Search

From the juvenile leaves of Eucalyptus incrassata, a new euglobal having an acylphloroglucinol-sesquiterpene structure, euglobal-In-1 (1), has been isolated along with the known euglobal-III (2) and -V (3). The structure and stereochemistry of 1 were established by spectroscopic methods.

A potent germination inhibitor was found in the n-hexane soluble fraction of the methanolic extract of Eucalyptus pulverulenta. This inhibitor was identified as grandinol (1) which had been isolated from E. grandis. On the cress germination test, 1 showed I50 at 10 ppm. The other eight compounds in the fraction containing 1 on silica gel chromatography were also identified. Compounds (2) and (3) are regarded as phloroglucinol metabolites characteristic of the Eucalyptus species. The known compound (4) may be a good taxonomical marker for E. pulverulenta, and (5) ~ (9) are possibly common metabolites of Eucalyptus.

Unlike the G-inhibitors isolated from the leaves of Eucalyptus grandis , synthetic G-inhibitors showed no inhibition of photosynthetic electron transport. These findings indicated that small amounts of impurities present in the natural samples were responsible for the inhibition of photosynthetic electron transport. In support of this, grandinol and homograndinol were isolated from the leaves of E. grandis and were shown to be the active photosynthetic electron transport inhibitory components in the E. grandis preparation of G-inhibitors.

A growth regulator (G) occurs at high concentrations in adult leaves of E. grandis Maiden. Low concentrations of G are present in juvenile leaves of this species and also in adult leaves of some other Myrtaceae. Low concentrations of G (5×10(-6) and 10(-5) M) promote rooting in mung-bean cuttings and elongation in Avena coleoptile sections; high concentrations (5×10(-4) M) inhibit. These and other bioassay results indicate that G may have auxin-like activity.

A growth regulator (G; 4-ethyl-1-hydroxy-4,8,8,10,10 pentamethyl-7,9-dioxo-2,3 dioxyabicyclo (4.4.0) decene-5) from Eucalyptus grandis (Maiden) reduced stomatal conductance and also photosynthetic capacity when fed through the transpiration stream of detached leaves. The concentration of G required for this effect was high (10(-4) molar), but the amount of G taken up (dose) was below the level which has previously been found in E. grandis leaves. Similar effects were observed in detached leaves of Xanthium strumarium L. though almost 10 times more G was required. G reduced CO(2)-dependent O(2) evolution from isolated cells of X. strumarium. In spinach (Spinacia oleracea L.) chloroplasts, electron transport through photosystem II was reduced by G. It is proposed that G affects stomatal conductance and photosynthesis by reducing photosystem II activity in both the guard cell chloroplasts and mesophyll cell chloroplasts.

Three closely related growth regulators (G) that are present in some myrtaceous plants were examined for possible anti-transpirant effects. The bioassay material involved cuttings of mung bean and Eucalyptus rupicola. Stomatal resistance was determined by a diffusion porometer. Water loss was equated with water uptake by the cutting over a 24-hour period. In both bioassays, G reduced water loss. The reduced water loss was associated with stomatal closure. This anti-transpirant effect of G was five to ten times less than that of abscisic acid. The stomatal resistance to the diffusion of water vapor from mung bean leaves increased within 1 hour of application of G. Marked stomatal closure occurred after 6 hours when 5 to 7 micrograms of G had accumulated in the leaves. These results and earlier evidence, suggest that G growth regulators are involved in the water economy of Eucalyptus and perhaps other related genera.

Naturally occurring derivatives of 2,3-dioxabicyclo[4.4 .0]decane from Eucalyptus grandis exercise control over a range of physiological functions in plants. These include root strike in cuttings, water uptake, membrane permeability, frost resistance and inhibition of electron transport in photosynthesis. The synthesis and breakdown of these compounds in vivo and in vitro are discussed. Synthetic approaches to the naturally occurring compounds and related structures are presented in some detail, and some preliminary structure-activity relationships for synthetic analogues are discussed.

(1980). Eucalyptus radiata Oil as a Renewable Biomass. Agricultural and Biological Chemistry: Vol. 44, No. 10, pp. 2495-2496.