The presence and the absence of a prokaryote type and a eukaryote type of acetyl-CoA carboxylase (EC 6.4.1.2; ACCase) were examined in members of 28 plant families by two distinct methods: the detection of biotinylated subunits of ACCase with a streptavidin probe, and the detection of the accD gene, which encodes a subunit of the prokaryotic ACCase, by Southern hybridization analysis. The protein extracts of all the plants studied contained a biotinylated polypeptide of 220 kDa, which was probably the eukaryotic ACCase. All the plants but those belonging to Gramineae also contained a biotinylated polypeptide of ca. 35 kDa, which is a putative subunit of the prokaryotic ACCase. In all plants but those in Gramineae, the ca. 35 kDa polypeptide was found in the protein extracts of plastids, while the 220 kDa polypeptide was absent from these plastid extracts. The plastid extracts of the plants in Gramineae contained the 220 kDa polypeptide, as did the homogenates of the leaves. Southern hybridization analysis demonstrated that all the plants but those in the Gramineae contained the accD gene. These findings suggest that most higher plants have the prokaryotic ACCase in the plastids and the eukaryotic ACCase in the cytosol. Only Gramineae plants might contain the eukaryotic ACCases both in the plastids and in the cytosol. The origin of the plastid-located eukaryotic ACCase in Gramineae is discussed as the first possible example of substitution of a plastid gene by a nuclear gene for a non-ribosomal component.

To date there is little information about brain development during infancy and childhood, although several quantitative studies have shown volume changes in adult brains. We performed three-dimensional magnetic resonance imaging (3D-MRI) in 28 healthy children aged 1 month to 10 years. We examined the volumes of whole brain and frontal and temporal lobes with an advanced method for segmenting images into gray matter (GM), white matter (WM) and cerebrospinal fluid (CSF) compartments. Growth spurts of whole brain and frontal and temporal lobes could be seen during the first 2 years after birth. During this period the frontal lobes grew more rapidly than the temporal lobes, the right--left asymmetry was more noticeable in the temporal lobes than in the frontal lobes and the increase in GM was larger than that in WM in the temporal lobes. Subsequently, WM volume increased at a higher rate than GM volume throughout childhood. Quantitative information on normal brain development may play a pivotal role in clarifying brain neurodevelopmental abnormalities.

Acetyl-CoA carboxylase (ACCase, EC 6.4.1.2) catalyzes the synthesis of malonyl-CoA, the first intermediate in fatty acid synthesis. We studied the llization of two forms, the prokaryote and the eukaryote forms, of ACCase in pea leaves by comparing the blotin polypeptides of the two ACCases in protein extract from leaves and plastids.We found that the two forms of ACCase were in diferent cell compartments of pea leaves; the prokaryote form was in the plastids, and the eukaryote form was elsewhere, probably in the cytosol. This result suested the existence of two sites of malonyl-CoA thes. The Gramineae, such as rice and wheat, which lack the accD gene encoding one of the subunits ofthe prokaryote form ofACCase in their chloroplast genomes, did not have the prokaryote form of the enzyme but had the eukaryote form. The selectlve grass herbicides of the diphenoxyproponic acid type and the cyclohexanedione type, in vitro, inhibited plastidic ACCase of the eukaryote form from wheat but did not inhibit that of the prokaryote form from pea, suggeting that the origin of the tolerance of intact pea plant toward these herbicides is partly in the insensitivity of the prokaryote form of the enzyme. The origin of the susceptibility of the Gramineae plants toward these herbicides seems to lie in the presence of the herbicide-sensitive eukaryote form and the absence ofthe insenitive prokaryote form due to the lack of the accD gene in plastid.Acetyl-CoA carboxylase (ACCase; EC 6.4.1.2) catalyzes the ATP-dependent carboxylation of acetyl-CoA to form malonyl-CoA. The reaction is the first committed step in the synthesis of fatty acid, providing the essential substrate for fatty acid synthesis. There are two forms of ACCase: a prokaryote form consisting of three protein components biotin carboxylase, carboxyltransferase, and biotin carboxylase carrier protein (1)-and a eukaryote form consisting of three functional domains on a single polypeptide (2-7). It has been believed that, in plants, plastids are the major site of fatty acid synthesis (8) and that only the eukaryote form ofthe enzyme in plastids participates in the synthesis (9, 10). Early studies reported the existence of the prokaryote form in the spinach chloroplast (11), but this finding has been dismissed because the prokaryote form has not yet been purified and the purified ACCases from various plants are all eukaryote form consisting of a subunit size of -200 kDa (5-7), like that of the mammal enzyme (2). ACCase gene encoding the 230-kDa polypeptide has been isolated from a photosynthetic eukaryote alga (12). This large polypeptide is probably nuclearencoded because this sequence is not found in the complete sequence ofchloroplast genomes (13-15). However, recently we have obtained evidence ofthe existence of the prokaryote form in pea chloroplasts by identifying one of the subunits of carboxyltransferase, the chloroplast-encoded accD protein (16). This finding supports the early studies and indicates the existence of two forms of ACCase in pea plants (16,17). ...

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Researchers report how sulfur deficiency affects glucosinolate biosynthesis in plants.