Summary Chloride (Cl−) has been recently described as a beneficial macronutrient, playing specific roles in promoting plant growth and water‐use efficiency (WUE). However, it is still unclear how Cl− could be beneficial, especially in comparison with nitrate (NO3−), an essential source of nitrogen that shares with Cl− similar physical and osmotic properties, as well as common transport mechanisms. In tobacco plants, macronutrient levels of Cl− specifically reduce stomatal conductance (gs) without a concomitant reduction in the net photosynthesis rate (AN). As stomata‐mediated water loss through transpiration is inherent in the need of C3 plants to capture CO2, simultaneous increase in photosynthesis and WUE is of great relevance to achieve a sustainable increase in C3 crop productivity. Our results showed that Cl−‐mediated stimulation of larger leaf cells leads to a reduction in stomatal density, which in turn reduces gs and water consumption. Conversely, Cl− improves mesophyll diffusion conductance to CO2 (gm) and photosynthetic performance due to a higher surface area of chloroplasts exposed to the intercellular airspace of mesophyll cells, possibly as a consequence of the stimulation of chloroplast biogenesis. A key finding of this study is the simultaneous improvement of AN and WUE due to macronutrient Cl− nutrition. This work identifies relevant and specific functions in which Cl− participates as a beneficial macronutrient for higher plants, uncovering a sustainable approach to improve crop yield.
Ciliates are very good models for studying post-translationally generated tubulin heterogeneity because they exhibit highly differentiated microtubular networks in combination with reduced genetic diversity. We have approached the analysis of tubulin heterogeneity in Paramecium through extensive isolation and characterization of monoclonal antibodies using various antigens and several immunization protocols. Eight monoclonal antibodies and 10 hybridoma supernatants were characterized by: i) immunoblotting on ciliate and pig brain tubulins as well as on peptide maps of Paramecium axonemal tubulin; ii) immunoblotting on ciliate tubulin fusion peptides generated in E coli, a procedure which allows in principle to discriminate antibodies that are directed against tubulin sequence (reactive on fusion peptides) from those directed against a post-translational epitope (non-reactive); and iii) immunofluorescence on Paramecium, 3T3 and PtK2 cells. Twelve antibodies labeled all microtubules in Paramecium cells and were found to be directed against tubulin primary sequences (nine of them being located in the alpha N-terminal domain, one in the beta C-terminal one, and two in alpha and beta central stretches). The remaining ones decorated only a specific subset of microtubules within the cell and were presumably directed against post-translational modifications. Among these, three antibodies are directed against an N-terminal acetylated epitope of alpha-tubulin whereas the epitopes of three other ones (TAP 952 degrees, AXO 58 and AXO 49 degrees) apparently correspond to still unidentified post-translational modifications, located in the C-terminal domain of both alpha- and beta-tubulins. The AXO 49 degrees specificity is similar to that of a previously described polyclonal serum raised against Paramecium axonemal tubulin [2]. The results are discussed in terms of identification and accessibility of the epitopes and immunogenicity of ciliate tubulin with reference to mammalian and ciliate tubulin sequences.
The cyst wall of Paraurostyla weissei consists of four morphologically distinct layers. It shows an ultrastructure and composition similar to that of the previously described kinetosome‐resorbing cysts, and its cytoplasm displays characteristics of “urostylid‐type” cysts. Therefore it is possible to consider it a “transition ciliate” between Stichotrichina and Sporadotrichina.
A macronuclear gene-sized molecule carrying an actin gene from the hypotrich ciliate, Histriculus cavicola, was characterized. Southern blot analysis using a coding region probe suggested that actin in H. cavicola is encoded by a single gene. A comparison of the promoter regions indicated that the H. cavicola actin gene has a TATA box in the 5' flanking region in a position identical to those in other oxytrich ciliates. The coding sequence of this gene is not interrupted by any introns, and codes for a protein of 375 amino acid residues. This protein shares a high degree of similarity with other oxytrichid actins, and a relatively low similarity with actins from other eukaryotes. Comparative analyses of sequences indicated that most of the amino acid substitutions in hypotrich actins are found in surface loops, while the core structures are well-conserved. The sites that interact with DNase I and several regions involved in actin-actin contact have diverged considerably in hypotrich actins, while nucleotide-binding sites are the best-conserved interaction motif.
The cyst wall of Opisthonecta henneguyi has been studied ultrastructurally and cytochemically by light and electron microscopy, as well as by chemical and electrophoretic analyses, to examine the structure of the cyst wall and its composition. The cyst wall consists of four morphologically distinct layers. The ectocyst is a thin dense layer. The mesocyst is the thickest layer and is composed of a compact material. The endocyst is a thin layer like the ectocyst, but less dense. The granular layer varies in thickness and is composed of a granular material. In the resting cyst, kinetosomes of both oral apparatus and trochal band as well as the myoneme system are maintained, and only cilia are resorbed. The sugars present in the cyst wall are predominantly N-acetylglucosamine (90%) and glucose (10%). The mesocyst is composed of chitin, and the endocyst includes glycoproteins and acid mucopolysaccharides. During secretion of the cyst wall, the endocyst and granular layer are secreted from precursors synthesized "de novo". No cytoplasmic precursors of ectocyst and mesocyst have been detected.
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