Persistence of plant hormone levels in rice shoots grown under microgravity conditions in space: its relationship to maintenance of shoot growth

Abstract

We investigated the effects of microgravity environment on growth and plant hormone levels in dark-grown rice shoots cultivated in artificial 1 g and microgravity conditions on the International Space Station (ISS). Growth of microgravity-grown shoots was comparable to that of 1 g-grown shoots. Endogenous levels of indole-3-acetic acid (IAA) in shoots remained constant, while those of abscisic acid (ABA), jasmonic acid (JA), cytokinins (CKs) and gibberellins (GAs) decreased during the cultivation period under both conditions. The levels of auxin, ABA, JA, CKs and GAs in rice shoots grown under microgravity conditions were comparable to those under 1 g conditions. These results suggest microgravity environment in space had minimal impact on levels of these plant hormones in rice shoots, which may be the cause of the persistence of normal growth of shoots under microgravity conditions. Concerning ethylene, the expression level of a gene for 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, the key enzyme in ethylene biosynthesis, was reduced under microgravity conditions, suggesting that microgravity may affect the ethylene production. Therefore, ethylene production may be responsive to alterations of the gravitational force.

Diverse Roles of MAX1 Homologues in Rice

“…Whereas expression of Os08g0167000 (MR = 13.711), which encodes one of the half-size adenosine triphosphate-binding cassette transporter subgroup G (ABCG), was induced by salicid acid and repressed by auxin treatment [ 198 ]. Finally, Os05g0447200 is AUX2 , one of the auxin-responsive genes, and was highly induced under microgravity conditions [ 199 ].…”

Adaptation to real 1/6 g moon gravity contributes to plant development and expeditious acclimation to super-freezing

“…In addition to gravity-associated membrane alteration, we think several microgravity induced physiological changes may also be beneficial to frozen protection: 1) Concentrations of soluble sugars, glucose, sucrose and total starch were substantially increased in Space shuttle flight sweetpotato stem 54 , and soluble sugars enhanced in tobacco callus cells under rotation simulated microgravity 55 ; 2) In space, microgravity environment had no obvious effect to rice shoots auxins, but reduced the expression of ACC synthase, the key enzyme of ethylene biosynthesis 3 , and ethylene is a negative regulator of cold resistance; 3) Numerous experiments indicated that calcium in cells increased under real or simulated conditions 5,56 ; 4) Genes expression changed under real microgravity in space and simulated ground experiments. Functions of "major space genes" include Ca 2+ and lipid signaling, cell membrane biosynthesis, total metabolism, carbohydrates and lipid response to stress, auxin-signaling, and heat shock protein (HSP) thought to support the organization of cytoskeleton in adaptive response to microgravity [57][58][59][60] .…”

“…Over the past 20 years, our understanding of the impact of microgravity on organism physiology has increased. Plant-based life regeneration ecosystems have helped scientists to study plant growth in a ground-controlled environment by simulating short duration of altered-gravity, and the improved design of plant growth chambers in the International Space Station (ISS) has allowed researchers to study the mechanisms of life adaptation to approximate zerogravity condition [2][3][4][5][6] . Because plants could be an essential integral part of longterm bioregenerative life support system 2 , plant culture in space remains a high priority strategy for all space exploration plans.…”

Transcriptional regulation of MdPIN3 and MdPIN10 by MdFLP during apple self-rooted stock adventitious root gravitropism

“…To maintain normal root gravitropism, plants must receive and respond to the gravity signal appropriately [37]. We investigated the effects of a microgravity environment on the root growth and endogenous hormone IAA in 12–2.…”