PRINCIPAL INVESTIGATOR(S ): Samuel P. Johnson, and T. W. Tibbitts 



EXPERIMENT TITLE/NUMBER : The Liminal Angle of Plagiogeotropic Organ Under 



Weightlessness, P-1017 



PROGRAM/MISSION : Biosatellite II 



CLASSIFICATION : Plant - Pepper plant ( Capsicum annuum ) 



DISCIPLINE(S) : Behavioral science, Cell biology 



OBJECTIVES : To determine if a weightless environment would produce results in 

 plants similar to those noted in response to rotation on a horizontal 

 clinostat, i.e., the liminal angle will be decreased, accompanied by a 

 differential mobilization of carbohydrates and amino acids. 



PROTOCOL : Four 35 day old plants were flown and photographed at ten-minute 

 intervals during orbit. Five auxiliary 25 day old plants were placed inside 

 the unit for carbohydrate, amino acid and nitrogen analyses. Two control 

 groups of plants were subjected to horizonal and vertical rotation on the 

 clinostat and one control group served as a radiation mockup. The samples 

 prepared for chemical analyses were composed of: (1) leaves from large or 

 prime plants, (2) leaves from small or auxiliary plants, (3) stems from small 

 plants, and (4) growing tips from small plants. Several vibration tests were 

 conducted to determine the effect of the flight launch vibration profile. The 

 plants were also subjected to acoustic levels that simulated the launch and 

 recovery flight environments. 



EQUIPMENT : Flight package with a camera positioned in the center of four 

 plants which, through a three-mirror optical system, photographed the four 

 plants from the side and top. Illumination was provided by 15-watt incandes- 

 cent lamps, producing 200 foot-candles of light for 5 sec. every 10 min. The 

 unit weighed 12 pounds. 



RESULTS : A reduction in the liminal angle of the petiole with the stem was 

 found and was similar to that produced in the laboratory using the horizontal 

 clinostat. The carbohydrates were similar in concentration in the control and 

 orbital plants, but the amino acid change was greater in the orbital plants. 



CONCLUSIONS : Carbohydrates and, to some extent, amino acids play a direct 

 role in the response of plants to geoinduction. The carbohydrates presumably 

 provided energy for the accelerated growth and/or elongation of the cells 

 along the convex curvature of the plagiogeotropic organ, thereby resulting in 

 a decrease in the liminal angle. 



PUBLICATIONS : 9, 133, 303 



146 



