Light dependence of protoplasmic streaming in Nitella flexilis L. as measured by means of laser-velocimetry

Abstract

Laser-velocimetry was applied in order to study the effect of light on the velocity of protoplasmic streaming (pps) in Characean cells. A change from dark to light (= 6 W · m(-2)) leads to an acceleration of streaming by about 15-30% with a time-constant of approx. 300 s. The transition from light to dark causes a transient decrease of velocity below the original dark level. This response occurs with a time constant of about 500 s. It returns to its initial value with a time-constant of about 2000 s. This may indicate that a control loop of cytosolic homeostasis takes a decrease in pCa more seriously than an increase. A possible involvement of temperature effects caused by illumination was excluded by measuring the influence of temperature. Steady-state velocity of streaming changed by 5% per 1° C. Irradiation with infra-red light (λ > 780 nm) did not cause a change in velocity. The absence of a light effect on streaming velocity in the presence of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU) shows that photosynthesis and not phytochrome is involved. The role of light-induced changes of pCa is discussed, especially with respect to the hypothesis of Vanselow and Hansen (1989, J. Membr. Biol. 110, 175-187) that photosynthesis acts on the plasmalemma K(+)-channel via light-induced uptake of Ca(2+) into the chloroplasts.

Light-induced cytosolic calcium transients in green plant cells. I. Methodological aspects of chlorotetracycline usage in algae and higher-plant cells

“…6B,8) con®rm that the changes in [Ca 2+ ] c are a consequence of photosynthesis and do not result from the action of, for example, phytochrome or the blue-light receptor (Staal et al 1994). The results here are in line with various reports on light-induced uptake of Ca 2+ into the chloroplasts (Muto et al 1982;Kreimer et al 1985;Moore et al 1986) and its release in the dark (Miller and Sanders 1987;Plieth and Hansen 1992).…”

“…Plieth and Hansen 1992). The Appendix documents experiments showing that the temperature sensitivity of CTC¯uo-rescence is (dF/F)/dT 2.1%/°C.…”

“…This hinders the in-vivo detection of faster responses for testing causal relationships in signal transduction chains by means of a kinetic analysis. Equally, the attempt of Plieth and Hansen (1992) to use changes in the velocity of cytoplasmic streaming as an indirect measure of changes in [Ca 2+ ] c suered from low temporal resolution caused by the slow phosphorylation of myosin (McCurdy and Harmon 1992). Vanselow and Hansen (1989) used the eect of [Ca 2+ ] c on the conductivity of a K + channel in the plasma membrane of Nitella as a monitor of light-induced changes in [Ca 2+ ], and obtained a temporal resolution which enabled the detection of a common time constant in chlorophyll¯uorescence and in [Ca 2+ ] c .…”

Light-induced cytosolic calcium transients in green plant cells. ll. The effect on a K + channel as studied by a kinetic analysis in Chara corallina

“…1B, the dominant eect was a depolarisation upon illumination. In order to exclude the involvement of a temperature eect, the temperature was measured by an immersed NTC resistor (Plieth and Hansen 1992). The light-induced changes stayed below 0.5°C (Fig.…”

“…The uptake of Ca 2+ into chloroplasts is well documented, especially as the studies with isolated chloroplasts exclude the involvement of other organelles (Muto and Miyashi 1986). As a ®rst approach, Plieth and Hansen (1992) used changes in the velocity of cytoplasmic streaming as an indirect measure of changes in [Ca 2+ ] c and found a correlation between changes in velocity and plasma-membrane potential in Chara. However, the dominant time constant of the changes in streaming velocity was slower by a factor of 10 than that of the changes in membrane potential.…”