Interactions between plant hormones regulate submergence-induced shoot elongation in the flooding-tolerant dicot Rumex palustris.

Rumex palustris has the capacity to respond to complete submergence with hyponastic (upward) growth and stimulated elongation of petioles. These adaptive responses allow survival of this plant in habitats with sustained high water levels by re-establishing contact with the aerial environment. Accumulated ethylene in submerged petioles interacts with ethylene receptor proteins and operates as a reliable sensor for the under-water environment. Further downstream in the transduction pathway, a fast and substantial decrease of the endogenous abscisic acid concentration and a certain threshold level of endogenous auxin and gibberellin are required for hyponastic growth and petiole elongation. Interactions of these plant hormones results in a significant increase of the in vitro cell wall extensibility in submerged petioles. Furthermore, the pattern of transcript accumulation of a R. palustris alpha-expansin gene correlated with the pattern of petiole elongation upon submergence.

Cardenolide and Neutral Lipid Biosynthesis from Malonate in Digitalis lanata.

DIGITALIS LANATA plants were grown on water culture in a controlled environment and in the young, growing leaves free sterols (0.335 micromol/g FW), triacylglycerols (0.97 micromol/g FW) and cardenolides (1.82 micromol/g FW) were the major apolar and polar lipids. The cardenolide-containing fraction from these tissues was separated into 26 cardenolides by HPLC. The 5 major components (accounting for 60 % of the occurring glycosides) lanatosides A and C, acetyldigoxin, acetyldigitoxin, and glucoevatromonoside were identified by FABMS. Incorporation experiments with [2- (14)C]-acetate, [2- (14)C]-malonate, [2- (14)C]-mevalonate, and [U- (14)C]-sucrose (absorbed by excised, young, growing leaves) showed the labelling of all the occurring cardenolides after a 3 day incorporation period (as judged by HPLC). Comparing the simultaneous synthesis of labelled sterols and triacylglycerols, malonate could be considered as the most effective precursor in cardenolide synthesis, reaching an incorporation value of 4.1 % in a 4 day incorporation period. A time-course experiment revealed a temporary accumulation of (14)C in glucoevatromonoside, which may play a role as an intermediate in cardenolide production of DIGITALIS LANATA.

Rapid, quantitative HPLC analysis ofAsclepias fruticosa L. andDanaus plexippus L. cardenolides.

The cardenolide extracts from latex and aerial parts ofAsclepias fruticosa and ofDanaus plexippus reared onA. fruticosa orA. curassavica were purified by adsorption chromatography on silica gel. HPLC analysis on a C18 reverse-phase column with an acetonitrile-water gradient as mobile phase, separated 28 compounds with a UV spectrum typical forcardenolides. Afroside and gomphoside (major components), as well as calotropagenin, calotoxin, calotropin, calactin, uscharidin, uscharin, and voruscharin, occurred as single peaks in the profiles of latex and aerial plant parts ofA. fruticosa. Calactin and calotropin were the major cardenolides inDanaus plexippus reared onA. fruticosa orA. curassavica. Quantitative data obtained with digitoxin as internal standard showed that 1.3-1.5% of the leaf cardenolides were sequestered byDanaus plexippus in which levels of 70-80µg cardenolide per butterfly were measured. The calotropin from the leaves was almost completely sequestered, and 10-13% of the calactin was stored by the butterfly, assuming that no conversion occurred in larval tissues.

Quantitative aspects of latex lipid synthesis in Euphoribia lathyris L. seedlings.

Changes in the dry weight of the endosperm of Euphorbia lathyris L. seedlings showed that 2 mg material was taken up by the cotyledons after 10 d germination. A similar amount of sucrose could be taken up by these seedlings after removal of the endosperm. The maximum yield of latex triterpenes synthesized from this exogenously supplied substrate was in the same order of magnitude as the daily latex lipid increase in 19 µg per seedling. Cotyledons and adjacent 1-2 cm segment of the hypocotyl were the most active tissues in latex trieterpene synthesis. Excised cotyledons were able to accumulate 1-1.5 mg sucrose in 48 h from a sugar concentration higher than 0.1 mol l(-1). In this period a maximum amount of 8-10 µg latex triterpenes could be synthesized from this substrate. [(14)C]Mevalonic acid was rapidly taken up by excised cotyledons but not metabolized by the laticifers. This exogenously supplied precursor was rapidly converted to squalene and triterpenes by the adjacent tissue, and after 48 h incubation most of the (14)C in the nonsaponifiable fraction was traced in the phytosterolds.

Lipid synthesis in the laticifers of Euphorbia lathyris L. seedlings.

Various solutions of labeled precursors were absorbed by the cotyledons of etiolated Euphorbia lathyris L. seedlings. Incorporation of (14)C into triterpenes from [2-(14)C]mevalonic acid, [1-(14)C]acetate, [3-(14)C]pyruvate, [U-(14)C]glyoxylate, [U-(14)C]glycerol, [U-(14)C]serine, [U-(14)C]xylose, [U-(14)C]glucose, and [U-(14)C]sucrose was obtained. The [(14)] triterpenes synthesized from [(14)C] sugars were mainly of latex origin. [(14)C]mevalonic acid was only involved in terpenoid synthesis outside the laticifers. Exogenously supplied glyoxylate, serine, and glycerol were hardly involved in lipid synthesis at all. The (14)C-distribution over the various triterpenols was consistent with the mass distribution of these constituents in gas liquid chromatography when [(14)C]sugars, [(14)C]acetate, and [(14)C]pyruvate were used. These precursors were supplied to the seedlings in the presence of increasing amounts of unlabeled substrates. The amount of substrate directly involved in lipid synthesis as well as the absolute triterpenol yield was calculated from the obtained [(14)C]triterpenols. The highest yield was obtained in the sucrose incorporated seedlings, being 25% of the daily increase of latex triterpenes in growing seedlings.