Randomised controlled trial to evaluate the effect of foot trimming before and after first calving on subsequent lameness episodes and productivity in dairy heifers

The objective of this study was to assess both independent and combined effects of routine foot trimming of heifers at 3 weeks pre-calving and 100 days post calving on the first lactation lameness and lactation productivity. A total of 419 pre-calving dairy heifers were recruited from one heifer rearing operation over a 10-month period. Heifers were randomly allocated into one of four foot trimming regimens; pre-calving foot trim and post-calving lameness score (Group TL), pre-calving lameness score and post-calving foot trim (Group LT), pre-calving foot trim and post-calving foot trim (Group TT), and pre-calving lameness score and post-calving lameness score (Group LL, control group). All heifers were scored for lameness at 24 biweekly time points for 1 year following calving, and first lactation milk production data were collected. Following calving, 172/419 (41.1%) of heifers became lame during the study (period prevalence), with lameness prevalence at each time-point following calving ranging from 48/392 (12.2%) at 29–42 days post-calving to 4/379 (1.1%) between 295 and 383 days after calving. The effects of the four treatment groups were not significantly different from each other for overall lameness period prevalence, biweekly lameness point prevalence, time to first lameness event, type of foot lesion identified at dry off claw trimming, or the 4% fat corrected 305-day milk yield. However, increased odds lameness was significantly associated with a pre-calving trim alone (P = 0.044) compared to the reference group LL. The odds of heifer lameness were highest between 0 and 6 weeks post-partum, and heifer farm destination was significantly associated with lameness (OR 2.24), suggesting that even at high standard facilities, environment and management systems have more effect on heifer foot health than trimming

An enzymic method for measuring the molecular weight exclusion limit of plasmodesmata of bundle sheath cells of C4 plants

Bundle sheath cell strands have been prepared from four C4 plant species and used to study the molecular weight exclusion limit of plasmodesmata located in the cell wall of bundle sheath cells. By measuring the activity and the inhibition of enzymes located within the bundle sheath cells of the strands in the absence or presence of a variety of inhibitors of different molecular weight, the molecular weight exclusion limit of the plasmodesmata located within the cell walls of bundle sheath cells has been determined. Using a variety of Reactive dyes (of different molecular weight) which inhibit a number of cytosohc enzymes, as well as a graded series of Reactive Yellow 2 derivatives as probes, it has been shown that compounds with molecular weights greater than about 900 daltons do not pass through the plasmodesmata of bundle sheath cells of C4 plants

Regulation of C4 photosynthesis: purification and properties of the protein catalyzing ADP-mediated inactivation and Pi-mediated activation of pyruvate, Pi dikinase

Pyruvate,Pi dikinase regulatory protein (PDRP) has been highly purified from maize leaves, and its role in catalyzing both ADP-mediated inactivation (due to phosphorylation of a threonine residue) and Pi-mediated activation (due to dephosphorylation by phosphorolysis) of pyruvate,Pi dikinase has been confirmed. These reactions account for the dark/light-mediated regulation of pyruvate,Pi dikinase observed in the leaves of C4 plants. During purification to apparent homogeneity the ratio of these two activities remained constant. The molecular weight of the native PDRP was about 180,000 at pH 8.3 and 90,000 at pH 7.5. Its monomeric molecular weight was 45,000. It was confirmed that inactive pyruvate,Pi dikinase free of a phosphate group on a catalytic histidine was the preferred substrate for activation. Michaelis constants for orthophosphate and the above form of active pyruvate,Pi dikinase were determined, as well as the mechanism of inhibition of the PDRP-catalyzed reaction by ATP, ADP, AMP, and PPi. For the inactivation reaction, Km values were 1.2 microM for the active pyruvate,Pi dikinase and 52 microM for ADP. CDP and GDP but not UDP could substitute for ADP. The inactivation reaction is inhibited by inactive pyruvate,Pi dikinase competitively with respect to both active pyruvate,Pi dikinase and ADP. Both the activation and inactivation reactions catalyzed by PDRP have a broad pH optimum between 7.8 and 8.3. The results are discussed in terms of the likely mechanism of dark/light regulation of pyruvate,Pi dikinase in vivo

Regulation of C4 photosynthesis: purification and properties of the protein catalyzing ADP-mediated inactivation and Pi-mediated activation of pyruvate, Pi dikinase

Pyruvate,Pi dikinase regulatory protein (PDRP) has been highly purified from maize leaves, and its role in catalyzing both ADP-mediated inactivation (due to phosphorylation of a threonine residue) and Pi-mediated activation (due to dephosphorylation by phosphorolysis) of pyruvate,Pi dikinase has been confirmed. These reactions account for the dark/light-mediated regulation of pyruvate,Pi dikinase observed in the leaves of C4 plants. During purification to apparent homogeneity the ratio of these two activities remained constant. The molecular weight of the native PDRP was about 180,000 at pH 8.3 and 90,000 at pH 7.5. Its monomeric molecular weight was 45,000. It was confirmed that inactive pyruvate,Pi dikinase free of a phosphate group on a catalytic histidine was the preferred substrate for activation. Michaelis constants for orthophosphate and the above form of active pyruvate,Pi dikinase were determined, as well as the mechanism of inhibition of the PDRP-catalyzed reaction by ATP, ADP, AMP, and PPi. For the inactivation reaction, Km values were 1.2 microM for the active pyruvate,Pi dikinase and 52 microM for ADP. CDP and GDP but not UDP could substitute for ADP. The inactivation reaction is inhibited by inactive pyruvate,Pi dikinase competitively with respect to both active pyruvate,Pi dikinase and ADP. Both the activation and inactivation reactions catalyzed by PDRP have a broad pH optimum between 7.8 and 8.3. The results are discussed in terms of the likely mechanism of dark/light regulation of pyruvate,Pi dikinase in vivo

Pyruvate,Pi dikinase and NADP-Malate dehydrogenase in C4 photosynthesis: properties and mechanism of light/dark regulation

[Extract] C4 Cycle and its Significance in Photosynthesis\ud \ud This review considers two key enzymes of the C4 pathway of photosynthesis, pyruvate,Pi dikinase (PPDK) and NADP-malate dehydrogenase (NADPMDH). I Besides their critical roles in C4 photosynthesis, these enzymes also share in common the fact that their activity is rapidly modulated by changes in light intensity. We will describe the radically different mechanisms by which this light-mediated modulation of activity is achieved . The kinetic and physical properties of these enzymes, and other mechanisms by which they are regulated, will also be reviewed. There have been recent reviews of the biochemistry of C4 photosynthesis (28, 31) and the light modulation of other photosynthetic enzymes, particularly in C3 plants (1-3, 16-18), so these areas will not be covered here

The enzymes in C4 photosynthesis

[Extract] The history of the resolution of C4 photosynthesis follows a pattern of demonstrating the operation of unique photosynthetic biochemistry by various means and then identifying the enzymes necessary to support that biochemistry. Critical to the developing understanding of this process was the recognition of two types of photosynthetic cells in C4 plants (mesophyll and bundle sheath) with quite different enzyme complements and distinct biochemical roles (see Fig. 3.1). As currently interpreted (see Edwards and Walker, 1983; Hatch, 1987) the reactions unique to the C4 pathway serve, in association with some remarkable modifications of leaf anatomy and ultrastructure, to concentrate CO2 in bundle sheath cells for utilisatiqn by the photosynthetic carbon reduction cycle carboxylase, ribulose L5-bisphosphate carboxylase-oxygenase (Rubisco). The Rubisco-mediated oxygenase reaction and associated photorespiration\ud are thereby eliminated

Acclimation of photosynthesis, H2O2 content and antioxidants in maize (Zea mays) grown at sub-optimal temperatures

Maize plants were grown at 14, 18 and 20 °C until the fourth leaf had emerged. Leaves from plants grown at 14 and 18 °C had less chlorophyll than those grown at 20 °C. Maximal extractable ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity was decreased at 14 °C compared with 20 °C, but the activation state was highest at 14 °C. Growth at 14 °C increased the abundance (but not the number) of Rubisco breakdown products. Phosphoenolpyruvate carboxylase (PEPC) activity was decreased at 14 °C compared with 20 °C but no chilling-dependent effects on the abundance of the PEPC protein were observed. Maximal extractable NADP-malate dehydrogenase activity increased at 14 °C compared with 20 °C whereas the glutathione pool was similar in leaves from plants grown at both temperatures. Foliar ascorbate and hydrogen peroxide were increased at 14 °C compared with 20 °C. The foliar hydrogen peroxide content was independent of irradiance at both growth temperatures. Plants grown at 14 °C had decreased rates of CO2 fixation together with decreased quantum efficiencies of photosystem (PS) II in the light, although there was no photo-inhibition. Growth at 14 °C decreased the abundance of the D1 protein of PSII and the PSI psaB gene product but the psaA gene product was largely unaffected by growth at low temperatures. The relationships between the photosystems and the co-ordinate regulation of electron transpor