The capacity to develop tolerance to photoinhibition of photosynthesis was assessed in jack pine seedlings (Pinus banksiana Lamb.). Photoinhibition induced at 5 °C in control jack pine seedlings grown at 20 °C was saturated above an irradiance of 1000 μmol ∙ m−2 ∙ s−1 but was detectable at an irradiance as low as 25 μmol ∙ m−2 ∙ s−1. However, 20 °C seedlings shifted to 5 °C were 2-fold more tolerant to photoinhibition than 20 °C unshifted control seedlings, as detected by either the light-dependent decrease in photochemical efficiency or the apparent quantum yield of O2 evolution. The extent of this tolerance of photoinhibition was dependent upon time, photoperiod, and irradiance during exposure to the low-temperature shift. Furthermore, the tolerance of photoinhibition was correlated with anthocyanin accumulation in 20 °C grown seedlings shifted to 5 °C. In addition, seedlings shifted to 5 °C and an 8-h photoperiod exhibited a 2-fold higher yield of photosystem II electron transport, which was associated with an increased capacity to keep QA, the first stable quinone electron acceptor of photosystem II, oxidized at high irradiance. This was consistent with a 2-fold higher rate of photosynthesis on a chlorophyll basis. We propose that the combination of light attenuation by anthocyanin in the epidermis and enhanced rates of photosynthesis may, in part, account for the reduced sensitivity of jack pine to photoinhibition at low temperature. Key words: anthocyanin, light attenuation, low temperature, Pinus banksiana Lamb, (jack pine), photosynthesis, photoinhibition, photoperiod.
The 20S proteasome (multicatalytic proteinase) was purified from maize (Zea mays L. cv DEA 1992) roots through a five-step procedure. After biochemical characterization, it was shown to be similar to most eukaryotic proteasomes. We investigated the involvement of the 20S proteasome in the response to carbon starvation in excised maize root tips. Using polyclonal antibodies, we showed that the amount of proteasome increased in 24-h-carbon-starved root tips compared with freshly excised tips, whereas the mRNA levels of ␣3 and 6 subunits of 20S proteasome decreased. Moreover, in carbon-starved tissues, chymotrypsin-like and caseinolytic activities of the 20S proteasome were found to increase, whereas trypsin-like activities decreased. The measurement of specific activities and kinetic parameters of 20S proteasome purified from 24-h-starved root tips suggested that it was subjected to posttranslational modifications. Using dinitrophenylhydrazine, a carbonyl-specific reagent, we observed an increase in carbonyl residues in 20S proteasome purified from starved root tips. This means that 20S proteasome was oxidized during starvation treatment. Moreover, an in vitro mild oxidative treatment of 20S proteasome from non-starved material resulted in the activation of chymotrypsin-like, peptidyl-glutamyl-peptide hydrolase and caseinolytic-specific activities and in the inhibition of trypsin-like specific activities, similar to that observed for proteasome from starved root tips. Our results provide the first evidence, to our knowledge, for an in vivo carbonylation of the 20S proteasome. They suggest that sugar deprivation induces an oxidative stress, and that oxidized 20S proteasome could be associated to the degradation of oxidatively damaged proteins in carbon starvation situations.Living organisms are subjected to numerous biotic or abiotic stresses. Daily, at a cellular level, changing environmental growth conditions trigger the synthesis of new sets of proteins necessary for the acclimation response, and the degradation of regulatory proteins, damaged proteins, and proteins that have become useless. Thus, in plant cells subjected to carbon starvation, the activity of enzymes involved in sugar metabolism and respiration (Journet et al., 1986;Brouquisse et al., 1991;Irving and Hurst, 1993), nitrogen reduction and assimilation Peeters and Van Laere, 1992), regulation of cell division and growth (Chevalier et al., 1996), or protein synthesis (Webster and Henry, 1987;Tassi et al., 1992) decreases and, in most cases, the corresponding proteins are likely subjected to proteolysis. In contrast, the activity of enzymes related to the catabolism of proteins (Tassi et al., 1992;James et al., 1993James et al., , 1996Chevalier et al., 1995;Moriyasu and Ohsumi, 1996), amino acids , or lipids (Dieuaide et al., 1992;Ismail et al., 1997) increases. Genes encoding enzymes involved in protein and lipid catabolism have been shown to be induced by sugar depletion (Koch, 1996), and it is clear that the selective synthesis and degradation of...
Up to 20% of the [3H]leucine-labeled proteins synthesized by isolated chloroplasts in the light was degraded during subsequent incubation for 20-40 min. The degradation of these radioactive proteins was more rapid in the light than in the dark and was at least 2-fold greater in the presence of 5 mM ATP in light or darkness. Exogenous amino acids did not influence degradation rates, although they promoted protein synthesis. Overall, proteins from thylakoid and stromal fractions were degraded at comparable rates. Analysis by electrophoresis in denaturing polyacrylamide gels revealed that many proteins decreased in both fractions. Certain low molecular mass stromal proteins were lost almost completely during a 90 min incubation in the presence of ATP, while others were unaffected or decreased only slightly. Thus chloroplasts, like eukaryotic and prokaryotic cells and mitochondria, contain an ATP-stimulated proteolytic system. Protein degradationA TP-stimulation
BACKGROUND: A thermophilic lipase-producing Geobacillus thermodenitrificans strain AV-5 was isolated from the Mushroom Spring of Yellowstone National Park in WY, USA and studied as a source of lipase for transesterification of vegetable oils to biodiesel. RESULTS:A maximum activity of 330 U mL −1 was produced on 2% (v/v) waste cooking oil at 50 ∘ C, pH 8, aeration rate of 1 vvm and agitation speed of 400 rpm. However, the higher lipase productivity (14.04 U mL −1 h −1 ) was found at a volumetric oxygen transfer coefficient (k L a) value of 18.48 h −1 . The partially purified lipase had a molecular weight, temperature and pH optimum of 50 kDa, 65 ∘ C and pH 9, respectively, and was thermo-alkali stable: at 70 ∘ C, it retained 81% activity and 45% stability; at pH 10 it lost only 15% and 2.6% of its maximum activity and stability, respectively. Enzyme kinetic studies with p-nitrophenyl laurate as substrate revealed high substrate specificity (k m of 0.440 mmol L −1 ) and kinetic activity (v max of 556 nmol mL min −1 ) of lipase. CONCLUSIONS: The k L a was found to be highly dependent on aeration and agitation rates. Following optimization of fermentation medium and parameters, a 7.5-fold increase in lipase production by G. thermodenitrificans was attained. The lipase activity and substrate specificity (as k m ) are among the highest reported in the literature for bacterial lipases. It was demonstrated that the enzyme can produce biodiesel from waste cooking oil with a conversion yields of 76%. Fermentation studies on lipase productionEffect of temperature and pH on lipase production Bacterial lipases are greatly influenced by physical fermentation parameters such as temperature and pH. Most thermophilic aerobic geobacilli have optimal growth and enzyme production in
Galactomannan hydrolysis in isolated endosperms of fenugreek seeds is promoted by the presence of the embryo. Incubation in a large volume in the absence of the axis also results in endosperm mobilization and an increase in endo-p-mannanase activity. This is prevented when endosperms are incubated in a small volume, or when abscisic acid is present in the large volume. Fenugreek endosperms contain abscisic acid which is present in greater concentrations when these tissues have been incubated in a small volume rather than in a large volume. Antibodies prepared against purified tomato endo-p-mannanase detect the fenugreek enzyme on Western blots. Endosperms contain equal amounts of this enzyme whether they are incubated in a large volume, or in a small volume, or in the presence of abscisic acid. Thus, increased enzymic activity may not be related to increased synthesis, but rather to activation or release from the cells into the galactomannan-containing cell walls.
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