An Endogenous Growth Pattern of Roots Is Revealed in Seedlings Grown in Microgravity

Abstract

In plants, sensitive and selective mechanisms have evolved to perceive and respond to light and gravity. We investigated the effects of microgravity on the growth and development of Arabidopsis thaliana (ecotype Landsberg) in a spaceflight experiment. These studies were performed with the Biological Research in Canisters (BRIC) hardware system in the middeck region of the space shuttle during mission STS-131 in April 2010. Seedlings were grown on nutrient agar in Petri dishes in BRIC hardware under dark conditions and then fixed in flight with paraformaldehyde, glutaraldehyde, or RNAlater. Although the long-term objective was to study the role of the actin cytoskeleton in gravity perception, in this article we focus on the analysis of morphology of seedlings that developed in microgravity. While previous spaceflight studies noted deleterious morphological effects due to the accumulation of ethylene gas, no such effects were observed in seedlings grown with the BRIC system. Seed germination was 89% in the spaceflight experiment and 91% in the ground control, and seedlings grew equally well in both conditions. However, roots of space-grown seedlings exhibited a significant difference (compared to the ground controls) in overall growth patterns in that they skewed to one direction. In addition, a greater number of adventitious roots formed from the axis of the hypocotyls in the flight-grown plants. Our hypothesis is that an endogenous response in plants causes the roots to skew and that this default growth response is largely masked by the normal 1 g conditions on Earth.

Spaceflight Induces Specific Alterations in the Proteomes of Arabidopsis

“…Many of the proteins identified here as differentially abundant in spaceflight are associated with auxin metabolism, and a large number are associated with cell wall modification that makes sense in light of the morphologies demonstrated by spaceflight roots (Millar et al, 2011;Paul et al, 2013;Nakashima et al, 2014). Of the differentially represented proteins presented in Table 1, 95 are associated with cell walls or cell wall metabolism either by Gene Ontology annotation or by reference when using SUBA3 searches (Tanz et al, 2013).…”

Division Plane Orientation Defects Revealed by a Synthetic Double Mutant Phenotype

“…Left-handed twisting occurs in Ler plants treated with the microtubuledestabilizing drug propyzamide (Nakamura et al, 2004) and in mutants such as microtubule organization1 (Whittington et al, 2001;Sugimoto et al, 2003), lefty1, and lefty2 (Thitamadee et al, 2002). In addition to mutations that alter microtubule dynamics, sometimes mutants that modulate actin dynamics, ethylene levels, or auxin transport also have altered cell file rotation patterns (Buer et al, 2003;Yuen et al, 2003;Millar et al, 2011;Roy and Bassham, 2014). Although cell file rotation occurred in the tan1 air9 mutants, the roots themselves did not show obvious root skewing in classical tilted agar experiments.…”

Expression of stress-related genes in zebrawood (Astronium fraxinifolium, Anacardiaceae) seedlings following germination in microgravity

“…The high germination rate and rapid root growth seen in the A. fraxinifolium seeds exposed to spaceflight has been observed in other species, such as Linum usitatissimum (Levine et al , 2003), Glycine max (Levine et al , 2000) and Arabidopsis (Millar et al , 2011). The limited time available on the spaceflight precluded reliable observation of any difference in shoot length in the microgravity and terrestrially germinated seedlings, but early shoot growth stimulation has been observed in other, faster developing plants, such as rice seedlings subjected to simulated microgravity, such as clinorotation (Jagtap et al , 2011), where chlorophyll content was also increased.…”