Plants in Space: Novel Physiological Challenges and Adaptation Mechanisms

Abstract

Any space exploration initiative, such as the human presence in the Moon and Mars, must incorporate plants for life support. To enable space plant culture we need to understand how plants respond to extraterrestrial conditions, adapt to them and compensate their deleterious effects at multiple levels. Gravity is a major difference between the terrestrial and the extraterrestrial environment. Gravitropism is the process of establishing a growth direction for plant organs according to the gravity vector. Gravity signals are sensed at specialized tissues by the motion of amyloplasts called statoliths and transduced to produce a cellular polarization capable of influencing the transport of auxin. Gravity alterations eventually result in changes in the lateral balance of auxin in the root, producing deviations of the growth direction. Under microgravity, auxin changes affect the root meristem causing increased cell proliferation and decreased cell growth. The nucleolus, the nuclear site of production of ribosomes, is a marker of this unbalance, which could alter plant development. At the molecular level, microgravity induces a reprogramming of gene expression that mostly affects plant defense systems against abiotic stresses, indicating that these categories of genes are involved in the adaptation to extraterrestrial habitats. Nevertheless, no specific genes for plant response to gravitational stress have been identified. Despite this stress, plants survive, developing until the adult stage and reproducing under microgravity conditions. A major research challenge is to identify environmental factors, such as light, which could interact, modulate or balance the impact of gravity, contributing to the tolerance and survival of plants under spaceflight conditions. Understanding the crosstalk between light and gravity sensing will contribute to the success of the next generation agriculture in human settlements outside the Earth. Plants are needed for space exploration: Space Plant Biology."Je ne sais pas si les mondes sont habités, et, comme je ne le sais pas, je vais y voir!" ("I do not know if the worlds are inhabited, and, as I do not know that, I'll go there and see!") -Jules Verne, "From the Earth to the Moon" (1867).This quote, from one of the most famous books by Jules Verne, which was written more than a century and a half ago, reflects an intense human dream, which, at the same time is a major challenge for the humankind: to go out of our planet Earth and see how are "the other worlds", in particular, whether we, as living beings and, especially, as intelligent living beings, are alone in the Universe, or we have companions with whom we can interact. Science-fiction literature is full of stories talking about the relationships between humans and aliens, whether they are peaceful or hostile.In 2019, the entire world has commemorated the 50 th anniversary of the first human footprint on the surface of the Moon, and in 2020, the twenty years of the continuous presence of humans as crew members of the International S...

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

“…Red light increased meristem and nucleolar size, as observed in the confocal microscopy images. In addition, ultrastructural analysis of meristematic cell nucleoli showed more active nucleoli in the red-light-photostimulated seedlings, as shown by the relative distribution of the nucleolar subcomponents, according to previously described models of the nucleolar structure in relation to activity [ 75 , 76 ]. This observation suggests that red light indeed counteracts the decoupling between cell proliferation and growth, as reported in the aforementioned prior experiments in space and simulated microgravity [ 35 , 37 ].…”

Optimising plant form and function for controlled environment agriculture in space and on earth

“…The effects of long-term cultivation in a low gravity environment on plant growth and development are consequently poorly understood. 63 It might be expected, however, that ideal space crops will require some augmentation of their gravity perception, either through enhanced sensitivity to gravity itself or by using other environmental signals that are more easily controlled, such as light. 63 The gravitropic response varies both within and between species, and so the modifications necessary may vary similarly dependent upon the crop 64,65 It would be advantageous if new functions of plants for space also went beyond the immediate needs for growth and yield.…”

Understanding Reduced Gravity Effects on Early Plant Development Before Attempting Life-Support Farming in the Moon and Mars

“…On the contrary, the pattern of roots grown at 0.3 g is basically similar to the control pattern, indicating that auxin polar transport is not altered at these partial-g levels. Medina et al, 2021). Actually, comprehensive studies on these processes are still insufficient and it appears that, similar as the intensity of the gravitational stress, different taxonomic categories display a different adaptability.…”