Bioluminescent enzyme assay for the indication of plant stress in enclosed life support systems.

The application of bioluminescent sensors for monitoring key metabolites and enzymes that are indicators of stress in plants is demonstrated. The sensitivity of bioluminescent assay for NAD(P)H and NAD(P)(+) was about 0.5 and 1 nmol, respectively. The levels of NAD(P)H and NAD(P)(+) in radish (Raphanus sativus) root extracts from controls and from stress-induced conditions were compared. To induce environmental stress, the plants were grown in enclosed environmental chambers with low pressure (9 or 32 kPa), high humidity (>80%) and low oxygen partial pressure (down to 3.3-6.5 kPa). The concentrations of NAD(P)(+) and NAD(P)H in plants varied under stress conditions. Decreasing both total pressure from 101.5 to 32 or 9 kPa and partial pressure of oxygen increased the ratio of NAD(P)(+) /NAD(P)H from 0.2 to 4 or 6, respectively. The increase in this ratio suggests that plants are undergoing stress in these hypobaric environments. The developed bioluminescent assay for quantification of pyridine nucleotides in plant tissues is rapid, low-cost and easily performed.

Effects of trimming on dairy cattle hoof weight bearing surfaces and pressure distributions

Claw lameness can be associated to biomechanical factors caused by unbalanced pressure distribution under the hooves when cows are confined in modern dairy operations with hard concrete flooring. In the present study, an original claw subdivision4 was slightly modified to differentiate between the anterior (typical sole lesion spot) and posterior portions of the medial sole, and to emphasize the maximum pressures applied only on the area of contact without including the total area within these regions during midstance. The results, obtained showed significance (p < 0.044) for the interaction among Group, Leg and region (G*L*R). It was observed that the rear portion of the claws (heels) on the hind limb of untrimmed cows, are more stressed than the heel region on trimmed cows (23 % versus 16.72% of total pressure applied on the claw for untrimmed and trimmed respectively). The typical sole lesion spot pressures were increased slightly on trimmed cows as compared to untrimmed (20.20% versus 15.9%). The front feet presented differences in pressure concentration on the lateral sole between both groups (29% versus 23.25% for untrimmed versus trimmed respectively). It was concluded that, although the differences were small (5%) changes in pressure concentration, untrimmed cows stress more the sole lateral as compared to trimmed on the front feet, and on the rear feet, they stress more the heel region whereas trimmed cows tend to have a slight better balance among regions. Conversely, when cows are trimmed, the typical sole lesion spot concentrates more pressure than the heel itself (20.20% versus 16.72% respectively) and may favor the occurrence of sole ulcers.

Laminite (manqueira) pode ser associado a fatores mecânicos, causados por falta de balanceamento na distribuição de pressão na sola dos cascos de vacas confinadas em instalações modernas, que utilizam pisos de concreto. No presente estudo, a subdivisão original dos cascos de vacas leiteiras foi modificada para diferenciar-se entre a porção anterior (local típico de lesão) e posterior da sola medial dos cascos, e para enfatizar as pressões máximas aplicadas somente na área de contato não levando em consideração a área total da sola. Os resultados mostraram significância estatística (p < 0.044) para a interação entre Grupo, Pata e Região (G*L*R). Foi observado que a porção posterior (calcanhar) das patas traseiras de vacas não-casqueadas foram estressadas mais intensamente que de vacas casqueadas (23 % versus 16.72% da pressão total aplicada nas patas em não-casqueadas e casqueadas respectivamente). As pressões na região do local típico de lesão aumentaram em animais casqueados comparado com não-casqueados (20.20% versus 15.9%). As patas da frente apresentaram diferenças na concentração de pressão da sola lateral (29% versus 23.25% em não-casqueadas versus casqueadas, respectivamente). Foi concluído que, apesar das diferenças serem pequenas (5%) mudanças nas concentrações de pressão, vacas não-casqueadas estressaram mais a porção da sola lateral, comparado a vacas casqueadas nas patas da frente, enquanto nas traseiras elas estressam mais a região do calcanhar, e as vacas casqueadas tendem a ter uma distribuição melhor de pressão entre as regiões. No entanto, quando as vacas são casqueads, a região típica de lesão tende a concentrar mais pressão do que o próprio calcanhar (20.20% versus 16.72% respectivamente) podendo favorecer a incidência de úlcera de sola.

Water cycle and its management for plant habitats at reduced pressures.

Experimental and mathematical models were developed for describing and testing temperature and humidity parameters for plant production in bioregenerative life support systems. A factor was included for analyzing systems operating at low (10-101.3 kPa) pressure to reduce gas leakage and structural mass (e.g., inflatable greenhouses for space application). The expected close relationship between temperature and relative humidity was observed, along with the importance of heat exchanger coil temperature and air circulation rate. The presence of plants in closed habitats results in increased water flux through the system. Changes in pressure affect gas diffusion rates and surface boundary layers, and change convective transfer capabilities and water evaporation rates. A consistent observation from studies with plants at reduced pressures is increased evapotranspiration rates, even at constant vapor pressure deficits. This suggests that plant water status is a critical factor for managing low-pressure production systems. The approach suggested should help space mission planners design artificial environments in closed habitats.

Water cycles in closed ecological systems: effects of atmospheric pressure.

In bioregenerative life support systems that use plants to generate food and oxygen, the largest mass flux between the plants and their surrounding environment will be water. This water cycle is a consequence of the continuous change of state (evaporation-condensation) from liquid to gas through the process of transpiration and the need to transfer heat (cool) and dehumidify the plant growth chamber. Evapotranspiration rates for full plant canopies can range from ~1 to 10 L m-2 d-1 (~1 to 10 mm m-2 d-1), with the rates depending primarily on the vapor pressure deficit (VPD) between the leaves and the air inside the plant growth chamber. VPD in turn is dependent on the air temperature, leaf temperature, and current value of relative humidity (RH). Concepts for developing closed plant growth systems, such as greenhouses for Mars, have been discussed for many years and the feasibility of such systems will depend on the overall system costs and reliability. One approach for reducing system costs would be to reduce the operating pressure within the greenhouse to reduce structural mass and gas leakage. But managing plant growth environments at low pressures (e.g., controlling humidity and heat exchange) may be difficult, and the effects of low-pressure environments on plant growth and system water cycling need further study. We present experimental evidence to show that water saturation pressures in air under isothermal conditions are only slightly affected by total pressure, but the overall water flux from evaporating surfaces can increase as pressure decreases. Mathematical models describing these observations are presented, along with discussion of the importance for considering "water cycles" in closed bioregenerative life support systems.

Plant adaptation to low atmospheric pressures: potential molecular responses.

There is an increasing realization that it may be impossible to attain Earth normal atmospheric pressures in orbital, lunar, or Martian greenhouses, simply because the construction materials do not exist to meet the extraordinary constraints imposed by balancing high engineering requirements against high lift costs. This equation essentially dictates that NASA have in place the capability to grow plants at reduced atmospheric pressure. Yet current understanding of plant growth at low pressures is limited to just a few experiments and relatively rudimentary assessments of plant vigor and growth. The tools now exist, however, to make rapid progress toward understanding the fundamental nature of plant responses and adaptations to low pressures, and to develop strategies for mitigating detrimental effects by engineering the growth conditions or by engineering the plants themselves. The genomes of rice and the model plant Arabidopsis thaliana have recently been sequenced in their entirety, and public sector and commercial DNA chips are becoming available such that thousands of genes can be assayed at once. A fundamental understanding of plant responses and adaptation to low pressures can now be approached and translated into procedures and engineering considerations to enhance plant growth at low atmospheric pressures. In anticipation of such studies, we present here the background arguments supporting these contentions, as well as informed speculation about the kinds of molecular physiological responses that might be expected of plants in low-pressure environments.