Chloroplast Accumulation Response Enhances Leaf Photosynthesis and Plant Biomass Production

Abstract

Plant photosynthetic performance is affected by various environmental factors, including light, temperature, and CO 2 concentration (Kaiser et al., 2015; Yamori, 2016). In particular, light is not only an essential energy source for photosynthesis but also is a key factor in the coordination of plant growth and development that helps to maximize photosynthetic performance (Christie, 2007; Kami et al., 2010). The blue light (BL) receptor, phototropin (phot), mediates various BL responses that facilitate photosynthesis; these include phototropism, chloroplast movement, stomatal opening, and leaf flattening (Christie, 2007). Light-induced chloroplast movement is one of the most important responses for the utilization of photosynthetic light (Suetsugu and Wada, 2013). Chloroplasts move toward weak light-irradiated areas to efficiently absorb light (the accumulation response), whereas they move away from excess light to avoid photodamage (the avoidance response; Suetsugu and Wada, 2013). In Arabidopsis (Arabidopsis thaliana), the accumulation response is regulated by phot1 and phot2 (Sakai et al., 2001), whereas the avoidance response is regulated mainly by phot2 (Jarillo et al., 2001; Kagawa et al., 2001). The importance of phototropin-mediated responses in photosynthetic performance and plant growth has been examined using mutant Arabidopsis plants defective in phototropin-mediated responses. Under a condition in which weak BL is superimposed on red light, phot1 mutant plants exhibit reduced photosynthetic performance and growth because of attenuated chloroplast accumulation, weak stomatal opening, and curled leaves (Takemiya et al., 2005; Inoue et al., 2008). The nonphototropic hypocotyl3 (nph3) mutants also are

Impaired chloroplast positioning affects photosynthetic capacity and regulation of the central carbohydrate metabolism during cold acclimation

“…In line with these observations, we found similar rates of net CO2 assimilation in Col-0 and chup1 at growth PAR intensity under ambient and low temperature (see Fig. 2 A) Under control long day growth conditions, neither of the recorded chlorophyll fluorescence parameters significantly differed between Col-0 and chup1 which was also observed previously under short day growth conditions (Gotoh et al, 2018). This suggests that potential limitation of CO2 net assimilation rates in chup1 rather arises from biochemistry than photochemistry.…”

“…100 µmol photons m -2 s -1 , and long day growth conditions neither we (data not shown) nor others observed any effect on biomass accumulation (Kasahara et al, 2002). In contrast, for plants grown under short day conditions the accumulation response, which is also defective in chup1 mutants, was shown to enhance leaf photosynthesis and plant biomass production (Gotoh et al, 2018). In line with these observations, we found similar rates of net CO2 assimilation in Col-0 and chup1 at growth PAR intensity under ambient and low temperature (see Fig.…”

“…8h light phase, chup1 plants displayed reduced photosynthesis and biomass accumulation over a wide range of light intensities, i.e. 50 -300 µmol m -2 s -1 (Gotoh et al, 2018). In their study, Gotoh and co-workers compared different mutants affected in chloroplast positioning and finally concluded that trade-offs of biomass production and photoprotection are essentially driven by chloroplast movement under changing growth light.…”

CHLOROPLAST UNUSUAL POSITIONING 1 is a new type of actin nucleation factor in plants

“…The chloroplast accumulation response is crucial for efficient photosynthesis and biomass production when light is limited (Gotoh et al, 2018), and the avoidance response minimizes photo-damage of chloroplasts in excess light (Kasahara et al, 2002). CHUP1 and cp-actin filaments are indispensable for these chloroplast movements.…”

“…In fluctuating light conditions, chloroplasts dynamically change their positions within the cell according to the quality, intensity, and direction of the incident light . Chloroplasts move toward weak light to capture as much energy as possible for photosynthesis (the accumulation response) (Gotoh et al, 2018;Zurzycki, 1955) but they rapidly move away from strong light to reduce light absorption (the avoidance response) (Kasahara et al, 2002;Zurzycki, 1957). Chloroplasts can move in any direction without rotating or rolling (Tsuboi and Wada, 2011;Tsuboi et al, 2009).…”