The p34 protein kinase encoded by the cdc2 gene is a key component of the eukaryotic cell cycle required for the G1-to S-phase transition and entry into mitosis. To study the regulation of plant meristem activity and cell proliferation, we have examined the tissue-specific accumulation of cdc2 transcripts in Arabidopsis thlana and the related crucifer radish (Raphanus saivus) by in situ hybridization usingA. thaliana cdc2 cDNA sequences as a probe. cdc2 transcripts accumulated in leaf primordia and within the vegetative shoot apical meristem. During flower development, high levels of expression were observed in meristems, in the basal regions ofdeveloping organs, in the developing vasculature, and assocated with rib meristems elaborated late in the development ofsome floral organs. In root tips, cdc2 transcripts accumulated in the meristematic region and adjacent daughter cells but were not detected in the quiescent center. There was strong hybridization throughout the pericycle, and a further localized accumulation of cdc2 transcripts was observed in the initial stages ofthe activation ofa new meristem at sites of lateral root development. We conclude that cdc2 expression is a critical factor in the regulation of meristem activity and establishment of proliferative competence.The p34 protein kinase encoded by cdc2 is a key component of the eukaryotic cell cycle required for the Gj-to S-phase transition and entry into mitosis (1-3). p34 protein kinases become active only after forming a complex with a cyclin, and mutant analysis in Saccharomyces cerevisiae and Schizosaccharomyces pombe have demonstrated the presence of both positive regulators (e.g., cdc25+ and nim1 +) and negative regulators (e.g., wee1+) of M-phase p34 protein kinase activity (1-3). p34 protein kinases are highly conserved in evolution and have been found in all eukaryotes analyzed, including several plant species. cdc2 cDNA clones from Arabidopsis thaliana (4, 5), alfalfa (6), pea (7), and maize (8) complement cdc2 mutants in Sc. pombe or mutants in the equivalent gene (cdc28) in S. cerevisiae.Molecular cloning of plant cdc2 sequences provides the basis for mechanistic analysis of the regulation of cell proliferation in relation to the unique stem cell organization of higher plants mediating continuing organogenesis during postembryonic growth. In the present paper, we demonstrate by in situ hybridization analysis of the tissue-specific accumulation of cdc2 transcripts in A. thaliana and the related crucifer radish (Raphanus sativus) that the spatial and temporal pattern of cdc2 expression is a critical factor in regulation of meristem activity.MATERIALS AND METHODS Plant Material. A. thaliana ecotypes Columbia and Landsberg erecta were grown in the greenhouse under a 16-h light/8-h dark regimen. To isolate RNA from roots, plants were grown in liquid MS medium (9). For auxin induction, radish (cv. Scarlet Globe) seeds were surface sterilized and germinated in the dark (10). Roots were cut into 2-cm pieces and incubated in the dark at ...

The ABA-induced MA12 cDNA from maize, which encodes a set of highly phosphorylated embryo proteins, was used to isolate the corresponding genomic clone. This gene, called RAB-17 (responsive to ABA), encodes a basic, glycine-rich protein (mol. wt. 17,164) containing a cluster of 8 serine residues, seven of them contiguous. It is a homologue of the rice RAB-21 gene (Mundy J, Chua NH, EMBO J 7; 2279-2286, 1988). Phosphoamino acid analysis of the isolated protein indicates that only the serine residues are phosphorylated and a putative casein-type kinase phosphorylatable sequence was identified in the protein. The pattern of expression and in vivo phosphorylation of the RAB-17 protein was studied during maize embryo germination and in calli of both meristematic or embryonic origin. ABA treatment induced the synthesis of RAB-17 mRNA and protein in calli, however, the RAB-17 proteins were found to be highly phosphorylated only in embryos.

In this paper we consider the Split Delivery Vehicle Routing Problem (SDVRP), a relaxation of the known Capacitated Vehicle Routing Problem (CVRP) in which the demand of any client can be serviced by more than one vehicle. We define a feasible solution of this problem, and we show that the convex hull of the associated incidence vectors is a polyhedron (PSDVRP), whose dimension depends on whether a vehicle visiting a client must service, or not, at least one unit of the client demand. From a partial and linear description of PSDVRP and a new family of valid inequalities, we develop a lower bound whose quality is exhibited in the computational results provided, which include the optimal resolution of some known instances—one of them with 50 clients. This instance is, as far as we know, the biggest one solved so far.

Nitric oxide and S-nitrosothiols (SNOs) are widespread signaling molecules that regulate immunity in animals and plants. Levels of SNOs in vivo are controlled by nitric oxide synthesis (which in plants is achieved by different routes) and by S-nitrosoglutathione turnover, which is mainly performed by the S-nitrosoglutathione reductase (GSNOR). GSNOR is encoded by a single-copy gene in Arabidopsis (Arabidopsis thaliana; Martínez et al., 1996;Sakamoto et al., 2002). We report here that transgenic plants with decreased amounts of GSNOR (using antisense strategy) show enhanced basal resistance against Peronospora parasitica Noco2 (oomycete), which correlates with higher levels of intracellular SNOs and constitutive activation of the pathogenesisrelated gene, PR-1. Moreover, systemic acquired resistance is impaired in plants overexpressing GSNOR and enhanced in the antisense plants, and this correlates with changes in the SNO content both in local and systemic leaves. We also show that GSNOR is localized in the phloem and, thus, could regulate systemic acquired resistance signal transport through the vascular system. Our data corroborate the data from other authors that GSNOR controls SNO in vivo levels, and shows that SNO content positively influences plant basal resistance and resistance-gene-mediated resistance as well. These data highlight GSNOR as an important and widely utilized component of resistance protein signaling networks conserved in animals and plants.