Sharon Sowa

Effects of nitrous oxide on mitochondrial and cell respiration and growth in Distichlis spicata suspension cultures

The reversible inhibition of respiratory activity could provide a novel approach to the preservation of traditionally hard to store plant germplasm such as clonal materials and recalcitrant seed. The gaseous anesthetic nitrous oxide caused a reversible, dose-dependent, partial inhibition of dioxygen utilization in mitochondrial particles isolated from cell suspension cultures of the salt-tolerant marsh grass Distichlis spicata, with maximal inhibition of 33% after 30 minutes exposure to an atmosphere of 80% nitrous oxide plus 20% oxygen. Respiration of whole cells required longer time to be affected by the anesthetic, and was reversibly inhibited an average of 19% when measured using a differential respirometer. Exposure to 80% nitrous oxide plus 20% oxygen for up to 10 days caused no measurable effect on cell growth.

The anesthetic nitrous oxide affects dioxygen utilization by bovine heart and bean seed mitochondrial particles

Nitrous oxide affects dioxygen utilization by both bean seed and bovine heart submitochondrial particles when either succinate or reduced cytochrome c are used as substrates. Bovine heart particles exhibit reversible, dose-dependent partial inhibition of respiratory activity when exposed to N2O. Bean seed particle respiration is stimulated by low levels of N2O, but higher concentrations are inhibitory. These findings can be explained in terms of one locus of anesthetic action: cytochrome c oxidase, the terminal component of the mitochondrial respiratory chain. Alterations in respiration rates are expected to make important contributions to anesthesia in animals and to control of germination in plants.

Biochemical changes during pollen germination measured in vivo by infrared spectroscopy

Abstract Biochemical changes during the germination of pine ( Pinus ponderosa Laws.), and spruce ( Picea pungens Engelm.) pollen grains were measured in vivo using Fourier transform infrared spectroscopy. Samples of dry, hydrated, and germinating pollen were analysed using cylindrical internal reflectance. Spectra were recorded at regular intervals up to the time of tube emergence. Germination was evaluated microscopically. The spectra revealed differences in exine structure/thickness and a significant difference in phytate content in pine and spruce pollen. Changes observed during germination included increased respiratory activity, changes in membrane lipid phase and amount, changes in protein amount and secondary structure, and changes reflecting the utilization of phytate and formation of cell walls. Infrared spectroscopy, in a short time and using a limited amount of sample, can provide biochemical insight to the process of pollen germination and has potential for the development of a more detailed analysis of pollen viability and vigor.

Effector molecules to probe cytochrome c oxidase activity in germinating Phaseolus vulgaris L. seeds

Summary The respiratory effector molecules carbon monoxide (CO), nitrous oxide (N 2 O), and deuterium oxide (D 2 O) were used to probe cytochrome c oxidase (EC 1.9.3.1) activity in mitochondrial particles and enzyme isolated from germinating bean seeds. Mitochondrial CO effects were dose-dependent and readily reversible, with maximal activity inhibition of 58 % and 81 % for mitochondria and oxidase, respectively, in the presence of 80 % CO. Cytochrome oxidase activity was reversibly inhibited 36 % in the presence of 80 % N 2 O. In the presence of 99.8 % D 2 O, mitochondrial and enzyme activities were 43 % and 52 % of control activities, with mitochondrial effects partially reversed in H 2 O. Visible spectra of mitochondrial and enzyme preparations showed that CO bound to cytochrome oxidase at heme a 3 , while N 2 O and D 2 O did not directly affect the ligand binding site. Seed germination was not changed in the presence of these molecules, but reductions were observed in seedling respiration and root length corresponding to reductions in cytochrome oxidase activity. As loss of vigor is the first step in seed deterioration, these results would indicate that cytochrome c oxidase activity may be important in the loss of viability.