Oxygen Transport and Root Respiration of Maize Seedlings

Abstract

Oxygen uptake and ATP/ADP ratio were simultaneously monitored during incubation of excised maize (Zea mays L. INRA 508) root tips under varying 02 partial pressure. Both variables were independent of 02 tension until a critical 02 pressure was reached. Below this pressure, ATP/ ADP ratio and respiratory rate declined. However, in tissues having a high glycolytic capacity, the correlation between the ATP/ADP ratio and the respiratory rate breaks down as 02 tension decreases, due to the increasing contribution of fermentative processes.In presence of 2 millimolar NaF, the ATP/ADP ratio varied solely as a function of the 02 tension, without interference by fermentative activity, and a close correlation links the ATP/ADP ratio and the respiratory rate of excised maize root tips over the whole range of 02 tensions tested.Using this correlation, a method is proposed for the quantitative determination of the relative cellular respiratory rate permitted by 02 transport from the aerial part of young maize seedlings along the seminal root placed in an anoxic environment.Data are presented which demonstrate the preeminent part played by the cortical air spaces in 02 transport. Their contribution to respiration was high in the first few centimeters nearest the seed and decreased rapidly as the distance from the aerated source increased. It is concluded that 02 transport might contribute to the survival or to adaptive responses of root tissues in flooded soils but that the ventilation of the apical growing zone was inadequate to sustain the growth.penetrating significantly into the cells. Its principal favorable effect would not be so much to feed the respiration but to detoxify the surrounding medium by oxidizing the reduced ions. Using the Oz-dependent chemiluminescence of plant tissues (18) The debate on the actual significance of 02 transport for root metabolism arises because the methods used do not quantify the amount of 02 actually used in the respiration of tissues along the root in situ.In earlier papers, it has been shown that the value of the ATP/ ADP ratio or of the energy charge in lettuce seeds (11,14) was controlled by the pO21. A method has been proposed, which uses the energy charge value as an indirect assessment ofthe respiration permitted by the internal 02 transport in tips of intact rice and maize roots placed in an anaerobic environment (13). This method has been used to demonstrate the efficiency of the internal ventilation in bulrush (17). This paper is a refinement of this approach. It shows that in the presence of fluoride a close correlation links the ATP/ADP ratio and the respiratory rate controlled by the pO2 in maize root tips. This correlation is used to demonstrate an 02 transport and to quantify its involvement in the respiratory metabolism along the seminal root of young maize seedlings.It is now widely accepted that O2 can move through the gas spaces of plant tissues (for review, see 19). Some water plants, such as yellow water lily (2), have developed anatomical devices very effi...

Fructan content of wheat seedlings(Triticum aestivumL.) under hypoxia and following re‐aeration

“…Although there was an increase in the amount of soluble sugars in roots and shoots, Menegus et al (1991) showed a decreased level of the key substrate for glycolysis, glucose-6-phosphate (G6P) in wheat plants suffering from oxygen deprivation, and this is thought to be afTected by ATP deficiency (Saglio, Raymond & Pradet, 1983). The lack of phosphorylated substrate causes a retarded glycolysis in spite of Numerous studies provide direct or indirect evidence linking fructan metabolism to environmental stress (Archbold, 1938;Hendry, 1987;Pollock & Cairns, 1991).…”

Critical Oxygen Pressure for Growth and Respiration of Excised and Intact Roots

“…The effect ofpO2 on the O2 uptake by excised root tips was studied by polarographic methods essentially as described in Saglio et al (12), except that NaF was not used. When respiratory measurements were performed in the liquid medium, the chamber of the polarographic cell was filled with the nutrient solution containing 0.1 M glucose.…”

“…We have established the existence of a close correlation between the value of ATP/ADP ratios and the respiratory rate under conditions of limiting 02 tension (12). This correlation permits a quantitative assessment of the relative respiratory rate of any organ, or part of organ, in intact plants (12).…”

“…This correlation permits a quantitative assessment of the relative respiratory rate of any organ, or part of organ, in intact plants (12). Using this relationship, we have compared the COP of excised and intact maize root tips and the results are discussed in relation to the 02 transport and root growth under conditions of limiting 02 tension.…”

“…In contrast to marsh plants, internal transport in mesophytes plays only a limited role in the 02 supply of nonadapted plants (12,13) and cannot meet the respiratory requirements of buried organs which draw most of their 02 from the rhizosphere. The harmful effects of low 02 tensions will greatly depend on the restrictions imposed on the respiration which provides most of the energy required by these nonchlorophyllous tissues.…”