Mitotic Disturbances in the Primary Root

Krikorian et al. (1996 and citations therein) had the opportunity of studying the mitotic activity and the chromosome disturbances in roots of several species. These experiments concerned roots of seedlings (oat, mung bean, and sunflower) grown in space. In the three species that were studied, the mitotic activity was substantially reduced after completing their first cell cycle after landing on Earth. In oat and sunflower roots, there were chromosomal aberrations ranging from aneuploidy7, breakage and bridge formation (Figure 6-19), but no chromosomal aberration was detected in Mung bean. The karyological disturbances were not questionable, but their cause had to be determined. Evaluation of the available facts indicated that indirect effects played a major role in these karyological disturbances and that plants grown in space were subjected to various stresses.

It must be pointed out that the culture conditions in space were not always satisfactory since the cabin atmosphere could contain gas, as ethylene for example, which could affect plant growth (Kiss et al. 1998). To some extent, this problem can be solved by using a 1 -g centrifuge in space that can permit to discriminate between the effects of gravity and those due to other space factors, such as cosmic radiation or cabin atmosphere. It should be also necessary to chemically fix the samples in space and not after their retrieval on Earth. Only a few experiments were done in these conditions and using seeds that were less sensitive than seedlings to all kind of stresses both before and during launch. Unfortunately, when a 1-g centrifuge was available, the period of growth was most often very short.

Figure 6-19. Cell divisions in sunflower root tips exposed to microgravity. A. Field showing various stages of division: interphase, prophase, meta-phase, anaphase are visible.

B. Field showing normal nucleus activity (arrows) and a chromosome bridge at telophase. C. Field with dislocated Feulgen staining nuclear components. The arrows show different damage to nuclei. Krikorian and O'Connor (1984), with permission.

1 A chromosome problem that happens when one or more whole chromosomes either are missing or are present in more than the typical number of copies.

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