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N.C. Yorio and G.W. Stutte

An experiment was conducted in the Biomass Production Chamber (BPC) at Kennedy Space Center to examine the effects of using continuously reused nutrient solution in an NFT system to support potato growth in batch and continuous planting scenarios. Tuberization was hastened and plant growth reduced on plants grown in the aged nutrient solution. We have previously reported that the effect is removed when the aged nutrient solution is filtered through activated charcoal. In order to investigate this apparent plant growth regulator response, an in vitro bioassay has been developed that allows for repeatable, small scale, and rapid testing of the tuber-inducing response. The bioassay is a liquid culture system that employs 600-mL Berzelius beakers capped with modified Sun transparent tissue culture bags, a light shield around the root zone, and a polyurethane foam support, which holds a micropropagated potato plantlet. With this bioassay, we have observed the same plant stunting and tuber initiation effects that were previously seen with the aged nutrient solution. The bioassay appears to be sensitive to environmental factors (PPF, photoperiod, and temperature) that influence tuberization. In addition, partially purified preparations of the apparent growth regulators have elicited the tuberization response. Currently, efforts are underway to examine the role of the microbial community associated with the BPC nutrient delivery system on the tuberization response.

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G.W. Stutte and N.C. Yorio

The relationship between whole canopy and single leaf measurements of gas exchange has not been well documented. Two experiments were conducted in the Biomass Production Chamber at Kennedy Space Center (20-m2 growing area) to compare whole canopy versus single leaf net carbon assimilation rate (Anet) measurement of a stand of tomato (Lycopersicon esculentum Mill. cv. Reimann Philipp) and soybean [Glycine max (L.) Merr. cv. Hoyt]. Both crops were grown under a 12/12 hour photoperiod under HPS lamps at PPF of 800 (mol·m–2·s–1, at 26/22°C (light/dark), and constant 65% RH for 90 days. CO2 concentration was controlled to 1200 (mol·mol–1 during the light cycle. Midday measurements of Anet of single leaves were obtained weekly from upper canopy leaves using a portable photosynthesis system. Whole canopy measurements of Anet were calculated daily from CO2 addition data obtained at 5-minute intervals by the BPC monitoring and control system. Single leaf rates exceeded whole canopy rates prior to full canopy coverage then averaged 0.63 of whole canopy for both species during the period of full canopy coverage. Results suggest that reliable estimates of canopy gas exchange can be obtained from single leaf measurements under relatively constant environment conditions.

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C.L. Mackowiak, R.M. Wheeler, and N.C. Yorio

Leaf stomatal conductance was monitored with a steady-state porometer throughout growth and development of soybean and potato plants grown at 500, 1000, 5000, and 10,000 (potato only) μmol mol-1 carbon dioxide (CO2). All plants were grown hydroponically with a 12-hr photoperiod and 300 μmol m-2 s-1 PPF. As expected, conductance at 1000 was < 500 μmol mol-1 for both species, but conductance at 5000 and 10,000 μmol mol-1 was ≥ that at 500 μmol mol-1. Subsequent short-term (24-hr) tests with potato and wheat plants grown at 1000 μmol mol-1 showed that raising CO2 to approx. 10,000 μmol mol-1 or lowering CO2 to 400 μmol mol-1 increased conductance compared to 1000 μmol mol-1 for potato, while only lowering CO2 to 400 μmol mol-1 increased conductance for wheat. Furthermore, raising the CO2 to 10,000 μmol mol-1 increased dark-period conductance in comparison to 1000 μmol mol-1 for potato, while dark-period conductance for wheat leaves was low regardless of the CO2 concentration. Results suggest that very high CO2 levels (e.g. 5000 to 10,000 μmol mol-1) may substantially increase water use of certain crops.

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N.C. Yorio, R.M. Wheeler, and R.C. Weigel

Growth measurements of potato (Solanum tuberosum L.) cvs. Norland (NL), Denali (DN), and Kennebec (KN) were taken from 21-day-old plantlets grown in vitro. Studies were conducted in a growth chamber, with nodal explants grown in culture tubes with loose-fitted Magenta 2-way caps containing Murashige and Skoog salts with either 0, 1, 2 or 3% sucrose. The cultures received either 100 or 300 μmol m-2 s-1 photosynthetic photon flux (PPF), and the growth chamber was maintained at either 400 or 4000 μmol mol-1 CO2. All cvs. showed significant increases in growth on 0% sucrose media at 4000 μmol mol-1 CO2, indicating an autotrophic response. At 400 μmol mol-1 CO2, all cvs. showed an increase in total plantlet dry weight (DW) with increasing sucrose under both PPF levels. Within any sucrose treatment, the highest total DW for all cvs. resulted from 300 μmol m-2 s-1 PPF and 4000 μmol mol-1 CO2. At 4000 μmol mol-1 CO2, shoot DW declined with sucrose above 2% for DN and sucrose above 1% for NL at both PPF levels, suggesting that high sucrose levels may hinder growth when CO2 enrichment is used.

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N.C. Yorio, M. Sanwo, and C.S. Brown

Light-emitting diodes (LEDs) are a potential light source for growing plants in space flight systems because of their superior safety and reliability, small mass and volume, electrical efficiency, and longevity. To determine the influence of narrow-spectrum LEDs on plant growth and metabolism, wheat (Triticum aestivum L. `Superdwarf') plants were grown under red LEDs (peak emission 660 nm) and compared to plants grown under daylight fluorescent, red LEDs + 1% blue fluorescent light (BL), and red LEDs + 10% BL. Plants were taller, had longer flag leaves, and delayed seed development when grown under red LEDs or red LEDs + 1% BL compared to those grown with 10% BL or under daylight fluorescent. Viable seeds (290% germination) were produced in all plants regardless of the light treatment. Total dry matter (DM), head DM, and seed DM were similar in the plants grown under the four light regimes, and there were no differences in the starch content of the seeds. Starch levels were 4-times greater and sucrose levels were 2.5-times greater in leaves of plants grown under the red LEDs compared to daylight fluorescent. Daylight fluorescent leaves showed a 1.8-fold increase in sucrose phosphate synthase (SPS) activity, a regulatory enzyme of sucrose synthesis. These results indicate that wheat can be grown successfully under red LEDs, but there are differences in carbohydrate concentration and metabolism in photosynthetic tissue.

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G.W. Stutte, N.C. Yorio, and R.M. Wheeler

Photoperiod treatments were imposed on potato (Solanum tuberosum L. cv. Norland) grown in the Biomass Production Chamber (BPC) at Kennedy Space Center under HPS lamps (670 μmol m-2s-1 PPF) at 1200 μmol mol-1 CO2. Stand A decreased with dark cycle length, which correlated with the change in leaf starch concentration during the dark cycle, but not absolute starch concentration. A series of growth chamber experiments were performed to characterize the effect of photoperiod and PPF on CO2 assimilation and starch mobilization in single leaves. Plants grown on a 12/12 photoperiod at either low (300 μmol m-2s-1) or high (600 μmol m-2s-1) PPF were subjected to short-term photoperiod treatments of 8/16, 16/8, and 24/0 and diurnal CO2 assimilation rates, CO2 response curves, and leaf starch content were determined. CO2 compensation point was not affected by either photoperiod or PPF. However, Amax (when normalized for PPF) decreased with increasing photoperiod. Anet correlated with the changes in specific leaf weight and starch content during the dark cycle.

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N.C. Yorio, C.L. Mackowiak, R.M. Wheeler, and J.C. Sager

Potato (Solanum tuberosum L. cvs. Norland and Denali) plants were grown under high-pressure sodium (HPS), metal halide (MH), and blue-light-enhanced SON-Agro high-pressure sodium (HPS-S) lamps to study the effects of lamp spectral quality on vegetative growth. All plants were initiated from in vitro nodal cultures and grown hydroponically for 35 days at 300 μmol·m–2·s–1 photosynthetic photon flux (PPF) with a 12-hour light/12-hour dark photoperiod and matching 20C/16C thermoperiod. `Denali' main stems and internodes were significantly longer under HPS compared to MH, while under HPS-S, lengths were intermediate relative to those under other lamp types, but not significantly different. `Norland' plants showed no significant differences in stem and internode length among lamp types. Total dry weight of `Denali' plants was unaffected by lamp type, but `Norland' plants grown with HPS had significantly higher dry weight than those under either HPS-S or MH. Spectroradiometer measurements from the various lamps verified the manufacturer's claims of a 30% increase in ultraviolet-blue (350 to 450 nm) output from the HPS-S relative to standard HPS lamps. However, the data from `Denali' suggest that at 300 μmol·m–2·s–1 total PPF, the increased blue from HPS-S lamps is still insufficient to consistently maintain short stem growth typical of blue-rich irradiance environments.

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N.C. Yorio, C.L. Mackowiak, R.M. Wheeler, and G.W. Stutte

The effects of elevated CO2 on stomatal density and index were investigated for five crop species currently being studied for NASA's Advanced Life Support program. Lettuce (cv. Waldmann's Green) and radish (cv. Giant White Globe) were grown at 400, 1000, 5000, or 10,000 μmol·mol–1 CO2, tomato (cvs. Red Robin and Reimann Philip 75/59) were grown at 400, 1200, 5000, or 10,000 μmol·mol–1 CO2, and wheat (cv. Yecora Rojo) and potato (cv. Denali) were grown at 400, 1000, or 10,000 μmol·mol–1 CO2 within controlled-environment growth chambers using nutrient film technique hydroponics. Leaf impressions were made by applying clear silicone-based RTV coating to the adaxial and abaxial leaf surfaces of three canopy leaves of each crop at each CO2 treatment. Impressions were examined using a light microscope, whereby the number of stomatal complexes and epidermal cells were counted to calculate stomatal density and stomatal index. Results indicate that stomatal density increased for lettuce and radish at 10,000 μmol·mol–1 CO2, whereas tomato density was highest at 1200 μmol·mol–1 CO2. Potato had the lowest density at 1000 μmol·mol–1 CO2, and there was no effect of CO2 on density for wheat. Stomatal index correlated with density for lettuce and tomato; however, stomatal index for radish, potato, and wheat was not influenced by CO2. This suggests that there may be a species-specific CO2 response to epidermal cell size that influences stomatal density and stomatal index.

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C.L. Mackowiak, R.M. Wheeler, G.W. Stutte, N.C. Yorio, and L.M. Ruffe

Peanut (Arachis hypogaea L.) plants were grown hydroponically, using continuously recirculating nutrient solution. Two culture tray designs were tested; one tray design used only nutrient solution, while the other used a sphagnum-filled pod development compartment just beneath the cover and above the nutrient solution. Both trays were fitted with slotted covers to allow developing gynophores to reach the root zone. Peanut seed yields averaged 350 g·m-2 dry mass, regardless of tray design, suggesting that substrate is not required for hydroponic peanut production.

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N.C. Yorio, C.L. Mackowiak, B.V. Peterson, and R.M. Wheeler

In vitro growth of white potato (Solanum tuberosum L.) cv. Norland was investigated comparing two types of culture vessel enclosures. Nodal cuttings were aseptically transferred to 25 × 150 mm glass culture vessels containing a solidified medium consisting of Murashige and Skoog salts, 1% sucrose, and pH adjusted to 5.8. The vessels were capped with loose-fitted (1 cm gap between the top of the vessel and the top of the cap) Magenta 2-way caps or Bellco Kap-uts with calculated air changes hr-1 of 2.25 and 1.43, respectively. Instantaneous PPF attenuations of 15% for Magenta caps and 23% for Bellco caps were also measured. The cultures were maintained for 28 d in an environmental growth chamber under Daylight fluorescent lamps with a 16 hr light/8 hr dark photoperiod, 200 μmol m-2s-1 PPF maintained for each cap type, constant 23 C, 65% relative humidity, and CO2 enrichment of 1000 μmol mol-1 external to the culture vessels. Results showed that increased plantlet height, fresh weight, and dry weight was obtained for plantlets cultured with Magenta caps. The differences in growth and internal CO2 concentration of the vessels correlated well with the difference in air exchange rates, suggesting that increased air exchange of culture vessels resulted in increased mixotrophic plantlet growth.