SKOR, a K+ channel identified in Arabidopsis, displays the typical hydrophobic core of the Shaker channel superfamily, a cyclic nucleotide-binding domain, and an ankyrin domain. Expression in Xenopus oocytes identified SKOR as the first member of the Shaker family in plants to be endowed with outwardly rectifying properties. SKOR expression is localized in root stelar tissues. A knockout mutant shows both lower shoot K+ content and lower xylem sap K+ concentration, indicating that SKOR is involved in K+ release into the xylem sap toward the shoots. SKOR expression is strongly inhibited by the stress phytohormone abscisic acid, supporting the hypothesis that control of K+ translocation toward the shoots is part of the plant response to water stress.

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A culture procedure using temporary immersion in a liquid medium was tested for somatic embryogenesis of Hevea brasiliensis (Mtill. Arg.). Embryogenic callus was placed under regeneration conditions, either on a gelled medium (Phytagel, Sigma, St. Louis, MO) or in a container designed for temporary immersion. The latter technique has some advantages over the use of a gelled medium during both the early steps of somatic embryogenesis, i.e., embryo development, and later on, i.e., during maturation, desiccation and germination. Somatic embryo production in a liquid medium was three to four times greater than on a semi-solid medium: 400 embryos/g fresh weight under the best embryogenesis induction conditions. Somatic embryogenesis had to be initiated on a gelled medium before the embryogenic callus was transferred to temporary immersion, and the amounts of 3,4-dichlorophenoxyacetic acid and N6-benzyladenine had to be reduced. Temporary immersion resulted in substantially more consistent, synchronized somatic embryo development, reducing the number of abnormal embryos by half and stimulating germination. All of the late events could be carried out in the temporary immersion container. Effective drying conditions were achieved after 12 wk without immersion and without selection of the embryos. Temporary immersion during germination greatly stimulated root development ( + 60%) and epicotyl emergency (+ 35%), combined with increased synchronization and a substantially reduced workload.

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~UMMARYIn order to improve the late phases of Theobroma cacao L. embryogenesis from tissues of maternal origin, zygotic embryogenesis and somatic embryogenesis were compared, with respect to morphological, histological, and physiological parameters. Zygotic embryogenesis could be divided into three steps: (a) embryogenesis sensu stricto, (b) a growth period in which cotyledonary embryos reached their final dimensionsl and (c) a maturation period in which embryos accumulated protein and starch reserves, dehydrated to a water content equal to 30%, and underwent a modification in soluble sugar composition. Monosaceharides and sucrose contents decreased to the benefit of the oligosaccharides raffinose and stachyose. The formation of somatic embryos by use of basic protocols was studied to define the limiting factors that could lie behind their poor development. Morphological abnormalities of somatic embryos, which represented 80% of the total population, were described. A histological study showed that somatic embryos lacked starch and protein reserves; moreover, their water content was much higher than that of their zygotic counterparts. Introducing a growth period into the culture protocol made for better embryo development. Adding sucrose and abscisic acid to the maturation medium was effective in increasing reserve synthesis and resulted in higher germination, conversion, and acclimatization rates.

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Somatic embryogenesis from Theobroma cacao L. flower buds, as previously reported on five Forastero hybrid genotypes, was tested on several other genotypes, belonging to the three cocoa-tree groups: Forastero, Trinitario and Criollo. The results gave evidence of genotypic efficiencies. Explants were cultivated under two successive conditions: callogenesis and expression media. The morphological and histological responses were different for embryogenic or non-embryogenic genotypes. For embryogenic genotypes, only staminodes and stamen filaments were able to produce somatic embryos: after a few days on the expression medium, groups of callus cells went through the meristematic and then embryonic stages, and finally formed somatic embryos. Many of them showed abnormalities. Simultaneously, some embryogenic cells were visible. These started to divide to form pro-embryos which however were unable to evolve into proper somatic embryos.

Cereal Chem. 77(1): [11][12][13][14][15][16][17] A biochemical study of the main durum wheat milling fractions (bran, embryo, and semolina) showed that peroxidases (POD) were present in multiple forms in the kernel and appeared to be tissue specific: one form for the embryo, one for the endosperm, one for the subaleuronic layer, and one for the outer layers. Large varietal differences were found regarding both the composition and the POD activity. POD activity, detected by diaminobenzidine, was found mainly in the cell wall of the subaleurone layer and inside some specific, differentiated cells of the embryo. Immunolocalization with antibodies of durum wheat POD showed the presence of POD in several layers of the pericarp (epidermis) and the seed coat (testa), in the embryo, and also in the endosperm. In this latter tissue, the staining intensity decreased gradually from the outer layers toward the center of the kernel. The localization of POD in durum wheat kernel suggests specific functions for different forms.