| Abstract: | A microscope mount was designed so that specimen temperaturescould be monitored and controlled without impairing phase contrastoptics and used to measure rates of protoplasmic streaming between0 and 25 ?C in trichome cells of Lycopersicon esculentum, Lycopersiconhirsutum, Citrullus vulgaris, Tradescantia albiflora, Digitalispurpurea, and Veronica persica. Between 10 and 20 ?C the rates of streaming varied from 2–6µm s–1 depending on the temperature, and differencesbetween the species were small. The temperature coefficientof streaming rates was found to increase as the temperaturewas lowered so that the plot of log rate against temperaturehad a steeper slope at the lower temperatures. The largest temperature cofficients were for the warmth-requiringL. esculentum (tomato) and C. vulgaris (water melon), and thesmallest for the temperate-zone plants V. persica (speedwell)and D. purpurea (foxglove). The changes in rate always occurredover a range of temperature; no ‘critical temperature’wasobserved below which streaming abruptly stopped and above whichit was active, although the amount of streaming as well as therate decreased as the lowest temperatures were approached. The temperatures experienced by the specimens during the experimentdid not affect the recovery of normal streaming rates betweenabout 10 and 20 ?C. In a population of a wild tomato, Lycopersicon hirsutum Humb.and Bonpl., collected from different altitudes in Peru and Ecuador,i.e. from locations of different environmental temperature,the rate of protoplasmic streaming at 5 ?C was greatest in thevarieties collected from the highest altitudes. The resultssuggest that streaming rates correlate with genetic adaptationto low temperature in the species examined. |
