate sucrose into the phloem, molecular pumps (SWEET-translocators) are active in the leaves of crop plants. These ATP-driven “sugar pumps” are depicted in a unique model.
In Chapter 7, a systems approach to cell metabolism, with reference to ATP as the free-energy-currency and cytoplasmic protein stabilizer is treated in detail. Gene expression, epigenetics, transcriptomics, metabolomics, and fluxomics are described, with reference to the genome of Arabidopsis thaliana. On several pages, Kutschera refers to the work of Otto Warburg (1883–1970), the little-known pioneer in biochemistry and organismic energetics.
In Chapter 8, seed germination is described, with reference to the Sachsian model organism Rizinus communis. As a highlight, the biophysics and biochemistry of germination in Brassica napus should be mentioned, notably with respect to ATP-levels and germination potential (in MPa).
In Chapter 9, cell respiration is treated at length, with a description of metabolic scaling theory, models of the ATP-synthase and the role of reactive oxygen species (ROS). In this context, soil respiration is highlighted, and the author again discusses the topic of climate change (carbon cycle).
The most comprehensive Chapter deals with photosynthesis – in Ch. 10, the author describes plants as “living sunlight-powerplants and CO2-removers”. On ca. 70 pages, illustrated by 38 Figures, Kutschera describes all key discoveries in photosynthesis research over the past 200 years, with a focus on the work of Julius Sachs, Robert Hill (1899–1990) and Melvin Calvin (1911–1997). In Figure 10.38, the terrestrial carbon-cycle is depicted, based on work published in September 2018. The author points out that, with reference to climate change, ca. 1/3 of anthropogenic CO2-emissions is recycled by land plants (plus marine photoautotrophs) and refers to Sachs’s principle of energy conservation in the biosphere via the “assimilation of carbonic acid”.
Chapter 11 deals with sex and gender in plants, and a description of the mechanisms of growth, inclusive life cycle research. The author describes in detail the discoveries and definitions of Sachs with respect to sexual reproduction, meristematic activity in stems and cell elongation. The biophysical bases of cell elongation is summarized and illustrated, as well as comparative analyses of the life cycles of green algae and different land plants.
Chapter 12, entitled phytohormones – wonder-rice and suicidal germination, not only summarizes the structure and function of plant growth-promoting substances, but also deals with applied aspects. All groups of phytohormones are discussed with reference to crop yield, the “green revolution” and the most recent discovery to combat parasitic plants, such as Striga spp. Suicidal germination, based on 2018-papers, is outlined and the benefit of this new strategy explained.
Chapter 13 deals with photomorphogenesis, light competition and shade avoidance. For the first time in the history of botanical writings, both Sachsians experiments with which he discovered photomorphogenesis, are depicted and described (his forgotten 1865-experiment and Sachs’ famous later documentation of light-induced modulation of growth, i.e., the Cucurbita-image). Photosensors such as phytochromes, cryptochromes and phototropins are described and the mechanism of light-regulated growth outlined. Kutschera points to questionable Arabidopsis-studies, which were performed using seedlings raised on sterile sucrose-containing agar and explains what Sachs would have said to such an artificial system. Chlorophyll biosynthesis and chloroplast development are summarized.
In Chapter 14, mineral nutrition of plants is summarized and mycorrhiza-research described, with reference to the popular claim that trees “talk with each other” via fungal hyphae. Bacterial bio-fertilizer are also described.
In Chapter 15 the assimilation and fixation of nitrogen is described with reference to the legume-rhizobium-symbiosis, symbiosomes and applied aspects. Synthetic mineral fertilizer, based on the Haber-Bosch-principle, are summarized with reference to Vaclav Smil’s important insights on this topic.
In Chapter 16 the Florigen-concept based on Sachs’ 1863-experiments is described, inclusive other aspects of flowering, senescence, cytokinines and apoptosis.
In Chapter 17 the interaction between animals and plants is described with reference to secondary metabolites. The author also provides a brief summery of phytopathology, with reference to the classical work of Sachs’ colleague and friend Anton de Bary (1831–1888).
Chapters 18 and 19 deal with plant movements, with a focus on Dionaea (flytrap) and other carnivorous plants. The author describes key insights of Sachs, quoted from the second edition of his Vorlesungen über Pflanzenphysiologie (1887). The Sachsian principle of the unity of life is described and tropisms depicted-analyzed in many details. At the end of Chapter 19, the concept of plant intelligence is introduced and rejected (with reference to Sachs, who argued that sensitivity is a key to survival in the plant world).
In Chapter 20 general conclusions and an outlook is provided. First, Kutschera explains to the general reader why Sachs was a genius of biology. Then he reproduces a number of unpublished aphorisms taken from the notebooks of Sachs. Then, a comparison between research in medicine and plant physiology is provided, with reference to a forgotten paper of Sachs (1859), wherein he clearly pointed out that we can only feed a growing world population based on plant science. Duckweeds as source for food are described, and the question discussed whether or not it would be possible to feed the world based on organic farming. The text ends with a description of transgenic plants (GMOs) and golden rice.
The book is dedicated to the memory of one of Sachs’ successors of the chair of botany at the University of Freiburg i. Br. (Germany), where the 1868-book was written: Hans Mohr (1930–2016). Accordingly, at the end of the book, the author juxtaposes philosophical insights published by Sachs on the “art of logical thinking” with those of Hans Mohr. Taking these aspects into account, it is fair to say that this textbook also should be of interest to general readers interested in the philosophy of science. Kutschera’s Magnum Opus is supplemented by 314 high-quality Figures, inclusive of many color images. Unfortunately, comparatively few non-German biologists read German. Therefore, a translation of this book in English is highly recommended.