Basic versus applied research: Julius Sachs (1832-1897) and the experimental physiology of plants

Julius Sachs (1868): The father of plant physiology

The year 2018 marks the 150th anniversary of the first publication of Julius von Sachs' (1832-1897) Lehrbuch der Botanik (Textbook of Botany), which provided a comprehensive summary of what was then known about the plant sciences. Three years earlier, in 1865, Sachs produced the equally impressive Handbuch der Experimental-Physiologie der Pflanzen (Handbook of Experimental Plant Physiology), which summarized the state of knowledge in all aspects of the discipline known today as plant physiology. Both of these books provided numerous insights based on Sachs' seminal experiments. By virtue of a reliance on detailed empirical observation and the rigorous application of chemical and physical principles, it is fair to say that the publication of these two monumental works marked the beginning of what can be called "modern-day" plant science. Moreover, Sachs' Lehrbuch der Botanik prefigured the ascendance of plant molecular biology and the systems biology of photoautotrophic organisms. Regrettably, many of the insights of this great scientist have been forgotten by the generations who followed. It is only fitting, therefore, that the anniversary of the publication of the Lehrbuch der Botanik and the career of "the father of plant physiology" should be honored and reviewed, particularly because Sachs established the physiology of green organisms as an integral branch of botany and incorporated a Darwinian perspective into plant biology. Here we highlight key insights, with particular emphasis on Sachs' detailed discussion of sexual reproduction at the cellular level and his endorsement of Darwinian evolution.

Regulation of root development in Arabidopsis thaliana by phytohormone-secreting epiphytic methylobacteria

In numerous experimental studies, seedlings of the model dicot Arabidopsis thaliana have been raised on sterile mineral salt agar. However, under natural conditions, no plant has ever grown in an environment without bacteria. Here, we document that germ-free (gnotobiotic) seedlings, raised on mineral salt agar without sucrose, develop very short root hairs. In the presence of a soil extract that contains naturally occurring microbes, root hair elongation is promoted; this effect can be mimicked by the addition of methylobacteria to germ-free seedlings. Using five different bacterial species (Methylobacterium mesophilicum, Methylobacterium extorquens, Methylobacterium oryzae, Methylobacterium podarium, and Methylobacterium radiotolerans), we show that, over 9 days of seedling development in a light-dark cycle, root development (hair elongation, length of the primary root, branching patterns) is regulated by these epiphytic microbes that occur in the rhizosphere of field-grown plants. In a sterile liquid culture test system, auxin (IAA) inhibited root growth with little effect on hair elongation and significantly stimulated hypocotyl enlargement. Cytokinins (trans-zeatin, kinetin) and ethylene (application of the precursor ACC) likewise exerted an inhibitory effect on root growth but, in contrast to IAA, drastically stimulated root hair elongation. Methylobacteria are phytosymbionts that produce/secrete cytokinins. We conclude that, under real-world conditions (soil), the provision of these phytohormones by methylobacteria (and other epiphytic microbes) regulates root development during seedling establishment.

Plant gnotobiology: Epiphytic microbes and sustainable agriculture

In 1963, a monograph by Thomas D. Luckey entitled Germfree Life and Gnotobiology was published, with a focus on animals treated with microbes and reference to the work of Louis Pasteur (1822-1895). Here, we review the history and current status of plant gnotobiology, which can be traced back to the experiments of Jean-Baptiste Boussingault (1801-1887) published in 1838. Since the outer surfaces of typical land plants are much larger than their internal areas, embryophytes "wear their guts on the outside." We describe the principles of gnotobiological analyses, with reference to epiphytic metylobacteria, and sunflower (Helianthus annuus) as well as Arabidopsis as model dicots. Finally, a Californian field experiment aiming to improve crop yield in strawberries (Fragaria ananassa) is described to document the practical value of this novel research agenda.

Ernst Haeckel's biodynamics 1866 and the occult basis of organic farming

One hundred and 50 years ago (Sept. 1866), Ernst Haeckel published a monograph entitled General Morphology of Organisms, wherein key terms, such as Protista, Monera, ontogeny, phylogeny, ecology and the 'biogenetic law' where introduced. In addition, Haeckel coined the word "biodynamics" as a synonym for "general physiology." In contrast, Rudolf Steiner's "biodynamic agriculture," which originated in 1924, and was promoted via Ehrenfried Pfeiffer's book of 1938 with the same title, is an occult pseudoscience still popular today. The misuse of Haeckel's term to legitimize disproven homeopathic principles and esoteric rules within the context of applied plant research is unacceptable.