Photosynthetic Redox Imbalance Governs Leaf Sectoring in theArabidopsis thalianaVariegation Mutantsimmutans,spotty,var1, andvar2 

Abstract

We hypothesized that chloroplast energy imbalance sensed through alterations in the redox state of the photosynthetic electron transport chain, measured as excitation pressure, governs the extent of variegation in the immutans mutant of Arabidopsis thaliana. To test this hypothesis, we developed a nondestructive imaging technique and used it to quantify the extent of variegation in vivo as a function of growth temperature and irradiance. The extent of variegation was positively correlated (R 2 = 0.750) with an increase in excitation pressure irrespective of whether high light, low temperature, or continuous illumination was used to induce increased excitation pressure. Similar trends were observed with the variegated mutants spotty, var1, and var2. Measurements of greening of etiolated wild-type and immutans cotyledons indicated that the absence of IMMUTANS increased excitation pressure twofold during the first 6 to 12 h of greening, which led to impaired biogenesis of thylakoid membranes. In contrast with IMMUTANS, the expression of its mitochondrial analog, AOX1a, was transiently upregulated in the wild type but permanently upregulated in immutans, indicating that the effects of excitation pressure during greening were also detectable in mitochondria. We conclude that mutations involving components of the photosynthetic electron transport chain, such as those present in immutans, spotty, var1, and var2, predispose Arabidopsis chloroplasts to photooxidation under high excitation pressure, resulting in the variegated phenotype.

Phylogenetic viewpoints on regulation of light harvesting and electron transport in eukaryotic photosynthetic organisms

“…During de-etiolation, the NDH-like complex rapidly starts to interact with PSI, and after just 48 h in light, the PSI-NDH supercomplex is assembled (Peng et al 2008). This result may support the speculated co-operation between NDH and the plastid terminal oxidase PTOX, which is known to be crucial for the early leaf development and for the proper chloroplast biogenesis (Rosso et al 2006(Rosso et al , 2009. Alternatively, the etioplastic NDH-like complex might be physiologically nonfunctional until the appearance of its assembly partner, PSI.…”

The FtsH Protease Heterocomplex in Arabidopsis: Dispensability of Type-B Protease Activity for Proper Chloroplast Development

“…Leaf variegation predicts a threshold of unknown factors that determine chloroplast development in a cell-autonomous fashion (e.g., Rosso et al, 2009). We demonstrate that the threshold is determined by the total amount of the FtsH heterocomplex rather than the total number of protease sites.…”

Redox potential (Eh) and pH as drivers of soil/plant/microorganism systems: a transdisciplinary overview pointing to integrative opportunities for agronomy

“…As early as 1949, Stout observed that induction of the reproductive development of sugar beet is correlated with changes in the oxidation-reduction balance of certain regions of the plant (Stout 1949). Root growth, flowering, development of floral organs, leaf sectoring, and photoperiodism are regulated by the redox potential (Becker et al 2006;Foreman et al 2003;Rosso et al 2009;SanchezFernandez et al 1997;Xing et al 2006). Reactive oxygen species (ROS) are key actors in the regulation of plants' dormancy and germination (Bailly et al 2008).…”