Effect of Hypobaria on Genetic Expression of Ethylene

Effect of Hypobaria on Genetic Expression of Ethylene, Gas Exchange, and Crop Productivity Que Ngo Department of Horticulture Texas A&M University May 29, 2003

INTRODUCTION • Importance of NASA ALS System – Plant Growth and Maintenance – Control of Environmental Factors

Why Plants? • Source of nutrition FOOD! • Psychology of eating • Supplement gases to other systems

Why Use Low Pressure? • Avoid high expenses of shipping equipment and materials into space • Less leakage in a low pressure system • Less N 2 required to supplement CO 2 and O 2 (active gases)

Problems with Ethylene • Earlier systems were leaky and did not detect ethylene • Ethylene accumulation on the International Space Station (50 ppb) and the Russian Mir • Newer, “tighter” systems revealed ethylene accumulation

Advantages of Using Low Pressure • Reduced ethylene levels under low pressure • Studies examining hypoxia and hypobaria (He, 2003, unpublished data; Paul and Ferl, 2002, in press)

Ethylene Biosynthesis (Bleecker and Kende, 2000)

Triple Response of Arabidopsis Ø Elongation of hypocotyl and root is inhibited Ø Radial swelling of hypocotyl Ø Exaggeration of apical hook curvature (Solano and Ecker, 1998)

Mutants of Arabidopsis • Ethylene-insensitive mutants – Examples: etr 1, ein 2 • Constitutive response mutants – Examples: eto, ctr 1

RATIONALE FOR PROPOSED RESEARCH • Problems with sealed environments in space • Arabidopsis thaliana as a model plant system • Previous low pressure studies

Figure 1. TAMU Generation II Low Pressure Plant Growth System. (Spanarkel and Drew, 2002)

Figure 2. Schematic View of TAMU Generation III Low Pressure Plant Growth System. (Davies et al. , 2003)

Figure 3. TAMU Generation III LPPG.

PROPOSED RESEARCH OBJECTIVES 1) To characterize plant gas exchange and plant growth and development under hypobaria 2) To use molecular biology techniques to look at genetic expression of key ethylene biosynthetic enzymes, ACC synthase and ACC oxidase

HYPOTHESES 1) 2) 3) 4) Normal plant growth and development Comparable gas exchange levels Decreased ethylene levels *Enhanced genetic expression of ACS and ACO in ethylene sensitive mutants and little or no expression in ethylene insensitive mutants* (initially, examining plant morphology responses)

PROPOSED EXPERIMENTAL METHODS • Low pressure plant growth system – Monitor and manipulate constituent gases • Plant growth conditions – Arabidopsis grown on calcined clay under ambient (101 k. Pa) and sub-ambient conditions (as low as 30 k. Pa) • Determination of plant growth and morphology

PROPOSED EXPERIMENTAL METHODS • Gas exchange measurements – Gas chromatograph measures input/output of constituent gases • Ethylene measurements – Sample analysis via injection into digital gas chromatograph with a photo detector

PROPOSED EXPERIMENTAL METHODS • Northern analysis – Identify and characterize ACS and ACO activity in Arabidopsis mutants subjected to ambient and sub-ambient conditions – Examine all members of the ACS and ACO multigene family in Arabidopsis (Switch to lettuce or wheat in the event that Arabidopsis is unresponsive to hypobaria)

SIGNIFICANCE AND APPLICATION • Optimal conditions for plant growth in low pressure environments • Use of Arabidopsis as model system to develop NASA baseline crops

REFERENCES Bleecker AB, Kende H (2000) Ethylene: a gaseous signal molecule in plants. Annual Review of Cell Developmental Biology 16: 1 -18 Davies FT, Lacey RE, He, C-J (2003) Plant growth at sub-ambient atmospheric pressures with control of the partial pressure of constituent gases. Proposal submitted to NASA He C-J, Davies FT, Lacey RE, Drew MC, Brown DL (2003) Effect of hypobaric conditions on gas exchange, ethylene evolution and growth of lettuce and wheat. J Plant Physiol (in press)

REFERENCES Musgrave ME, Gerth WA, Scheld HW, Strain BR (1988) Growth and mitochondrial respiration of mungbeans (Phaseolus aureus Roxb. ) germinated at low pressure. Plant Physiology 86: 19 -22 Paul A-L, Ferl RJ (2002) Molecular aspects of stress-gene regulation during space flight. Journal of Plant Growth Regulators (in press) Solano R, Ecker JR (1998) Ethylene gas: perception, signaling and response. Current Opinion in Plant Biology 1: 393 -398

REFERENCES Spanarkel R, Drew MC (2002) Germination and growth of lettuce (Lactuca sativa) at low atmospheric pressure. Physiologia Plantarum 116(4): 468 -477