Reduction in the length of the oral apparatus produced by the temperature-sensitive mutation short-1 (sh1) involved suppressed growth of the oral primordium in all stages of development. Temperature shift-up and heat-shock experiments revealed that the temperature-sensitive period of this mutation coincided with nearly the entire stomatogenic phase (stages 1–6) in sexual reproduction. Low- and high-sensitivity phases were noted, corresponding to the periods of slow (stages 1 and 2) and rapid (stage 3 to stage 6) elongation of the oral primordium, respectively. The action of sh1 is thus concentrated after stage 2. The mutation hypothetically results in defective membrane growth and extension in the oral primordium, leading to restriction in incorporation of basal bodies into the developing membranelles.

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