Alterations in photosynthesis in Arabidopsis lacking IMMUTANS, a chloroplast terminal oxidase

Abstract

Green and white variegation in the Arabidopsis immutans (im) mutant is caused by a nuclear recessive gene. The green sectors contain cells with normal-appearing chloroplasts, while cells in the white sectors have photooxidized plastids lacking organized lamellae. In the present experiments, we found that the green im sectors have enhanced rates of carbon assimilation (monitored by (14)CO(2) uptake) and that there are corresponding increases in the activities of Rubisco and SPS, elevated starch and sucrose pool sizes, and an altered pattern of carbohydrate partitioning that favors sucrose over starch. We hypothesize that these increases are due, at least in part, to interactions with white sectors, perhaps to compensate for reductions in total source tissue. Consistent with this idea, the im white sectors accumulate low levels of sucrose and acid invertase activities are markedly increased in the white versus green cells. This suggests that there is a sucrose gradient between the green and white sectors, and that sucrose is transported from the green to white cells in response to sink demand. The expression of photosynthetic genes is not appreciably altered in the green im sectors versus wild type, but rather there is an up-regulation of genes involved in defense against oxidative stress and down-regulation of genes involved in cell wall biosynthesis. We postulate that changes in photosynthesis in the im green cells are driven by a need for photoprotection (especially early in chloroplast biogenesis) and due to source-sink interactions.

Dual Role of the Plastid Terminal Oxidase in Tomato

“…It is accompanied by a slight increase in carotenoid content (although it does not appear to be statistically significant for all carotenoids). Such an increase was also reported in green sectors of variegated leaves from the immutans mutant (Baerr et al, 2005) and is accompanied by an increase in the rate of carbon assimilation (Aluru et al, 2007). These observations were interpreted as the necessity for green sectors to compensate for the limited photosynthetic and metabolic activities of adjacent white sectors.…”

Subunits of the Plastid ClpPR Protease Complex Have Differential Contributions to Embryogenesis, Plastid Biogenesis, and Plant Development inArabidopsis

“…(4) Plastid mutants, sometimes with weak embryo phenotypes, that have pale-green/virescent or variegated phenotypes but can develop autotrophically and can be maintained as a homozygous population. Examples are Arabidopsis mutants impaired in partially redundant genes, such as TRANSLOCON INNER MEMBRANE COMPLEX 40 (Kovacheva et al, 2005), PsaD (Ihnatowicz et al, 2004), ATP SYNTHASE-C (Bosco et al, 2004), and thylakoid FTSH proteases (Adam et al, 2006;Sakamoto, 2006), or functions that lead to reduced fitness but are otherwise not strictly essential (e.g., thylakoid alternative oxidase [IMMUTANS]) (Aluru et al, 2007).…”

giganteaSuppressesimmutansVariegation by Interactions with Cytokinin and Gibberellin Signaling Pathways

“…Profiling experiments have revealed that this enhancement is likely caused by a reprogramming of photosynthetic gene expression in the green cells, perhaps elicited during leaf development in response to sink demand (i.e. elevated photosynthetic capacity is part of a growth strategy to compensate for total reductions in source tissue; Aluru et al, 2001Aluru et al, , 2007. This explanation does not seem to apply to imgi2, however, because imgi2 plants are not variegated.…”