Developmental Analysis of Seeds Grown on Mir

Objectives

This experiment addressed the problem of seed-to-seed cycling in microgravity, using the species Brassica rapa, a mustard plant with a very short life cycle. It is the third in a series of plant growth studies developed within the Shuttle-Mir Science project that were conducted in the Svet greenhouse on Mir (also refered to as the "Greenhouse 3" experiment). The goal of the "Developmental Analysis of Seeds Grown on Mir" experiment was to understand how the effects of microgravity influenced plant growth by:

1. Analyzing space flight effects on plant growth and development processes throughout the life cycle through inflight observations, video recording, gas exchange measurements, and postflight analysis of plant material harvested and fixed, dried or frozen on orbit.

2. Collecting seed produced on orbit and growing this seed to produce new plants, comparing the production of seeds by plants from space-produced seeds to that of plants from ground-produced seeds.

3. Analyzing floral initiation and early reproductive development during space flight, comparing plants from seeds produced on the ground, in space, or by plants grown from seeds produced in space.

4. Evaluating the extent of space flight influence on cell shape in plant organs, and assessing the implications on overall metabolism.

5. Determining the extent of space flight-mediated changes in cell structure, organization and physiology.

6. Analyzing the root medium in the Svet Root Modules.

7. Analyzing the microbial organisms present on plant tissue and in the root medium.

Shuttle-Mir Missions
NASA-5

Approach
The experiment involved three consecutive plantings of Brassica, beginning with seeds launched from the ground on the Shuttle (STS-84). These were the so-called "Earth seeds", or E1 seeds. Seeds produced in space from this first planting on Mir were collected, dried, and used in the second growth cycle. This second set of seeds was called "Space 1", or S1 seeds. Seeds generated in space from the second planting on Mir, the S2 seeds, were collected and planted in the third planting in space, along with Earth seeds and S1 seeds. Surplus seeds produced by the plants during the first two growing cycles were used to supply dried material for postflight analysis, as well as seeds for subsequent planting in Svet. Additional developmental and physiological information was obtained from fixed plant samples obtained during the growing cycles, from dried plants taken at final harvest stages, and from plants freshly harvested and frozen at the end of the third planting.

Results
The Greenhouse 3 experiment was the first to successfully investigate growth of plants over multiple generations in space, and the results showed that plants were able to grow and reproduce in microgravity. This investigation provided a wealth of information and material for future study. The experiment design allowed researchers to depart from the past practice of comparing space flight plants only to ground-based controls, since reference plants (produced from seed that had been brought from Earth) were grown alongside the second generation space plants for comparison purposes.

The results of analyses completed to date indicate no significant differences between space flight and ground control material in first generation plants. However, second generation space plants were significantly smaller than second generation ground control plants. Ethylene gas on the Mir station was found to be a primary determinant of plant size. Data also indicated that the quality of seeds produced on orbit is lower than that of seeds produced in the ground control, thus leading to the smaller second generation plant size. The weight per seed of seeds produced on orbit was significantly lower than that of seeds produced in the postflight ground control. This diminished seed quality is believed to be caused by the different ripening kinetics inside the seed pod in microgravity. Further investigations with the dried seeds as well as the fixed and frozen plant material may provide additional information about the nature of reduced growth by the plants from first generation space seeds.

Earth Benefits
By giving space biologists a look at developmental events beyond the seedling stage, this experiment was an important contribution not only to gravitational biology, but also to the study of space life support systems. Data from this experiment on gas exchange, dry matter production and seed production provided essential information on providing a plant-based food supply for humans on long-duration space flights.

Publications
Musgrave, M. E., A. Kuang, Y. Xiao, G. E. Hingham, L. G. Briarty, M. A. Levinski, V. N. Sychev and I. G. Podolski. 1998. Repeated seed-to-seed experiments with Brassica rapa on the Mir Space Station. Gravitational and Space Biology Bulletin 12: 56.

Bingham, G. E., S. B. Jones, D. Or, I. Podolsky, V. Sytchev. 1998. Water management lessons from plant full life cycle experiments on Mir. Gravitational and Space Biology Bulletin 12: 56.

Principal Investigators
Mary E. Musgrave, Ph.D.
Louisiana State University

Dr. Rita Levinskih
Institute of Biomedical Problems

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Page last updated: 07/16/1999

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