Alternative Respiration Pathways and Secondary Metabolism in Plants with Different Adaptive Strategies under Mineral Deficiency

The costs of adaptation respiration, the contribution of different biochemical pathways of respiration and alternative oxidases to the adaptation to mineral deficiency were compared in plant species representing different types of adaptive strategies: ruderal (Ru) (Amaranthus retroflexus L. and Leonurus quinquelobatus Gilib.) and predominantly stress-tolerant type (St) (Dactylis glomerata L. and Medicago sativa L.). The adaptation component of the total dark respiration was calculated on the basis of the relative growth rate and the ratio of dark respiration to gross photosynthesis. Adaptation costs were greater in less tolerant species. The inhibitory analysis showed that the contribution of glycolytic pathway decreased and the proportion of oxidative pentose phosphate pathway and residual respiration increased in the intolerant Ru-species under the conditions of abiotic stress. Conversely, in the tolerant St-species, the contribution of glycolysis increased. In all species studied, the contribution of the cytochrome pathway of substrate oxidation was reduced and the contribution of the alternative cyanide-insensitive and residual respiration increased under conditions of mineral deficiency; this phenomenon was particularly pronounced in a less tolerant species L. quinquelobatus. In the species characterized by Ru-strategy, stress increased the content of phenolic compounds and shikimic acid. We suppose that the adaptation respiration costs are associated with alternative biochemical pathways and alternative cyanide-resistant oxidase. The role of these pathways in the plants with St-strategy consists in maintaining the active state of oxidative pathways, whereas in the plants with Ru-strategy, they serve to burn excess metabolites and enhance the synthesis of secondary metabolites, which perform protective functions.