Effect of Chilling Temperatures on the Protoplasmic Streaming of Plants from Different Climates

Abstract

A microscope mount was designed so that specimen temperatures could be monitored and controlled without impairing phase contrast optics and used to measure rates of protoplasmic streaming between 0 and 25 °C in trichome cells of Lycopersicon esculentum, Lycopersicon hirsutum, Citrullus vulgaris, Tradescantia albiflora, Digitalis purpurea, and Veronica persica. Between 10 and 20 °C the rates of streaming varied from 2–6 μm s−1 depending on the temperature, and differences between the species were small. The temperature coefficient of streaming rates was found to increase as the temperature was lowered so that the plot of log rate against temperature had a steeper slope at the lower temperatures. The largest temperature cofficients were for the warmth-requiring L. esculentum (tomato) and C. vulgaris (water melon), and the smallest for the temperate-zone plants V. persica (speedwell) and D. purpurea (foxglove). The changes in rate always occurred over a range of temperature; no ‘critical temperature’was observed below which streaming abruptly stopped and above which it was active, although the amount of streaming as well as the rate decreased as the lowest temperatures were approached. The temperatures experienced by the specimens during the experiment did not affect the recovery of normal streaming rates between about 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 the varieties collected from the highest altitudes. The results suggest that streaming rates correlate with genetic adaptation to low temperature in the species examined.