Changes in energy status of leaf cells as a consequence of mitochondrial genome rearrangement.

The MSC16 cucumber (Cucumis sativus L.) mutant with lower activity of mitochondrial Complex I was used to study the influence of mitochondrial metabolism on whole cell energy and redox state. Mutant plants had lower content of adenylates and NADP(H) whereas the NAD(H) pool was similar as in wild type. Subcellular compartmentation of adenylates and pyridine nucleotides were studied using the method of rapid fractionation of protoplasts. The data obtained demonstrate that dysfunction of mitochondrial respiratory chain decreased the chloroplastic ATP pool. No differences in NAD(H) pools in subcellular fractions of mutated plants were observed; however, the cytosolic fraction was highly reduced whereas the mitochondrial fraction was more oxidized in MSC16, as compared to WTc. The NADP(H) pool in MSC16 protoplasts was greatly decreased and the chloroplastic NADP(H) pool was more reduced, whereas the extrachloroplastic pool was much more oxidized, than in WTc protoplast. Changes in nucleotides distribution in cucumber MSC16 mutant were compared to changes found in tobacco (Nicotiana sylvestris) CMS II mitochondrial mutant. In contrast to MSC16 cucumber, the content of adenylates in tobacco mutant was much higher than in tobacco wild type. The differences were more pronounced in leaf tissue collected after darkness than in the middle of the photoperiod. Results obtained after tobacco protoplast fractionating showed that the increase in CMS II adenylate content was mainly due to a higher level in extrachloroplast fraction. Both mutations have a negative effect on plant growth through perturbation of chloroplast/mitochondrial interactions.

Characterization of the photosynthetic apparatus in cortical bark chlorenchyma of Scots pine.

Winter-induced inhibition of photosynthesis in Scots pine (Pinus sylvestris L.) needles is accompanied by a 65% reduction of the maximum photochemical efficiency of photosystem II (PSII), measured as Fv/Fm, but relatively stable photosystem I (PSI) activity. In contrast, the photochemical efficiency of PSII in bark chlorenchyma of Scots pine twigs was shown to be well preserved, while PSI capacity was severely decreased. Low-temperature (77 K) chlorophyll fluorescence measurements also revealed lower relative fluorescence intensity emitted from PSI in bark chlorenchyma compared to needles regardless of the growing season. Nondenaturating SDS-PAGE analysis of the chlorophyll-protein complexes also revealed much lower abundance of LHCI and the CPI band related to light harvesting and the core complex of PSI, respectively, in bark chlorenchyma. These changes were associated with a 38% reduction in the total amount of chlorophyll in the bark chlorenchyma relative to winter needles, but the Chl a/b ratio and carotenoid composition were similar in the two tissues. As distinct from winter pine needles exhibiting ATP/ADP ratio of 11.3, the total adenylate content in winter bark chlorenchyma was 2.5-fold higher and the estimated ATP/ADP ratio was 20.7. The photochemical efficiency of PSII in needles attached to the twig recovered significantly faster (28-30 h) then in detached needles. Fluorescence quenching analysis revealed a high reduction state of Q(A) and the PQ-pool in the green bark tissue. The role of bark chlorenchyma and its photochemical performance during the recovery of photosynthesis from winter stress in Scots pine is discussed.