University of Wisconsin
On the nature of plant chromosome transition state: gravity, plant vigor and chromosome aberration (an hypothesis)
Chromosome aberrations were commonly observed in seeds carried into space and later germinated on earth. These aberrations were generally scored in root meristem cells, microspores, and consisted of chromosome fragments and recombinations. Significant chromosome abnormalitites, including fragmented chromosomes and chromosomal bridges, were found in roots of plant seedlings in space. Simultaneously, the space-flown seeds, under appropriate conditions, can genetically alter plant growth and productivity into a vigorous state. Neither the reasons for increases in chromosomal disturbance nor the mechanism for plant vigor observed from the space-flown seeds are known at present time. Generally, it is believed that cosmic radiation is one possibility, since ionizing radiation is known to cause such disturbances; but results obtained from space experiments with the specific aim of answering this question provided no evidence to support the notion that radiation effect is a major factor responsible for chromosome aberration from space flown seeds. Nevertheless, it has been suggested that weightlessness or space flight may affect chromosomal structure not directly but by increasing the likelihood of damage by altering sensitivity to other mutagenic factor(s). Thus, apparently, chromosome aberration induced by space or the vigor of plants derived from space treated seeds cannot simply be interpreted based on the widely accepted genetic concepts. In this note, we wish to submit and put forward an hypothesis that explains the possibility of an unknown chromosome state that can give rise to chromosome aberrations and also can genetically transform plants into a vigorous state in weightless conditions. The hypothesis is described with the following statements:
Let us first consider that the chromosome structure can exist in two different states, symbolized as Chre ↔ Chrs and are assumed to be reversible. Chre: Chromosome structure on earth. Chrs: Chromosome structure in space. The transition of chromosome structure in space will vary according to the altitude during the seeds travel in space. Therefore, the symbol of chromosome structure in space can be written as Chrs(ro→rn)(Ts). where r is the altitude of space and varies from 0 to n length of altitude; and Ts is Transition State. For example, currently most of the experimental plant seeds are traveling in space about 250 to 450 miles above the earth. The equation of the transition of chromosome structure from the Chre state to the Chrs state under the influence of the gravity factor while traveling in space can be written as:
Chre ↔ Chrs(r0→rn)(Ts) (1)
Chrs(r0→rn)(Ts)/ Chre ≈ P
P: is a Transition Constant.
The equation (1) demonstrates that gravity factor governs the equilibrium between two states of the chromosome structure. Therefore, P: (the transition constant) is variable as a function of the gravity factor. According to the present hypothesis, there are two possibilities for the appearance of chromosome aberration from space treated seeds. The first possibility is that the chromosome aberration appeared directly from the transition state of the chromosome structure itself (Chrs(r0→rn)(Ts)) without the effect of other physical factors such as cosmic rays or HZE particles. It could also be that the vigor of plant growth and development of space treated seeds comes from the transition state of the chromosome structure. The second possibility for the chromosome aberration is the result of the combining effect of other physical factors and weightlessness. This kind of alteration of chromosome structure as the result of influence of space conditions can be written as:
Chre ↔ Chrs(r0→rn)(Ts) → Chrs(r0→rn)(Cry)
Chrs(r0→rn)(cry) is designated as the cryptic state of Chrs(r0→rn)(Ts); and it is an irreversible transition process. All negative effects observed from the growth and development of space treated seeds were the result of the phenotype of chromosome aberration derived from the cryptic state of the chromosome. A complete and detailed report of this hypothesis will be published elsewhere. Due to the current advancement of the isolating technique of corn chromosomes, such as the B chromosome, the present hypothesis is therefore testable. We will attempt to demonstrate the reality of the presence of the transition states of chromosome structure. This theory is established in memory of the late Dr. Oliver E. Nelson.