Hubert Dr. Sauter

Transpiration-inhibiting abscisic acid analogs

Synthetic analogs of abscisic acid (ABA) and their inhibiting effect on transpiration rates of detached barley leaves are presented. By systematically varying the carbon skeleton of ABA, the influence of structural changes on biological activity was investigated. The results show that a properly substituted cyclohexane unit and a six-carbon side chain seem to be indispensable for high ABA-like activity, whereas the oxidation state of the terminal carbon atom in the side chain appears to be less essential. Thus, synthetic compounds have been created that exhibit biological activities comparable both in type and strength with ABA itself. On the basis of molecular models, a hypothesis of the geometric arrangement of essential substructural units is proposed.

Inhibition of ethylene production in sunflower cell suspensions by a novel oxime ether derivative.

During the incubation of undifferentiated cell suspensions of sunflower (Helianthus annuus L. cv. Spanners Allzweck) ethylene production was effectively inhibited by the novel oxime ether derivative LAB 181 508, [[(Isopropyliden)-amino]-oxy]-acetic acid-2-(methoxyl)-2-oxoethylester (PACME). The compound was most active during the first 6 days of incubation exhibiting a value of 50% inhibition at 9.5×10−6 mol×L−1. The pattern of changes in the internal 1-aminocyclopropanecarboxylic acid (ACC) and N-malonyl-ACC (MACC) levels paralleled the influence on ethylene formation. While the addition of ACC fully restored ethylene production, applied S-adenosyl-L-methionine (SAM) was not effective. Experiments with [14C]indole-3-acetic acid (IAA) revealed that LAB 181 508 did not affect auxin uptake into suspension cells of sunflower. The results suggest that LAB 181 508 reduces ethylene formation by inhibiting the conversion of SAM to ACC in the biosynthetic pathway. In comparison to the structurally related inhibitor of ACC synthase, aminoethoxyvinylglycine (AVG), LAB 181 508 reduced growth and viability of the suspension cells only slightly. Low phytotoxicity of LAB 181 508 combined with a less complicated chemical synthesis might offer interesting aspects for physiological research and horticultural and agricultural practice.

Comparative potency of different plant growth retardants in cell cultures and intact plants

A comparison of the efficiency of a broad range of plant growth retardants on cell division growth of 13 cell suspension cultures is presented. The results show that (1) the new plant bioregulator tetcyclacis (NDA) is the compound with the highest activity in inhibiting cell division of all cultures tested, and (2) cell cultures react species-specifically to various compounds. Significant correlations between the results from suspension cultures and intact seedlings of the same plant species demonstrate the usefulness of cell cultures for identifying substances with a growth-regulating potency. Futhermore, the usefulness of cell cultures for establishing structure-activity relationships was shown with structural analogues of chlormequat and mepiquat chloride.