Investigations on the Photoregulation of Chloroplast Movement and Leaf Positioning in Arabidopsis

Abstract

We recently investigated the roles of the phototropin 1 (PHOT1) LOV (light, oxygen or voltage) domains in mediating phototropic curvature in transgenic Arabidopsis seedlings expressing either wild-type PHOT1 or PHOT1 with one or both LOV domains inactivated by a single amino acid replacement. We have now investigated the role of the PHOT1 LOV domains in chloroplast movement and in leaf positioning in response to blue light. Low fluence rate blue light is known to mediate a chloroplast accumulation response and high fluence rate blue light an avoidance response in Arabidopsis leaves. As was the case for phototropism, LOV2 of PHOT1 is essential for chloroplast accumulation and LOV1 is dispensable. PHOT1 LOV2 is also essential to maintain developing primary leaves in a horizontal position under white light from above and LOV1 is again dispensable. A red light pulse given to dark-adapted light-grown plants followed by 2 h of darkness enhances both the chloroplast accumulation response under dim blue light and the chloroplast avoidance response under strong blue light. The effect is far-red reversible. This photoreversible response is normal in a phyB null mutant but does not appear in a phyA null mutant. These results suggest that phyA mediates the enhancement, induced by a red light pulse, of blue light-induced chloroplast movements.

Non‐invasive, whole‐plant imaging of chloroplast movement and chlorophyll fluorescence reveals photosynthetic phenotypes independent of chloroplast photorelocation defects in chloroplast division mutants

“…In phot1‐5 phot2‐1 , the lack of reflectance changes observed between 2 and 100 μmol m −2 sec −1 (Figure a) is likewise consistent with transmittance data showing the suppression of all chloroplast movement in this mutant (Kong et al ., ); however, phot1‐5 phot2‐1 exhibited a slight decrease in reflectance at intensities above 100 μmol m −2 sec −1 (discussed below). Reflectance measurements performed on the phot1‐5 single mutant (Huala et al ., ) indicated a very weak accumulation response under low light levels but a stronger avoidance response at higher light levels (Figure S2a), consistent with previous work (Suetsugu et al ., ; Han et al ., ).…”

“…The relative reflectances of phot1‐5 phot2‐1 compared with background reflectances from the black foam masks covering the soil showed that the decrease was distinguishable from noise and drift (Figure S7). Slight accumulation responses at higher intensities have been reported earlier for phot1‐5 phot2‐1 , and were attributed to leakiness in the phot2‐1 allele (Cho et al ., ; Han et al ., ). The full recovery of phot1‐5 phot2‐1 between the start and end of the photoperiod suggests that the process is completely reversible (Figure ).…”

“…Our reflectance measurements on the arc6‐5 and phot1‐5 phot2‐1 mutants yielded results similar to those reported previously (Kasahara et al ., ; Suetsugu et al ., ; Königer et al ., ; Han et al ., ), demonstrating that the reflectance of red light reports chloroplast movement as effectively as transmittance. Additionally, the similar kinetics of both the accumulation and avoidance responses in arc6‐5 and the double ftsZ2 and triple ftsZ mutants (Figures , and ), all with one or two drastically enlarged chloroplasts (Glynn et al ., ; Schmitz et al ., ; Crumpton‐Taylor et al ., ), suggests equivalent photorelocation deficiencies in mutants sharing comparable chloroplast morphologies.…”

Phototropism: Growing towards an Understanding of Plant Movement

“…For example, phot1 and phot2 are redundantly involved in stomatal opening and photosynthetic gas exchange (Kinoshita et al, 2001). Additionally, both phots positively regulate cotyledon and leaf blade expansion, flattening, and positioning in response to BL (Sakamoto and Briggs, 2002;Ohgishi et al, 2004;Takemiya et al, 2005;Inoue et al, 2008;Han et al, 2013), presumably to increase surface area for photosynthetic light capture. The surface area of chloroplasts within the mesophyll cells also determines efficiency of photosynthetic light absorption: Under low-light conditions, activation of phot1 and phot2 redundantly stimulates chloroplast positioning along the cellular edges perpendicular to the incident light to optimize absorption .…”

Blue Light Perception by Both Roots and Rhizobia Inhibits Nodule Formation in Lotus japonicus

“…LOV domains belong to the Per-ARNT-Sim (PAS) family (Christie et al 1999). PHOT control phototropism in seedlings, induce stomatal opening, and regulate chloroplast movement (Han et al 2013;Zhao et al 2013). CRY have two recognizable domains, a DNA photolyase-like domain at the N-terminus and C-terminal DQXVP acidic-STAES domains that are distinguished mainly by their C-terminal extensions (Ahmad and Cashmore 1993;Li et al 2013;Sakai and Haga 2012).…”