Mutants of Arabidopsis with Altered Regulation of Starch Degradation

Abstract

Mutants of Arabidopsis thaliana (L.) Heynh. with altered regulation of starch degradation were identified by screening for plants that retained high levels of leaf starch after a period of extended darkness. The mutant phenotype was also expressed in seeds, flowers, and roots, indicating that the same pathway of starch degradation is used in these tissues. In many respects, the physiological consequences of the mutations were equivalent to the effects observed in previously characterized mutants of Arabidopsis that are unable to synthesize starch. One mutant line, which was characterized in detail, had normal levels of activity of the starch degradative enzymes a-amylase, ,6-amylase, phosphorylase, D-enzyme, and debranching enzyme. Thus, it was not possible to establish a biochemical basis for the phenotype, which was due to a recessive mutation at a locus designated sexl at position 12.2 on chromosome 1. This raises the possibility that hitherto unidentified factors, altered by the mutation, play a key role in regulating or catalyzing starch degradation.

Fumaric acid: an overlooked form of fixed carbon in Arabidopsis and other plant species

“…Both fimmric acid (Fig. 4) and starch (Caspar et al 1991) levels also increase at higher light intensities. High light intensities may increase fiunaric acid levels by increasing photosynthetic rates.…”

“…Light has been shown to activate phosphoermlpyruvate carboxylase kinase leading, in turn, to higher levels of phosphoenolpyruvate carboxylase activity (Li et al 1996). Furnaric acid (Table 2) and starch (Caspar and Pickard 1989;Caspar et al 1991) also show similar distribution patterns, as both accumulate to high levels in leaves, stems and developing siliques of Arabidopsis, but are low in mature seeds and in roots. However, furnaric acid and starch levels do not always fluctuate in parallel.…”

“…Arabidopsis starch levels have been shown to increase with increasing light intensity (Caspar et al 1991). To determine whether light intensity also affects fumaric acid levels, furnaric acid was assayed in leaves fi-omArabidopsis grown under a range of light intensities.…”

“…For instance, starch levels increase with light intensity in Arabidopsis thaliana (Caspar et al 1991). Exogenous nitrate decreases starch accumtdation, while increasing organic acid concentrations, in tobacco (ScheibIe et aI.…”

Monogenic Recessive Mutations Causing Both Late Floral Initiation and Excess Starch Accumulation in Arabidopsis.

“…; Caspar et al, 1991), has been isolated and extensively analyzed. It was suggested that SEX1 may play a role in starch degradation.…”