Effect of osmotic stress on abscisic acid levels in xylem sap of sunflower (Helianthus annuus L.).

Addition of an osmoticum (-12 bars) to the rooting medium of sunflowers (Helianthus annuus L.) caused an increase in the level of abscisic acid (ABA) present in xylem exudate subsequently collected from cut shoots. Using tall and dwarf plants it was shown that there was a time lag in the appearance of increased levels of ABA in tall plants when compared with dwarf plants. The results indicate that the leaves, rather than the roots are the site of synthesis of ABA present in the xylem sap of osmotically stressed sunflower plants.

Effect of water stress on abscisic acid levels in white lupin (Lupinus albus L.) fruit, leaves and phloem exudate.

Abscisic acid (ABA) was identified by combined gas liquid chromatography-mass spectrometry in sieve-tube exudate collected from the cut stylar ends of white lupin fruit. Water stress caused an increase in ABA levels in leaf, seed and pod tissues and phloem exudate. When compared with levels in extracts of these tissues, the concentration of ABA in sieve-tube sap was very high. It is suggested that ABA is actively transported out of mature leaves in the phloem and this finding is discussed in terms of the ABA balance of the plant.

Effect of moisture stress on abscisic acid levels in Ricinus communis L. with particular reference to phloem exudate.

Abscisic acid (ABA) increased considerably in stem apices attached to Ricinus plants during a moisture stress but only slightly in stem apices which were detached and then allowed to lose water. A very marked rise in ABA also occurred in phloem-sap of moisture-stressed Ricinus plants. These results suggest that in apices of moisture-stressed plants the increased ABA does not arise in situ but is translocated to the apex after synthesis in the mature leaves.

Activity of gibberellins A24 and A 25 in five bioassay systems.

The growth-promoting activity of two C20 gibberellins, gibberellins A24 and A25, was determined in five bioassay systems and compared with that of gibberellic acid in four of the bioassays and with gibberellin A4 in the other. Gibberellin A24 was highly active in the oat mesocotyl, oat 1st leaf and cucumber hypocotyl assays. Gibberellin A25 was consistently less active than gibberellin A24 and was anactive over the tested range in the oat 1st leaf assay.

A simple system for determining the phloem mobility of compounds using excised pods of lupin (Lupinus albus L.).

Lupin pods were isolated from the plant and the pedicels placed in solutions of either radiolabeled sucrose, glucose, abscisic acid, or gibberellin A9 (GA9). Phloem exudate was collected from the cut stylar ends of the pods and both quantitative and qualitative data were obtained on the activity in the sap. Fed sucrose, abscisic acid, and GA9 were found in phloem exudate, but labeled glucose was immobile as the monosaccharide and activity in exudate appeared in sucrose.

Inhibitor content of phloem and xylem sap obtained from willow (Salix viminalis L.) entering dormancy.

It is shown that there is one growth inhibitor in the phloem sap and two in the xylem sap of willow (S. viminalis L.). The concentration of the inhibitor in the phloem sap, (+)-abscisic acid, increases as the plants enter dormancy. This is also shown for (+)-abscisic acid in the xylem sap, but the concentration of the second inhibitor decreases in a reciprocal manner.

Evidence for gibberellin-like substances in phloem exudate of higher plants.

Samples of sieve-tube sap were obtained as honeydew from aphids feeding on three species of higher plants. The honeydew was extracted, chromatographed and tested in several bioassays for the presence of gibberellin-like substances. The bioassay results indicated that gibberellin-like substances were translocated in the phloem of dandelion (Taraxacum officinale), broad bean (Vicia faba) and willow (Salix viminalis). Results obtained with willow showed that the concentration of gibberellin-like substances in the sieve-tube sap is daylength dependent, high levels being present in plants maintained under long days and low levels in short day plants.

Abscisic acid and related compounds in phloem exudate of Yucca flaccida haw. and coconut (Cocos nucifera L.).

Phloem sap collected from Yucca and coconut inflorescence stalks was shown to contain abscisic acid (ABA) and trace amounts of 2-trans ABA. In coconut sap, two compounds probably derived from ABA with mass spectra consistent with their being dihydrophaseic acid and either hydroxyphaseic acid or oxo-dihydrophaseic acid were also found to be present.

The biological activities of some new gibberellins (GAs) in six plant bioassays.

The biological activities of GA40, GA43, GA46, GA47, GA51 and GA4 20,4-lactone were tested over a wide range of concentrations in six plant bioassays. GA4 20,4-lactone showed the highest activity. Of the two 2α-hydroxylated compounds GA47 showed moderately high activity, and GA40 was slightly active. The 2ß-hydroxylated compunds GA43, GA46 and GA51 were virtually inactive.

The effect of fruit-removal on cytokinins and gibberellin-like substances in grape leaves.

Removal of fruit from potted cuttings of Vitis vinifera L. increased the concentration of a cytokininglucoside in leaf tissue extracts and decreased the level of extractable gibberellin-like substances. The glucoside (of zeatin riboside) is not present in xylem exudate of V. vinifera L., and appears to be synthesized in the leaves. Berry extracts contain zeatin-riboside and smaller amounts of cytokinin-glucoside. The changes in the level of these hormones are discussed in relation to previous results on abscisic acid and phaseic acid levels in grape leaves.

Identification of abscisic acid in flower buds of Coffea arabica (L.).

Extracts of flower buds of Coffea arabica (L.) collected before and after bud break contain abscisic acid. This was demonstrated using thin layer chromatography and gas chromatography combined with mass spectroscopy. Abscisic acid accounts for about 75% of the inhibitory activity in the acidic extract. The possible role of abscisic acid in the dormancy of coffee flower buds is discussed.

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

Auxin activity was detected in honeydew obtained from the aphid Tuberolachnus salignus (Gmelin) feeding on willow (Salix viminalis). Active uptake of (14)C-indolyl-3-acetic acid (IAA) into the sieve tubes was demonstrated by irrigating the cambial surface of willow bark with (14)C-IAA solution and assaying aphid stylet exudate. When, however, (14)C-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 (14)C-tryptophan contained only (14)C-tryptophan. When (14)C-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.

Activity of the aldehyde and alcohol of gibberellins A12 and A 14, two derivatives of gibberellin A 15 and four decomposition products of gibberellin A 3 in 13 plant bioassays.

The biological activities of the aldehyde and alcohol of gibberellins (GAs) A12 and A14, 3α-OH-GA15, 3ß-OH-GA15 wrong lactone (i.e. GA37 wrong lactone) and the four major decomposition products of GA3 (isogibberellic, allogibberic, epiallogibberic and Δ9(11)-dehydroallogibberic acids) were tested over a wide range of concentrations on 13 plant bioassays in order to ascertain certain of the structural requirements for biological activity. Generally modification of the basic GA-molecule decreased its activity in all assays except for derivatives of GA12 and GA14 (suggesting conversion of these derivatives to more polar, active GAs). Modification of the 3-OH from the usual 3ß to 3α configuration markedly reduced activity. Neither the presence of an inverted lactone ring (i.e. 3ß-OH-GA15 wrong lactone) nor changes to the lactone ring of GA3 (4→10) to form iso-GA3 (4→2) appreciably reduce activity. Further decomposition of GA3 to allogibberic and Δ9(11)-dehydroallogibberic acid reduced activity only slightly, but epimerization of allogibberic acid at C-9 essentially eliminated biological activity.