tropism

noun

Etymology: From -tropism (suffix meaning ‘growth towards; movement, turning’) (possibly based on geotropism and heliotropism), from Latin tropus + English -ism (suffix forming nouns of action, process, or result). Tropus is derived from Ancient Greek τρόπος (trópos, “a turn; a manner, style, way; figure of speech, trope; etc.”), from τρέπω (trépō, “to turn; to divert; to rotate or change orientation”) (from Proto-Indo-European *trep- (“to turn”)) + -ος (-os, suffix forming nouns of result or abstract nouns of action). Sense 1 (“turning of an organism or part of an organism towards or away from a stimulus”) is modelled after German Tropismus.

1. The turning of an organism (chiefly a plant) or part of an organism either towards or away from a stimulus; (countable) an instance of this.

   “Orientation and tropism are synonymous expressions; that gatherings [of Paramecium] take place is a consequence of the orientation, and therefore throws no light whatever upon the tropisms. (Gatherings, however, are not always indicative of a tropism, i.e., of an orientation, but may be due to kinesis […]”

   “Phototropic orientation of an embryo plant in zero gravity […] On earth, a germinated seedling can be placed in any position and the radicle will invariably turn the embryo plant "downward" and the hypocotle "upward". This is because positive root tropism toward gravity and negative stem tropism away from gravity. In the absence of gravity, will the plumules and the stem of the embryo plant reacting positively to phototropism guide the entire plant including the root system for its directional orientation?”

2. A capability or tendency for a pathogen (chiefly a virus) to infect a type of cell, tissue, organ, or host organism.

   “host tropism    tissue tropism”

   “Studies similar to those describe above for cells cultivated in vitro were performed using homogenates of tissues and organs from humans and rhesus monkeys to investigate tissue tropisms in susceptible species […] McLaren (personal communication) found an excellent correlation between poliovirus tissue tropisms and presence or absence of receptor activity in human and rhesus tissues and organs.”

3. Of a person: an instinctive predilection or tendency; also (generally), a liking, a preference.

   “It is reasonable to suppose that tropism will be less conspicuous in animals which are endowed with intelligence than in others; but well-marked tropisms are still to be found among the higher animals. Gregarious animals have a positive tropism toward the members of their own flock; the dog has a negative tropism toward his own kind and a positive tropism toward mankind.”