P. F. Wareing

Some physiological responses to d,l abscisin (dormin)

SummaryThe responses to synthetic d,l abscisin have been studied in a variety of tests. When fed in aqueous solution continuously to leaves of seedlings growing under long day conditions, d,l abscisin caused the cessation of extension growth and the formation of typical resting-buds in Betula pubescens, Acer pseudoplatanus and Ribes nigrum. Abscisin also inhibited the growth of non-dormant buds of potato when applied to the whole tubers, but was much less effective when applied to isolated tuber plugs.Abscisin accelerates the senescence of leaf discs of a wide variety of species, but is less effective when sprayed on to attached leaves, except at relatively high concentrations (50–100 ppm).Abscisin inhibited flower induction in the long day species, Lolium temulentum and Spinacia oleracea, when applied to the leaves during a period of exposure to 15-long-day cycles. Abscisin promoted flowering in the short-day plants Pharbitis nil, Ribes nigrum and strawberry when applied under long day conditions, but it did not induce flowering in certain other typical short day plants. Tuberization in Solanum andigena and two cultivars of S. tuberosum was promoted by abscisin when applied to the leaves of plants growing under long-day conditions.

Auxin-directed transport of radiophosphorus in stems

SummaryThe role of indolylacetic acid (IAA) in influencing the movement of radiophosphorus from a remote locus has been investigated in the decapitated stems of Pisum sativum (var. Meteor) and disbudded shoots of Populus robusta. It has been shown after only a few hours that the radioisotope accumulates at the region where the auxin was applied. By steam-girdling experiments with pea, it was established that auxin-induced transport occurs via the phloem and other obserbations suggest that this effect may be independent of growth. When tri-iodobenzoic acid was applied together with IAA at the stump or to the surface of the stem between the IAA source and the injection point of the tracer, the transport of 32P along the stem was greatly reduced. Of a number of auxin-type substances tested, only naphthoxyacetic acid gave a comparable response to that obtained with IAA, whilst other growth regulators such as kinetin or gibberellic acid did not stimulate 32P transport.Studies with isolated poplar cuttings showed that auxin-induced transport could only be demonstrated by completely disbudded shoots. Again, phloem transport seemed to be involved and the movement of 32P could be more readily induced in an acropetal direction.The results are discussed in relation to some recently proposed theories concerning the mechanism of translocation in the phloem.ZusammenfassungDer Einfluß der Indolylessigsäure (IES) auf die Wanderung von radioaktivem Phosphor wurde an dekapitierten Sprossen von Populus robusta nach Entfernung ihrer Knospen und an dekapitierten Stengeln von Pisum sativum (var. Meteor) untersucht. Bereits nach wenigen Stunden war eine Anhäufung von 32P am Ort der Auxinzufuhr zu erkennen. Durch Dampf-Ringelungsversuche ließ sich bei Pisum zeigen, daß der Auxin-induzierte Transport über das Phloem erfolgt; weitere Beobachtungen lassen darauf schließen, daß dieser Effekt unabhängig vom Wachstum sein dürfte. Wenn man gleichzeitig mit IES Trijodbenzoesäure (TIBA) auf die apikale Schnittfläche aufbringt oder in einer Zone zwischen Auxinquelle und Injektionsstelle des 32P als Paste auf die Oberfläche des Sprosses aufträgt, so wird der Längstransport des markierten Phosphors erheblich gehemmt.Es wurden auch noch einige andere Verbindungen von Wuchsstoffcharakter geprüft. Von ihnen führte nur Naphthyloxyessigsäure zu einem ähnlichen Effekt wie IES; andere Wachstumsregulatoren wie Kinetin oder Gibberellinsäure förderten den 32P-Transport nicht.Untersuchungen an isolierten Pappelsprossen zeigten, daß der auxininduzierte Stofftransport nur in solchen Sprossen zu beobachten ist, deren Knospen vollständig entfernt worden waren. Auch hier scheint es sich um einen Transport im Phloem zu handeln. Die Wanderung von 32P ließ sich stets leichter in akropetaler Richtung induzieren.Die geschilderten Ergebnisse werden in Beziehung zu einigen neuerdings vorgeschlagenen Theorien des Transportmechanismus im Phloem diskutiert.

Phytochrome and hormonal control of expansion and greening of etiolated wheat leaves.

SummaryUnrolling of etiolated wheat leaf segments is stimulated by short periods of exposure to red light. Both gibberellic acid and kinetin will stimulate unrolling in the dark, whereas abscisic acid (ABA) inhibits the unrolling response to these two hormones and to red light. Exposure to 5 minutes of red light leads to a rapid increase in endogenous gibberellin levels in etiolated wheat leaves, and this increase is followed by a rapid decline. Pre-treatment with ABA inhibits the increase in gibberellin levels in response to red light, but the ihibitory effect of ABA on unrolling cannot be ascribed only to its effect on gibberellin levels. Pre-treatment with red light reduces the lag-phase in chlorophyll development when wheat leaf segments are subsequently exposed to white light; the effect of red light may be replaced by pre-treatment with kinetin, but gibberellic acid is relatively ineffective in this respect.

The red light controlled production of gibberellin in etiolated wheat leaves.

SummaryMost of the gibberellin activity detectable in extracts of etiolated wheat leaf tissue occurs in a bound form. There is a rapid increase in extractable gibberellin-like substances following exposure of the tissue to red light with a concomitant fall in the amount of bound gibberellin. Actinomycin-D and AMo 1618 do not inhibit this initial phase of red light stimulated gibberellin production.It is concluded that red light stimulated gibberellin production in etiolated wheat leaf tissue is due to release from a bound form and to synthesis.

The effects of abscisic acid, kinetin and 5-fluorouracil on ribonucleic acid and protein synthesis in senescing radish leaf disks.

SummaryThe effects of abscisic acid and kinetin on RNA synthesis in senescing radish leaf disks were investigated using the improved resolution afforded by polyacrylamide gel electrophoresis. Kinetin stimulated and abscisic acid inhibited incorporation of radioactivity into cytoplasmic ribosomal RNA and soluble RNA. Chloroplast ribosomal RNA synthesis appeared to be confined to the period of leaf expansion and was not detected in fully mature leaves. The effects of kinetin in retarding and of abscisic acid in accelerating leaf senescence were not altered by the inhibition of cytoplasmic ribosomal RNA synthesis with 5-fluorouracil. Following inhibition of cytoplasmic ribosomal RNA synthesis with 5-fluorouracil, kinetin stimulated and abscisic acid inhibited incorporation of radioactivity into polydisperse RNA. These results are discussed in relation to the possible mode of action of kinetin and abscisic acid in senescing leaf tissue.

The hormonal control of wheat leaf unrolling.

SummaryThe unrolling of etiolated wheat leaf sections in the dark is stimulated by the application of gibberellic acid (GA3). GA3 is most effective if applied for a short time at the beginning of incubation. Kinetin also stimulated leaf unrolling in the dark. AMO1618 and CCC inhibit red light and kinetin-stimulated unrolling. Gibberellin-like substances extracted from red light-treated leaf tissue are effective in stimulating leaf unrolling.Ethylene production in leaf sections is stimulated by IAA, GA3 and kinetin and inhibited by ABA. A brief exposure to red light decreases the ability of the tissue to produce ethylene. It is concluded that ethylene plays no important role in the control of leaf unrolling by red light or by the application of hormones.

Further investigations into hormone-directed transport in stems

SummaryThe effect of IAA and three synthetic auxins on the upward movement of 32P-orthophosphate and 14C-sucrose has been investigated in decapitated stems of Phaseolus vulgaris L., Pisum sativum L., Coleus blumci L. and Helianthus annuus L. IAA greatly enhanced the accumulation of 32P-orthophosphate in Phaseolus vulgaris and Pisum sativum, whereas in C. blumei and H. annuus it did not. 2,4-D like IAA, caused an increase in 14C-sucrose and 32P-orthophosphate accumulation in Phaseolus vulgaris but, unlike IAA, caused no increase in Pisum sativum. The downward transport of 14C-IAA, 14C-NAA, 14C-2,4-D and 14C-2,4,5-T from the decapitated apex was also studied. Results are discussed in terms of current theories of hormone-directed transport.

Studies on the movement of indole auxins in willow (Salix viminalis L.)

SummaryAuxin activity was detected in honeydew obtained from the aphid Tuberolachnus salignus (Gmelin) feeding on willow (Salix viminalis). Active uptake of 14C-indolyl-3-acetic acid (IAA) into the sieve tubes was demonstrated by irrigating the cambial surface of willow bark with 14C-IAA solution and assaying aphid stylet exudate. When, however, 14C-IAA was applied to the peridermal tissues of the bark or to a mature leaf most of the radioactivity (collected in honeydew or stylet exudate) co-chromatographed with indolyl-3-acetyl-aspartic acid (IAAsp). The presence of IAAsp in honeydew was not affected by extraction procedure or by aphid metabolism. Honeydew obtained from willow treated with 14C-tryptophan contained only 14C-tryptophan. When 14C-IAA was applied in agar to the cut end of willow segments the radioactivity was found to move in a basipetally polar manner. The direction of movement of radioactivity in the sieve tubes, however, was found to be influenced by the proximity of the roots. Nevertheless, there was evidence that endogenous auxin in the sieve tubes does move in a predominantly basipetal direction.

The interchange of 14C-kinetin and 14C-gibberellic acid between the bark and xylem of willow

SummaryConsiderable two-way interchange of label derived from 14C-GA3 and 14C-kinetin has been shown to occur between the xylem and extra-cambial tissue of Salix viminalis L. Radial translocation of both growth substances from the transpiration stream to the sieve-tube sap has been demonstrated by the use of an aphid technique. This is the first record of the bark-xylem interchange of these two growth hormones.A high percentage of 14C-label is present in compounds other than GA3 and kinetin 8 hours after application.Mechanisms of lateral transfer are discussed together with their possible physiological significance.

The Effects of Kinetin and Contaminating Bacteria on the Incorporation of 32P-Orthophosphate into Various Fractions of Nucleic Acid Extracted from Radish Leaves

SummaryBy comparing 32P-orthophosphate incorporation into nucleic acid extracts of sterile and non-sterile radish leaf discs, it was shown that contaminating bacteria cause a 2–4 fold increase in the rate of precursor incorporation and alter the pattern of label distribution after fractionation of the extracts by sedimentation through sucrose gradients or chromatography on MAK1 columns. Using sterile senescing radish leaf discs, a stimulation of 32P-orthophosphate incorporation into various fractions of nucleic acid was observed as a result of kinetin treatment.