Several indications implied that the Arabidopsis FT ( FLOW-ERING LOCUS T) gene provides a possible functional link between the systemic pathways and the cell-autonomous pathways to flowering. FT is a major integrator of the genetic pathways to flowering in short and long days (4, 5); it encodes a signaling factor (6, 7) and is not expressed in the SAM proper (8) but can be detected, upon induction, in shoot apices (SAPs) containing young leaves (9). Flowering is delayed in mutant ft plants (10, 11), and when FT is overexpressed, flowering occurs earlier with a determinate inflorescence (12, 13). FT is regulated by the flowering-time gene CONSTANS in both long-and short-day plants (14,15), and grafting experiments in Arabidopsis have shown that systemic induction of flowering by CONSTANS is most likely mediated by FT (16,17). It was recently shown that a small fraction of heat-shock-induced FT RNA, originating in a single leaf, is found in the SAPs, suggesting that the FT mRNA itself may represent a major component of florigen (18).We chose tomato, a photoperiod-insensitive plant, to test the premise that orthologs of the Arabidopsis FT gene can initiate a conserved, long-distance, flower-promoting pathway in diverse flowering systems. The generality of the florigen hypothesis was supported by interspecies grafting experiments (2). Grafting results are independent of the validity of promoters, the resolution of in situ hybridization patterns, inferences derived from the activation of upstream genes, or interpretations of clonal analysis. The perennial habit; the compound shoots, which permit the analysis of multiple vegetative͞floral transition events in one plant (19); and the ease of grafting render tomato as a useful experimental platform for investigating the nature of florigen. We expanded the analysis in tomato with parallel experiments in long-day Arabidopsis and short-day tobacco.The primary shoot of tomato is terminated by an inflorescence, after which the apparent main axis consists of an upright array of reiterated axillary branches called sympodial units (SUs). Each SU arises from the most proximal axillary bud of the preceding unit and consists of three vegetative nodes and a terminal inflorescence (Fig. 1A). The distinction between the primary and compound sections of sympodial plants provides two basic criteria for flowering time: the number of leaves to the first inflorescence in the primary shoot and the number of leaves between inflorescences in the compound part. Here, we identify the tomato FT ortholog as SINGLE FLOWER TRUSS (SFT), a gene regulating primary shoot flowering time, sympodial habit, and flower morphology. All aspects of the sft phenotype were complemented by graft-transmissible SFT signals, suggesting that all are the consequence of a common flowering-time defect. Significantly, graft-transmissible SFT signals substituted for light dose and two inductive photoperiodic stimuli in different species as well. ResultsThe Tomato Ortholog of FT Is Disrupted in Late-Flowering sft Mutants....

The florigen paradigm implies a universal flowering-inducing hormone that is common to all flowering plants. Recent

Morphological, cytological and transport properties of the integument of Salamandra salamandra were investigated during natural ontogenetic development, from birth to adult. Three stages were operationally defined: I, larvae, from birth to metamorphosis; II, metamorphosis (judged externally by the colour change and loss of the gills); and III, post-metamorphosis to adult. Pieces of skin were fixed at various stages for immunocytochemical examinations, and the electrical properties were investigated on parallel pieces. Distinct cellular changes take place in the skin during metamorphosis, and lectin (PNA, WGA and ConA) binding indicates profound changes in glycoprotein composition of cell membranes, following metamorphosis. Band 3 and carbonic anhydrase I (CA I) were confined to mitochondria-rich (MR)-like cells, and were detected only in the larval stage. CA II on the other hand, was detected both in MR-like and in MR cells following metamorphosis. The electrical studies show that the skin becomes more tight (transepithelial resistance increases) upon metamorphosis, followed by manifestation of amiloride-sensitive short-circuit current (I(SC)) indicating that functional Na+ uptake has been acquired. The skin of metamorphosed adults had no finite transepithelial Cl- conductance, and band 3 was not detected in its MR cells. The functional properties of MR-like and MR cells remain to be established.

The onset of active Na(+) transport and activated Cl(-) conductance (G(Cl)) across the skin epithelium of Pelobates syriacus was investigated during natural ontogenetic development. Structural features, including band three and Peanut lectin bindings were tested in parallel and structure-function relationships were attempted. The 22 specimens studied were divided into two tadpole, three juvenile, and two adult stages, corresponding to the Taylor-Kollros standard table, in accordance with external morphology of their developmental stage. Onset of transepithelial electrical potential and drop in conductance occurred abruptly, coinciding with metamorphosis climax of tadpoles into juveniles at about stage XXI of development. Amiloride-sensitive Na(+) transport occurred a little later at stage XXIII, followed by the appearance of activated Cl(-) conductance, G(Cl). Parallel structural examination showed that skin MR cells occurred upon metamorphosis, as the tadpole integument transformed into the adult epithelium and could be associated with the occurrence of activated G(Cl). It was not related temporally with the appearance of band three protein in MR cells. Our findings support the association of G(Cl) with MR cells, whereas band three may only be a corollary of G(Cl) and not necessarily essential for its manifestation.

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