An Improved Bio‐assay for Abscisic Acid and Other Antitranspirants

Abstract

SUMMARY A greatly improved method is described for the bio‐assay of abscisic acid (ABA) and other compounds that possess ‘antitranspirant’ activity. As in the previous method, the stomatal responses are observed on pieces of isolated epidermis of Commelina communis immersed in small volumes of solution containing the compounds to be assayed. In new media, it is now possible to obtain linear responses to ABA concentrations over the range 10‐4‐10‐8 M in PIPES buffer at pH 6.8, and over the range 10‐7‐10‐10 M in citrate buffer at pH 5.5. In citrate buffer, it is possible to detect as little as 26 pg of ABA. In both media, the assay is unaffected by the presence of six other growth regulators (auxin, gibberellic acid, kinetin, coumarin, xanthinin and scopoletin) but the stomata closed partially in response to 10‐3 M chlorogenic acid.

Phytoalexins, Water‐stress and Stomata

“…Few studies have been made of the effects of phenolics on stomatal behaviour, but published data have generally agreed with those presented here. The inhibitory effects of chlorogenic acid correspond with those obtained by Ogunkanmi, Tucker & Mansfield (1973). However, Ogunkanmi et al (1973) observed no effects of scopoletin on stomatal opening, while in this study it caused slight inhibition of opening and some closure of open stomata.…”

“…The inhibitory effects of chlorogenic acid correspond with those obtained by Ogunkanmi, Tucker & Mansfield (1973). However, Ogunkanmi et al (1973) observed no effects of scopoletin on stomatal opening, while in this study it caused slight inhibition of opening and some closure of open stomata. The observation by Michniewicz & Rosej (1974) that ferulic acid increased transpiration rates of Phaseolus vulgaris leaves also supports our finding that ferulic acid had little effect on the opening of stomata that were initially closed, but stimulated wider opening of already open stomata.…”

REVERSIBLE EFFECTS OF FARNESOL ON COMMELINA COMMUNIS L.

“…Abaxial epidermis was removed using fine forceps and immediately laid on citrate buffer. Some samples were floated with the cuticle uppermost and cut into 70, 5 x 5 mm strips as described by Ogunkanmi et al (1973). Other samples were laid with the cuticle in contact with the buffer, but desiccation was found to be a problem during later incubation of the strips.…”

“…These folded strips (sample size 200) gave reproducible results providing care was taken to avoid measuring apertures in areas of trapped air or liquid. The two types of epidermal sample were incubated for 2 5 h at 25 °C in 4cm3 of solution in 12 illuminated glass vials supplied with COg-free air (Ogunkanmi et al, 1973). Control and farnesol treatments were fully randomized within each experiment.…”

“…Water stress experiments with Sorghum sudanense showed that in addition, another sesquiterpenoid was formed, the pattern of accumulation of which appeared better correlated with stomatal closure than that of ABA . It was detected in a bioassay specific for stomatal closure, using epidermis of Commelina communis (Ogunkanmi, Tucker and Mansfield, 1973) and was subsequently identified as all-trans farnesol. It was suggested that, like ABA, it served to reduce water loss in response to water stress through its action as an endogenous antitranspirant .…”