Effects of cyclic-AMP on the formation of crown-gall tumors on the primary leaves of Phaseolus vulgris var. Pinto

Cyclic-AMP was found to inhibit the number of crown-gall tumorsthat developed on the primary leaves of Pinto beans by 30 to50%. A significant amount of inhibition was still observed whenthis nucleotide was added to the leaves up to 24 hr after theaddition of the bacterium. (Received September 17, 1974; )     

Changes in cyclic-AMP phosphodiesterase activity during the formation of crown-gall tumors on potato discs

Cyclic-AMP phosphodiesterase activity was found in crown-galltumor tissue obtained from the inoculation of potato discs withAgrobacterium tumefacicns strain B6. Consistently more enzymeactivity was found, in this tumor tissue than in the correspondingnormal tissue. This difference in enzyme activity was observedwhen strains other than B6 were used to induce tumors, or whennormal and tumor potato tissue grown in culture were examinedfor phosphodiesterase activity. (Received January 27, 1978; )     

Inhibition of crown-gall tumor formation on potato discs by cyclic-AMP and prostaglandins E1 and E2

Cyclic-AMP was found to inhibit the induction of crown-galltumors on potato discs by as much as 60%. This inhibition couldbe obtained when cyclic-AMP was added up to 10 hr after inoculationof the potato discs with a tumor inducing strain of Agrobacteriumtumefaciens. Similar results were obtained with prostaglandinsE¹ and E². Some of the implications of these results will bediscussed. (Received September 30, 1976; )     

Participation of the adenyl cyclase system in estradiol-activated growth of tumors in rat mammary glands

Early effects of estradiol on the adenylate cyclase system in target tissues were investigated. The proliferative processes in the estradiol-dependent mammary tumours and uterus of the rat were arrested by ovariectomy. Subsequent hormonal treatment resulted in adenylate cyclase activation and the increase of the cAMP level in these tissues, probably to be connected with the initiation of the cell growth. These events were followed by a decrease of the cAMP content necessary for active proliferation of tumour cells. cAMP phosphodiesterase is not responsible for the increase in the cyclic nucleotide content, but provides for its further hydrolysis. The stimulation of the adenylate cyclase system at early steps of estradiol action is typical both for normal and transformed estradiol-dependent tissues.     

Promotion of crown-gall tumor initiation on primary pinto bean leaves by certain inorganic salts

Crown-gall tumor initiation by Agrobacterium tumefaciens (SMITHand TOWN.) CONN, strain B6, on Phaseolus vulgaris L. var. "Pinto"was found to be sensitive to the addition of various salts tothe freshly inoculated primary leaves. Calcium, magnesium, zincand ammonium sulfates, cobalt and nickel chlorides and potassiumnitrate increased the number of tumors on inoculated leavesby 100 to 200 percent. Maximal promotions were obtained at concentrationsof 10^–7 to 10^–5 M with all of these salts exceptpotassium nitrate which was most active at 10^–2M. Sodium,potassium, calcium, magnesium and aluminum chlorides, and sodium,potassium and nickel sulfates had little or no effect on tumorinitiation. The combination of sodium sulfate with magnesiumchloride gave promotions comparable to those obtained with magnesiumsulfate, indicating that both the magnesium and sulfate ionswere necessary for the promotion obtained with this latter salt.Combining any two of the active salts at their optimum concentrationsfor promotion resulted in a reciprocal inhibition of the promotionobtained with either salt alone, suggesting these salts to beactive by different and potentially antagonistic mechanisms.The possible nature of these promotions is discussed, but theyremain too obscure to warrant a specific proposal for theirmode of action. ¹Present adress: Department of Botany, University of Khartoum,Khartoum, Sudan.     

Pathogenesis of barley leaves by Helminthosporium teres I: Green island formation and the possible involvement of cytokinins

Infection sites/green islands were formed in host leaf tissue infected with drops of H. teres. They exhibited higher cytokinin-like activity, sugar and starch than their surrounding tissue and tissue under water drops. The cytokinin-like activity at the infection sites increased from 24 to 72 h of incubation. However, the cytokinin-like activity of the tissue surrounding the infection drops and the tissue under water drops fell from 24 to 72 h incubation. The culture filtrate extracts of the fungus also produced cytokinin-like activity which increased from 1 to 10 days incubation. Application of this culture filtrate extract evoked green island formation. Application of kinetin to host leaves duplicated the green island effect. Thin-layer chromatographic fractions of the tissue extracts and the culture filtrate extracts revealed that a major portion of cytokinin-like activity corresponded to zeatin and zeatin riboside. The presence of zeatin and zeatin riboside (both in tissue and culture filtrate extracts) was confirmed by high performance liquid chromatography. Increases in the amounts of cytokinin-like substances, particularly zeatin and zeatin riboside, attributed to pathogen influence are suggested to be involved in infection and pathogenicity of H. teres.     

Lymphocyte and macrophage adenyl cyclase activity in animals with enhanced cell-mediated resistance to infection and tumors.

As cyclic AMP has been associated with the inhibition of lymphocyte cytotoxicity, studies were performed to investigate adenyl cyclase activity in lymphocytes and macrophages of Toxoplasma-infected mice in which the efferent limb of the cell-mediated immune response had previously been found to be activated. In peritoneal or splenic lymphocytes from $\text{Balb}\text{c}$ mice chronically infected with Toxoplasma in which growth of an isogeneic bladder tumor was found to be inhibited, adenyl cyclase activity was significantly less than in lymphocytes from uninfected control mice. Stimulation by prostaglandin E₁ or NaF in vitro led to higher levels of adenyl cyclase activity in lymphocytes from unifected animals than in cells from Toxoplasma-infected animals. Similar observations were made with peritoneal macrophages from Toxoplasma-infected and uninfected mice. Lower levels of adenyl cyclase activity were also found in lymphocytes from tumor-bearing mice than in lymphocytes from nontumor-bearing controls. These data suggest that production of cyclic AMP by lymphocytes is inhibited with activation of certain cell-mediated immune functions.     

The responsiveness of leukocyte adenyl cyclase to tylophorine in asthmatic subjects

A brief exposure of human peripheral leukocytes from asthmatic children to tylophorine (an alkaloid occuring in $\text{Tylophora}\text{-}\text{asthmaticus}$) caused the stimulation of adenyl cyclase. This effect was not observed in the leukocytes from the nonasthmatic children or adults.