Effects of Amino Acids on Bean Leaf Abscission

Abstract

Stimulatory and inhibitory effects of auxin on leaf abscission were reported by Addicott and Lynch (1) using an abscission test with bean petiole explants. This test was modified by Gaur and Leopold (4), and then more extensively by Biggs and Leopold (2) in describing the range of auxin effects. Osborne (7) reported that besides auxins, diffusates from senescing leaves of various species were able to accelerate abscission of bean explants, while green leaf diffusates showed smaller effects. Since then, other workers (3,5) 2,000 ft-c, and a temperature of 24 ± 2 C. Approximately 13 days from seeding, the primary leaves were excised and the blades trimmed off. The petiole pieces were then cut by a 1 cm cutter so that the abscission zone was in the center of the explant with the pulvinus and about 1 mm of the midrib tissue on the distal side of the abscission zone and 5 mm of the petiole on the proximal side.Substances to be tested were dissolved in water and incorporated into a 1 % agar solution. The agar was poured into petri dishes to a depth of 4 mm and ten explants were imbedded into each dish with the proximal end in the agar. The dishes were subsequently returned to the same growth chamber except that they were now placed under a 400 ft-c light intensity. with a volume of water equal to the fresh weight of the leaves. 5 ml of this extract were poured onto a 6 cm AG 50W-X8 200 to 400 mesh cation exchange column (Calbiochem Corp.) and washed with 25 ml of water. The column was then eluted with 30 ml of 1 N ammonium hydroxide; this fraction contained onlv the amino acids and amides. After the amino acid and the neutral fractions were each flash evaporated to dryness, water was again added to the volume of original fresh weight. The pH was adjusted to 6 and the extracts were diluted 3.3 times with water before being incorporated into agar for the explant test. ResultsSince it had been suggested in various papers (12,13,14) that methyl donors might promote abscission through an incorporation into methylated pectins, several such compounds were checked using the bean abscission test. The compounds which were tested included those found to be most effective in plants for donating methyl groups to pectinic acid (9, 11), and each was tested over a concentration range of 10-7 to 5 X 10-3 Ai. Table I compares these methyl donors which are arranged in order of decreasing methylation efficiency with some non-methyl donors as modifiers of abscission in the bean abscission test. The most efficient methyl donors were, in general, far less effective in accelerating abscission than some other compounds, and the promotions were not proportional to the methyl donation abilities. Although formaldehyde is very effective in the promotion of abscission, the activity of this material was confined only to a concentration which probably does not oc-398 www.plantphysiol.org on May 7, 2018 -Published by Downloaded from

Pectin Esterase in Relation to Leaf Abscission in Coleus and Phaseolus

“…The low level of PE activity in coleus and the smallness of changes (14,20). Exogenous methionine accelerates abscission of bean, cotton and coleus petioles and tobacco flowers ( 14,17,20,24,25). This effect also is reversed by applied auxin (14,25).…”

“…This effect also is reversed by applied auxin (14,25). Choline, formaldehyde, serine and glycine-all potential methyl donors (21)-accelerate abscission of cotton and/or bean petioles (14,17).…”

Effects of d and l Amino Acids on Foliar Abscission

“…Alanine and glycine, 2 amino acids which have been reporte(d (13) to be miiore effective in promoting abscission in bean explants thani methionine, wvere conmpared wvith the latter compound for their effects on abscission in petiolules of bean. As shown in table I, experiment 1, alanine is mlore effective in an average of 12 days for the controls to less than 3 days.…”

“…As shown in table I, experiment 1, alanine is mlore effective in an average of 12 days for the controls to less than 3 days. The naturally occurring forms of these 4 amino acids had little or no promotive effects on abscission even at concentrations as high as 0.1 M. Glycine was also tested for its effect on abscission in the same plant material, since this amino acid along with the naturally occurring forms of alanine, aspartic acid, glutamic acid, and serine, were the amino acids reported to be the most effective in promoting abscission in bean explants (13). Glycine did not promote abscission in debladed petioles of cotton at concentrations as high as 0.10 M. Similar differences in the effects of the D and L forms of alanine, aspartic acid, glutamic acid, and serine on abscission in debladed petioles of Coleuts were also observed.…”

Changes in Abscission Processes with Aging

“…The mitochondria were quite active, giving QO2(N) values of about 1500 and P/O values of about 2.5 when oxidizing a mixture of pyruvate and succinate in the absence of inhibitors or uncouplers. Procedures for determining oxidative phosphorylation have been described (12 …”