Auxin and kinetin interaction in apical dominance.

The effects of auxin on the inhibition of lateral buds in decapitated bean plants are enhanced if kinetin is applied together with auxin. The uptake of (14)C-indoleacetic acid by the stumps of decapitated plants is increased in the presence of kinetin and leads to extensive transport of (14)C-indoleacetic acid in the stems. The increased bud inhibition resulting when auxin and kinetin are applied together may be due to greater amounts of auxin reaching the buds, but an alternative explanation is that metabolites are directed from the buds to the point of hormone application.

Auxin effects on the mobility of kinetin in the plant.

Kinetin (6-furfurylaminopurine) is generally considered to be relatively immobile within plants. Kinetin labeled with (14)C was applied to the stumps of decapitated bean plants, with or without simultaneous application of indoleacetic acid. Significantly greater amounts of kinetin moved downwards in the stem in the presence of added indoleacetic acid than in its absence.

A tracheid-differentiation factor from pine needles.

Exogenous indol-3yl-acetic acid (IAA), alone and together with several cytokinins, was ineffective in promoting the complete differentiation into tracheids of cambial derivatives of Pinus contorta Dougl.; IAA alone promoted cambial cell division and primary-wall growth in cambial derivatives throughout the stem's length. In contrast, a single pair of needles on a stem cutting in light promoted neither cambial cell division nor primary-wall growth in cambial derivatives but did promote complete differentiation of cambial cells into tracheids; tracheids differentiated only near the junction of the foliated short shoot with the stem. Clear inter-and intracellular differences in the extent of tracheid differentiation occurred in response to a single needle pair and have suggested the hypothesis that a specific tracheid-differentiation factor regulates the differentiation of cells into proto-, meta-, or secondary-xylem tracheary elements through an interaction with IAA.

The role of roots, cytokinins and apical dominance in the control of lateral shoot form in Solanum andigena.

The lateral bud of Solanum andigena has the potentiality to develop as a stolon or as a leafy, orthotropic shoot. Natural stolons are normally only produced from underground nodes, but aerial stolons can be induced to form by the application of a combination of indole-3-acetic acid and gibberellic acid (IAA/GA3) paste to the cut surface; under some conditions both natural or induced stolons are converted to upright, leafy shoots. The presence of roots was found to be necessary for the conversion of a natural stolon to a leafy shoot, but this root effect could be replaced by the synthetic cytokinin, 6-benzylaminopurine (BAP). By using α-(14)C-BAP it was demonstrated that cytokinin accumulates in the tip of an induced stolon, prior to its conversion to a leafy shoot caused by withdrawal of the IAA/GA3 paste. The application of IAA/GA3 to decapitated plants was shown to influence both the distribution and metabolism of the cytokinin. The possibility that the role of auxin in apical dominance, at least in part, is to control the distribution and metabolism of cytokinins is discussed.

Seed dormancy in Acer: Endogenous germination inhibitors and dormancy in Acer pseudoplatanus L.

Dormant seeds of Acer pseudoplatanus L. contain two zones of inhibition on paper chromatograms in "10:1:1" as detected by the lettuce and cress seed germination, and the wheat coleoptile bioassays. One zone at Rf 0.6-0.8 was partitioned into ethyl acetate at acid pH and was shown to contain ABA by its behaviour on GLC and isomerization under ultra-violet light. The other zone at Rf 0.9 was detected only in the germination bioassays and was partitioned into ethyl acetate over a range of pH indicating the presence of one or more neutral compounds.The inhibitors present in the embryo of dormant sycamore seeds inhibited the germination of non-dormant sycamore seeds at relatively low concentrations. A comparison with the effects of application of exogenous ABA indicated that endogenous ABA could not solely account for the inhibitory activity of seed extracts, which appeared to be due partly to the presence of ABA and partly to that of neutral compounds present in the embryo. Leaching treatments that removed dormancy led to a decrease in the level of inhibitors present mainly in the basic fraction. The exogenous application of kinetin to dormant sycamore seeds increased germination whereas gibberellic acid had no effect. Similar responses were obtained with lettuce seeds inhibited by the basic fraction of dormant sycamore seeds.It is suggested that an inhibitor-cytokinin interaction may be involved in the dormancy of sycamore seeds.

The effect of light on endogenous cytokinin levels in seeds of Rumex obtusifolius.

Exposure of Rumex obtusifolius seed to red light resulted in a rapid increase in extractable cytokinins. This increase can be reversed if the red light treatment is immediately followed by far-red irradiation. In germinating seed hardly any cytokinin activity could be detected in the butanol and aqueous extracts. An increase in the amount of activity present in the petroleum ether extracts of these seeds was, however, observed.The present findings suggest that cytokinin activity in light-sensitive seeds could be under the control of phytochrome.

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

The 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.

Further investigations into hormone-directed transport in stems.

The effect of IAA and three synthetic auxins on the upward movement of (32)P-orthophosphate and (14)C-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 (32)P-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 (14)C-sucrose and (32)P-orthophosphate accumulation in Phaseolus vulgaris but, unlike IAA, caused no increase in Pisum sativum. The downward transport of (14)C-IAA, (14)C-NAA, (14)C-2,4-D and (14)C-2,4,5-T from the decapitated apex was also studied. Results are discussed in terms of current theories of hormone-directed transport.

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

Most 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 hormonal control of wheat leaf unrolling.

The 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.

Polysomal changes in developing wheat leaves.

When leaf sections of 7-day old dark grown wheat leaves were incubated in white light, they unrolled and greened. Gibberellic acid was able to replace the light requirement and abscisic acid (ABA) inhibited the response to light. The percentage of ribosomes occurring as polysomes increased in response to light but not in response to GA3 treatment. Although ABA inhibited the unrolling and greening in light, it did not cause a preferential decrease or inhibition of polysome formation.

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

Considerable two-way interchange of label derived from (14)C-GA3 and (14)C-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 (14)C-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 (32)P-orthophosphate into various fractions of nucleic acid extracted from radish leaves.

By comparing (32)P-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 MAK(1) columns. Using sterile senescing radish leaf discs, a stimulation of (32)P-orthophosphate incorporation into various fractions of nucleic acid was observed as a result of kinetin treatment.

The effect of kinetin on the incorporation of labelled orotate into various fractions of ribonucleic acid of excised radish leaf discs.

Discs from senescing radish leaves were floated either on water or on a solution of kinetin and incubated in the dark. The kinetin-treated discs were fed with orotic acid-5-T and the control discs with orotic acid-6-C(14). The two lots of discs were combined and the RNA extracted by the phenol method. The H(3):C(14) ratio of the RNA after fractionation on sucrose density gradient was compared with the H(3):C(14) ratio of RNA extracted from two lots of control discs, one fed with orotic acid-5-T and the other with orotic acid-6-C(14) and then extracted together. In this way it was found that 21 hours treatment with kinetin causes a small but consistent stimulation of labelled precursor incorporation into all classes of RNA investigated.

Apical dominance and the effect of gravity on nutrient distribution.

The effect of orientation with resepct to gravity on the accumulation of phosphorus-32 into lateral and leader apices has been investigated in seedling trees of Betula pubescens. In upright, well-branched seedlings, showing only weak apical dominance, basally injected (32)P is distributed more or less equally among the lateral and leader apices. Re-orientation treatments which result in the assumption of strong dominance by a lateral apex also result in a marked accumulation of (32)P into that apex. This effect of orientation on nutrient transport is manifested within two to four days after application of the gravimorphic treatments.The results are discussed in the light of modern concepts of hormone-directed nutrient transport and a working hypothesis for the role of gravity in apical dominance of woody plants is suggested.

Cytokinins in Populus x robusta (schneid): Light effects on endogenous levels.

Cytokinin levels in both attached and detached mature leaves of poplar (Populus x robusta) increase transiently after short periods of exposure to red light. The degree and rapidity of response seems dependent on the physiological condition of the leaves. The cytokinin, 6-(2-hydroxybenzyl)amino purine riboside, specifically increases after red light treatment. Diurnal changes of leaf cytokinins occur, with a pronounced peak of activity being present at daybreak.

Cytokinins in Populus x robusta Schneid: A complex in leaves.

At least seven cytokinins have been detected in mature leaves of Populus x robusta Schneid after chromatography on Sephadex LH-20. Two of these have similar elution volumes to zeatin and zeatin riboside. A third appears to be a cytokinin glucoside. A fourth is a new, unidentified cytokinin, susceptible to mild oxidation, and yielding two cytokinin active products after acid hydrolysis. This cytokinin complex has been found in fully expanded leaves, a tissue in which cell division is completed.

Effects of abscisic acid on the levels of endogenous gibberellin-like substances in Solanum andigena.

Treatment of young, fully expanded leaves of Solanum andigena with synthetic abscisic acid resulted in marked increases in gibberellin-like substances. Abscisic acid treatment caused increases in the gibberellin content of leaves excised from both short day and long day grown plants.

Non-uniform distribution and seasonal variation of endogenous indol-3yl-acetic acid in the cambial region of Pinus contorta Dougl.

Endogenous, free indol-3yl-acetic acid (IAA) levels were measured in the main stem in the 10-year-old cambial zone, in the adjoining differentiating xylem, and in the adjoining mature xylem of 15-20-year-old Pinus contorta Dougl. by single-ion-current monitoring, combined gas chromatography - mass spectrometry, on several dates from early spring to early winter. Microscopy was used to determine the state of cambial activity on each harvest date. The IAA levels were found to be nearly constant at 1 µg g(-1) DW in the cambial zone from March to July, then to increase to near 2 µg g(-1) DW during the remainder of the growth season. No clear correlation was evident between number of fusiform cells per radial file and IAA content in the cambial zone. By contrast, the IAA content in differentiating xylem was higher than that in the adjoining meristematic zone on all harvest dates and also exhibited marked seasonal variation, peaking near 16 µg g(-1) DW in mid summer, and declining to 1 µg g(-1) DW in autumn. In mature xylem, IAA levels were very low and showed negligible variation. The fresh weight to dry weight ratio of differentiating xylem was greater than that of the cambial zone, and greater in the cambial zone than in mature xylem.