Ethylene has been thought to be an important factor for the induction of defense responses against pathogen attack, but its function in these responses has not been well denned. Here we show the direct involvement of ethylene in the formation of necrotic lesions and in basic pathogenesis-related (PR) protein gene induction in tobacco. Increase in ethylene production as well as accumulation of l-aminocyclopropane-l-carboxylic acid oxidase (ACO) gene transcript obviously preceded the lesion appearance in tobacco mosaic virus (TMV)-infected leaves in an N gene-dependent synchronous lesion formation system. Inhibitors of ethylene biosynthesis or action significantly suppressed both lesion formation and basic PR gene expression. Induction of these genes was enhanced in 1aminocyclopropane-1-carboxylic acid (ACC)-treated leaves especially in ACO-overexpressing transgenic tobacco plants. Further, we found that ethylene production during hypersensitive reaction is restricted at the level of ACO activity.
Our final goal is to breed dwarf cultivars of foxglove (Digitalis purpurea L.) using Agrobacterium rhizogenes. For this aim, we examined an effective method for hairy root induction, the phytohormone condition for regeneration from the root and traits of the regenerants. In the case of using a filter paper soaked with 1/2MS liquid medium for co-cultivation of leaf pieces with the bacteria, 30-40 hairy roots per 100 pieces were expected to be induced. Higher effect was given for regeneration from the hairy root through callus in zeatin addition than with BA, kinetin and no phytohormone added. In potted plants, numerical values of plant height, number of leaves, spike length, number of florets and leaf size were lower in a strain of transformants than in non -transformants, and both types of the plants exhibited similar plant forms and leaf morphologies. These traits provide novel possibilities for the breeding of dwarf cultivars of foxglove.
To establish a transformation system and contribute to breeding of dwarf cultivars in Vaccaria pyramidata using Agrobacterium rhizogenes, regeneration from a hairy root and traits of the regenerant were examined. The hairy roots were induced and actively grew on phytohormone -free 1/2MS media
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