The adenosine triphosphate (ATP) content of pea root tips is about 0.40 mmole/kg fresh weight. The effects of partial and complete anaerobiosis, and of carbon monoxide and hydrogen cyanide, on the ATP level are described. The ATP content was shown to correspond closely to the oxygen uptake under these conditions. However, there was no relation between the ATP level and the rate of mitosis, a situation which is in contrast with that in sea urchin eggs. In anaerobic conditions, mitoses in pea root tips could continue at a reduced rate, even though the ATP content had fallen to 1.5 per cent of the normal value in air The ATP level in anaerobic conditions corresponded closely to the expected rate of ATP regeneration from known anaerobic sources of energy. Calculations show that even this severely restricted supply of energy would be more than adequate to drive the anaphase chromosome movements, so it is suggested that the concept of a mitotic energy reservoir is superfluous in root tips. No evidence could be found for the involvement during mitosis in sea urchin eggs of a non-respiratory ferrous complex such as occurs in pea root tips. Hence the dilemma remains, that whereas mitoses in both sea urchin eggs and pea root tips are arrested by respiratory inhibitors, yet the biochemical mechanisms of the arrest in the two types of cell are totally distinct.

Adenosine Triphosphate↗

PubMed1962

Oxygen tension and the rates of mitosis and interphase in roots.

The object of this work was to determine the influence of a wide range of oxygen tensions upon the relative rates of respiration, mitosis, and interphase in pea root tips, compared with the normal rates of these processes in air. From the rates of disappearance of mitotic figures in excised tips kept in various oxygen tensions, the relative rates of mitosis were found to decrease gradually from 122 per cent in 100 per cent oxygen to 24 per cent in 0.0007 per cent oxygen. From the mitotic indices of intact seedlings, the relative rates of interphase were found to decrease sharply from 82 per cent in 10 per cent oxygen to 6 per cent in 5 per cent oxygen. The data on relative rates of respiration, mitosis, and interphase in root tips were compared, and it was shown that the three processes are perfectly distinct in their quantitative relationships to low oxygen tensions.

Cell Division↗

PubMed1962

Participation of a non-respiratory ferrous complex during mitosis in roots.

A systematic survey was undertaken, of the effects of carbon monoxide and hydrogen cyanide (in the presence of 20 per cent oxygen), in darkness and light, on the relative rates of respiration, mitosis, and interphase in pea root tips. The inhibition of respiration by carbon monoxide was light-sensitive, but the inhibition by hydrogen cyanide was light-stable. The inhibitions were presumably due to combination of the inhibitor with the iron of cytochrome oxidase, in its divalent and trivalent forms respectively. In contrast, the inhibitions of mitosis by both poisons proved to be light-sensitive. The light-sensitive inhibition of mitosis by carbon monoxide shows that an iron complex is responsible for the process. That the inhibition of mitosis by hydrogen cyanide is also light-reversible shows that, in contrast with cytochrome oxidase, the mitotic iron complex remains always in the divalent state. The relative affinities of the mitotic ferrous complex, in molar units, were 0.68 for CO/O(2), and 0.37 for HCN/O(2). The properties of the complex are analogous to, yet distinct from, Gastrophilus haemoglobin and reduced cytochrome oxidase. It is considered that the arrest of mitosis by oxygen lack, carbon monoxide, and hydrogen cyanide is definitely due to interference with this unidentified, non-respiratory ferrous complex.

Carbon Monoxide↗

PubMed1961