Irradiation studies on the karyology of charophyta. I. X-rays and gamma-rays.

Abstract

The present study deals with the effects of X-rays, gamma-rays on the karyology of some selected taxa of charophyta, antheridia having being exposed to radiations. Species of Nitella viz., N. opaca (n=6), N. flagelliformis (n=9) and N. acuminata (n=18) and four of Chara viz., C. fibrosa (n=14), C. globularis var. virgata (n=14), C. setosa (n=28) and C. zeylanica var. diaphora f. oerstidiana (n=42) were employed as experimental materials in various irradiation experiments. X-ray and gamma-ray doses ranged from 100 to 2000 rads. The materials in each case, after exposure to required amount of radiation, were transferred to fresh culture medium and were examined cytologically at varying periods of time. In all experiments controls were maintained.The qualitative changes that were observed in all the taxa with both types of radiations to a greater or lesser extent were: stickiness and of clumping of chromosomes at metaphase and anaphase, chromosome erosion, chromatid gaps, chromosome and chromatid breaks at metaphase and anaphase, anaphase bridges, laggards, unequal grouping of chromosomes, unequal separation, ring chromosomes and rarely, formation of micronuclei.The quantitative estimates of affected cells, based on percentages of those showing chromosome breakage at metaphase and anaphase and cells showing anaphase bridges, showed that levels of radiosensitivity of different taxa differed. The chromosomes of N. opaca having the lowest chromosome number (n=6) and of N. flagelliformis (n=9) with longest chromosomes seem to be more sensitive in comparison to other taxa, while C. zeylanica, with highest chromosome number in the series (n=42) as also with shortest chromosomes, was found to be more radioresistant of all the taxa investigated. However, charophyte taxa in the present study were shown to be more sensitive to radiations as compared with many other algal taxa belonging to other groups investigated earlier. The irradiation studies lend further support to the now more widely held view that Charophyta constitute a very distinctive group amongst algae. The generally held view that algae in general are more resistant to radiations in comparison to higher plants does not seem to apply to the members of Charophyta. On the basis of the present study it has been shown that the chromosomes of N. opaca and N. flagelliformis are as sensitive as to radiations as those of higher plants. The results obtained in the study were adequately discussed.