Effect of {alpha}-Tomatine on the Permeability of Plant Storage Tissues

The effect of the steroidal glycoalkaloid -tomatine on effluxof cell material from disks of beetroot, potato, apple, andcarrot has been investigated. A concentration of 1 mM tomatinecaused large increases in efflux from all tissues but 10 µMhad no effect. Leakage from potato and apple, but not from beetrootand carrot, was stimulated by 100 µM. tomatine, althoughlosses were smaller. Alkaloid-induced efflux of cell materialwas reduced considerably by addition of 1 mM CaCl₂ and to alesser extent by 1 mM MgCl₂. Cholesterol and its acetate didnot reduce leakage from beetroot but higher concentrations ofthe former caused small reductions in loss of material frompotato. The significance of these findings in relation to theaction of other membrane-active compounds is discussed.     

Effect of {alpha}-Tomatine on the Response of Wheat Coleoptile Segments to Exogenous Indole-3-acetic Acid

A concentration of 10^–5 M tomatine had no effect on leakagefrom, or elongation of, wheat coleoptile segments, but consistentlyreduced IAA-enhanced extension growth by c. 50 per cent. Therewas no evidence of chemical interaction between the alkaloidand the auxin in solution, and IAA action was not affected bypre-treatment for up to 3 h with 10^–5 M tomatine. Studieswith [2-¹⁴C]IAA revealed that 10^–5 M tomatine did notinhibit uptake of auxin into segments. The effect of pre-treatingsegments for up to 3 h with IAA could be virtually nullifiedby 10^–5 M tomatine, as could also IAA-induced changesin properties of coleoptile cell walls. Results are discussedin relation to the ability of tomatine to disrupt membrane functionand to current hypotheses implicating membranes in the primaryaction of auxin.     

Response of Tissues2

Efflux of K⁺ from tomato fruit pericarp disks was not affectedby 100 µM tomatine, and only slightly by 1 mM. No differentialresponses to the alkaloid were observed in disks obtained fromfruits at different stages of development, and there was noevidence of any correlation between the level of endogenoustomatine and the effect of exogenous tomatine. Growth of tomatoseedlings in liquid nutrient medium was unaffected by 1 mM tomatinewhereas the growth oflettuce seedlings was stunted in the presenceof 100 µM alkaloid. The polyene antibiotic nystatin gavesimilar resultsto tomatine, having little effect on tomato tissuesbut causing marked inhibition of lettuce seedling development.     

Changes in the Alkaloid Content of Developing Fruits of Tomato (Lycopersicon esculentum Mill.): II. EFFECTS OF ARTIFICIAL ACCELERATION AND RETARDATION OF RIPENING

Fruit ripening in normal red-, orange- and yellow-fruited cultivarsof tomato was accelerated by treatment with Ethrel and suchfruits had lower tomatine levels than untreated controls. Fruitsin which ripening was retarded by incubating under reduced pressurehad higher alkaloid levels than controls. In each case, fruitripeness (as measured by pigmentation) showed a strong negativecorrelation with fruit tomatine. Ethrel treatment of fruitsof the non-ripening mutants nor and rin caused only a smalldevelopment of carotenoid pigment but markedly enhanced tomatinedisappearance. Pigmentation and tomatine were again negativelycorrelated although the quantitative relationship differed.Under normal circumstances, tomatine disappearance from tomatofruits-is apparently governed by the physiological (cf. chronological)age of the fruit rather than by its growth or ripening characteristicsalone. Key words: Tomato, Fruit ripening, Acceleration, Retardation, Tomatine     

Changes in the Alkaloid Content of Developing Fruits of Tomato (Lycopersicon esculentum Mill.): I. ANALYSES OF CULTIVARS AND MUTANTS WITH DIFFERENT RIPENING CHARACTERISTICS

Normal ripening red-, orange- and yellow-fruited cultivars oftomato showed similar patterns of fruit growth and tomatineaccumulation to those of non-ripening mutants. In all fruits,the tomatine concentration declined continuously from an earlystage although the absolute amount per fruit showed a biphasicpattern of accumulation and decline. The turning point' occurredat an earlier developmental stage in normal fruits than in mutants.Normal fruits also had a lower initial and higher final tomatinecontent than mutants on a per fruit basis although, on a unitweight basis, their initial concentration was higher and finalconcentration lower. Small, prematurely-ripened red fruits hadalkaloid levels intermediate between large, unripe, green fruitsand large, ripe, red fruits. It is concluded that growth andripening processes may both contribute to the decline in fruittomatine. Key words: Tomato, Fruit ripening, Tomatine     

Effect of {alpha}-Tomatine on the Integrity and Biochemical Activities of Isolated Plant Cell Organelles

Respiration in isolated mung bean shoot mitochondria was notaffected by either of the tomatine treatments (10^–3 M,pH 5, and 10^–5 M, pH 8) but was reduced in the excisedshoots by both treatments, although only at the higher of thetwo temperatures (5 °C and 25 °C). Inhibition was gradualand took at least 2 h. Tomatine treatment of excised shootsalso resulted in an increased leakage of K+. PS II activityin isolated spinach leaf chloroplasts was reduced only by thehigh pH tomatine treatment at 25 °C. Again, about 2 h treatmentwas required before significant effects were observed but thealkaloid did not cause disintegration of the chloroplast asmeasured by pigment release. Disruption of lysosomes isolatedfrom cauliflower inflorescence tissue and release of acid phosphatasewas enhanced by tomatine. Initially only 10^–5 M tomatineat pH 8 was effective but, later, effects could only be obtainedwith 10^–3 M alkaloid at pH 5. The differential susceptibilityof these organelles to tomatine is discussed in relation tomembrane structure and to the mode of toxicity of the alkaloid.