1981. Cytokinin interaction with free radical metabolism and senescence: Effects on endogenous lipoxygenase and purine oxidation. -Physiol. Plant. 53: 9-12.A typical system comprising xanthine-xanthine oxidase, which produces superoxide free radicals, significantly increased endogenous levels of the seneseence-associated hpoxygenase enzyme while cytokinin reversed this effect. It is suggested that in its interaction with free radicals cytokinin may have a dual effect: a) it may inhibit purine oxidation by the formation of a 2,8 dihydroxy purine which lowers the substrate affinity of xanthine oxidase; b) it may act as a direct free radical scavenger by virtue of H abstraction from the a-carbon atom in the amine bond.
SUMMARYThe germination inhibitor contained in the glume and hull of Aegilops kotschyi, an IranoTuranian graminaceous species growing in Israel, was investigated. It appears to function via the gibberellin (GA) metabolism of the plant and is coumarin-or abscisin-like in action.
Large and small Aegilops Kotschyi caryopses have low α-amylase activity. After imbibition in water a marked increase takes place in α-amylase activity in the large, hulled and dehulled caryopses and only a slight increase in the small ones. Exogenously applied gibberellic acid (GA3) enhances α-amylase activity in both caryopses, and also improves germination of the small, hulled caryopses.Removing parts of the hull from different sites on the palea or lemma of the small caryopses improves germination. The most pronounced effect was obtained when the segment was removed from the palea just above the embryo. When this excised site was covered with a strip of wet filter paper before germination, the resulting germination was essentially similar to that of the non-excised controls.The role of GA3 and seed coat in improving germination of small Aegilops caryopses is discussed.
SUMMARYThe possibility that asymmetric hormone distribution causes downward bending of weeping mulberry {Morus alba var. pendula) twigs was investigated. By extraction, bioassay and gas chromatography it was shown that while upper and lower twig sections had no differences in auxin activity, the two sides differed considerably in content of GA and ABA. The lower side contained high levels of endogenous GA while the upper side had higher concentrations of ABA. The significance of these results and their possible role in the weeping habit of tree growth are discussed. It is suggested that the high GA levels coupled to low ABA content induce greater lignification on the lower side of the twig and that this tissue is less sensitive to auxin and has a lower growth response than the upper side of the twig thus causing a downward inclination of growth.
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