Saxifraga cernua, a perennial herb distributed throughout the arctic and subarctic regions, shows high levels of dark respiration. The amount of respiration exhibited by leaves and whole plants at any temperature is influenced by the pretreatment temperature. Plants grown at 10°C typically show higher dark respiration rates than plants grown at 20°C. The levels of alternative‐pathway respiration (or cyanide‐insensitive respiration) in leaves of S. cernua grown at high and low temperatures were assessed by treating leaf discs with 0.25 mol m−3 salicylhydroxamic acid during measurements of oxygen consumption. Alternative pathway respiration accounted for up to 75% of the total respiration. Tissues from 20°C‐grown plants yielded a Q10 of 3.37 for normal respiration, and of 0.97 for alternative‐pathway respiration. Tissues from 10°C‐grown plants yielded a Q10 of 2.55 for normal respiration, and of 0.79 for alternative‐pathway respiration. The alternative pathway does not appear to be as temperature sensitive as the normal cytochrome pathway. A simple energy model was used to predict the temperature gain expected from these high rates of alternative‐pathway respiration. The model shows that less than 0.02°C can be gained by leaves experiencing these high respiration rates.

ABSTRACT. In a survey of several plant species found at Churchill, Manitoba, in the transition zone between the low and subarctic regions, we measured leaf respiration in terms of total respiration and alternative pathway respiration rates. Leaves of arctic plants exhibit higher rates of total respiration and alternative (cyanide insensitive) respiration than temperate species. There is a negative correlation between plant height and alternative pathway activity. Shorter plants have higher rates of alternative pathway respiration. More alternative pathway activity may mean that there is less energy in the form of ATP available for growth. A shorter growth habit keeps these plants in the still air close to the ground. This prevents cooling, water loss and physical damage due to wind abrasion. Thus plants with high rates of alternative pathway respiration may be better adapted to the arctic environment. The alternative pathway respiration of Orchis roturuiijolia was shown to be under the influence of the biological clock. Key words: Subarctic, plant respiration, alternative pathway, cyanide insensitive RÉSUMÉ. Lors d'une étude sur plusieurs esp&ces de plantes qui poussentà Churchill, au Manitoba, dans la bande de transition entre l'Arctique inférieur et la zone subarctique, on a mesur6 la respiration des feuilles en termes de taux de respiration totale et par voie alterne. I1 en ressort que les feuilles des plantes de l'Arctique ont des taux plus élevts de respiration totale et alterne (insensible au cyanure) que les e s w e s des régions tempérées. I1 existe une corrélation négative entre la hauteur des plantes et la respiration par voie alterne. Les plantes plus petites ont des taux de respiration par voie alterne plus élevés. Une plus grande activité par voie alterne pourrait signifier qu'il y a moins d'énergie sous forme d' ATP (adénosine triphosphate) disponible pour la croissance. En raison de leur petite taille, ces plantes se maintiennent dans l'air calme prh du sol, ce qui 6vite le refroidissement, la perte d'eau et les dommages physiques causés par l'érosion éolienne. Les plantes qui ont des taux tlevts de respiration par voie alterne sont donc peut-6tre mieux adapt6es à l'environnement arctique. On a trouvé que la respiration par voie alterne de l'orchis rotundifdia h i t influencte par l'horloge biologique. Mots clés: subarctique, respiration des plantes, voie alterne, insensible au cyanure Traduit pour le journal par Ntsida Loyer.

Rates of oxygen uptake were measured in leaves of Saxifraga cernua which had been exposed to an 1 8-h photoperiod. These rates were compared to those in plants which had been exposed to continuous tight. Rates of total dark respiration and alternative pathway respiration measured at the end of the photoperiod gradually decreased over the initial 3 d of exposure to an 18-h photoperiod. Thereafter, respiratory rates were constant. Rates of total dark respiration and alternative pathway respiration decreased during the 6h dark period. Rates of normal and alternative pathway respiration are equally affected during the dark period. The respiratory rates had reached a new minimum level 3 d after the initiation of a dark period. These results suggest that respiration rates in arctic plants are high because of the long photoperiod in the arctic. The kinetics of photoperiod induced changes in respiration are slow enough to suggest the involvement of the biological clock in setting respiration rates. Indeed, total dark respiration and alternative pathway respiration show a definite circadian rhythm. Free-running experiments show that normal respiration changes much tess (has a smaller amplitude of variation) than alternative pathway respiration and that alternative pathway respiration accounts for most of the rhythmicity of respiration.

A major structural component of the inner face of the nuclear envelope in vertebrates and invertebrates is the nuclear lamina, an array of 1–3 extrinsic membrane proteins, lamins A, B and C. These proteins are highly homologous to intermediate filaments and are classified as type V. We report the first purification, antigenic characterization and immunocytochemical localization of putative plant lamin proteins from pea nuclei. We conclude that plant cells contain this ancestral class of intermediate filaments in their nuclei and that regulation of nuclear envelope assembly/disassembly and mitosis in plants may be similar to that in animal cells.