Light signals counteract alterations caused by simulated microgravity in proliferating plant cells

Abstract

Light and gravity are fundamental cues for plant development. Our understanding of the effects of light stimuli on plants in space, without gravity, is key to providing conditions for plants to acclimate to the environment. Here we tested the hypothesis that the alterations caused by the absence of gravity in root meristematic cells can be counteracted by light. Methods: Seedlings of wild-type Arabidopsis thaliana and two mutants of the essential nucleolar protein nucleolin (nuc1, nuc2) were grown in simulated microgravity, either under a white light photoperiod or under continuous darkness. Key variables of cell proliferation (cell cycle regulation), cell growth (ribosome biogenesis), and auxin transport were measured in the root meristem using in situ cellular markers and transcriptomic methods and compared with those of a 1 g control. Results: The incorporation of a photoperiod regime was sufficient to attenuate or suppress the effects caused by gravitational stress at the cellular level in the root meristem. In all cases, values for variables recorded from samples receiving light stimuli in simulated microgravity were closer to values from the controls than values from samples grown in darkness. Differential sensitivities were obtained for the two nucleolin mutants. Conclusions: Light signals may totally or partially replace gravity signals, significantly improving plant growth and development in microgravity. Despite that, molecular alterations are still compatible with the expected acclimation mechanisms, which need to be better understood. The differential sensitivity of nuc1 and nuc2 mutants to gravitational stress points to new strategies to produce more resilient plants to travel with humans in new extraterrestrial endeavors.

Red Light Enhances Plant Adaptation to Spaceflight and Mars g-Levels

“…In contrast, light did not appear to influence the orientation of roots in microgravity, which showed considerable differences with the oriented roots of seedlings grown at 1 g ( Figure 1 ). These features are in agreement with the results of experiments performed in simulated microgravity [ 59 ]. Photoactivation with directional red light suppressed the orientation of hypocotyls achieved under white light.…”

“…This genetic response took place even in etiolated seedlings, in the absence of an effective light signal. The culture of seedlings in simulated microgravity under a photoperiod regime was capable of reverting many of the alterations found on etiolated seedlings incubated in the same facility for microgravity simulation [ 59 ]. Actually, light induces variable tropism in the aerial part of the plant (shoot and leaves; hypocotyl in seedlings) and in roots.…”

Root growth direction in simulated microgravity is modulated by a light avoidance mechanism mediated by flavonols

“…The intimate interaction between gravi‐ and phototropism has been recognized in multiple studies (Kiss, Correll, et al, 2003; Kiss, Mullen, et al, 2003; Manzano et al, 2021; Okada & Shimura, 1992; Vitha et al, 2000). Gravitropism is generally the dominant tropism in the root (Kiss, Correll, et al, 2003; Kiss, Mullen, et al, 2003).…”

“…Nevertheless, the exposure of the root to light has a negative effect on the plant's physiology. We have investigated how having root protected from and the shoot exposed to light influences the The intimate interaction between gravi-and phototropism has been recognized in multiple studies Manzano et al, 2021;Okada & Shimura, 1992;Vitha et al, 2000). Gravitropism is generally the dominant tropism in the root .…”

“…On the other hand, results from real and simulated microgravity experiments suggest a positive impact of unilateral light exposure on seedling growth and development in comparison to etiolated seedlings. This light condition partly mitigates the negative impact of microgravity on these processes (Manzano et al, 2021; Villacampa, Ciska, et al, 2021; Villacampa, Sora, et al, 2021).…”