Assessment of the respiratory costs of adaptation in plant species that differ in their responses to insufficient and excessive mineral nutrition

The effects of insufficient and excessive mineral nutrition on the relative growth rate (RGR); the rate of total dark respiration (SigmaR); gross phot osynthesis (Pg); and the contents of endogenous IAA, ABA, and cytokinins (C K) were studied in 20-60-day-old seedlings of plant species that differed i n their responses to these factors: beet root (Amaranthus retroflexus L.), orchard-grass (Dactylis glomerata L.), and common wheat (Triticum aestivum L.). The changes in the level of mineral nutrition lowered the RGR and Pg v alues and the IAA/ABA and CK/ABA ratios and increased the SigmaR and SigmaR /Pg values and ABA content, especially in A. retroflexus and T. aestivum. T he authors propose a new way to assess the respiratory cost of adaptation t o stress based on the relation between the RGR and the SigmaR/Pg values. Th e adaptation component of SigmaR is shown to relate to the ABA content.