Non-Identical Mechanisms of Mitotic Arrest by Respiratory Inhibitors in Pea Root Tips and Sea Urchin Eggs

Abstract

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 airThe 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.In a variety of tissues, the progress of dividing cells through the visible phases of mitosis has been shown to be relatively indifferent to inhibition of the energy-yielding metabolic pathways. These observations were interpreted by Bullough (3) to mean that preparations for the oncoming mitosis, including the generation of the necessary energy, were completed before prophase. This idea was elaborated by Swann (4) into the stimulating concept of a hypothetical "energy reservoir," which was supposed to be progressively filled during interphase, and subsequently drained during mitosis.Although the concept of an energy reservoir was developed by these authors specifically to explain their own observations on cell divisions in mouse ear epidermis (5) and sea urchin eggs (4) respectively, later reviewers have tended to regard the hypothesis as a generalization of more universal validity (6-9 Utkin's (12) work was unfortunately not carried beyond cytological examination of the tissue, but he made the natural suggestion that, although a certain amount of energy might be stored, some additional energy is required during mitosis. Both Amoore and Epel conducted physiological and biochemical studies of the tissue, aimed at discovering how much energy might actually be available to the tissue under conditions of metabolic inhibition. Amoore (11) measured oxygen uptake by the pea root tips and Epel (1) measured adenosine triphosphate (ATP) content of the sea urchin eggs. In this way, both authors were able to compare (or contrast) the observed rates of mitosis with the probable energy levels existing in the tissue, and hence to develop hypotheses as to the biochemical mech...

Metabolic inhibitors block anaphase A in vivo.

“…One obvious concern is that mammalian cells (PTK0 and those of monocot plants (Allium and Tradescantia) may have different mechanisms of energizing chromosome motion. We note, for example, a number of conflicting reports on the effects of inhibitors on animal vs. plant cells during division (2,14,39,40,44). We fully acknowledge the wide evolutionary spread between these organisms, but nevertheless must recognize that certain characteristics are common to mitosis in all of them.…”

“…Subsequent work by Epel (14) and Amoore (1,2), however, indicated that the "energy reservoir" and "points of no return" concepts are not tenable (see also reference 30). For example, when sea urchin eggs are cultured in the presence of carbon monoxide they can be stopped at any stage of mitosis (14).…”

Chromosome Velocity During Mitosis as a Function of Chromosome Size and Position

“…(3) Hence velocity as a function of load (resistance) can be obtained by measuring the velocity of chromosomes differing in size. Furthermore, by relation (1) velocity as a function of load provides an indirect, but quantitative measure of the mitotic forces acting on chromosomes which differ in resistance to motion. A unique relationship between velocity and load has already been suggested from the indirect analysis of a different chromosomal situation (19), and the present study provides additional evidence for comparison with the earlier interpretation.…”