Meristem differentiation

KNOXlgenes regulate the shoot apical meristem differentiation, and upregulate cytokinin biosynthesis and decrease gibberellin accumulation in plants, ectopic expression of KNOXl genes induces adventitious shoot regeneration in vitro-cultured explants (Sakamoto et al., 2006 Srinivasan et al., 2011). 

Fig. 1. Infection and early development of root nodules. (A) Infection thread (IT) and curled root hair (CRH) 48 hr after inoculation. (B) Nodule meristem differentiation in root cortical parenchyma prior to infection thread proliferation. Arrowhead points to mitotic figure (M). (C) Bacterial (Ba) release from infection thread into host cell cytoplasm. Bacteria are surrounded by a polysaccharide matrix (P) within the infection thread and immediately upon release. (D) After release from the infection thread bacteria (Ba) are enclosed within the peribacteroid membrane (PBM) and the polysaccharide matrix (P) formerly surrounding the bacteria is degraded. Bars indicate approximate sizes. 

By contrast, nodule meristem development in indeterminate nodules, such as those of Medicago and Pisum, is initiated in the inner cortex adjacent to the endodermis (Dudley et al., 1987). The meristem of indeterminate nodules functions for months or even years in the case of some woody perennials (Dart, 1977). The meristem differentiates into a dome shape due to cell division in a single plane. Cell division followed by cell enlargement results in an elongate, cylindrical-shaped nodule (Fig. 5). As nodules grow, other meristematic areas often differentiate, resulting in the formation of a branched, corraloid-type nodule. 

The rapid vegative growth, which includes development of shoots, leaves, and flowers, is controlled by a variety of transcription factors.483 Among these are homeodomain proteins that control differentiation of meristem cells 484-486 The induction of flowering is... 

The root apex is covered with a calyptra extending proximally up to about 600 pm from the tip. The apical meristem is of the closed type, with each of the three root tissue systems, i.e. the vascular cylinder, the cortex, and the calyptra/epidermis, arising from its own independent groups of initials.16 Cellular differentiation had already started at a distance of about 600 pm from the tip in the 16 h-control while very little differentiation could be seen in roots from treated seeds. 

In plants, the three different tomato IMP genes are differentially and developmentally regulated (Gillaspy et ah, 1995). Expression of the LeIMP2 gene is spatially restricted to a discreet domain within the plant and is found only within epidermal and cortex cells of specific stem/leaf junctions in an abaxial-specific pattern and in the shoot apical meristem. Furthermore, unlike yeast, inositol and Fi+ repress expression of the FeIMP2 promoter (Styer et ah, 2004). 

For thermal analysis, shoot and root meristems were analyzed using a differential scanning calorimeter (DSC) Mettler TA 4000. Samples were rapidly cooled to — 100°C and then warmed in the DSC from —100 to 100°C at 10°C min . The data were analyzed using TCII TA Processor and Graph Ware TA 72 software. The ratio of unfrozen water was calculated from the... 

As with the animal monomeric and heterotrimeric G-proteins, the proteins identified appeared to show differential expression within the plant tissues. Northern blot analysis showed that transcripts encoding GPAl were most abundant in vegetative tissue and least abundant in floral and apical meristems [89], whilst immunogold staining supported this and also showed that GPAl was strongly expressed in vascular tissue [153]. 

Auxin has been implicated in a bewildering array of growth responses. At the level of the cell, these responses involve rapid changes in cell expansion, effects on cell division and meristem activity, as well as differentiation of specific cell types [1]. In an effort to understand molecular aspects of auxin signaling, many researchers have focused on rapid biochemical responses associated with auxin-induced cell elongation. These include activation of a plasma membrane H -ATPase [2], changes in the behavior of ion channels... 

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