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.

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

Sunflower plants (7 weeks old) were transferred from a modified Hoagland solution to a N-free nutrient medium and kept there for 7 days. Abscisic acid (ABA) was determined in several parts of the plants and in exudates collected from the roots of some of these plants.



N-deficiency considerably increased the ABA content of the leaves, especially the older ones, and also considerably increased the ABA content of the upper parts of the stem when compared to the control plants. In the roots and the exudates of these plants no ABA could be detected.



After dissecting the stems the ABA content in the roots of the control plants with normal N supply dropped quickly, probably due to rapid metabolization. Judging by results obtained, it seems unlikely that the roots are responsible for the remarkable increase of the ABA content in the shoots caused by N-deficiency.

Influence of N‐Deficiency on the Abscisic Acid Content of Sunflower Plants

Plastid 3-hydroxy-3-methylglutaryl coenzyme A reductase has distinctive kinetic and regulatory features: Properties of the enzyme and positive phytochrome control of activity in pea seedlings

The stem growth in darkness or in continuous red light of two pea cultivars, Alaska (Le Le, tall) and Progress No. 9 (le le, dwarf), was measured for 13 d. The lengths of the first three internodes in dark-grown seedlings of the two cultivars were similar, substantiating previous literature reports that Progress No. 9 has a tall phenotype in the dark. The biological activity of gibberellin A20 (GA20), which is normally inactive in le le geno-types, was compared in darkness and in red light. Alaska seedlings, regardless of growing conditions, responded to GA20. Dark-grown seedlings of Progress No. 9 also responded to GA20, although red-light-grown seedlings did not. Gibberellin A1 was active in both cultivars, in both darkness and red light. The metabolism of [13C3H]GA20 has also been studied. In dark-grown shoots of Alaska and Progress No. 9 [13C3H]GA20 is converted to [13C3H]GA1, [13C3H]GA8, [13C]GA29, its 2α-epimer, and [13C3H]GA29-catabolite. [13C3H] Gibberellin A1 was a minor product which appeared to be rapidly turned over, so that in some feeds only its metabolite, [13C3H]GA8, was detected. However results do indicate that the tall growth habit of Progress No. 9 in the dark, and its ability to respond to GA20 in the dark may be related to its capacity to 3β-hydroxylate GA20 to give GA1. In red light the overall metabolism of [13C3H]GA20 was reduced in both cultivars. There is some evidence that 3β-hydroxylation of [13C3H]GA20 can occur in red light-grown Alaska seedlings, but no 3β-hydroxylated metabolites of [13C3H]GA20 were observed in red light-grown Progress. Thus the dwarf habit of Progress No. 9 in red light and its inability to respond to GA20 may be related, as in other dwarf genotypes, to its inability to 3β-hydroxylate GA20 to GA1. However identification and quantification of native GAs in both cultivars showed that red-light-grown Progress does contain native GA1. Thus the inability of red light-grown Progress No. 9 seedlings to respond to, and to 3β-hydroxylate, applied GA20 may be due to an effect of red light on uptake and compartmentation of GAs.

Gibberellins in dark- and red-light-grown shoots of dwarf and tall cultivars of Pisum sativum: The quantification, metabolism and biological activity of gibberellins in Progress no. 9 and Alaska.

'Wilty' (JI 1069), a mutant of Pisum sativum, has been examined for its ability to produce abscisic acid (ABA) under water stress. ABA was measured using combined gas chromatography-mass spectrometry and multiple-ion-monitoring employing a deuterated internal standard. In intact draughted plants, 'Wilty' produced less ABA than a non-wilty line (JI 1194) and maximum production was delayed. Detached leaves of the wilty mutant lost significantly more water than control leaves but did not show an increase in ABA content. Non-stressed mutant material from both intact plants and isolated leaves contained less ABA than control tissue.

The Physiology of a Wilty Pea: Abscisic Acid Production under Water Stress

Wilting tall or dwarf peas produced a marked increase in abscisic acid (ABA). Evidence from light- and dark-grown peas does not support the concepts that differences in ABA are associated with differences in height or that ABA is a correlative inhibitor of stem elongation.

G. M. Simpson

Papers

Abscisic acid associated with wilting in dwarf and tall Pisum sativum