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Abiotic stresses such as drought, flooding, and temperature stress have ­similar effects in a broad range of organisms. Depending on their predisposition, organisms are nevertheless variably sensitive to stress. Biotic stress exerted by pathogens can be rather specific to the host organisms. Hosts have evolved recognition systems for elicitors excreted by pathogenic symbionts (Bar and Avni, this volume), which are further processed by common signaling pathways. , 2006, 2009). Particularly the first steps of the signaling machinery are similar in both cases, while subsequent steps differentiate between symbioses and stress 23 the beneficial and detrimental interactions.

Symbiosis,” he said was a balancing act between two extremes: complete immunity and deadly infective disease. He suspected that some of the supposed “symbionts” described in the literature would prove to be actually “parasites” on further investigation. Famous microbiologist, K. F. Meyer (1925, p. 95) agreed that “symbiotic” “communal life” was “merely an example of true parasitism or even of disease” (Meyer, 1925, p. 97). But he raised another issue when discussing his experiments on bacterial symbionts in snails.

That mitochondria arose as symbionts was postulated later. The concept is typically traced to Richard Altmann at Leipzig. But Altmann’s theory was quite different. His model accounted for the origin of bacterial-like cells, as well as nucleated cells. The cytoplasmic granules that he wrote of had been reported by others who believed them to be inert. But Altmann (1890) named them “bioblasts”: they were diverse “elementary organisms” and he suggested that the primordial cells without nuclei first emerged when bioblasts came together into a colony and a membrane formed around them.