Plants were grown in the greenhouse or in the field under standard conditions. We used the B73 wild-type line. For cytokinin induction experiments, 2-week-old seedlings were excised at the shoot-root junction, and stood in water supplemented with different concentrations of cytokinin. After treatments, the seedlings were dissected into a shoot fraction (apical and axillary shoot meristems, stem and 4-5 young leaf primordia) or a leaf fraction (expanding and mature leaves). For embryo culture experiments, pollinated ears at either 13 days after pollination (first leaf stage) or 16 days after pollination (second to third leaf stage) were sterilized in 30% commercial bleach solution for 20 min then rinsed five times with sterile water. The embryos were dissected out and cultured on maize embryo culture medium (1 £ Murashige and Skoog salts, 1 £ Gamborg's vitamins, 2% sucrose, 0.7% agar, pH 5.7) in some cases with the addition of cytokinin (kinetin, 10 25

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In this study the clinico-pathological aspects of cutaneous and mucocutaneous plasmacytomas were investigated in 63 dogs (one dog with two tumours). The tumours were most commonly observed in the skin of the trunk and legs. Yorkshire Terrier (n = 8) was the most commonly affected breed and males were affected more commonly than females (36 versus 23, respectively). Plasmacytomas were histologically classified into mature, hyaline, cleaved, asynchronous, monomorphous blastic and polymorphous blastic cell types. Monomorphous blastic cell type was the most frequent type (n = 21), followed by cleaved (n = 19) and asynchronous (n = 11) cell types. Secondary amyloid depositions were observed in eight cases. Immunohistochemical staining showed monoclonal lambda light chain positivity in all cases. In the immunohistochemical staining for cyclin D1, which is a prognostic marker in human plasma cell tumours, moderate numbers of positive tumour cells were observed in only one case of (muco)cutaneous plasmacytoma. All other cases were negative or contained few positive tumour cells. On the other hand, high numbers of tumorous plasma cells reacted positively with cyclin D1 in three out of six cases of canine multiple myelomas. Prognosis of the (muco)cutaneous plasmacytomas was good, except in one dog which developed a lymphoma afterwards. No significant correlations were observed between the cell type and the location of the tumour, presence of amyloid or prognosis.

Macrophages generally constitute a major component of the tumour stroma. Although conventionally considered to be cytotoxic effector cells, macrophages have recently been described as promoters of tumour progression. The present study shows that selective depletion of peritoneal or liver macrophages prior to CC531 tumour cell inoculation resulted in highly differentiated tumours in rats. In contrast, tumours from control rats, in which macrophages are abundantly present, showed a desmoplastic stromal reaction with hallmark features of malignancy, such as neovascularization and matrix remodelling, indicating that the presence of macrophages is associated with malignant histopathological differentiation. Remarkably, macrophage-depleted rats, bearing highly differentiated tumours, had a worse prognosis, as they displayed a higher tumour load and poorer survival. Thus, while macrophages direct tumours towards malignant tumour histology, their role in anti-tumour defence is important. The selective inhibition of macrophage functions involved in malignant progression without interfering with cytotoxic ability may therefore identify important new targets for cancer therapy.