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NASA NTRS1997

Plastids and gravitropic sensing

Data and theories about the identity of the mass that acts in gravitropic sensing are reviewed. Gravity sensing may have evolved several times in plants and algae in processes such as gravitropism of organs and tip-growing cells, gravimorphism, gravitaxis, and the regulation of cytoplasmic streaming in internodal cells of Chara. In the latter and in gravitaxis, the mass of the entire cell may function in sensing. But gravitropic sensing appears to rely upon the mass of amyloplasts that sediment since (i) the location of cells with sedimentation is highly regulated, (ii) such cells contain other morphological specializations favoring sedimentation, (iii) sedimentation always correlates with gravitropic competence in wild-type plants, (iv) magnetophoretic movement of rootcap amyloplasts mimics gravitropism, and (v) starchless and intermediate starch mutants show reduced gravitropic sensitivity. The simplest interpretation of these data is that gravitropic sensing is plastid-based.

Review, Tutorial↗

NASA NTRS1996

Space stress and genome shock in developing plant cells

In the present paper I review symptoms of stress at the level of the nucleus in cells of plants grown in space under nonoptimized conditions. It remains to be disclosed to what extent gravity "unloading" in the space environment directly contributes to the low mitotic index and the chromosomal anomalies and damage that is frequently, but not invariably, demonstrable in space-grown plants. Evaluation of the available facts indicates that indirect effects play a major role and that there is a significant biological component to the susceptibility to stress damage equation as well. Much remains to be learned on how to provide strictly controlled, optimal environments for plant growth in space. Only after optimized controls become possible will one be able to attribute any observed space effects to lowered gravity or to other significant but more indirect effects of the space environment.

Review, Tutorial↗

NASA NTRS1990

Comparative effectiveness of a clinostat and a slow-turning lateral vessel at mimicking the ultrastructural effects of microgravity in plant cells

The object of this research was to determine how effectively the actions of a clinostat and a fluid-filled, slow-turning lateral vessel (STLV) mimic the ultrastructural effects of microgravity in plant cells. We accomplished this by qualitatively and quantitatively comparing the ultrastructures of cells grown on clinostats and in an STLV with those of cells grown at 1 g and in microgravity aboard the Space Shuttle Columbia. Columella cells of Brassica perviridis seedlings grown in microgravity and in an STLV have similar structures. Both contain significantly more lipid bodies, less starch, and fewer dictyosomes than columella cells of seedlings grown at 1 g. Cells of seedlings grown on clinostats have significantly different ultrastructures from those grown in microgravity or in an STLV, indicating that clinostats do not mimic microgravity at the ultrastructural level. The similar structures of columella cells of seedlings grown in an STLV and in microgravity suggest that an STLV effectively mimics microgravity at the ultrastructural level.

STS Shuttle Project↗

NASA NTRS2005

Measurement of hydraulic characteristics of porous media used to grow plants in microgravity

Understanding the effect of gravity on hydraulic properties of plant growth medium is essential for growing plants in space. The suitability of existing models to simulate hydraulic properties of porous medium is uncertain due to limited understanding of fundamental mechanisms controlling water and air transport in microgravity. The objective of this research was to characterize saturated and unsaturated hydraulic conductivity (K) of two particle-size distributions of baked ceramic aggregate using direct measurement techniques compatible with microgravity. Steady state (Method A) and instantaneous profile measurement (Method B) methods for K were used in a single experimental unit with horizontal flow through thin sections of porous medium providing an earth-based analog to microgravity. Comparison between methods was conducted using a crossover experimental design compatible with limited resources of space flight. Satiated (natural saturation) K ranged from 0.09 to 0.12 cm s-1 and 0.5 to >1 cm s-1 for 0.25- to 1- and 1- to 2-mm media, respectively. The K at the interaggregate/intraaggregate transition was approximately 10(-4) cm s-1 for both particle-size distributions. Significant differences in log(10)K due to method and porous medium were less than one order of magnitude and were attributed to variability in air entrapment. The van Genuchten/Mualem parametric models provided an adequate prediction of K of the interaggregate pore space, using residual water content for that pore space. The instantaneous profile method covers the range of water contents relevant to plant growth using fewer resources than Method A, all advantages for space flight where mass, volume, and astronaut time are limited.

NASA Center JSC↗

NASA NTRS2011

Crop and Substrate Tests with Single Use Rooting "Pillows" for the VEGGIE Plant Growth Hardware

No abstract available

Masa, Gioia↗

NASA NTRS2016

Comparative Study of Lettuce and Radish Grown Under Red and Blue LEDs and White Fluorescent Lamps

Growing vegetable crops in space will be an essential part of sustaining astronauts during long-range missions. To drive photosynthesis, red and blue light-emitting diodes (LEDs) have attracted attention because of their efficiency, longevity, small size, and safety. In efforts to optimize crop yield, there is also recent interest in analyzing the subtle effects of additional wavelengths on plant growth. For instance, since plants often look purplish gray under red and blue LEDs, the addition of green light allows easy recognition of disease and the assessment of plant health status. However, it is important to know if wavelengths outside the traditional red and blue wavebands have a direct effect on enhancing or hindering the mechanisms involved in plant growth. In this experiment, a comparative study was performed on two short cycle crops of red romaine lettuce (Lactuca sativa cv. "Outredgeous") and radish (Raphanus sativa cv. 'Cherry Bomb'), which were grown under two light treatments. The first treatment being red (630 nm) and blue (450 nm) LEDs alone, while the second treatment consisted of daylight tri-phosphor fluorescent lamps (CCT approximately 5000 K) at equal photosynthetic photon flux (PPF). The treatment effects were evaluated by measuring the fresh biomass produced, plant morphology and leaf dimensions, leaf chlorophyll content, and adenosine triphosphate (ATP) within plant leaf/storage root tissues.

Food Production↗

NASA NTRS1995

Microgravity and clinorotation cause redistribution of free calcium in sweet clover columella cells

In higher plants, calcium redistribution is believed to be crucial for the root to respond to a change in the direction of the gravity vector. To test the effects of clinorotation and microgravity on calcium localization in higher plant roots, sweet clover (Melilotus alba L.) seedlings were germinated and grown for two days on a slow rotating clinostat or in microgravity on the US Space Shuttle flight STS-60. Subsequently, the tissue was treated with a fixative containing antimonate (a calcium precipitating agent) during clinorotation or in microgravity and processed for electron microscopy. In root columella cells of clinorotated plants, antimonate precipitates were localized adjacent to the cell wall in a unilateral manner. Columella cells exposed to microgravity were characterized by precipitates mostly located adjacent to the proximal and lateral cell wall. In all treatments some punctate precipitates were associated with vacuoles, amyloplasts, mitochondria, and euchromatin of the nucleus. A quantitative study revealed a decreased number of precipitates associated with the nucleus and the amyloplasts in columella cells exposed to microgravity as compared to ground controls. These data suggest that roots perceive a change in the gravitational field, as produced by clinorotation or space flights, and respond respectively differently by a redistribution of free calcium.

short duration↗

NASA NTRS1999

Arabidopsis alcohol dehydrogenase expression in both shoots and roots is conditioned by root growth environment

It is widely accepted that the Arabidopsis Adh (alcohol dehydrogenase) gene is constitutively expressed at low levels in the roots of young plants grown on agar media, and that the expression level is greatly induced by anoxic or hypoxic stresses. We questioned whether the agar medium itself created an anaerobic environment for the roots upon their growing into the gel. beta-Glucuronidase (GUS) expression driven by the Adh promoter was examined by growing transgenic Arabidopsis plants in different growing systems. Whereas roots grown on horizontal-positioned plates showed high Adh/GUS expression levels, roots from vertical-positioned plates had no Adh/GUS expression. Additional results indicate that growth on vertical plates closely mimics the Adh/GUS expression observed for soil-grown seedlings, and that growth on horizontal plates results in induction of high Adh/GUS expression that is consistent with hypoxic or anoxic conditions within the agar of the root zone. Adh/GUS expression in the shoot apex is also highly induced by root penetration of the agar medium. This induction of Adh/GUS in shoot apex and roots is due, at least in part, to mechanisms involving Ca2+ signal transduction.

NASA Discipline Plant Biology↗

NASA NTRS1997

Root cytoskeleton: its role in perception of and response to gravity

We have critically evaluated the possible functions of the plant cytoskeleton in root gravisensing and graviresponse and discussed the evidence that microtubules (MTs) and actin microfilaments (MFs) do not control differential cell growth during bending of roots. On the other hand, MF and MT networks are envisaged to participate in gravisensing because of the mechanical properties of the cytoskeletal structures that interconnect plant cell organelles with the plasma membrane. In restrained gravisensing, forces are suggested to be transmitted to membranes because large-scale gravity-dependent repositioning of organelles is effectively prevented due to the cytoskeleton-mediated anchorage of their envelopes at the plasma membrane. From the cytoskeletal point of view, we can also envisage an unrestrained gravity sensing when cytoskeletal tethers are not strong enough to preserve the tight control over distribution of organelles and the latter, if heavy enough, are allowed to sediment towards the physical bottom of cells. This situation obviously occurs in root cap statocytes because these uniquely organized cells are depleted of prominent actin MF bundles, endoplasmic MT arrays, and ER elements in their internal cytoplasm. Nevertheless, indirect evidence clearly indicates that sedimented root cap statoliths are enmeshed within fine but dynamic MF networks and that their behaviour is obviously under, at least partial, cytoskeletal control. The actomyosin-enriched domain among and around amyloplasts is proposed to increase the perception of gravity due to the grouping effect of sedimenting statoliths. Cytoskeletal links between myosin-rich statoliths, and cell peripheries well equipped with dense cortical MTs, membrane-associated cytoskeleton, as well as with ER elements, would allow efficient restrained gravisensing only at the statocyte cell cortex. As a consequence of cytoskeletal depletion in the internal statocyte cytoplasm and bulk sedimentation of large amyloplasts, restrained gravisensing is spatially restricted to the bottom of the statocyte irrespective of whether roots are vertical or horizontal. This spatial aspect allows for efficient gravisensing via amplification of gravity-induced impacts on the cellular architecture, a phenomenon which is unique to root cap statocytes.

NASA Discipline Plant Biology↗

NASA NTRS1982

A comparative study of monocot and dicot root development in normal /earth/ and hypogravity /space/ environments

The anatomy and fine structure of roots from oat and mung bean seedlings grown under hypogravity conditions aboard NASA's Space Shuttle were examined and compared to those of roots from ground control plants grown under similar conditions. Oat roots from both sets of plants exhibited normal tissue organization and ultrastructural features, with the exception of cortex cell mitochondria, which characteristically showed a 'swollen' morphology. Flight-grown mung bean roots differed significantly from the controls in that root cap cells were somewhat disorganized and degraded in appearance, especially at the cap periphery. At the EM level, these cells exhibited a loss organelle integrity and a condensed cytoplasm. The potential significance of this finding for the putative gravity-sensing cap cells were noted.

Slocum, R. D.↗

NASA NTRS2003

Root phototropism: how light and gravity interact in shaping plant form

The interactions among tropisms can be critical in determining the final growth form of plants and plant organs. We have studied tropistic responses in roots as an example of these type of interactions. While gravitropism is the predominant tropistic response in roots, phototropism also plays a role in the oriented growth in this organ in flowering plants. In blue or white light, roots exhibit negative phototropism, but red light induces positive phototropism. In the flowering plant Arabidopsis, the photosensitive pigments phytochrome A (phyA) and phytochrome B (phyB) mediate this positive red-light-based photoresponse in roots since single mutants (and the double phyAB mutant) were severely impaired in this response. While blue-light-based negative phototropism is primarily mediated by the phototropin family of photoreceptors, the phyA and phyAB mutants (but not phyB) were inhibited in this response relative to the WT. The differences observed in phototropic responses were not due to growth limitations since the growth rates among all the mutants tested were not significantly different from that of the WT. Thus, our study shows that the blue-light and red-light systems interact in plants and that phytochrome plays a key role in integrating multiple environmental stimuli.

Non-NASA Center↗

NASA NTRS2019

New Perspectives for Watering Substrate-Based Root Modules in Microgravity in the Advanced Plant Habitat (APH)

The Advanced Plant Habitat (APH) was installed on the International Space Station (ISS) in October 2017. Following a successful EVT (Experiment Verification Test) study at Kennedy Space Center (KSC), using Arabidopsis lines with varying levels of lignin, two inaugural studies were carried out on ISS in 2018 under the same experimental design, with the corresponding ground controls at KSC. The APH for this study deploys a substrate-based root module designed for plant growth in microgravity. Upon experiment initiation (such as for the EVT), the root module is primed (liquid imbibition) by flooding the root zone to initiate seed germination and to remove air from the porous tubing and particulate media. In the APH ISS inaugural study, the speed of supplying water to initially dry media was found to adversely affect the overall moisture distribution within the root module in microgravity (but not at 1g). Non-destructive estimations of Arabidopsis plant growth were carried out by monitoring changes in rosette leaf area on a daily basis. These data indicated that the original priming procedure caused patchy moisture distribution that affected plant growth and survival. An improved methodology for priming the second root module of PH-01 was devised and implemented in the second experiment. Leaf area and color estimates suggested that the modified priming scheme improved moisture distribution and plant growth. These data, when compared with the EVT study, suggest that nondestructive measurements of plant growth can aid towards optimization of plant growth conditions in microgravity.

Monje O.↗

NASA NTRS2019

Early Prototype Development of the Passive Orbital Nutrient Delivery System (PONDS)

Long-duration space missions will eventually require a fresh food supply to supplement crew diets, which means growing crops in space. The Passive Orbital Nutrient Delivery System (PONDS) is a new plant growth approach that contains both an area for a contained substrate and a reservoir for water and/or plant nutrient solutions. Ground studies have shown that the system facilitates both reliable water delivery to seeds for germination (e.g., while avoiding overwatering), and transport of water from the reservoir for improved plant growth while providing nutrients and oxygen to the root zone. In ground prototypes a capillary mat wicking material passively links the water/nutrient solution reservoir to a removable rooting module containing a substrate adapted to support plant growth. Oxygen permeable membranes are incorporated into both the reservoir walls and the rooting modules, bringing in oxygen from outside of the system into the reservoir and then into the rooting modules where the plant roots proliferate. Water is delivered from the reservoir to the substrate contained within the rooting module through the use of wicking material inserted into the plant growth substrate both from the bottom and from the sides of the rooting module. The capillary mat material is intrinsically hydrophilic and continuously wicks water to the substrate throughout the plant growth interval. The system is therefore self-watering in terms of supplying water to the root zone encompassed within the rooting module on demand. At the top, a hydrophilic phenolic foam plug surrounds the wick in the seed insertion zone, and both contains the substrate within the rooting module, and facilitates removal of excess moisture from the capillary mat wick before it can encompass seeds prior to germination. This work is supported by NASA’s Space Life and Physical Sciences and Research Applications Division (SLPSRAD).

Levine, Howard G.↗

NASA NTRS2013

VEG-01: Veggie Hardware Verification Testing

The Veggie plant/vegetable production system is scheduled to fly on ISS at the end of2013. Since much of the technology associated with Veggie has not been previously tested in microgravity, a hardware validation flight was initiated. This test will allow data to be collected about Veggie hardware functionality on ISS, allow crew interactions to be vetted for future improvements, validate the ability of the hardware to grow and sustain plants, and collect data that will be helpful to future Veggie investigators as they develop their payloads. Additionally, food safety data on the lettuce plants grown will be collected to help support the development of a pathway for the crew to safely consume produce grown on orbit. Significant background research has been performed on the Veggie plant growth system, with early tests focusing on the development of the rooting pillow concept, and the selection of fertilizer, rooting medium and plant species. More recent testing has been conducted to integrate the pillow concept into the Veggie hardware and to ensure that adequate water is provided throughout the growth cycle. Seed sanitation protocols have been established for flight, and hardware sanitation between experiments has been studied. Methods for shipping and storage of rooting pillows and the development of crew procedures and crew training videos for plant activities on-orbit have been established. Science verification testing was conducted and lettuce plants were successfully grown in prototype Veggie hardware, microbial samples were taken, plant were harvested, frozen, stored and later analyzed for microbial growth, nutrients, and A TP levels. An additional verification test, prior to the final payload verification testing, is desired to demonstrate similar growth in the flight hardware and also to test a second set of pillows containing zinnia seeds. Issues with root mat water supply are being resolved, with final testing and flight scheduled for later in 2013.

Massa, Gioia↗

NASA NTRS1998

Biocompatibility of sweetpotato and peanut in a hydroponic system

'Georgia Red' peanut (Arachis hypogaea L.) and TU-82-155 sweetpotato [Ipomoea batatas (L.) Lam] were grown in monocultured or intercropped recirculating hydroponic systems in a greenhouse using the nutrient film technique (NFT). The objective was to determine whether growth and subsequent yield would be affected by intercropping. Treatments were sweetpotato monoculture (SP), peanut monoculture (PN), and sweetpotato and peanut grown in separate NFT channels but sharing a common nutrient solution (SP-PN). Greenhouse conditions ranged from 24 to 33 degrees C, 60% to 90% relative humidity (RH), and photosynthetic photon flux (PPF) of 200 to 1700 micromoles m-2 s-1. Sweetpotato cuttings (15 cm long) and 14-day-old seedlings of peanuts were planted into growth channels (0.15 x 0.15 x 1.2 m). Plants were spaced 25 cm apart within and 25 cm apart between growing channels. A modified half-Hoagland solution with a 1 N: 2.4 K ratio was used. Solution pH was maintained between 5.5 and 6.0 for treatments involving SP and 6.4 and 6.7 for PN. Electrical conductivity (EC) ranged between 1100 and 1200 microS cm-1. The number of storage roots per sweetpotato plant was similar for both SP and SP-PN. Storage root fresh and dry mass were 29% and 36% greater, respectively, for plants in the SP-PN treatment than for plants in the SP treatment. The percent dry mass of the storage roots, dry mass of fibrous and pencil roots, and the length-to-diameter ratio of storage roots were similar for SP and SP-PN sweetpotato plants. Likewise, foliage fresh and dry mass and harvest index were not significantly influenced by treatment. Total dry mass was 37% greater for PN than for SP-PN peanut plants, and pod dry mass was 82% higher. Mature and total seed dry mass and fibrous root dry mass were significantly greater for PN than for SP-PN plants. Harvest index (HI) was similar for both treatments. Root length tended to be lower for seedlings grown in the nutrient solution from the SP-PN treatment.

Non-NASA Center↗

NASA NTRS1989

The diageotropica mutant of tomato lacks high specific activity auxin binding sites

Tomato plants homozygous for the diageotropica (dgt) mutation exhibit morphological and physiological abnormalities which suggest that they are unable to respond to the plant growth hormone auxin (indole-3-acetic acid). The photoaffinity auxin analog [3H]5N3-IAA specifically labels a polypeptide doublet of 40 and 42 kilodaltons in membrane preparations from stems of the parental variety, VFN8, but not from stems of plants containing the dgt mutation. In roots of the mutant plants, however, labeling is indistinguishable from that in VFN8. These data suggest that the two polypeptides are part of a physiologically important auxin receptor system, which is altered in a tissue-specific manner in the mutant.

NASA Discipline Number 29-20↗

NASA NTRS2010

Mutualism in a Reduced Gravity Environment (MuRGE)

MuRGE (Mutualism in a Reduced Gravity Environment) is a NASA flight-research experiment to investigate the microgravity effects associated with cell-cell communication and beneficial microbe-host interactions using a plant-fungal model system. This investigation will use a clinostat, an instrument that slowly rotates the plants to negate the effects of gravitational pull on plant growth (gravitropism) and development, to simulate microgravity. I will be using the endophytic fungus Piriformospora indica (Pi) and the model plant species Arabidopsis thaliana (At). P. indica has been shown to colonize roots of various plant species, including A. thaliana, and to increase plant growth and resistance to stress. The fungus has the ability to grow from spores or in axenic cultures without the presence of a host. P. indica spores and P. indica extract will be used to inoculate Arabidopsis seeds germinated on a clinostat in order to determine if simulated microgravity affects the interaction between the fungus and its plant host.

Patel, Karishma K.↗

NASA NTRS2010

[Mutualism in a Reduced Gravity Environment (MuRGE)]

Patel, Karishma↗