SEASONAL-CHANGES OF MITOCHONDRIA IN HARDENED TO COLD AND UNHARDENED WINTER-WHEAT PLANTS

Study of the mitochondria in etiolated seedlings of winter wheat (Trit icum aestivum L.) grown during the winter-spring and summer months rev ealed seasonal changes in oxidative and phosphorylating activity of th e organelles and in their sensitivity to Ca2+ ions. During the winter- spring period, mitochondria were characterized by a reduced rate of ox ygen uptake, but higher values of the ADP/O ratio. Cold hardening of p lants during this period caused an increase of mitochondrial affinity for Ca2+ (as indicated by shifting of the first respiratory maximum fr om 5 muM to 3 muM), appearance of a second respiratory maximum (at 15 muM Ca2+), and expansion of the range of stimulating concentrations of Ca2+. These changes of mitochondria corresponded to a higher level of plant frost resistance in winter-spring than in summer. It is conclud ed that seasonal periodicity in the state of mitochondria and whole pl ants is a reflection of biorhythms of vital processes occurring in see ds.