Plant development under simulated microgravity conditions - Simulated microgravity induced alterations in Arabidopsis cell wall

Abstract

Plant growth is influenced by a complex interaction of gravi- and phototropism. Insights on the impact of gravity on plant development can be achieved using altered gravity conditions like hyper-g or real and simulated μg. Plant development depends also on other factors like humidity, nutrients and light regime. Thus standardized conditions are necessary to exclude effects that could be induced by the cultivation method instead of altered gravity. Plant research in μg is performed using various setups employing different cultivation methods, which lead to a lack of reproducibility and comparability of obtained results. In order to overcome these serious deficits, a new hardware called ARADISH was developed for Arabidopsis cultivation in simulated μg on a 2D clinostat. The hardware offers standardized conditions, is flexible, reliable and cheap. The cultivation method differs from the conventional cultivation in petri dishes. The main differences between the 2 cultivation methods (petri dish versus ARADISH) are plant growth along agar medium versus a more natural growth of roots through the medium; illumination of the whole plant (including roots) versus Illumination of shoots, with faint and more natural illumination of roots. Viability stains confirmed that in ARADISH the plant viability is guaranteed for 1 g and an extended exposure of 5 days to simulated μg. Using ARADISH, plant growth was affected in a positive way resulting in smaller root/shoot ratios, suggesting more favorable growth conditions compared to petri dish cultivation. The ARADISH allowed seed-to-seedling experiments in simulated μg with a large amount of sample material. This enabled to study long-term effects on plant development in context of callose deposition as stress indicator and the analysis of the cell wall polysaccharide RGII in context of modification and alteration of cell wall properties. In roots and stems grown under simulated μg an enhanced callose deposition in the vascular tissue indicated a stressful environment for a developing plant. The analysis of the RGII polysaccharide showed that the amount of dimers did not change in simulated μg. However, a more detailed analysis revealed that there where changes in the total abundance of RGIIs single monosaccharides suggesting modifications in the complex polysaccharide molecule which could influence its three dimensional structure and in consequence the mechanical properties of cell walls.