Figure 4.
Effect of cold shocks (abrupt cooling and rewarming) on SE Vm. A, After microelectrode impalement into an SE, forisomes (asterisks) disperse in response to Ca2+ influx triggered by the local wounding. cc, Companion cell; sp, sieve plate. B, Recondensed forisomes in recovered SEs that are ready for cold shocks. The microelectrode tip is indicated by the arrow. C, Three typical cold shock-triggered (top graphs) electrical responses (bottom graphs) recorded in different SEs under control conditions in BM. The time courses of cold shocks were recorded by a thermocouple, and electrical responses were recorded by voltage-sensitive microelectrodes. D, Three typical cold shock-triggered (top graphs) electrical responses (bottom graphs) recorded in different SEs preincubated with 1 mm La3+. E, Relationship between cold shocks (expressed as ΔT, the difference between the initial temperature before the cold shock and the lowest temperature reached during the cold shock) and the peak of the first voltage transient (ΔV1) recorded in SEs under control conditions (black circles; n = 25) and after preincubation with 1 mm La3+ (white circles; n = 8). Data points of the control curve were fitted to sigmoid correlation (according to Eq. 1). F, Relationship between the peak of the second voltage transient (ΔV2) and the cold shock (ΔT) under control conditions and preincubated in the membrane-impermeant 1 mm La3+. Data points of the control curve were fitted to Equation 1. G, Relationship between the entire signal length and the peak of the second voltage transient (ΔV2) under control conditions and after preincubation of SEs with 1 mm La3+. H, Correlation between the voltage transients ΔV2 and ΔV1 under control conditions. I and J, Correlation between forisome response time (time until dispersion; I) as well as recovery time (time until recontraction; J) and cold shocks (ΔT) under control conditions (Thorpe et al., 2010). The quantity of nonreactive forisomes is displayed in the dashed areas of I and J.