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General (polygenic) resistance of plant hosts to an attack by a range of pathogens is an important feature of plant defense responses against the infection. In search of biochemical markers defining this resistance, cell suspensions derived from leaves of potato (Solanum tuberosum L .) cvs. Tarpan and Bzura that are polygenically susceptible and resistant to Phytophthora infestans, respectively, were inoculated with culture filtrate (CF) of the fungus. Cell suspension of Tarpan responded to CF treatment by a higher extracellular alkalinization and more significant reduction in their viability and growth than those of the Bzura cultivar. The stimulation of phenylalanine ammonia-lyase (PAL ) activity but not of β-1,3-glucanase, was significantly higher in CF treated Bzura cells than in Tarpan ones. The obtained results suggest that sensitivity to the fungal toxins and variation of PAL activity may represent useful markers for the evaluation of polygenic resistance in potato.

1. Treatment of the etiolated maize seedlings with the plant hormone, gibberellic acid results in a significant enhancement of heavy polyribosome formation.2. This is accompanied by highly increased incorporation of the labelled RNA precursors into RNA engaged in the polyribosomal complex, as well as by an increased rate of protein synthesis in vivo.3. Determination of the specific radioactivity of particular RNA classes isolated from polyribosomes reveals that gibberellic acid stimulates mostly the synthesis of the rapidly labelled, nonribosomal RNA fraction.4. A considerable amount of this rapidly labelled RNA fraction, whose synthesis is preferentially stimulated by exogenous gibberellic acid contains poly(A) sequences, as shown by affinity chromatography on oligo(dT)-cellulose, indicating that phytohormone causes an increased transcription of mRNA in etiolated maize seedlings.5. When [3H]adenosine served as the RNA precursor it was found that the ratio between the heteropolymeric and polyadenylic parts of the poly(A)-RNA chain markedly changed under gibberellin treatment, suggesting that, in addition to an increased rate of mRNA synthesis, the plant hormone also affects the process of post-transcriptional polyadenylation of the newly made mRNA precursors. Possible extension of the polyadenylate segment in the presence of gibberellin may account for a longer functional half-life of the mRNA synthesized in plants treated with the phytohormone, and may explain significantly enhanced heavy polyribosome formation, as well as a higher efficiency of protein synthesis in plants treated with gibberellic acid.