The importance of chloroplast movement, nonphotochemical quenching, and electron transport rates in light acclimation and tolerance to high light in Arabidopsis thaliana

Abstract

Citation: Howard, M. M., A. Bae, and M. Königer. 2019. The importance of chloroplast movement, nonphotochemical quenching, and electron transport rates in light acclimation and tolerance to high light in PREMISE: While essential for photosynthesis, excess light can damage plants. We investigated how growth light conditions affect two photoprotective strategies, chloroplast movement and nonphotochemical quenching (NPQ), as well as electron transport rates (ETR), and the relative importance of these processes in the short-term stress tolerance of Arabidopsis thaliana. METHODS:We grew wild-type (WT) and mutant plants with impaired chloroplast movement (phot1, phot2, phot1 phot2, chup1) or NPQ (npq1) at low (160 μmol photons m −2 s −1 ) or intermediate light (400 μmol photons m −2 s −1 ) before quantifying transmission changes due to chloroplast movement, NPQ, ETR, and the ability to recover from a short-term high-light treatment. RESULTS:Plants with impaired chloroplast avoidance movement (phot2, phot1 phot2, chup1) did not recover as well from a short-term high light treatment as the WT or npq1 and phot1 mutants. Plants grown at intermediate light recovered more completely from the same stress treatment regardless of their genotype and despite reduced degrees of transmission changes due to chloroplast movement. This result was due in part to all genotypes having up to a 2-fold increase in ETR max and a slight increase in NPQ max . CONCLUSIONS:Growth light conditions affect which mechanisms are important in dealing with short-term high-light stress. The chloroplast avoidance response is important for low-light-grown plants, while increases in ETR max and NPQ max allow plants grown at intermediate light intensities to avoid being damaged.

Impairment of chloroplast movement reduces growth and delays reproduction of Arabidopsis thaliana in natural and controlled conditions

“…For example, when leaves of npq1, phot2 , and phot2npq1 mutants were exposed to high light in combination with low temperatures, the photoprotective effects of these two mechanisms were additive, with chloroplast movement protecting leaves from photoinhibition to a larger degree than NPQ (Cazzaniga et al, 2013). Similar results were obtained when the short‐term stress tolerance of low‐light acclimated npq1 , chup1 , phot2 , and phot1phot2 mutants was compared (Howard et al, 2019).…”

“…The phot2 plants were less adversely affected than the phot1phot2 mutants in both growth conditions. Compared to WT, both mutants have extreme accumulation responses and lack an avoidance response, but only phot2 plants can move their chloroplasts from a dark position into the accumulation position and vice versa (Howard et al, 2019). However, this probably does not explain the difference in growth, but points to pleiotropic effects: phototropins mediate not only chloroplast relocation, but redundantly regulate stomatal opening (Kinoshita et al, 2001).…”

“…If too much light is present, PHOT2 triggers an avoidance response, which helps minimize photoinhibition (Jarillo et al, 2001; Kagawa et al, 2001; Sakai et al, 2001; Kasahara et al, 2002). In summary, the phot1 mutants cannot accumulate their chloroplasts, phot2 plants accumulate their chloroplasts at the top of the palisade cells and do not show an avoidance response, while phot1phot2 mutants accumulate their chloroplasts regardless of the specific light intensity (Howard et al, 2019). There is also evidence that temperatures modulate the chloroplast movement in the wild type (WT): chilling temperatures induce a stronger avoidance response at nonsaturating strong light intensities than moderate temperatures (Łabuz et al, 2015).…”

Phototropin 1 and 2 Influence Photosynthesis, UV-C Induced Photooxidative Stress Responses, and Cell Death

“…Since the deepoxidation of violaxanthin, leading to zeaxanthin is decreased in phot mutants, they seem to elevate the zeaxanthin level through its synthesis from β-carotene. Recently, a lower NPQ value for the phot1phot2 mutant was also observed by Howard and co-workers [101].…”

Spectrum of Light as a Determinant of Plant Functioning: A Historical Perspective

“…Omitting the history of this idea's development, we only point to the work of Kasahara et al (2002) [61], offering direct evidence from A. thaliana mutants defective in chloroplast avoidance movement: An impaired avoidance response made plants more susceptible to photodamage. Although there are recent data questioning the efficiency (at least in high irradiance-grown plants [62,63]) or the need of the avoidance response and even assuming the advantages of its lack [64], its significance for protecting the photosynthetic apparatus from very intense light remains evident [65].…”