Anaerobic stress resulted in a change i n the protein accumulation patterns in shoots of several Echinochloa (barnyard grass) species and Oryza safiva (1.) (rice) as resolved by two-dimensional gel electrophoresis. O f the six Echinochloa species investigated, E. phyllopogon (Stev.) KOSS, E. muricafa (Beauv.) Fern, E. oryzoides (Ard.) Fritsch Clayton, and E. crus-galli (1.) Beauv. are tolerant of anaerobiosis and germinate i n the absence of oxygen, as does rice.In contrast, E. crus-pavonis (H.B.K.) Schult and F. colonum (1.) Link are intolerant and do not germinate without oxygen. Computer analysis of the protein patterns from the four tolerant species and rice indicated that the anaerobic response is of five classes: class 1 proteins, enhanced under anaerobiosis (9 to 13 polypeptides ranging from 16-68 kD); class 2 proteins, unique to anaerobiosis (1 to 5 polypeptides ranging from 17-69 kD); class 3 proteins, remained constant under aerobiosis and anaerobiosis; class 4 proteins, prominent only i n air and repressed under anoxia (3 to 7 polypeptides ranging from 19-45 kD); and class 5 proteins, unique to aerobiosis (1 to 4 polypeptides ranging from 18-63 kD). In the intolerant species, E. colonum and E. crus-pavonis, no polypeptides were enhanced or repressed under anoxia (class 1 and class 4, respectively), whereas in the tolerant Ecbinochloa species and rice, a total of at least 9 to 13 anaerobic stress proteins and 4 to 7 "aerobic" proteins were noted. lmmunoblotting identified two of the major anaerobic stress proteins as fructose-1,6-bisphosphate aldolase and pyruvate decarboxylase. Based on the differential response of the intolerant species to anaerobiosis, we suggest that another set of genes, whose products may not necessarily be among the major anaerobic stress polypeptides, might confer tolerance in Echinochloa under prolonged anaerobic stress.

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Induction of ferritin synthesis in cultured cells by heme or iron is accompanied by degradation of the ferritin repressor protein (FRP). Intermediates in the degradative pathway apparently include FRP covalently linked in larger aggregates. The effect of iron on FRP degradation is enhanced by porphyrin precursors but is decreased by inhibitors of porphyrin synthesis, which implies that heme is an active agent. These results suggest that translational induction in this system may be caused by enhanced repressor degradation. While unique among translational regulatory systems, this process is common to a variety of other biosynthetic control mechanisms.

Based on localization and high activities of pyrroline-5-carboxylate reductase and proline dehydrogenase activities in soybean nodules, we previously suggested two major roles for pyrroline-5-carboxylate reductase in addition to the production of the considerable quantity of proline needed for biosynthesis; namely, transfer of energy to the location of biological N2 fixation, and production of NADP+ to drive the pentose phosphate pathway. The latter produces ribose-5-phosphate which can be used in de novo purine synthesis required for synthesis of ureides, the major form in which biologically fixed N2 is transported from soybean root nodules to the plant shoot. In this paper, we report rapid induction (in soybean nodules) and exceptionally high activities (in nodules of eight species of N2-fixing plants) of pentose phosphate pathway and pyrroline-5-carboxylate reductase. There was a marked increase in proline dehydrogenase activity during soybean (Glycine max) ontogeny. The magnitude of proline dehydrogenase activity in bacteroids of soybean nodules was sufficiently high during most of the time course to supply a significant fraction of the energy requirement for N2 fixation. Proline dehydrogenase activity in bacteroids from nodules of other species was also high. These observations support the above hypothesis. However, comparison of pentose phosphate pathway and pyrroline-5-carboxylate reductase activities of ureide versus amide-exporting nodules offers no support. The hypothesis predicts that pyrroline-5-carboxylate and pentose phosphate pathway activities should be higher in ureide-exporting nodules than in amideexporting nodules. This predicted distinction was not observed in the results of in vitro assays of these activities.P5CR2 catalyzes the NAD(P)H-dependent reduction of P5C to form proline. The activity of P5CR is substantially higher in soybean nodules than that reported for other plant and animal tissues (1 1 addition to the production of the considerable quantity of proline needed for biosynthesis, particularly of cell wall glycoproteins. These possible roles are: the production ofreduced carbon skeletons (proline) whose subsequent oxidation contributes to fueling energy-intensive biological N2 fixation; and the production of NADP+ which makes possible, in a manner described below, the assimilation of biologically fixed N2 into ureides, the major form in which biologically fixed N2 is transported from soybean root nodules to the plant shoot (19,21). Increasing the availability of NADP+, as a consequence of the reduction of P5C to proline, should increase flux through the PPP, since this flux is tightly regulated by the intracellular concentration of NADP+ (12). P5C has been shown to stimulate the activity of the PPP in human fibroblasts, Chinese hamster ovary cells, rabbit kidney cells (18), human erythrocytes (27), and rat and mice lens (24). Based on analogy with these results in animal systems, Kohl et al. (I 1) proposed that the high P5CR activity in soybean nodules might function to i...

Previously, we have shown that the ventralizing factor bone morphogenetic protein 4 (BMP-4) can inhibit Xenopus neurogenesis. The erythroid transcription factor GATA-1 functions downstream of the BMP-4 signaling pathway and mediates BMP-4-induced erythropoiesis. We have found that similar to BMP-4, GATA-1b inhibits neuralization of Xenopus animal cap (AC) cells. The neural inhibition is not seen with GATA-1a, although both GATA-1a and GATA-1b RNAs are translated at the same efficiency and induce globin expression equally in AC cells. GATA-1b RNA injection into AC cells neither induces expression of Xbra (a general mesoderm marker) nor affects expression of XK81 (epidermal keratin) or BMP-4 and Xvent-1 (two ventral markers). These data suggest that GATA-1b retains the epidermal fate of the AC. Intact GATA-1b protein is required for both inhibition of neurogenesis and induction of globin expression. Our findings indicate that GATA-1b can function in ectoderm to specifically regulate neural inducing mechanisms, apparently related to the expression of chordin, a neuralizing gene. Furthermore, tadpole stage embryos injected with GATA-1b are devoid of all dorsoanterior structures including neural tissue. This report provides evidence that the two transcription factors, derived from a recent genome duplication, share a common biological activity (stimulation of erythropoiesis) while also exhibiting a distinct function (inhibition of neurogenesis).