Since 1950, maleic hydrazide (MH) has been introduced into agriculture as a major commercial herbicide and a depressant of plant growth in numerous circumstances such as suppression of sprouting of vegetables and stored food crops, control of sucker growth on tobacco plants, ratardation of flowering and prolongation of dormancy period. Since 1951 MH has been known as an effective chromosome-breaking agent in higher plants, in sharp contrast with its low effect on the chromosomes and general health of tested mammals. The selectivity of action of MH in plants and animals was obviously the main reason of low interest devoted to the chemical by people working the field of environmental mutagenesis. In early works the inhibitory effects of MH on plant growth were mainly considered to result from the suppression of plant metabolism (inhibition of enzymic activity) and interference of the compound with plant hormones and growth regulators. More recently, numerous experiments performed with various plant species have shown that MH acts as an inhibitor of the synthesis of nucleic acids and proteins. Similar results have been obtained with animal tumour cells. The chromosome-breaking effect of MH on plant chromosomes resembles very closely the chromosome-breaking properties of alkylating agents and other mutagenic compounds such as mitomycin C. MH-induced chromosomal aberrations have also been recorded in grasshoppers, fish and mice, although tests with some mammalian cell lines gave negative results. Among higher plants, selective sensitivity to the toxic effects of MH is well proved. This phenomenon seems to be due to the differential ability of various plant species to detoxicate the chemical. Plants can break down MH into several products, one of which, hydrazine, is a well-known mutagen and carcinogen. MH does not seem to be toxic to bacteria and fungi. The compound is degraded by soil microflora and hence can be utilized as a source of nitrogen nutrition. MH proved to be of low toxicity to mammals, but in some instances it decreased the fertility of rats. The reported carcinogenic effects of MH in mice and rats raise the question of its risks to man.

Cytotoxic effects of maleic hydrazide.

SUMMARYThe present communication deals with a discussion on the significance of chromosome numbers in Charophyta. After presenting a brief review of the various views held on the basic chromosome numbers in the taxa of Chara, Nitella and Tolypella, the role of polyploidy in the evolution of Charophyta and the possible ways in which polyploid taxa might have originated in nature have been considered. On the basis of present evidences aneuploids seem to show restricted geographical distribution as compared to euploids. Maximum degree of polyploidy has been found to be prevalent in Chara zeylanica within the tribe Chareae and Nitella tenuissima and Nitella furcata within the tribe Nitelleae. Significance of polyploidy in relation to sex, taxonomy, external form, chromosome length, pH, and altitude has also been discussed with some specific examples.

Significance of Chromosome Numbers in Charophyta — A Discussion

Some New Records of Chromosome Numbers in Indian Charophyta

SUMMARYThe effects of four different chemicals (colchicine, MH, caffeine and theobromine) on four taxa belonging to Chara and Nitella have been studied cytologically. Out of four different chemicals, MH did not produce any immediate cytological effects, which however, appeared subsequently when the materials were transferred to chemical free medium subsequent to treatments. All the chemicals brought about mitotic inhibition in all the algae investigated, to some extent or the other, levels of inhibition depending upon the concentrations of the chemicals or durations of treatment in the same concentrations. Of the four chemicals, theobromine proved to be most potent mitotic inhibitor. Colchicine has induced polyploidy, even upto the level of tetraploidy in C. globularis and C. braunii. Cytokinetic inhibition was brought about rarely by colchicine in C. globularis and more frequently by caffeine and theobromine treatments resulting in binucleate cells. Pycnotic nuclei were observed in all the treatments of ...

Y. S. R. K. Sarma

Papers

A new Chromosome Number in Nitella Tenuissima (Desv.) Kütz. Em. R.D.W.

Effects of Chemicals on Some Members of Indian Charophyta I