T-2 Toxin Decreases Logarithmic Growth Rates of Tobacco Callus Tissues

Abstract

T-2 toxin, a mycotoxin produced by Fusarium tricinctum, decreases logarithmic growth rates of tobacco (Nicotiana tabacum L.) pith callus tissues. Toxin concentrations as low as 0.003 ,uM will decrease growth rates; a concentration of 0.081 aM will halt growth completely. Additional exogenous cytokinin will reduce the inhibition by toxin only when the initial cytokinin and toxin concentrations are quite low (about 0.01 jaM). When inhibited tissues are transferred to media lacking toxin, they assume the faster, control rates ahnost immediately. Maximal yields of tissue (yields at the point at which no sugar was detected in the medium) are not affected by toxin concentrations of 0.01 to 0.036 ,uM.Logarithmic growth rates of tobacco pith callus tissues can be controlled by the concentration of exogenous cytokinin supplied in the growth medium (5, 6). Maximal yields of callus, on the other hand, are dependent on the sugar concentration (7,11). A reversible inhibitor that decreases growth rates in log phase, without decreasing maximal yields, could be valuable in determining the mechanism by which cytokinins control growth rates. Such an inhibitor would make it possible to vary growth rates without changing cytokinin concentration. We now report that T-2 toxin, a naturally occurring mycotoxin, is such an inhibitor.T-2 toxin, 4,15-diacetoxy-8-(3-methylbutyrloxy)-12,13 expoxy-A'-trichothecene-3-ol, is produced by Fusarium tricinctum (cda.) Snyd. & Hans. This toxin is one of more than twenty 12, 13-epoxytrichothecene toxins that affect both plants and animals (1, 3, 9). For example, Marasas et al. (9) reported that growth (fresh weight and length) of pea seedlings was depressed RESULTSInitial experiments indicated that T-2 toxin decreased callus yields when supplied at concentrations ranging from 0.003 to 0.081 ,uM (Fig. 1). At low 2iP' and T-2 concentrations, 2iP can decrease toxin inhibition to a limited degree.When the growth of the tissues was followed with standard kinetic measurements, tissues supplied with 11.5 Mm IAA, 0.1 Mm 2iP, and 0, 0.018, or 0.036 Mm T-2 toxin grew logarithmically with doubling times of 3.3, 5.5, and 7.55 days, respectively (Fig. 2).The reversibility of T-2 toxin inhibition is illustrated in Figure 3. Tissues were planted initially on medium containing 11.5 ,uM IAA and 0.1 puM 2iP, with or without 0.018 ,uM T-2 toxin. After 14 days, some tissues treated with toxin were transferred to fresh medium containing 11.5 uM and 0.1 uM 2iP, but without toxin. Almost immediately after transfer from toxin medium, tissues assumed the same growth rate as the tissues that had never been treated with toxin.Measurements of medium sugar for the experiment shown in Figure 2 indicated that 0.68, 0.74, and 0.65 g dry weight of tissue was produced/g sucrose during log phase from tissues treated with 0, 0.018, or 0.036 uM toxin, respectively. In a subsequent experiment, toxin-treated and control tissues were allowed to go to maximal yield (the point at which no sugar was detected in the medium). Dry we...

Aflatoxin B1—its effects on anin vitroplant system

“…This apparent reversal of inhibition would indicate that normal metabolic events could proceed, once Downloaded by [JAMES COOK UNIVERSITY] at 02:08 17 March 2015 (Helgeson et al 1973). Such an observation substantiates the probability of a direct toxic effect on AFBi exposure.…”

Competitive Inhibition of Beef Heart Cyclic AMP Phosphodiesterase by Cytokinins and Related Compounds

“…In spite of the widespread natural occurrence of cytokinins and the diverse metabolic effects which they are now known to promote in both plants and animals (1-13), relatively little has been learned about their mechanism of action at the molecular level. This prompted the design and synthesis of a class of potent anticytokinins, structurally related to the cytokinins, in the hope that the antimetabolites might extend the study of cytokinins to new biological systems and provide useful information pertinent to the mechanism of cytokinin action (14)(15)(16)(17).…”

“…In spite of the widespread natural occurrence of cytokinins and the diverse metabolic effects which they are now known to promote in both plants and animals (1-13), relatively little has been learned about their mechanism of action at the molecular level. This prompted the design and synthesis of a class of potent anticytokinins, structurally related to the cytokinins, in the hope that the antimetabolites might extend the study of cytokinins to new biological systems and provide useful information pertinent to the mechanism of cytokinin action (14)(15)(16)(17).On the basis of the similar effects obtained with N6-(A2-isopentenyl)adenosine and dibutyryl cyclic AMP, the cytokinins have been postulated to mediate their effects in phytohemagglutinin-treated human lymphocytes by involvement in cyclic AMP metabolism (13). This postulate was consistent with the finding that the cytokinin trans-zeatin ribonucleoside was inhibitory to the cyclic AMP phosphodiesterases from beef brain and crown-gall tumor cells, the latter of which was Abbreviations: Dibutyryl cyclic AM1P, N6,02'-(dibutyryl)adenosine cyclic 3': 5'-monophosphate; cyclic AMP, adenosine cyclic 3': 5'-monophosphate; trans-zeatin ribonucleoside, N6-(4-hydroxy-3-methyl-trans-2-butenyl)adenosine; 8-bromo …”

“…This prompted the design and synthesis of a class of potent anticytokinins, structurally related to the cytokinins, in the hope that the antimetabolites might extend the study of cytokinins to new biological systems and provide useful information pertinent to the mechanism of cytokinin action (14)(15)(16)(17).…”

Fusarium tricinctum T-2 Toxin Inhibits Auxin-promoted Elongation in Soybean Hypocotyl

“…Vanderhoef and Key (16) and Vanderhoef et al (17) showed that cytokinin inhibited auxin-promoted elongation more severely than control elongation. On the other hand, Helgeson et al (6) have shown that T-2 toxin can decrease cytokinin-controlled growth rates in the tobacco callus After a 1-hr preincubation of 1-cm hypocotyl sections in toxin, tissue was transferred to the growth chamber. After 15 min auxin was added.…”