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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Plant Defense Proteins: Recent Discoveries and Applications

Proteins play pivotal roles in safeguarding plants against numerous biotic and abiotic stresses. Understanding their biological functions and mechanisms of action is essential for advancing plant biology, agriculture, and biotechnology. This review considers the diversity and potential applications of plant defense proteins including pathogenesis-related (PR) proteins, chitinases, glucanases, protease inhibitors, lectins, and antimicrobial peptides. Recent advances, such as the omics technologies, have enabled the discovery of new plant defense proteins and regulatory networks that govern plant defense responses and unveiled numerous roles of plant defense proteins in stress perception, signal transduction, and immune priming. The molecular affinities and enzymatic activities of plant defense proteins are essential for their defense functions. Applications of plant defense proteins span agriculture, biotechnology, and medicine, including the development of resistant crop varieties, bio-based products, biopharmaceuticals, and functional foods. Future research directions include elucidating the structural bases of defense protein functions, exploring protein interactions with ligands and other proteins, and engineering defense proteins for enhanced efficacy. Overall, this review illuminates the significance of plant defense proteins against biotic stresses in plant biology and biotechnology, emphasizing their potential for sustainable agriculture and environmental management.

G-proteins↗
NASA NTRS2018

Using Remote Sensing to Assess of Growth and Distribution for Floating Invasive Plants and Growth Response Times to Altered Environments

Management of aquatic weeds in complex watersheds and river systems present many challenges to assessment, planning and implementation of management practices for aquatic invasive plants. The Delta Region Areawide Aquatic Weed Project (DRAAWP), a USDA (U. S. Dept. of Agriculture)-sponsored area-wide project, is working to enhance planning, decision-making and operational efficiency of invasive plant management in the California Sacramento-San Joaquin Delta. Satellite and airborne remote sensing are used to map area of plant coverage and estimate biomass density to aid operations and assess management impacts on plant communities. Modeling at local and watershed scales using the SWAT (Soil Water Assessment Tool) modeling tool provides insight into land-use effects on water quality. Environmental variability in the Delta occurs across a range of time scales from long-term climate and seasonal trends to short-term water flow mediated variations. Controlled environment growth studies have been conducted to quantify the growth response of invasive aquatic plants to water quality and other environmental factors. Response time for invasive species response are examined at time scales of weeks, day, and hours using a combination of study duration and growth assessment techniques to assess water quality, temperature (air and water), and light effects. These provide response parameters for plant growth models in response to environmental variation and interact with management and economic models associated with aquatic weed management. Plant growth models are to be informed by remote sensing and applied spatially across the Delta to balance location and type of aquatic plant, growth response to altered environments and phenology. Initial utilization of remote sensing tools developed for mapping of aquatic invasive plants improved operational efficiency in management practices. These assessment methods provide a comprehensive and quantitative view of aquatic invasive plant communities in the California Delta.

Floating↗
NASA NTRSDate not supplied

The Plant Water Management Experiments: Soil

A simple means of watering plants in the low-g environment aboard orbiting spacecraft is not obvious. Since the beginning of spaceflight, numerous approaches have been pursued to water plants that seek to maximize plant viability and system reliability, while minimizing crew time and system complexity. We are not there yet. The Plant Water Management (PWM) Soil experiments seek to apply recent advances in low-g capillary fluidics phenomena to the challenges faced by plant growth operations aboard spacecraft. The primary challenge is to establish earth-like flows minimizing low-g specific adaptations required of the plants. This is difficult due to the ever-present fluid physics challenges of poorly-wetting multiphase inertial-visco-capillary flows in geometrically complex conduits and containers. In this paper, we present recent flight results for the PWM Soil experiments where arcillite ‘soil reservoirs’ are arranged in a non-wetting host soil that serves as an O2-breathing wetting barrier. In this way, a largely terrestrial water-soil environment is mimicked where, as liquid is evapo-transpired through the growing plant foliage, the effective water table passively ‘falls’ reducing viscous lengths and increasing water uptake for the plant. We present data from 6 days of 24-7 experiments on the ISS testing 3 different plant root models. We also present and correlate a capillary flow model which captures the primary features of the flow. Our summary is valued for the assessment of current and future low-g plant watering systems employing soil media.

microgravity↗
NASA NTRS2002

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.

NASA Discipline Plant Biology↗
DOE OSTI2024

Plant-specific microbial diversity facilitates functional redundancy at the soil-root interface

Abstract Aims Plant-specific microbial diversity reflecting host-microbe coevolution was frequently shown at the structural level but less on the functional scale. We studied the microbiome of three compartments at the soil root interface (root endosphere, rhizosphere, bulk soil) of medicinal plants cultivated under organic management in Egypt. The study aimed to examine the impact of the rhizosphere on microbial community composition and diversity in desert agricultural soil, as well as to identify specific functions associated with the rhizosphere. Methods The microbiome community structure, diversity, and microbial functioning were evaluated through the utilization of 16S rRNA gene amplicon and shotgun metagenome sequencing. Results We found the typical rhizosphere effect and plant-species-specific enrichment of bacterial diversity. The annual plants Calendula officinalis and Matricaria chamomilla ( Asteraceae ) were more similar than the perennial Solanum distichum ( Solanaceae ). Altogether, plant species explained 50.5% of the variation in bacterial community structures in the rhizosphere. Our results indicate a stronger effect of the plant species in terms of modulating bacterial community structures in the rhizosphere than in root endosphere samples. The plant-driven rhizosphere effect could be linked to redundant plant beneficial functions in the microbiome, while enrichment of specific genes related to amino acid ion transport and metabolism, carbohydrate transport and metabolism, defense mechanisms, and secondary metabolites biosynthesis were more specific. Conclusions The study explores the microbiome continuum at the soil-root interface of medicinal plant species, revealing significant bacterial community structure shifts and plant specificity. The study provides insights into the essential microbiome components contributing to rhizosphere functionality.

Wicaksono, Wisnu Adi (ORCID:0000000215561981)↗
DOE OSTI2025

Functional team selection as a framework for local adaptation in plants and their belowground microbiomes

Abstract Multicellular organisms are hosts to diverse communities of smaller organisms known as microbiomes. Plants have distinctive microbiomes that can provide important functions related to nutrition, defense, and stress tolerance. Empirical studies provide convincing evidence that in some—but not all—circumstances, belowground microbiomes help plants adapt to their local environment. The purpose of this review is to develop functional team selection (FTS) as a framework to help predict the conditions necessary for root microbiomes to generate local adaptation for their plant hosts. FTS envisions plants and their microbiomes as complex adaptive systems, and plant adaptations as emergent properties of these systems. If plants have the capacity to recognize and cultivate beneficial microbes and suppress pathogens, then it is possible for plants to evolve the capacity to gain adaptations by curating their microbiome. In resource-limited and stressful environments, the emergent functions of complex microbial systems may contribute to positive feedback linked to plant vigor, and ultimately, local adaptation. The key factors in this process are: (i) selective force, (ii) host constitution, (iii) microbial diversity, and (iv) time. There is increasing interest in harnessing beneficial microbial interactions in agriculture and many microbial growth-promoting products are commercially available, but their use is controversial because a large proportion of these products fail to consistently enhance plant growth. The FTS framework may help direct the development of durable plant-microbiome systems that enhance crop production and diminish pathogens. It may also provide valuable insights for understanding and managing other kinds of host-microbe systems.

Environmental Sciences & Ecology↗
DOE OSTI2025

The Co-Firing of Pine Biomass and Waste Coal in 100 and 600 MW Power Plants: A Sustainable Approach to Reduce GHG Emissions

Climate change is a global issue that has gained much attention recently. Co-firing biomass with coal/waste coal reduces the electricity sector’s GHG emissions sustainably. This study uses commercial software to model waste coal and biomass co-firing in 100 MW and 600 MW power plants. The objective is to assess the effects of fluid types (subcritical and supercritical), plant capacities (100 MW and 600 MW), boiler types (pulverized coal and circulating fluidized bed boilers), biomass and waste coal co-firing ratios (0:100, 20:80, 40:60, 60:40, 80:20, and 100:0), and carbon capture and storage efficiencies (0%, 90%, 95%, and 97%) on performance parameters such as net plant efficiency, heat rate, net plant CO2 and SO2, and particulate matter emissions. The feedstocks selected for this investigation include anthracite waste coal and loblolly pine biomass. As the biomass fraction increases from 0% to 100%, co-fired power plants net efficiency increases by 3–8%. Supercritical plants had a 6% higher net plant efficiency than the subcritical plants. The study found that the biomass’s high heating value decreased the fuel flow rate and reduced plant CO2 emissions by 10–16%. With 100% biomass power plant feed and 90% carbon capture and storage efficiency, CO2 emissions drop by 83% and SO2 and PM emissions drop to zero.

Bhoi, Prakashbhai R. (ORCID:0000000333104888)↗
NASA NTRS1985

The Role of Gravity on the Reproduction of Arabidopsis Plants

The presence of gravity as a necessary environmental factor for higher plants to complete their life cycle was examined. Arabidopsis thalliana (L.) Heynh. Columbia strain plants were grown continuously for three generations in a simulated micro-g environment as induced by horizontal clinostats. Growth, development and reproduction were followed. The Arabidopsis plants were selected for three generations on clinostats because: (1) a short life cycle of around 35 days; (2) the cells of third generation plants would in theory be free of gravity imprint; and (3) a third generation plant would therefore more than likely grow and respond like a plant growing in a micro-g environment. It is found that gravity is not a required environmental factor for higher plants to complete their life cycle, at least as tested by a horizontal clinostat. Clinostatting does not prevent the completion of the plant life cycle. However, clinostatting does appear to slow down the reproductive process of Arabidopsis plants. Whether higher plants can continue to reproduce for many generations in a true micro-g environment of space can only be determined by long duration experiments in space.

Hoshizaki, T.↗
NASA NTRS1994

P-MASS and P-GBA: Two new hardware developments for growing plants in space

Plant growth, and especially plant performance experiments in microgravity are limited by the currently available plant growth facilities (low light levels, inadequate nutrient delivery and atmosphere conditioning systems, insufficient science instrumentation, infrequent flight opportunities). In addition, mission durations of 10 to 14 days aboard the NSTS Space Shuttle allow for only brief periods of microgravity exposure with respect to the life cycle of a plant. Based on seed germination experiments, using the Generic BioProcessing Apparatus hardware (GBA), two new payloads have been designed specifically for plant growth. These payloads provide new opportunities for plant gravitational and space biology research and emphasize the investigation of plant performance (photosynthesis, biomass accumulations) in microgravity. The Plant-Module for Autonomous Space Support (P-MASS) was designed to utilize microgravity exposure times in excess of 30 days on the first flight of the recoverable COMET satellite (Commercial Experiment Transporter). The Plant-Generic Bioprocessing Apparatus (P-GBA), is designed for the National Space Transportation System (NSTS) Space Shuttle middeck and the SPACEHAB environment. The P-GBA is an evolution from the GBA hardware and P-MASS (plant chamber and instrumentation). The available light levels of both payloads more than double currently available capabilities.

Hoehn, Alexander↗
NASA NTRS2006

An Axenic Plant Culture System for Optimal Growth in Long-Term Studies: Design and Maintenance

The symbiotic co-evolution of plants and microbes leads to difficulties in understanding which of the two components is responsible for a given environmental response. Plant-microbe studies greatly benefit from the ability to grow plants in axenic (sterile) culture. Several studies have used axenic plant culture systems, but experimental procedures are often poorly documented, the plant growth environment is not optimal, and axenic conditions are not rigorously verified. We developed a unique axenic system using inert components that promotes plant health and can be kept sterile for at least 70 d. Crested wheatgrass (Agropyron cristatum cv. DII) plants were grown in sand within flow-through glass columns that were positively pressured with filtered air. Plant health was optimized by regulating temperature, light level, CO2 concentration, humidity, and nutrients. The design incorporates several novel aspects, such as pretreatment of the sand with Fe, graduated sand layers to optimize the air-water balance of the root zone, and modification of a laminar flow hood to serve as a plant growth chamber. Adaptations of several sterile techniques were necessary for maintenance of axenic conditions. Axenic conditions were verified by plating and staining leachates as well as rhizoplane stain. This system was designed to study nutrient and water stress effects on root exudates, but is useful for assessing a broad range of plant-microbe-environment interactions. Based on total organic C analysis, 74% of exudates was recovered in the leachate, 6% was recovered in the bulk sand, and 17% was recovered in the rhizosphere sand. Carbon in the leachate after 70 d reached 255 micro-g/d. Fumaric, malic, malonic, oxalic, and succinic acids were measured as components of the root exudates.

Henry, Amelia↗
NASA NTRS2011

The Effect of Plant Cultivar, Growth Media, Harvest Method and Post Harvest Treatment on the Microbiology of Edible Crops

Systems for the growth of crops in closed environments are being developed and tested for potential use in space applications to provide a source of fresh food. Plant growth conditions, growth media composition and harvest methods can have an effect on the microbial population of the plant, and therefore should be considered along with the optimization of plant growth and harvest yields to ensure a safe and palatable food crop. This work examines the effect of plant cultivar, growth media, and harvest method on plant microbial populations. Twelve varieties of leafy greens and herbs were grown on a mixture of Fafard #2 and Arcillite in the pillow root containment system currently being considered for the VEGGIE plant growth unit developed by Orbitec. In addition, ,Sierra and Outredgeous lettuce varieties were grown in three different mixtures (Fafard #2, Ardllite, and Perlite/Vermiculite). The plants were analyzed for microbial density. Two harvest methods, "cut and come again" (CACA) and terminal harvest were also compared. In one set ofexpe'riments red leaf lettuce and mizuna were grown in pots in a Biomass Production System for education. Plants were harvested every two weeks by either method. Another set of experiments was performed using the rooting pillows to grow 5 varieties of leafy greens and cut harvesting at different intervals. Radishes were harvested and replanted at two-week intervals. Results indicate up to a 3 IOglO difference in microbial counts between some varieties of plants. Rooting medium resulted in an approximately 2 IOglO lower count in the lettuce grown in arscillite then those grown in the other mixtures. Harvest method and frequency had less impact on microbial counts only showing a significant increase in one variety of plant. Post harvest methods to decrease the bacterial counts on edible crops were investigated in these and other experiments. The effectiveness of PRO-SAN and UV-C radiation is compared.

Hummerick, Mary P.↗
NASA NTRS2019

Does Seed Sanitization Affect the Plant Rhizosphere Microbiome and Its Ability to Compete with the Human Associated Pathogen, E. coli on Salad Crops?

Cultivation of crops in controlled environmental agricultural systems may limit microbial colonization and reduce diversity of the microbial communities. Practices like seed and growth medium sanitization may further impact microbial communities in the mature plant and the plant’s capacity to limit the growth of pathogens through competition. As humans expand their travels to space, understanding plant growth, health, and development in closed environments will be critical to the success of producing a safe, supplemental food source for astronauts. To determine the persistence of a potential human pathogen in plant growth and development, sanitized and unsanitized seeds from, mizuna (Brassica rapa var japonica) and red romaine lettuce (Lactuca sativa cultivar ‘Outredgeous’), were inoculated with Escherichia coli, ATCC 21445, germinated under simulated International Space Station (ISS) environmental conditions and harvested every 7 days until maturity. The persistence of E. coli in the rhizosphere was determined by plating on selective media, real time PCR (Polymerase Chain Reaction) and community sequencing of the rhizosphere communities. E. coli was detected in the crops’ roots and leaves for several weeks post germination. At day 28, plants from sanitized seeds had significantly higher counts of E. coli on the roots than those from unsanitized seeds. E. coli was also detected on a few uninoculated plants indicating airborne cross contamination among plants in the same growth chamber and suggesting an influence of the natural microbiome on human pathogen survival and persistence in leafy greens. Sequencing analysis revealed variations in composition and diversity between the communities. Understanding the microbial community of the rhizospheric microbiome is only the first step in determining the relationships between plants. Additional studies to include genotypic and phenotypic variations in the plants should be considered to determine if the natural microbes in the rhizosphere may contribute to the health and therefore, safety of the edible plants.

Khodadad, Christina L. M.↗
NASA NTRSDate not supplied

The Plant Water Management Experiments: Hydroponics 3 & 4

As humans consider longer-duration missions in space, NASA has identified production of fresh vegetables aboard spacecraft as beneficial for crew nutrition, mental wellbeing, and enabling bioregenerative life support (i.e., air, water, and waste processing). Current low-g plant growth techniques have successfully grown a variety of leafy and flowering plants. However, unique microgravity fluidics challenges to maintain plant moisture levels persist which hamper overall system reliability. The Plant Water Management (PWM) experiments seek to demonstrate low-cost, low-mass, reusable plant growth systems that leverage recent advances in low-g capillary fluidics phenomena to provide routine, largely passive, water delivery to plants. This paper presents findings from a series of PWM-Hydroponics 3 & 4 experiments, which were collected during three ISS flight operations that occurred in March, May, and July of 2021. Open hydroponic capillary channel flows with synthetic evapo-transpiring plant models were used. Tests demonstrated flow stability for single and parallel channel flow configurations across a range of flow rates, plant types, and plant arrangements. Technology demonstrations of both passive aeration and bubble phase separation are reported. We provide details of the data reduction and archive. Insights from the successful flight demonstrations provide a foundation from which follow-on PWM-Hydroponics 5 & 6 experiments on ISS, potentially incorporate living plants, are being considered. Xx Summary of positives and negatives..

Marc B. Wasserman↗
NASA NTRSDate not supplied

A Simulated High CO 2 Spaceflight Environment Increases Plant Preference for Ammonium as a Nitrogen Source.

Future long-duration missions will require a sustainable supply of food to support human crews. The spaceflight cabin environment often contains very high concentrations of CO 2 due to release of CO 2 by astronauts that is not completely scrubbed from the cabin, and it is therefore crucial to understand plant responses to elevated CO 2 (eCO 2 ) environments. Much focus has been given to changes in plant photosynthetic and performance parameters in response to eCO 2 , but the effects of eCO 2 on nitrogen (N) uptake are poorly understood. Shoot nitrate reduction may be reduced at eCO 2 , likely due to less reductant available for nitrate reduction because of reduced photorespiration and increased carbon fixation 1. Relative growth rate can be reduced at eCO 2 when N is provided only as nitrate and can be unaffected when N is supplied as ammonium 1. However, N uptake in response to eCO 2 has, to our knowledge, not yet been studied. An increased ‘preference’ for plants to take up N as ammonium at eCO 2 could have important implications for growth in the space environment, where N is currently only supplied as nitrate. In this study, novel stable isotope approaches were used in conjunction with hydroponics and isotope ratio mass spectrometry to determine the effect of eCO 2 on N preference for ammonium or nitrate in spring barley and lettuce when both N forms are provided equally. Several varieties of spring barley displayed increased ammonium preference at eCO 2 (720 ppm) compared to ambient CO 2 (410 ppm), though this was not true for all varieties 2. In most cases, increases in ammonium preference were driven by increases in ammonium uptake at eCO 2 and not decreases in nitrate uptake. Current research is assessing whether similar responses are observed in the candidate space crop lettuce, at levels of CO 2 like those observed on ISS (3000 ppm), and these results will also be presented. This work will enable the development of optimized nutrient regimes for candidate crops in space environments and the selection of crop varieties adapted to eCO 2 environments. Plants adapted to ammonium nutrition may play a role in future plant-based bioregenerative life support systems with higher ammonium concentrations due to waste recycling 3. Moreover, this research will further our understanding of plant responses to the eCO 2 environment brought about by climate change, allowing the development of future-proof crops that will help to maintain food security. References: 1. Bloom (2015). The increasing importance of distinguishing among plant nitrogen sources. Current Opinion in Plant Biology 25, 10-16. 2. Fountain (2023). Understanding interactions of barley (Hordeum vulgare) with soil nitrogen cycling activity and links to plant nitrogen preference. Ph.D. Thesis, The University of Sheffield. 3. Schiefloe et al. (2023). From urine to food and oxygen: effects of high and low NH4+:NO3- ratio on lettuce cultivated in a gas-tight hydroponic facility. Frontiers in Plant Science 14:1229476.

nitrogen↗
DOE OSTI2025

Next generation Arctic vegetation maps: Aboveground plant biomass and woody dominance mapped at 30 m resolution across the tundra biome

The Arctic is warming faster than anywhere else on Earth, placing tundra ecosystems at the forefront of global climate change. Plant biomass is a fundamental ecosystem attribute that is sensitive to changes in climate, closely tied to ecological function, and crucial for constraining ecosystem carbon dynamics. However, the amount, functional composition, and distribution of plant biomass are only coarsely quantified across the Arctic. Therefore, we developed the first moderate resolution (30 m) maps of live aboveground plant biomass (g m −2 ) and woody plant dominance (%) for the Arctic tundra biome, including the mountainous Oro Arctic. We modeled biomass for the year 2020 using a new synthesis dataset of field biomass harvest measurements, Landsat satellite seasonal synthetic composites, ancillary geospatial data, and machine learning models. Additionally, we quantified pixel-wise uncertainty in biomass predictions using Monte Carlo simulations and validated the models using a robust, spatially blocked and nested cross-validation procedure. Observed plant and woody plant biomass values ranged from 0 to ∼6000 g m −2 (mean ≈ 350 g m −2 ), while predicted values ranged from 0 to ∼4000 g m −2 (mean ≈ 275 g m −2 ), resulting in model validation root-mean-squared-error (RMSE) ≈ 400 g m −2 and R 2 ≈ 0.6. Our maps not only capture large-scale patterns of plant biomass and woody plant dominance across the Arctic that are linked to climatic variation (e.g., thawing degree days), but also illustrate how fine-scale patterns are shaped by local surface hydrology, topography, and past disturbance. By providing data on plant biomass across Arctic tundra ecosystems at the highest resolution to date, our maps can significantly advance research and inform decision-making on topics ranging from Arctic vegetation monitoring and wildlife conservation to carbon accounting and land surface modeling.

Climate change↗
DOE OSTI2025

Reduce Revenue Versus Increase Expenditure: Fires and Plant Invasion Drive Soil Carbon Loss With Different Mechanisms in a Mediterranean Shrubland

Fires and plant invasions threaten Mediterranean ecosystems substantially, particularly in the context of changing climate. Our study utilized a data-model integration approach to assess the response of soil organic carbon (SOC) to fires and plant invasion under three Shared Socio-Economic Pathway (SSP) scenarios (SSP1-26, SSP2-45, and SSP5-85). We parameterized the CLM-Microbe model and then investigated the individual and interactive impacts of fires and plant invasion on soil C by comparing factorial simulations of initialization (fire/no wildfire in 2021), fire module on/off, and with and without plant invasion during 2023–2100 in a Mediterranean ecosystem. The simulations indicated a marked C loss due to the 2021 wildfire, projected fires, and plant invasion across all future climate scenarios. Specifically, the 2021 wildfire, projected fires, and plant invasion reduced the SOC (0–30 cm) by 0.12, 0.26, and 0.15 kg C m −2 under SSP1-26, 0.12, 0.30, and 0.12 kg C m −2 under SSP2-45, and 0.12, 0.24, and 0.13 kg C m −2 under SSP5-85, respectively. However, fires and plant invasion decreased SOC through distinct mechanisms. The effects of the 2021 wildfire occurred due to its negative legacy on soil microbial community and, thus, litter accumulation, suppressing the formation of soil carbon via decomposition. Influences of projected fires happen via consuming fuel and suppressing carbon input to soils. In contrast, the impacts of plant invasions were due to enhanced microbial respiration, leading to C loss. In conclusion, these findings emphasize the need for tailored C sequestration strategies considering the disparate effects of fires and plant invasions in the Mediterranean climate.

microbe↗
NASA NTRS1991

Calcium localization in lettuce leaves with and without tipburn: comparison of controlled-environment and field-grown plants

An electron microprobe was used to determine tissue concentrations of Ca across 20-mm-long leaves of 'Green Lakes' crisphead lettuce (Lactuca sativa L.) with and without tipburn injury. Concentrations within the fifth and 14th leaves, counted from the cotyledons, from plants grown under controlled-environment conditions were compared to concentrations within similar leaves obtained from plants grown under field conditions. Only the 14th leaf from plants grown under controlled-environment conditions developed tipburn. Injured areas on these leaves had Ca concentrations as low as 0.2 to 0.3 mg g-1 dry weight. Uninjured areas of tipburned leaves contained from 0.4 to 0.5 mg g-1 dry weight. Concentrations across the uninjured 14th leaf from field-grown plants averaged 1.0 mg g-1 dry weight. Amounts across the uninjured fifth leaves from both environments averaged 1.6 mg g-1 dry weight. In contrast, Mg concentrations were higher in injured leaves than in uninjured leaves and thus were negatively correlated with Ca concentrations. Magnesium concentrations averaged 4.7 mg g-1 dry weight in injured leaves compared with 3.4 mg g-1 dry weight in uninjured leaves from both environments. Magnesium concentrations were uniform across the leaf. Potassium concentrations were highest at the leaf apex and decreased toward the base and also decreased from the midrib to the margin. Potassium averaged 51 mg g-1 dry weight in injured and uninjured leaves from both environments. No significant differences in K concentration were present between injured and uninjured leaves. This study documented that deficient concentrations of Ca were present in areas of leaf tissue developing tipburn symptoms and that concentrations were significantly higher in similar areas of other leaves that had no symptoms. This study also documented that Ca concentrations were significantly lower in enclosed leaves that exhibited tipburn symptoms than in exposed leaves that did not exhibit tipburn. Also, the amounts of Ca in plants that developed tipburn in controlled environments were lower than in plants of the same cultivar that did not develop tipburn in field plantings. The reduced levels of Ca in plants grown in controlled environments were associated with faster development rates compared with field-grown plants.

Non-NASA Center↗
NASA NTRS1989

Effects of root-zone acidity on utilization of nitrate and ammonium in tobacco plants

Tobacco (Nicotiana tabacum L., cv. 'Coker 319') plants were grown for 28 days in flowing nutrient culture containing either 1.0 mM NO3- or 1.0 mM NH4+ as the nitrogen source in a complete nutrient solution. Acidities of the solutions were controlled at pH 6.0 or 4.0 for each nitrogen source. Plants were sampled at intervals of 6 to 8 days for determination of dry matter and nitrogen accumulation. Specific rates of NO3- or NH4+ uptake (rate of uptake per unit root mass) were calculated from these data. Net photosynthetic rates per unit leaf area were measured on attached leaves by infrared gas analysis. When NO3- [correction of NO-] was the sole nitrogen source, root growth and nitrogen uptake rate were unaffected by pH of the solution, and photosynthetic activity of leaves and accumulation of dry matter and nitrogen in the whole plant were similar. When NH4+ was the nitrogen source, photosynthetic rate of leaves and accumulation of dry matter and nitrogen in the whole plant were not statistically different from NO3(-) -fed plants when acidity of the solution was controlled at pH 6.0. When acidity for NH4(+) -fed plants was increased to pH 4.0, however, specific rate of NH4+ uptake decreased by about 50% within the first 6 days of treatment. The effect of acidity on root function was associated with a decreased rate of accumulation of nitrogen in shoots that was accompanied by a rapid cessation of leaf development between days 6 and 13. The decline in leaf growth rate of NH4(+) -fed plants at pH 4.0 was followed by reductions in photosynthetic rate per unit leaf area. These responses of NH4(+) -fed plants to increased root-zone acidity are characteristic of the sequence of responses that occur during onset of nitrogen stress.

NASA Discipline Life Support Systems↗