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.
Caryopses of Aegilops kotschyi Boiss. from different positions within the same spikelet differ greatly in their degree of dormancy. Imposition of this dormancy pattern is a correlative phenomenon within the spikelet, inasmuch as the uppermost developing caryopsis is least dormant and its development is associated with the dormancy status imposed on the lower (one or two) caryopses. Differences in pigmentation of the caryopses follow a corresponding pattern.Spikelets of Aegilops kotschyi Boiss. are normally composed of three florets, of which the terminal one is not fertile. Germinability of the two caryopses which are normally produced differs markedly. The upper one (from the subterminal floret) attains a high capacity for germination shortly after anthesis, while the lower one (from the basal floret) retains a high level of dormancy for a long time (6). The present study was made to investigate the endogenous phenomena involved in the imposition of this differential dormancy within the spikelet.
MATERIALS AND METHODSPlants of Aegilops kotschyi Boiss. were grown from mature caryopses, collected as random samples from the natural habitat, near Be'er Sheva, in May 1971. We found that growth at low temperature or with improved mineral nutrition cause a marked increase in the fertility of the terminal floret in the spikelets.In one experiment, plants were grown from seed to full maturity (Dec. 1971-May 1972 in the phytotron of the Faculty of Agriculture of the Hebrew University at Rehovot (2) in 16-hr photoperiods , at day/night temperature regimes of 27/22, 22/22, 22/17, and 17/12 C (day = 0800-1600, night = 1600-0800). The drained plant containers were irrigated each morning with half-strength Hoagland nutrient solution (4), and each afternoon with tap water. In all but the 17/12 C temperature regimes, the plants almost exclusively produced the typical spikelets with two caryopses each. At 17/12 C, about one-third of the spikelets contained caryopses in all three florets.In another experiment, plants were grown from seed to full maturity outdoors, in the natural growing season for this species (Dec. 1971-May 1972 at Bar-Ilan University. A planting medium consisting of sandy loam-vermiculite-peat moss-compost (5:1:1:1) was used. The drained plant containers were irrigated three times each week. One group was irrigated with tap water, the other with half-strength Hoagland nutrient solution. The first group produced typical spikelets with two caryopses each. About one-third of the spikelets produced by the second group contained caryopses in all three florets. The three caryopses thus produced did not differ greatly in mature dry weight. This was true in both experiments, although weight of the phytotrongrown caryopses was almost double that of the ones grown in the open (Table I).Germinability of the different caryopses was tested at 20 C in darkness (interrupted for counting and removal of germinated seedlings) in 9-cm Petri dishes containing one layer Whatman No. 2 filter paper and 4 ml of distilled H20. ...
SUMMARY
Onset of seed dormancy in caryopses of Aegilops kotschyi was investigated. Neither of the two caryopses in the spikelet was germinable until the fourth week after anthesis. After this, germinability of the upper caryopsis increased progressively while that of the lower one remained low. Drying by lyophilization improved germinability of the upper caryopsis, but only during the phase of increasing germinability. Excision of the upper floret at, or soon after anthesis, enhanced germinability of the remaining lower caryopsis. This response became progressively weaker as excision was delayed. The possibility is discussed that dormancy of the lower caryopsis depends on competition between the upper and lower caryopsis for an essential metabolite.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.