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Monoclonal antibodies (mAB) have been produced which recognize the physiologically active 2‐cis‐(S‐form of the endogenous plant growth regulator, abscisic acid (ABA). Cross‐reaction with the ABA‐catabolites, phaseic and dihydrophaseic acid, is negligible, and (R)‐ABA, 2‐trans‐ABA, the ABA‐conjugate, ABA‐β‐D‐glucopyranosyl ester, as well as the putative ABA precursor, xanthoxin, are totally unreactive. In addition to being very specific, the mAB exhibit high affinites for 2‐cis‐(S)‐ABA: the K values were 7.9 × 109 l/mol and 3.7 × 109 l/mol for antibodies from two different clones. By mAB‐radioimmunoassay (RIA), 4 pg 2‐cis‐(S)‐ABA (99.5% confidence level) can be detected. mAB‐RIA can be used to quantitate ABA directly in unprocessed plant extracts.

Using serpentine fluorescence as an indicator of alkaloid production in cultured CATHARANTHUS ROSEUS cells, 6 cell lines producing alkaloid in excess of 300 mg/l were selected from more than 2 x 10 (5) individual colonies and their alkaloid production was monitored over a period of 8 years. Rapid loss of productivity invariably occurred during the first few months of cultivation, and spontaneous recovery of the initial production rates was never observed. Production of the indole alkaloid precursor, secologanin, followed the same pattern. Recovery of high alkaloid yielding strains was, however, possible at any time by repetition of the clonal selection procedure, but these strains were again instable. Clonal selection of high yielding plant cell strains apparently favours an inherent instability.

Vacuoles were isolated from different plant cell cultures and the transport mechanism for alkaloid uptake at the tonoplast membrane, as well as the compartmentation of enzymes and products inside the cells were investigated. While serpentine, the major alkaloid of Catharanthus roseus cells, is definitely located inside the vacuole, two key enzymes of the indole-alkaloid pathway, strictosidine synthase and a specific glucosidase, are located in the cytosol. Transport of alkaloids across the tonoplast into the vacuolar space has been characterized as an active, engergy-requiring mechanism, which is sensitive to the temperature and pH of the surrounding medium, stimulated by K(+) and Mg(2+), and inhibited by N,N'-dicyclohexylcarbodiimid and Cu(2+). The alkaloids accumulate inside the vacuoles against a concentration gradient, and the uptake system is specific for alkaloids indigenous to the plant from which the vacuoles have been isolated.

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