. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MARINE PLANKTONIC CHEMICAL DEFENSE 227 ing rapid depolarization and hyperpolarization and leading to synchronized ciliary motion for movement (Febvre- Chavalier et al., 1989). Protozoa also have cell-surface signal receptors that rec- ognize vertebrate and plant hormones as varied as polypep- tides, cytokines, indolacetic acid, and opiates (Csaba, 1996). These vertebrate and plant signal molecules can promote chemotaxis (Kohidai ct ul.. 1994), phagocytosis (Rabino- vitch and De Stefano, 1971; Renaud et ul.. 1995). and other

- Image ID: RHMART
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MARINE PLANKTONIC CHEMICAL DEFENSE 227 ing rapid depolarization and hyperpolarization and leading to synchronized ciliary motion for movement (Febvre- Chavalier et al., 1989). Protozoa also have cell-surface signal receptors that rec- ognize vertebrate and plant hormones as varied as polypep- tides, cytokines, indolacetic acid, and opiates (Csaba, 1996). These vertebrate and plant signal molecules can promote chemotaxis (Kohidai ct ul.. 1994), phagocytosis (Rabino- vitch and De Stefano, 1971; Renaud et ul.. 1995). and other
Library Book Collection / Alamy Stock Photo
Image ID: RHMART
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MARINE PLANKTONIC CHEMICAL DEFENSE 227 ing rapid depolarization and hyperpolarization and leading to synchronized ciliary motion for movement (Febvre- Chavalier et al., 1989). Protozoa also have cell-surface signal receptors that rec- ognize vertebrate and plant hormones as varied as polypep- tides, cytokines, indolacetic acid, and opiates (Csaba, 1996). These vertebrate and plant signal molecules can promote chemotaxis (Kohidai ct ul.. 1994), phagocytosis (Rabino- vitch and De Stefano, 1971; Renaud et ul.. 1995). and other responses (Kovaacs et al.. 1997). Protozoa also produce hormone molecules (LeRoith et al.. 1982) that may interact with cell receptors (Marino and Wood. 1993). The adaptive significance for these signaling molecules in protists is poorly understood, but evolution of such signals and their receptors probably led to cellular hormonal systems in higher organisms (Carr, 1989). Almost nothing is known about such signaling in most environmentally important protists, especially in marine environments. Receptor sensitivities and reaction times depend on dif- fusion of signal molecules and binding strengths. The sig- nal-to-noise ratio (S/N) scales as (tDCR)"5 (Dusenbery, 1992). where R is the effective receptor radius, C the signal concentration for a signal with diffusion constant D, and t the integration time. For S/N - 1.1 — 0.1 s. R - 0.1 /im and D ~ 1(T6 cm2 s~', C is about 10~y M, a value consistent with observations. Receptor sensitivity—the minimal concentration for detectable S/N—scales as (Rt)~2. Since small cells cannot increase receptor size, longer integration times may be used to increase sensitivity (Dusenbery. 1992). Behavioral responses to signals Signaling between cells in multicellular organisms en- compasses such activities as cell movement and adhesion, development, differentiation, and programmed cell death (apoptosis); electrochemical signal propagatio

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