Structure of potato tubers formed during spaceflight

Potato (Solanum tuberosum L. cv. Norland) explants, consistingof a leaf, axillary bud, and small stem segment, were used asa model system to study the influence of spaceflight on theformation of sessile tubers from axillary buds. The explantswere flown on the space shuttle Columbia (STS-73, 20 Octoberto 5 November 1995) in the ASTROCULTURE^TM flight package, whichprovided a controlled environment for plant growth. Light andscanning electron microscopy were used to compare the preciselyordered tissues of tubers formed on Earth with those formedduring spaceflight. The structure of tubers produced duringspaceflight was similar to that of tubers produced in a controlexperiment. The size and shape of tubers, the geometry of tubertissues, and the distribution of starch grains and proteinaceouscrystals were comparable In tubers formed in both environments.The shape, surface texture, and size range of starch grainsfrom both environments were similar, but a greater percentageof smaller starch grains formed in spaceflight than on Earth.Since explant leaves must be of given developmental age beforetubers form, instructions regarding the regular shape and orderedtissue geometry of tubers may have been provided in the presenceof gravity. Regardless of when the signalling occurred, gravitywas not required to produce a tuber of typical structure. Key words: Spaceflight, development, potato tuber, microgravity     

Structure of potato tubers formed during spaceflight

Potato (Solanum tuberosum L. cv. Norland) explants, consisting of a leaf, axillary bud, and small stem segment, were used as a model system to study the influence of spaceflight on the formation of sessile tubers from axillary buds. The explants were flown on the space shuttle Columbia (STS-73, 20 October to 5 November 1995) in the ASTROCULTURE (TM) flight package, which provided a controlled environment for plant growth. Light and scanning electron microscopy were used to compare the precisely ordered tissues of tubers formed on Earth with those formed during spaceflight. The structure of tubers produced during spaceflight was similar to that of tubers produced in a control experiment. The size and shape of tubers, the geometry of tuber tissues, and the distribution of starch grains and proteinaceous crystals were comparable in tubers formed in both environments. The shape, surface texture, and size range of starch grains from both environments were similar, but a greater percentage of smaller starch grains formed in spaceflight than on Earth. Since explant leaves must be of given developmental age before tubers form, instructions regarding the regular shape and ordered tissue geometry of tubers may have been provided in the presence of gravity. Regardless of when the signalling occurred, gravity was not required to produce a tuber of typical structure.     

Leaf temperatures under controlled environmental conditions

A wind tunnel and an external microwave energy source formed the basis of an experimental technique to investigate many complex functional relationships between climatic parameters and leaf temperatures. The results of preliminary experimental plant-environment interactions are compared with published theoretical results obtained by solving the energy balance equation for a single leaf.     

Redistribution of bodily fluids under conditions of microgravity and in microgravity models

This review is focused on the redistribution of blood and other bodily fluids along the body axis in the cranial direction under conditions of microgravity or during simulation of the physiological effects of microgravity. This redistribution of bodily fluids in the direction of the thorax or head results in respective physiological responses and induces a whole cascade of secondary adaptation mechanisms. Changes in central venous pressure, heart cavity volume, kidney functioning, and hormonal volume regulation lead to adaptive modifications in bodily fluid sectors. Modification of the hemodynamic in the splanchnic vascular system influences the organs of the abdominal cavity. Pharmacological correction accelerates the adaptation of the human body to unusual living conditions.     

Bacterial biofilm formation under microgravity conditions

Although biofilm formation is widely documented on Earth, it has not been demonstrated in the absence of gravity. To explore this possibility, Pseudomonas aeruginosa, suspended in sterile buffer, was flown in a commercial payload on space shuttle flight STS-95. During earth orbit, biofilm formation was induced by exposing the bacteria to sterile media through a 0.2-microm (pore size) polycarbonate membrane. Examination of these membranes by confocal microscopy revealed biofilms to be present and that these biofilms could persist in spite of vigorous agitation. These results represent the first report of biofilm formation under microgravity conditions.     

Automorphogenesis of maize roots under simulated microgravity conditions

Plant seedlings show exaggerated growth responses on a three-dimensional clinostat. Such an automorphogenesis appears to be one of major factors which govern the life cycle of higher plants under a microgravity environment. On the three-dimensional clinostat, maize roots exhibited curvatures in three different portions; 1) the basal region just protruding from the coleorhiza, 2) the region between the mature and the elongation zone, and 3) the elongation zone, several mm from the tip. Even non-clinostatted control roots showed some degree of curvature. The curvature occurred at random without any dorsiventrality. There was no difference in the osmotic concentration of the cell sap between the convex and the concave halves of any region. However, the convex, rapidly expanding side exhibited a higher extensibility of the cell wall in some regions, which appears to be a cause of the curvature. In order to understand the role of gravity in regulation of plant growth and development, we should clarify a series of events by which an automorphogenesis is induced under simulated microgravity conditions.     

Development of potato minitubers in microgravity

Stem segments of aseptically grown potato (Solanum tuberosum L. cv. Zarevo) were cultivated for 4 weeks under laboratory conditions and were then grown for 8 d on board the "Mir" orbital space station. Timing was such that minitubers initiated and developed during the 8 d on the "Mir". Under space flight and stationary conditions, spherical minitubers were formed with no statistically significant differences in either the frequency of tuber formation or tuber size. These observations are the first to document the formation of vegetative reproductive organs and of well developed amylogenic storage tissue during the microgravity conditions of orbital space flight. In these minitubers, a majority of the starch was stored in parenchyma, with numerous amyloplasts per cell. In space flight tissue, however, grain size of starch was decreased and lamellae within the amyloplasts was locally enlarged. Furthermore, mitochondria of these tissues were characterized by increased matrix density and well developed cristae.     

Escherichia coli biofilms formed under low-shear modeled microgravity in a ground-based system

Bacterial biofilms cause chronic diseases that are difficult to control. Since biofilm formation in space is well documented and planktonic cells become more resistant and virulent under modeled microgravity, it is important to determine the effect of this gravity condition on biofilms. Inclusion of glass microcarrier beads of appropriate dimensions and density with medium and inoculum, in vessels specially designed to permit ground-based investigations into aspects of low-shear modeled microgravity (LSMMG), facilitated these studies. Mathematical modeling of microcarrier behavior based on experimental conditions demonstrated that they satisfied the criteria for LSMMG conditions. Experimental observations confirmed that the microcarrier trajectory in the LSMMG vessel concurred with the predicted model. At 24 h, the LSMMG Escherichia coli biofilms were thicker than their normal-gravity counterparts and exhibited increased resistance to the general stressors salt and ethanol and to two antibiotics (penicillin and chloramphenicol). Biofilms of a mutant of E. coli, deficient in sigma(s), were impaired in developing LSMMG-conferred resistance to the general stressors but not to the antibiotics, indicating two separate pathways of LSMMG-conferred resistance.     

Repair of cellular radiation damage in space under microgravity conditions

The influence of microgravity on the repair of x-ray-induced DNA double-strand breaks was studied in the temperature-conditional repair mutant rad54–3 of diploid yeast Saccharomyces cerevisiae. Cells were exposed on the ground and kept at a low temperature until microgravity conditions were achieved. In orbit, they were incubated at the permissive temperature to allow repair. Before re-entry they were again cooled down and kept at a low temperature until final analysis. The experiment, which was flown on the shuttle Atlantis on flight STS-76 (SMM-03), showed that repair of pre-formed DNA double-strand breaks in yeast is not impaired by microgravity. Received: 1 September 1998 / Accepted in revised form: 23 March 1999     

Engineering ketocarotenoid biosynthesis in potato tubers

Consumption of astaxanthin is increasingly associated with a range of health benefits. Attempts to engineer ketocarotenoid biosynthesis in plants have been successful although there are no reports of nutritionally significant levels of astaxanthin in plant storage organs. Thus, in this study, ketocarotenoid biosynthesis was engineered in potato tubers. Both Solanum tuberosum and Solanum phureja transgenic lines were produced that expressed an algal bkt1 gene, encoding a beta-ketolase, and accumulated ketocarotenoids. Two major ketocarotenoids were detected, ketolutein and astaxanthin. The level of unesterified astaxanthin reached ca. 14 microg g(-1) DW in some bkt1 expressing lines of S. phureja but was much lower in the S. tuberosum background. Co-transformation of S. tuberosum with crtB, encoding phytoene synthase, and the bkt1 gene was achieved in order to determine whether this would enhance the levels of S. tuberosum ketocarotenoid.     

Selection of housekeeping genes for qRT-PCR analysis in potato tubers under cold stress

Quantitative real-time polymerase chain reaction (qRT-PCR) is currently the most sensitive method used for quantitative gene expression studies. However, minimal variation in the amount of material and presence of inhibitors affecting enzyme efficiency can lead to significant quantification errors. Accurate data normalization is vital using reference genes as internal controls. Many so-called housekeeping genes or reference genes with assumed stable expression can exhibit either up- or downregulation depending on the developmental stage or other environmental conditions. We have evaluated six reference genes (actin, APRT, 18S rRNA, ef1α, β-tubulin and ribosomal protein L2) for qRT-PCR profiling experiments in potato tuber tissues of five varieties during cold storage at different temperatures and treatment periods. Genes were ranked according to their expression stability by BestKeeper, geNorm and NormFinder software tools in the same order. This means that any of them can be used for this purpose. The results indicated that ef1α and APRT were the most stably expressed genes in the potato tuber tissues under different cold storage regimes. We therefore recommend use of this pair of genes as internal controls for gene expression studies under the described conditions.     

Selection of individual tubers in potato breeding

Summary Out of 720 field-grown potato first year seedlings plants with best tuber apearance and large and medium size tubers with best shape were respectively selected. The tuber progeny of each group was evaluated in field experiments. It was demonstrated that the selection of individual tubers was very effective in the elimination of clones with irregular tuber shape and deep eyes. The tuber progeny of selected tubers was not inferior to the tuber progeny of selected plants. Possible applications of the results to practical potato breeding are discussed.     

Energy metabolism pathways in rat muscle under conditions of simulated microgravity

Evidence from rats flown in space suggests that there is a decrease in the ability of the soleus muscle to oxidize long chain fatty acids during space flight. The observation suggests that a shift in the pathways involved in muscle fuel utilization in the absence of load on the muscle has occurred. It is also possible that the reduction is part of a general down-sizing of metabolic capacity since energy needs of inactive muscle are necessarily less. The rodent hind limb suspension model has proved to be a useful ground based model for studying the musculo-skeletal systems changes that occur with space flight. Microarray technology permits the screening of a large number of the enzymes of the relevant pathways thereby permitting a distinction to be made between a shift fuel utilization pattern or a general decrease in metabolic activity. The soleus muscle was isolated from 5 control and 5 hindlimb suspended rats (21 days) and the Affymetrix system for assessing gene expression used to determine the impact of hindlimb unloading on fuel pathways within the muscle of each animal. RESULTS: Suspended rats failed to gain weight at the same rate as the controls (337 +/- 5 g vs 318 +/- 6 g, p < 0.05) and muscle mass from the soleus was reduced (135 +/- 3 mg vs 48 +/- 4 mg, p < 0.05). There was a consistent decrease (p < 0.05) in gene expression of proteins involved in fatty acid oxidation in the suspended group whereas glycolytic activity was increased (p < 0.05). Gene expressions of individual key regulatory enzymes reflected these changes. Carnitine palmitoyltransferase I and II were decreased (p < 0.05) whereas expression of hexokinase, phosphofructokinase and pyruvate kinase were increased (p < 0.05). CONCLUSION: Disuse atrophy is associated with a change in mRNA levels of enzymes involved in fuel metabolism indicative of a shift in substrate utilization away from fat towards glucose.