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Sheetal Rao, Scott Finlayson, Chuanjiu He, Ronald Lacey, Raymond Wheeler, and Fred T. Davies

The NASA Advanced Life Support (ALS) System for space habitation will likely operate under reduced atmospheric pressure (hypobaria). There are engineering, safety, and plant growth advantages in growing crops under low pressure. In closed production environments, such as ALS, excessive plant-generated ethylene may negatively impact plant growth. Growth of lettuce (Lactuca sativa) in the Low Pressure Plant Growth (LPPG) system was enhanced under low pressure (25kPa), due in part to decreased ethylene production. Under reduced pO2, ethylene production decreased under low as well as ambient conditions (He et al., 2003). During hypobaria, the expression of genes encoding ethylene biosynthesis enzymes, namely ACC synthase (ACS) and ACC oxidase (ACO), is not known. The primary objective of this research was to characterize the expression of ACS and ACO genes in response to hypobaria. Three-week-old Arabidopsis was used to determine the effects of hypobaria (25 kPa) and reduced O2 (12 kPa pO2) at the molecular level. Candidate gene expression was tested using quantitative real-time PCR at different times after treatment. Under low pressure, ACO1 expression is induced in the initial 12 hours of treatment, gradually decreasing with increased exposure. At 12 kPa pO2, ACO1 was induced under ambient conditions, suggesting that plants under low pressure may be more tolerant to hypoxic stress. The mechanism for enhanced growth of lettuce under hypobaric conditions will be studied further by analysis of the ACS and ACO gene families, and stress-responsive genes, namely late-embryogenesis abundant (LEA) proteins and dehydrins.

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James D. Spiers, Fred T. Davies, Scott A. Finlayson, Chuanjiu He, Kevin M. Heinz, and Terri W. Starman

This research focused on the effects of nitrogen fertilization on jasmonic acid accumulation and total phenolic concentrations in gerbera. The phytohormone jasmonic acid is known to regulate many plant responses, including inducible defenses against insect herbivory. Phenolics are constitutive secondary metabolites that have been shown to negatively affect insect feeding. Gerbera jamesonii `Festival Salmon Rose' plants were grown in a growth chamber and subjected to either low fertilization (only supplied with initial fertilizer charge present in professional growing media) or high fertilization (recommended rate = 200 mg·L-1 N). Plants were fertilized with 200 mL of a 15N–7P–14K fertilizer at 0 or 200 mg·L-1 N at each watering (as needed). Treatments consisted of ±mechanical wounding with a hemostat to one physiologically mature leaf and the subsequent harvest of that leaf at specified time intervals for jasmonic acid quantification. Total phenolics were measured in physiologically mature and young leaves harvested 0 and 10 hours after ±mechanical wounding. Low-fertility plants had reduced aboveground dry mass, were deficient in nitrogen and phosphorus, and had about a 10× higher concentration of total phenolics when compared to high fertility plants. In low-fertility plants, young leaves had greater concentrations of phenolics compared to physiologically mature leaves. There were no differences in total phenolics due to wounding. The effect of nitrogen fertilization on jasmonic acid accumulation will also be discussed.