The molecular pathway of p53-dependent apoptosis (programmed cell death) is poorly understood. Because p53 binds to the basal transcription-repair complex TFIIH and modulates its DNA helicase activities, we hypothesized that TFIIH DNA helicases XPB and XPD are members of the p53-mediated apoptotic pathway. Whereas transfer of a wild-type p53 expression vector by microinjection or retroviral infection into primary normal human fibroblasts resulted in apoptosis, primary fibroblasts from individuals with xeroderma pigmentosum (XP), who are deficient in DNA repair and have germ-line mutations in the XPB or XPD gene, but not in the XPA or XPC gene, have a deficiency in the apoptotic response. This deficiency can be rescued by transferring the wild-type XPB or XPD gene into the corresponding mutant cells. XP-D lymphocytes also have a decreased apoptotic response to DNA damage by adriamycin, indicating a physiologically relevant deficiency. The XP-B or XP-D mutant cells undergo a normal apoptotic response when microinjected with the Ich-1, and ICE genes. Analyses of p53 mutants and the effects of microinjected anti-p53 antibody, Pab421, indicate that the carboxyl terminus of p53 may be required for apoptosis. Direct microinjection of the p53 carboxy-terminal-derived peptide (amino acid residues 319-3331 resulted in apoptosis of primary normal human fibroblasts. These results disclose a novel pathway of p53-induced apoptosis.
This study tested the hypothesis that a controlled water deficit during grain filling of wheat (Triticum aestivum) could accelerate grain-filling rate through regulating the key enzymes involved in Suc-to-starch pathway in the grains. Two high lodgingresistant wheat cultivars were field grown. Well-watered and water-deficit (WD) treatments were imposed from 9 DPA until maturity. The WD promoted the reallocation of prefixed 14 C from the stems to grains, shortened the grain-filling period, and increased grain-filling rate or starch accumulation rate (SAR) in the grains. Activities of Suc synthase (SuSase), soluble starch synthase (SSS), and starch branching enzyme (SBE) in the grains were substantially enhanced by WD and positively correlated with the SAR. ADP Glc pyrophosphorylase activity was also enhanced in WD grains initially and correlated with SAR with a smaller coefficient. Activities of granule-bound starch synthase and soluble and insoluble acid invertase in the grains were less affected by WD. Abscisic acid (ABA) content in the grains was remarkably enhanced by WD and very significantly correlated with activities of SuSase, SSS, and SBE. Application of ABA on well-watered plants showed similar results as those by WD. Spraying with fluridone, an ABA synthesis inhibitor, had the opposite effect. The results suggest that increased grainfilling rate is mainly attributed to the enhanced sink activity by regulating key enzymes involved in Suc-to-starch conversion, especially SuSase, SSS, and SBE, in wheat grains when subjected to a mild water deficit during grain filling, and ABA plays a vital role in the regulation of this process.Starch in the endosperm of wheat (Triticum aestivum) is the major form of carbon reserves and comprises 65% to 75% of the final dry weight of the grain (Housley et al., 1981;Dale and Housley, 1986;Hurkman et al., 2003). Grain filling is therefore mainly a process of starch biosynthesis and accumulation. It is generally accepted that four enzymes may play a key role in this process: Suc synthase (SuSase; EC 2.4.1.13), ADP Glc pyrophosphorylase (AGPase; EC 2.7.7.27), starch synthase (StSase; EC 2.4.1.21), and starch branching enzyme (SBE; EC 2.4. 1.18;Hawker and Jenner, 1993; Ahmadi and Baker, 2001;Hurkman et al., 2003). SuSase catalyses the cleavage of Suc, the main transported form of assimilates in wheat plants (Fisher and Gifford, 1986), to form UDP-Glc and Fru, which is thought to be the first step in the Suc-to-starch conversion. Its activity is considered to be linked to sink strength in the developing rice (Oryza sativa) grain and tomato (Lycopersicon esculentum) fruit (Sun et al., 1992;Wang et al., 1993;Kato, 1995). AGPase produces ADP-Glc, the primer of the starch chain (Smith and Denyer, 1992), and is regarded as the rate-limiting enzyme in starch biosynthesis (Preiss, 1988). StSase, composed of both soluble and granule-bound isoforms, elongates the amylose and amylopectin chains (Déjardin et al., 1997). Soluble StSase (SSS) activity is reported to be positively correlate...
A petrogenetic grid is presented for the system KFMASH (K,O-FeO-MgO-A1,and corundum with H,O in excess, which was calculated using the computer program THERMOCALC and the Powell and Holland internally consistent thermodynamic dataset. By removing the normal constraint of having quartz in excess, both quartz-bearing and quartz-absent equilibria are shown. Quartz-absent equilibria are particularly relevant at high-T and low-P conditions, because of their common occurrence at these conditions. The calculated mineral assemblage and mineral compositional variations in terms of FeMg-, and (Fe, Mg)SiAlL, exchange vectors are broadly compatible with observations on natural rocks, particularly when non-KFMASH components are taken into account.
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