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Abstract <p>Crassulacean Acid Metabolism (CAM) has long been regarded primarily as a photosynthetic adaptation to extremely arid environments, whereas leaf respiration and its contribution to maintaining CAM remain insufficiently characterized. This study provides new insights into leaf respiration of the facultative CAM species <i>Hylotelephium triphyllum</i> (Haw.) Holub, with particular emphasis on diurnal changes in the operation of the cytochrome (CP) and alternative (AP) respiratory pathway. Parameters of PS&#xa0;II chlorophyll fluorescence and content of organic acids were also analysed. The rate of CO<sub>2</sub> release in the dark was the highest in the early morning, decreased throughout the day, and nearly ceased at night. O<sub>2</sub> consumption reached 3.3–3.9 mg/(g DW&#xa0;h) during the day and was 30–40% lower at the beginning of the night. The respiratory quotient (RQ) (mol CO<sub>2</sub>/mol O<sub>2</sub>) was close to 1 in the morning, declined during the daytime, and approached zero at night, indicating substantial re-assimilation of respiratory CO<sub>2</sub>. Calculations showed that approximately one-third of the daily respiratory CO<sub>2</sub> efflux was utilized for malate synthesis. The relative contributions of CP and AP changed markedly over the diurnal cycle, reaching minimum CP activity at midday due to a shift toward increased AP and decreased CP. High temperatures (35–40°C) significantly affected CP and AP activity and their ratio, largely because of a stronger temperature-induced decrease in the CP respiratory quotient (Q<sub>10</sub>). These results suggest that alternative oxidase participates in the oxidation of reductants transferred from chloroplasts to mitochondria during the daytime, when stomata are closed and the pool of malic acid has already been depleted. Field measurements of PS&#xa0;II fluorescence revealed signs of photoinhibition, especially at midday under elevated temperature and high light. Altogether, the results of this study contribute to a more comprehensive understanding of the protective and adaptive mechanisms employed by facultative CAM plants in their natural habitats.</p>

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Respiration and Energy Dissipation in Leaves of Hylotelephium triphyllum (Crassulaceae) during Crassulacean Acid Metabolism Expression in Taiga Zone of the European Northeast

  • 期刊论文

  • 发表日期：

    2026年3月30日

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  • T. K. Golovko,
  • M. A. Shelyakin,
  • I. G. Zakhozhiy,
  • R. V. Malyshev

摘要

Abstract

Crassulacean Acid Metabolism (CAM) has long been regarded primarily as a photosynthetic adaptation to extremely arid environments, whereas leaf respiration and its contribution to maintaining CAM remain insufficiently characterized. This study provides new insights into leaf respiration of the facultative CAM species Hylotelephium triphyllum (Haw.) Holub, with particular emphasis on diurnal changes in the operation of the cytochrome (CP) and alternative (AP) respiratory pathway. Parameters of PS II chlorophyll fluorescence and content of organic acids were also analysed. The rate of CO2 release in the dark was the highest in the early morning, decreased throughout the day, and nearly ceased at night. O2 consumption reached 3.3–3.9 mg/(g DW h) during the day and was 30–40% lower at the beginning of the night. The respiratory quotient (RQ) (mol CO2/mol O2) was close to 1 in the morning, declined during the daytime, and approached zero at night, indicating substantial re-assimilation of respiratory CO2. Calculations showed that approximately one-third of the daily respiratory CO2 efflux was utilized for malate synthesis. The relative contributions of CP and AP changed markedly over the diurnal cycle, reaching minimum CP activity at midday due to a shift toward increased AP and decreased CP. High temperatures (35–40°C) significantly affected CP and AP activity and their ratio, largely because of a stronger temperature-induced decrease in the CP respiratory quotient (Q10). These results suggest that alternative oxidase participates in the oxidation of reductants transferred from chloroplasts to mitochondria during the daytime, when stomata are closed and the pool of malic acid has already been depleted. Field measurements of PS II fluorescence revealed signs of photoinhibition, especially at midday under elevated temperature and high light. Altogether, the results of this study contribute to a more comprehensive understanding of the protective and adaptive mechanisms employed by facultative CAM plants in their natural habitats.