The Arabidopsis cryptochrome 2 I404F mutant is hypersensitive and shows flavin reduction even in the absence of light.

MAIN CONCLUSION: The cryptochrome photoreceptor mutant cry2I404F exhibits hyperactivity in the dark, hypersensitivity in different light conditions, and in contrast to the wild-type protein, its flavin chromophore is reducible even in the absence of light. Plant cryptochromes (cry) are blue-light photoreceptors involved in multiple signaling pathways and various photomorphogenic responses. One biologically hyperactive mutant of a plant cryptochrome that was previously characterized is Arabidopsis cry1L407F (Exner et al. in Plant Physiol 154:1633-1645, 2010). Protein sequence alignments of different cryptochromes revealed that L407 in cry1 corresponds to I404 in cry2. Point mutation of Ile to Phe in cry2 in this position created a novel mutant. The present study provided a baseline data on the elucidation of the properties of cry2I404F. This mutant was still able to bind ATP-triggering conformational changes, as confirmed by partial tryptic digestion and thermo-FAD assays. Surprisingly, the FAD cofactor of cry2I404F was reduced by the addition of reductant even in the absence of light. In vivo, cry2I404F exhibited a cop phenotype in the dark and hypersensitivity to various light conditions compared to cry2 wild type. Overall, these data suggest that the hypersensitivity to red and blue light and hyperactivity of this novel mutant in the dark can be mostly accounted to structural alterations brought forth by the Ile to Phe mutation at position 404 that allows reduction of the flavin chromophore even in the absence of light.

Seed pre-treatment in rice reduces damage, enhances carbohydrate mobilization and improves emergence and seedling establishment under flooded conditions.

BACKGROUND AND AIMS: Early flooding helps control weeds but reduces seedling establishment in direct-seeded rice (Oryza sativa). When combined with appropriate management practices, the use of genotypes that better tolerate flooding during emergence can enhance crop establishment in flood-prone areas. Management options include seed pre-treatment and we tested the influence of pre-soaking for 24 h prior to sowing or of priming (soaking for 24 or 48 h followed by drying). METHODOLOGY: The effects on seedling establishment after 21-day flooding of pre-soaking seeds for 24 h before sowing and/or of priming seeds were examined together with physiological responses connected with reactive oxygen scavenging. Seeds of four lines with contrasting abilities to tolerate flooding at the germination stage were compared. Seeds were primed using KCl solutions (48 h) or water (24 h) and pre-soaked using water. Lipid peroxidation and activities of reactive oxygen-scavenging enzymes were measured in seeds before sowing. Carbohydrate mobilization in germinating seeds and seedling growth were also monitored at intervals. PRINCIPAL RESULTS: Seed pre-treatment by pre-soaking or by priming increased survival of flooding and accelerated and improved seedling establishment, especially in tolerant genotypes. Primed seeds had less lipid peroxidation and higher superoxide dismutase (SOD) and catalase (CAT) activities than non-primed seeds. Amylase activities and starch breakdown were also hastened in primed seeds. Survival after flooding was positively correlated with amylase activity but negatively correlated with the extent of lipid peroxidation. CONCLUSIONS: Pre-soaking and priming improved seedling establishment in flooded soil, enhanced the capacity to scavenge reactive oxygen species in seeds by increasing SOD and CAT activities, and hastened carbohydrate mobilization. Tolerant genotypes responded better to these treatments, emphasizing the effectiveness of combining genetic tolerance with appropriate seed pre-treatment to improve seedling establishment of rice sown in flooded soils.