High Efficiency, Heterosis, and Homeostasis in Mitochondria of Wheat

Abstract

Abstract.-Mitochondria of a wheat hybrid 31MS X 28 when assayed polarographically exceeded mitochondria of parents of the hybrid in ADP: 0 ratios and in respiratory control when they utilized alpha-ketoglutarate, malate, and succinate. The ADP: 0 ratios of the hybrid mitochondria for the three substrates were 5.8 i 0.2, 3.8 1 0.15, and 3.4 + 0.2, respectively. High P:0 ratios were also observed in manometric assays. Mixtures of parental mitochondria exceeded averages of the parents, i.e., they exhibited complementation and approached activities of hybrid mitochondria. Complementation was observed only with NAD-linked substrates. Dinitrophenol uncoupled all mitochondria, but uncoupling was smallest in hybrid mitochondria. Hybrid mitochondria had the greatest ATPase activity. Mixtures exhibited complementation in ATPase activity. ATPase activity was stimulated least in hybrid mitochondria and in parental mixtures. The results were discussed from the point of view that the high P: 0 ratios gave us direct evidence that heterosis is indeed characterized by high efficiency. It is also pointed out that because of consistent repeatability and their specificity to hybrids, P:0 ratios studied in rapidly isolated mitochondria of hybrids may give us revealing information on supramaximal ef ficiency of oxidative phosphorylation.The correlation of high mitochondrial oxidation and phosphorylation with heterosis in seedlings of maize has been described.1-3 In other words, it has been shown that hybrids which exhibit morphological superiority over their parents (judged by rate of growth of seedlings) yield M. (isolated mitochondria) which exceed in activity the mitochondria of parents of the hybrids.2 It was also demonstrated that complementation4 by parental mitochondria directly reflected activity of mitochondria of hybrids: high heterosis, high complementation; no heterosis, no complementation; negative heterosis, negative complementation. These findings implied that mitochondria of hybrids may be efficient systems. Mitochondrial efficiency is generally described by the P: 0 or ADP:O ratio;5 the generally accepted "theoretical" ratio is 3 for NAD-linked substrates and 2 for flavoprotein-mediated oxidation of succinate. The ratio for KGA (alpha-ketoglutarate) is 4, since there is an additional phosphorylation at the substrate level. Such ratios are relatively rarely observed with isolated mitochondria apparently due to the very high lability of coupling of oxidation and phosphorylation.6Studies of efficiencies of mitochondria of hybrids and their parents may be of great interest and very informative from the point of view of the nature of energetics of rapidly growing (i.e., hybrid) individuals. However, such studies may be fruitless for several reasons. First, very little knowledge of mitochondrial ef-302

The possible use of mitochondrial complementation as an indicator of yield heterosis in breeding hybrid wheat

“…Other parameters of heterosis such as ATPase (SARKISSIAN and SRIVASTAVA, 1969a), cytochrome oxidase and NADH: cytochrome c reductase (SARKISSIAN and SRIVASTAVA, 1971) may provide more rapid and less exacting methods for the routine screening of parental material. Significant levels of complementation in the present study might have resulted from carrying out a greater number of replicate experiments as four is probably near the minimum number with the level of variation normally associated with biochemical techniques of this complexity.…”

“…Until the discovery of the phenomenon of mitochondrial complementation (MCDANIEL and SARKISSIAN, 1966), this necessitated producing sufficient quantities of the hybrid varieties to allow comparative yield trials to be carried out. It has been shown, however, that in maize (SARKISSIAN and SRIVA-STAVA, 1967), wheat (SARKISSIAN and SRIVASTAVA, 1969a) and barley (MCDANIEL, 1970) heterosis for seedling characters in F1 hybrids can be correlated with the mitochondrial activity of 1 : 1 mixtures of mitochondria extracted from the parental lines. Consequently it has been suggested (SARKISSIAN and SRIVASTAVA, 1967) that mitochondrial complementation may be a means of estimating potential combining ability without the necessity, in the first instance, for producing the actual F1 hybrid combination.…”

Differences between Adenosine Triphosphatases from Monocotylous and Dicotylous Plants

“…For preparation of mitochondria the procedure described by Sarkissian and Srivastava (8) was slightly modified. All steps were performed at 2 to 4 C. The tissue material (100-150 g) was homogenized for 15 sec in a Waring Blendor with 1 liter of a buffer containing 0.5 M sucrose, 50 mm tris-Cl (pH 7.2), 2 mm EDTA, and 0.75 BSA/ml.…”

Absence of a correlation between mitochondrial complementation and root weight heterosis in sugarbeets

“…Mitochondrial complementation (the increased oxidative phosphorylation efficiency of mixed mitochondria from certain inbreds) has been reported as correlated with seedling heterosis in corn (Zeu muys L.) (MCDANIEL & SARKISSIAN, 1966,1968, wheat (Triticum aestivum L.) (SARKISSIAN & SRIVASTAVA, 1969,1971, and barley (Hordeurn vulgure L.) (MCDANIEL, 1969(MCDANIEL, , 1972. HOBSON (1971) observed only small complementation effects for yield heterosis in wheat inbreds.…”