While exposure of C₃ plants to elevated CO₂ would be expected to reduce production of reactive oxygen species (ROS) in leaves because of reduced photorespiratory metabolism, results obtained in the ...present study suggest that exposure of plants to elevated CO₂ can result in increased oxidative stress. First, in Arabidopsis and soybean, leaf protein carbonylation, a marker of oxidative stress, was often increased when plants were exposed to elevated CO₂. In soybean, increased carbonyl content was often associated with loss of leaf chlorophyll and reduced enhancement of leaf photosynthetic rate (Pn) by elevated CO₂. Second, two-dimensional (2-DE) difference gel electrophoresis (DIGE) analysis of proteins extracted from leaves of soybean plants grown at elevated CO₂ or O₃ revealed that both treatments altered the abundance of a similar subset of proteins, consistent with the idea that both conditions may involve an oxidative stress. The 2-DE analysis of leaf proteins was facilitated by a novel and simple procedure to remove ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from soluble soybean leaf extracts. Collectively, these findings add a new dimension to our understanding of global change biology and raise the possibility that oxidative signals can be an unexpected component of plant response to elevated CO₂.
Postemergence (POST) application of 4‐hydroxyphenyl pyruvate dioxygenase (HPPD) inhibitors in combination with a photosystem II (PSII) inhibitor, such as atrazine ...6‐chloro‐N‐ethyl‐N9‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine, is common practice in sweet corn (Zea mays L.) production. Given the sensitivity of sweet corn to HPPD‐inhibiting herbicides, the objective of this work was to determine the extent to which cytochrome P450 (CYP) genotype and PSII‐inhibitors affect crop sensitivity to HPPD‐inhibiting herbicides. Greenhouse experiments were used to identify PSII‐inhibitors that were least injurious when combined with the HPPD‐inhibitors, mesotrione 2‐(4‐mesyl‐2‐nitrobenzoyl)‐3‐hydroxycylohex‐2‐enone, tembotrione {2‐2‐chloro‐4‐(methylsulfonyl)‐3‐(2,2,2‐trifluoroethoxy)methylbenzoyl‐1,3‐cyclohexanedione}, and topramezone {3‐(4,5‐dihydro‐3‐isoxazolyl)‐2‐methyl‐4‐(methylsulfonyl)phenyl(5‐hydroxy‐1‐methyl‐1H‐pyrazol‐4‐yl)methanone}. Subsequently, HPPD‐inhibitors were tested individually with PSII‐inhibitors atrazine, or bentazon 3‐(1‐methylethyl)‐(1H)‐2,1,3‐benzothiadiazin‐4(3H)‐one2,2‐dioxide, or alone in field experiments on all three CYP genotypic classes; hybrids homozygous for mutant CYP alleles (cypcyp), hybrids homozygous for functional alleles (CYPCYP), and heterozygous hybrids (CYPcyp). Leaf bleaching within 1 wk of herbicide application increased when a PSII‐inhibitor was combined with an HPPD‐inhibitor; however, the relatively low level of injury was short‐lived. Tank mixing atrazine to mesotrione, tembotrione, or topramezone in sweet corn did not increase risk of yield loss compared to HPPD‐inhibitor applied alone. The synergistic effect on weed control between certain PSII‐ and HPPD‐inhibitor combinations reported previously does not hold true regarding sweet corn sensitivity to these herbicides. Among three HPPD‐inhibitors tested in sweet corn, topramezone was the safest, regardless of PSII combination. Mutant CYP alleles, namely CYPcyp and cypcyp hybrids, are the main cause of sweet corn sensitivity to mesotrione, tembotrione, and other CYP‐metabolized herbicides; therefore, breeding efforts to eliminate mutant CYP alleles should remain a high priority.
Ignorance of biodata is costly in sociology. Gender theorists remain unaware that until the demographic transition, infants were suckled every 15 minutes for two years, less often another two. A ...nearly continuous cycle of pregnancy and lactation barred women from the activities that brought the most prestige and power until the advent of modern sanitation after 1880. Women entered the public arena in large number only after technology altered the social consequences of human physiology. Yet wives still spend twice as much time in housework and child care as husbands. Data about the effects of both biology and culture on social interaction would enhance studies of ethnocentrism within the household.
The influence of growth temperature on the free sugar and sucrose phosphate synthase content and activity of spinach (Spinacia oleracea) leaf tissue was studied. When plants were grown at 25°C for 3 ...weeks and then transferred to a constant 5°C, sucrose, glucose, and fructose accumulated to high levels during a 14-d period. Predawn sugar levels increased from 14- to 20-fold over the levels present at the outset of the low-temperature treatment. Sucrose was the most abundant free sugar before, during, and after exposure to 5°C. Leaf sucrose phosphate synthase activity was significantly increased by the low-temperature treatment, whereas sucrose synthase and invertases were not. Synthesis of the sucrose phosphate synthase subunit was increased during and after low-temperature exposure and paralleled an increase in the steady-state level of the subunit. The increases in sucrose and its primary biosynthetic enzyme, sucrose phosphate synthase, are discussed in relation to adjustment of metabolism to low nonfreezing temperature and freezing stress tolerance.
Sucrose synthase (SuSy) plays an important role in sucrose degradation and occurs both as a soluble and as a membrane-associated enzyme in higher plants. We show that membrane association can vary in ...vivo in response to gravistimulation, apparently involving SuSy dephosphorylation, and is a reversible process in vitro. Phosphorylation of SuSy has little effect on its activity but decreases its surface hydrophobicity as reported with the fluorescent probe bis-ANS. We postulate that phosphorylation of SuSy (and perhaps other membrane proteins) is involved in the release of the membrane-bound enzyme in part as a result of decreased surface hydrophobicity.
Sucrose is formed in the cytoplasm of leaf cells from triose phosphates exported from the chloroplast. Flux control is shared among key enzymes of the pathway, one of which is sucrose-phosphate ...synthase (SPS). Regulation of SPS by protein phosphorylation is important in vivo and may explain diurnal changes in SPS activity and carbon partitioning. The signal transduction pathway mediating the light activation of SPS in vivo appears to involve metabolites and novel "coarse" control of the protein phosphatase that dephosphorylates and activates SPS. Regulation of the phosphorylation of SPS may provide a general mechanism whereby sucrose formation is coordinated with the rate of photosynthesis and the rate of nitrate assimilation. There are apparent differences among species in the properties of SPS that may reflect different strategies for the control of carbon partitioning. The SPS gene has recently been cloned from maize; results of preliminary studies with transgenic tomato plants expressing high levels of maize SPS support the postulate that SPS activity can influence the partitioning of carbon between starch and sucrose.
The inactivation of phosphorylated nitrate reductase (NR) by the binding of 14-3-3 proteins is one of a very few unambiguous biological functions for 14-3-3 proteins. We report here that serine and ...threonine residues at the +6 to +8 positions, relative to the known regulatory binding site involving serine-543, are important in the interaction with GF14ω, a recombinant plant 14-3-3. Also shown is that an increase in ionic strength with KCl or inorganic phosphate, known physical effectors of NR activity, directly disrupts the binding of protein and peptide ligands to 14-3-3 proteins. Increased ionic strength attributable to KCl caused a change in conformation of GF14ω, resulting in reduced surface hydrophobicity, as visualized with a fluorescent probe. Similarly, it is shown that the 5′ isomer of AMP was specifically able to disrupt the inactive phosphorylated NR:14-3-3 complex. Using the 5′-AMP fluorescent analog trinitrophenyl-AMP, we show that there is a probable AMP-binding site on GF14ω.
The 14-3-3 family of proteins are highly conserved signaling proteins in eukaryotes that bind to their client proteins, usually through specific phosphorylated target sequences. While the 14-3-3 ...proteins are thought to interact with a wide array of cellular proteins, there have been few studies addressing the in-vivo role of 14-3-3. As one approach to study this in-vivo role, we generated transgenic Arabidopsis plants constitutively overexpressing a directed mutant of 14-3-3 isoform ω that inhibits phosphorylated nitrate reductase (pNR) in a largely divalent-cation-independent manner in vitro. The transgenic plants had increased relative phosphorylation of NR at the regulatory Ser-534 site and decreased NR activity measured in the presence of 5 mmol·L-1 MgCl2 relative to nontransgenic plants. In addition, total NR protein was increased and the protein half-life was increased about two-fold. Two-dimensional difference gel electrophoresis analysis of proteins extracted from leaves of plants expressing the mutant 14-3-3 identified numerous cellular proteins that were altered in abundance. In particular, several β-glucosidase and glutathione S-transferase isoforms were decreased in abundance relative to wild type plants suggesting a possible alteration in stress or defense responses.
The 14-3-3 family of proteins are highly conserved signaling proteins in eukaryotes that bind to their client proteins, usually through specific phosphorylated target sequences. While the 14-3-3 ...proteins are thought to interact with a wide array of cellular proteins, there have been few studies addressing the in-vivo role of 14-3-3. As one approach to study this in-vivo role, we generated transgenic
Arabidopsis
plants constitutively overexpressing a directed mutant of 14-3-3 isoform ω that inhibits phosphorylated nitrate reductase (pNR) in a largely divalent-cation-independent manner in vitro. The transgenic plants had increased relative phosphorylation of NR at the regulatory Ser-534 site and decreased NR activity measured in the presence of 5 mmol·L
-1
MgCl
2
relative to nontransgenic plants. In addition, total NR protein was increased and the protein half-life was increased about two-fold. Two-dimensional difference gel electrophoresis analysis of proteins extracted from leaves of plants expressing the mutant 14-3-3 identified numerous cellular proteins that were altered in abundance. In particular, several β-glucosidase and glutathione S-transferase isoforms were decreased in abundance relative to wild type plants suggesting a possible alteration in stress or defense responses.
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