Fig 1.
Chloroplast photorelocation movement induced by strong blue light in kac1kac2.
(a) Analysis of chloroplast photorelocation movements by measuring the light-induced changes in leaf transmittance. A black trace represents a typical light-induced change in wild type under our light irradiation condition (indicated by a colored bar above a graph). Transmittance changes are indicated as ∆ transmittance (a transmittance value at the indicated time minus the transmittance at 0 min). After the measurement was performed for 10 min in darkness, samples were sequentially irradiated with continuous blue light at 3, 20, and 50 μmol m–2 s–1 for 60, 40, and 40 min, as indicated by white, sky blue, and blue arrows, respectively. The light was extinguished at 150 min (black arrow). Double-headed arrows indicate the chloroplast movements induced under the indicated light conditions. Red lines indicate the initial linear fragments (from 2 to 6 min after changes in light fluence rate) which were used for the calculation of the percentage transmittance change over 1 min (i.e., speed of leaf transmittance changes). (b-e) KAC-independent chloroplast movement was analyzed in chup1, pmi1, and thrum1 backgrounds (b, c), in the phototropin mutant background (d, e). Changes in leaf transmittance caused by the chloroplast photorelocation movement. Mean values from three independent experiments are shown. Error bars indicate standard errors.
Table 1.
Summary of the data on chloroplast photorelocation movements in Fig 1 and Fig 2.
Mutant phenotypes or inhibitor effect in wild type or kac1kac2 mutant backgrounds are indicated. Ac: accumulation response, Av: avoidance response, Av (kac-like): the avoidance response found in kac1kac2 mutants, -: no or severely defective responses. Here, strong blue-light-induced response in jac1 is categorized into kac-like avoidance response.
Fig 2.
Actin filament-dependent light-induced chloroplast movement in kac1kac2.
Chloroplast movement was analyzed in wild type and kac1kac2, which were treated with and without 10 μM latrunculin B. The other details are the same as in Fig 1, except there was a 20-min dark adaptation before the blue light irradiation. Mean values from four independent experiments are shown. Error bars indicate standard errors.
Fig 3.
Chloroplast photorelocation movement in uppermost mesophyll cells of kac1kac2 mutant plants.
(a) Strong-light-induced change in the chloroplast distribution on the uppermost mesophyll cell surface. Photographs of the mesophyll cell surface in dark-adapted or strong-blue-light-irradiated plants. Bar: 10 μm. (b) Comparison of the ratio of the area covered with chloroplasts to the whole cell surface area. Mean values from three independent leaves are shown. Ten cells per a leaf were analyzed. Error bars indicate standard errors. An asterisk indicates the statistically significant differences, assessed by Student’s t-test. n. s. indicates the statistically insignificant difference.
Fig 4.
Roles of KACs and CHUP1 in the nuclear avoidance response in pavement cells.
The time-course analysis of the nuclear avoidance response was performed in indicated lines. Dark-adapted plants were irradiated with strong blue light (50 μmol m–2 s–1). The percentage of nuclei in the light position is indicated. Values shown are means ± SD. Each data point was obtained from five leaves with 100 cells observed in each leaf.
Fig 5.
Distinct functions of KACs and CHUP1 in the nuclear photorelocation movement.
(a) Nuclear photorelocation movement induced using a microbeam. The area irradiated with blue light is indicated as squares with dotted lines. Bar: 20 μm. (b) Number of nuclei showing avoidance (blue), parallel (red), or no movement (light green) in the indicated mutants. Data for wild type and chup1 mutant plants from Higa et al. (2014a) are shown for comparison. (c) The number of plastids attached to a nucleus in pavement cells. Data were obtained from three leaves, with 20 cells observed in each leaf, and are presented as means ± SD. An asterisk indicates the statistically significant differences, assessed by Student’s t-test. n. s. indicates the statistically insignificant difference.
Fig 6.
A model for strong-blue-light-induced avoidance response.
In wild type, phot2 (and also phot1) perceive strong blue light and mediates cp-actin-filament-mediated avoidance response in CHUP1- and KAC-dependent manners. At least in kac1kac2 mutant plants, light-induced chloroplast movement is induced in actin-filament- and CHUP1-dependent manners (but cp-actin-filament-independent). PMI1 and THRUM1 regulate both cp-actin-dependent or–independent responses, but the relationship between these proteins, CHUP1, and KAC is unclear.