Intriguingly, it was found that the CDK inhibitors KRP1 and KRP2 were initially highly expressed in synchronised, initiating pericycle cells and subsequently down-regulated within 4 h of lateral root initiation ( Himanen et al., 2002). This result shows that CycB1 1 alone is not sufficient to drive LRP initiation. The CycB1 1 gene had been associated with LRP initiation previously ( Doerner et al., 1996) however, ectopic expression of CycB1 1 with the CDKA 1 promoter failed to increase the number of LRP. This is evidenced by later expression of the G2-M specific genes CycB1 1, CycB1 2, CDKB1 1 and CDKB2 2 in synchronised, initiating cells ( Himanen et al., 2002). Certain xylem-pole pericycle cells then become competent to progress through the G1–S transition and on to the G2-M checkpoint ( Casimiro et al., 2003). Interestingly, over-expression of CycD3 1 in the pericycle did not lead to an increased number of LRP, showing that it is not sufficient to promote LRP initiation ( de Jager et al., 2005). In addition, the G1–S-specific CDKA 1 is constitutively active in the xylem-pole pericycle cells ( Himanen et al., 2002). Consistent with this, the G1–S-specific CycD4 1 and CycD3 1 genes show expression associated with LRP initiation ( De Veylder et al., 1999 Himanen et al., 2002). A detailed transcriptome study of lateral root initiation using a synchronised population of pericycle cells that were simultaneously activated to form LRP showed that all pericycle cells are initially held at the G1–S checkpoint ( Himanen et al., 2002). LRP formation involves the controlled progression of anti- and periclinal cell divisions and specific cell cycle components have been identified in the regulation of this process ( de Jager et al., 2005 De Smet et al., 2006 Himanen et al., 2002 Malamy, 2005 Osmont et al., 2007). Malamy, in Advances in Botanical Research, 2010 2 Cell cycle control in the LRP marina (and possibly other recalcitrant seed species) and the main effect of the alginate coating was to reduce the incidence of fungal contamination.Paul A. It is suggested that fungal contamination constitutes a major cause of deterioration in stored, hydrated seeds of A. However, the number of seeds visibly contaminated with fungi and the rapidity with which this contamination became apparent were much reduced in alginate-coated seeds. Measures of water content and water and turgor potentials did not reveal signs of a mild water stress in either treatment. Measures of metabolic rate such as time to first germination in storage and rate of protein synthesis did not indicate differences between alginate-coated and naked seeds, although ultrastructural observations indicated that both germinative and deteriorative processes were occurring more slowly in the alginate-coated seeds. Encapsulating seeds from which the pericarp had been removed (naked seeds) in an alginate gel increased storage lifespan fourfold compared with naked seeds. and concentrated on root primordia as these constitute the tissue that undergoes most change during storage. Studies were undertaken on seeds of Avicennia marina (Forssk.) Vierh. This study was undertaken to test the hypotheses that germinative metabolism of recalcitrant seeds in storage induces a requirement for additional water, which may result in the development of mild water stress, and that a reduction of the rate of this germinative metabolism will increase the storage lifespan of recalcitrant seeds.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |