Cellular Basis of Hypocotyl Growth in Arabidopsis thaliana

Abstract

The Arabidopsis thaliana hypocotyl is widely used to study the effects of light and plant growth factors on cell elongation. To provide a framework for the molecular-genetic analysis of cell elongation in this organ, here we describe, at the cellular level, its morphology and growth and identify a number of characteristic, developmental differences between light-grown and dark-grown hypocotyls. First, in the light epidermal cells show a characteristic differentiation that is not observed in the dark. Second, elongation growth of this organ does not involve significant cortical or epidermal cell divisions. However, endoreduplication occurs, as revealed by the presence of 4C and 8C nuclei. In addition, 16C nuclei were found specifically in dark-grown seedlings. Third, in the dark epidermal cells elongate along a steep, acropetal spatial and temporal gradient along the hypocotyl. In contrast, in the light all epidermal cells elongated continuously during the entire growth period. These morphological and physiological differences, in combination with previously reported genetic data (1. Desnos, V. Orbovic, C. Bellini, j. Kronenberger, M. Caboche, j. Traas, H. Hofte [19961 Development 122: 683-693), illustrate that light does not simply inhibit hypocotyl growth in a cell-autonomous fashion, but that the observed growth response to light is a part of an integrated developmental change throughout the elongating organ.

The Energy-Signaling Hub SnRK1 Is Important for Sucrose-Induced Hypocotyl Elongation

“…Here, we make the new finding that a mechanism involving KIN10 activity and Tre6P metabolism regulates Suc-induced hypocotyl elongation under light/ dark cycles. Although hypocotyl elongation arises from cell expansion rather than growth through increases in cell number (Gendreau et al, 1997), our data are consistent with studies demonstrating that Tre6P metabolism is a crucial regulator of growth responses to Suc. For example, Arabidopsis seedlings overexpressing the bacterial Tre6P phosphatase otsB, which reduces [Tre6P], accumulate less biomass compared with the wild type when supplemented with Suc (Schluepmann et al, 2003).…”

“…In a different and nonexclusive scenario, SnRK1-mediated alterations in metabolic enzyme activity and growth-related transcripts prime the hypocotyls to capitalize upon increased Suc availability (Nunes et al, 2013a). This is an interesting question in the case of hypocotyl elongation, which arises from cell expansion rather than growth through cell division and biomass accumulation per se (Gendreau et al, 1997). These two possibilities are nonexclusive, because the phenotypic differences that we report between KIN10-ox lines and tps1 mutants (e.g.…”

Group III-AXTHGenes of Arabidopsis Encode Predominant Xyloglucan Endohydrolases That Are Dispensable for Normal Growth

“…S11A, zones 4-8; typified by the zone 7 image). This pattern suggests that XET activity is highest in the growing region of the hypocotyl (Gendreau et al, 1997;compare with Fig. 2d in Wolf et al, 2012).…”

ADF Proteins Are Involved in the Control of Flowering and Regulate F-Actin Organization, Cell Expansion, and Organ Growth in Arabidopsis

“…The longitudinally oriented actin cables in these cells are believed to serve as tracks for the myosin-mediated movement of secretory vesicles containing newly synthesized cell membrane and cell wall material toward the growing tip (reviewed in Taylor and Hepler, 1997). Although hypocotyl cells, like most other types of plant cells, expand by diffuse polar growth, during which cells expand in all directions to a certain degree (Gendreau et al, 1997;Kropf et al, 1998), it is conceivable that actin cables also are essential for the elongation of these cells because of their ability to facilitate the delivery of new cell wall and membrane material to growth sites. Misdelivery of such material resulting from the disruption of intracellular trafficking could account for the irregular cellular morphology observed in AtADF1-O hypocotyls.…”