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Phloeomyzus passerinii can induce a pseudogall within the bark of susceptible poplar genotypes, while in resistant genotypes the induction seems to be impeded by lignification processes. Phloeomyzus passerinii is a major pest of poplar stands in Europe, North Africa and the Near East. This aphid feeds in the cortical parenchyma of different poplar species and hybrids, and can affect their growth and survival through unknown mechanisms. In some genotypes, however, resistance prevents either the settlement or the development of aphid colonies. For a better understanding of tree reactions to aphid probing, we compared the anatomical and biochemical modifications undergone within the bark of stem cuttings, after different delays of either aphid colonization or mechanical wounding. To assess how resistance may modulate tree reactions, the comparison was performed using three poplar genotypes exhibiting different resistance levels. In these three genotypes, mechanical wounding induced a similar, localized, wound periderm. In contrast, aphid colonization triggered more extended reactions, which differed among genotypes. In the susceptible genotype, aphids induced a reaction tissue, characterized after a month by thin-walled hypertrophied cells and a depletion of soluble phenolic compounds and starch. Anatomical features of this reaction tissue suggest that the aphid initiates a pseudogall in the cortical tissues of its susceptible host. In the resistant genotypes, however, the differentiation of the reaction tissue was totally or partially inhibited, probably because of extended lignification processes. The implications of a pseudogall induction on susceptible hosts’ physiology, and the impact of lignification on aphid development and behavior, are discussed.

Human bladder carcinomas often express high levels of the epidermal growth factor (EGF) receptor. In three human bladder carcinoma cell lines (OBR, T24, and 647V), we show that two EGF receptor ligands, namely EGF and transforming growth factor alpha, enhanced the apoptosis due to serum starvation on cells cultured as monolayers. Conversely, EGF and transforming growth factor alpha prevented apoptosis when the same serum-starved cells were cultured as three-dimensional spheroids. Both stimulation and inhibition of apoptosis by EGF were associated with p21 WAF1/CIP1 overexpression. In 647V spheroids, EGF protection against radiation-induced apoptosis was negated by genistein and tyrphostin AG1478, suggesting that blockade of the EGF signal transduction in patients with bladder cancer may improve the radiotherapy efficacy.