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  • Author or Editor: L.H. Levine x
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Although plants are envisioned to play a central role in life support systems for future long-duration space travel, plant growth in space has been problematic due to horticultural problems of nutrient delivery and gas resupply posed by the weightless environment. Iterative improvement in hardware designed for growth of plants on orbital platforms now provides confidence that plants can perform well in microgravity, enabling investigation of their nutritional characteristics. Plants of B. rapa (cv. Astroplants) were grown in the Biomass Production System on the International Space Station. Flowers were hand-pollinated and seeds were produced prior to harvest at 39 days after planting. The material was frozen or fixed while on orbit and subsequently analyzed in our laboratories. Gross measures of growth, leaf chlorophyll, starch and soluble carbohydrates confirmed comparable performance by the plants in spaceflight and ground control treatments. Analysis of glucosinolate production in the plant stems indicated that 3-butenylglucosinolate concentration was on average 75% greater in flight samples than in ground control samples. Similarly, the biochemical make-up of immature seeds produced during spaceflight and fixed or frozen while in orbit was significantly different from the ground controls. The immature seeds from the spaceflight treatment had higher concentrations of chlorophyll, starch, and soluble carbohydrates than the ground controls. Seed protein was significantly lower in the spaceflight material. Microscopy of immature seeds fixed in flight showed embryos to be at a range of developmental stages, while the ground control embryos had all reached the premature stage of development. Storage reserve deposition was more advanced in the ground control seeds. The spaceflight environment thus influences B. rapa metabolite production in ways that may affect flavor and nutritional quality of potential space produce.

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Accumulation of glycinebetaine occurs in Chenopodiaceae members and is thought to assist in osmotic adjustment and protect cytoplasm from sodium toxicity. Red beet has an ability to tolerate high tissue sodium levels, which may result in increased glycinebetaine production. To test this hypothesis, two cultivars of red beet ['Scarlet Supreme' (SS) and `Ruby Queen' (RQ)] were grown under nonsaline (4.75 mM Na) and saline (54.75 mM Na) conditions in a recirculating hydroponic system for 42 days at elevated CO2 (1200 μmol•mol-1) in a growth chamber. Leaf glycinebetaine level, relative water content, and osmotic potential were measured at weekly intervals. Leaf glycinebetaine levels increased with plant age and reached a maximum of 67 μmol•g-1 dw under nonsaline and 101 μmol•g-1 dry weight (dw) under saline conditions at 42 days in SS; in RQ, the glycinebetaine levels reached a maximum of 91 μmol•g-1 dw under nonsaline and 121 μmol•g-1 dw under saline conditions by 26 days. The mean glycinebetaine levels were increased over two-thirds under saline conditions in both the cultivars. RQ accumulated significantly higher (37% more under nonsaline, and 46% more under salinity) glycinebetaine than SS. The turgid leaf osmotic potential of RQ was consistently higher than SS under nonsaline (2.23 MPa in RQ vs. 1.82 MPa in SS) and saline (2.48 MPa in RQ vs. 2.02 MPa in SS) conditions. The results indicate that higher glycinebetaine levels in the leaf could result in better osmotic adjustment, and glycinebetaine accumulation in red beet can vary among cultivars and is strongly affected by external salinity.

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