AtECB2 encodes a pentatricopeptide repeat (PPR) protein that regulates the editing of the plastid genes accD and ndhF. The ecb2-1 knockout shows an albino phenotype and is seedling lethal. In this study, we isolated an allelic mutant of the AtECB2 gene, ecb2-2, which showed delayed greening phenotype but could complete their life cycle. In this mutant, the Thr⁵⁰⁰ is converted to Ile⁵⁰⁰ in the 13^th PPR motif of the AtECB2 protein. Transmission electron microscopy demonstrated that chloroplast development was delayed in both the cotyledons and leaves of the mutant. An investigation of the chloroplast gene expression profile indicated that PEP (plastid-encoded RNA polymerase) activity in ecb2-2 cotyledons was not obviously affected, whereas it was severely impaired in ecb2-1. This result suggests that the PEP activities cause the different phenotypes of the ecb2-1 and ecb2-2 mutants. The editing efficiency of the three editing sites of accD (C794 and C1568) and ndhF (C290) in the mutant was dynamically altered, which was in agreement with the phenotype. This result indicates that the editing efficiency of accD and ndhF in the ecb2-2 mutant is associated with a delayed greening phenotype. As ecb2-2 can survive and set seeds, this mutant can be used for further investigation of RNA editing and chloroplast development in arabidopsis.

Cao ZL, Yu QB, Sun Y, Lu Y, Cui YL, Yang ZN (2011) A point mutation in the pentatricopeptide repeat motif of the AtECB2 protein causes delayed chloroplast development. J. Integr. Plant Biol. 53(4), 258–269.

The potential to cryopreserve embryonic axes of desiccation-sensitive (recalcitrant) seeds is limited by damage during the desiccation necessary for low temperature survival, but the basis of this injury and how to reduce it is not well understood. The effects of drying rate on the viability, respiratory metabolism and free radical-mediated processes were therefore investigated during dehydration of Quercus robur L. embryonic axes. Viability, assessed by evidence of germination and tetrazolium staining, showed a sharp decline at 0.27 and 0.8 g/g during rapid (<12 h) or slow (3 d) dehydration, respectively. Rapid dehydration therefore lowered the critical water content for survival. At any given water content rapid dehydration was associated with higher activities of the free radical processing enzymes, superoxide dismutase, catalase and glutathione reductase and lower levels of hydroperoxide and membrane damage. Rapid dehydration was also associated with lower malate dehydrogenase activity, and a reduced decline in phosphofructokinase activity and in levels of the oxidized form of nicotinamide dinucleotide. Ageing may have contributed to increased damage during slow dehydration, since viability declined even in hydrated storage after 3 d. The results presented are consistent with rapid dehydration reducing the accumulation of damage resulting from desiccation induced aqueous-based deleterious reactions.

Ntuli TM, Finch-Savage WE, Berjak P, Pammenter NW (2011) Increased drying rate lowers the critical water content for survival in embryonic axes of English oak (Quercus robur L.) seeds. J. Integr. Plant Biol. 53(4), 270–280.