J. M. Botía

Enhancement of phenolic compounds in olive plants (Olea europaea L.) and their influence on resistance against Phytophthora sp.

Abstract The total phenol levels in different olive organs and tissues are studied. The HPLC-MS studies point to the presence of oleuropein, catechin and tyrosol as some of the main phenolic compounds in these extracts. The effect of Brotomax treatment on phenolic compound levels in this plant and the possible role of these compounds as antifungal agents against Phytophthora sp. are also studied. An increase in the total phenol content of leaves and stems was observed 120 days after treatment with 0.3% Brotomax. The cortex was the stem tissue which showed the greatest accumulation of these secondary compounds. An in vitro study of the inhibitory effect of these compounds on fungal growth revealed that tyrosol was the most active agent, followed by catechin and oleuropein, their fungitoxic effect being greater when they acted synergically.

UV irradiation alters the levels of flavonoids involved in the defence mechanism of Citrus aurantium fruits against Penicillium digitatum

The effect of UV irradiation on the levels of the flavanone, naringin, and the polymethoxyflavone, tangeretin, in the peel of Citrus aurantium fruits is described, as changes in the synthesis and/or accumulation of these compounds after infection with Penicillium digitatum. The growth of P. digitatum on previously irradiated fruit was reduced by up to 45%. Changes in flavonoid levels were detected, associated with inhibition of fungus growth, the naringin content falling by 69% and tangeretin levels increasing by 70%. The possible participation of naringin and tangeretin in the defence mechanism of this Citrus species is discussed.

Citrus cultivars with high flavonoid contents in the fruits

Abstract The flavanone contents of some lesser known citrus cultivars grown in Cuba have been determined in research searching for citrus species/cultivars with high flavanone contents. The cultivar ‘Galleta’ of the mandarin (Citrus reticulata Blanco) has a higher hesperidin content than the hybrid mandarin ‘Nova’, which is currently being used for the commercial obtainment of this flavanone. The grapefruit cultivar ‘Isaac’ had higher naringin levels than reported in the literature for any citrus species or cultivar. These two species seem potential candidates for the industrial obtainment of flavanones. With regard to neohesperidin, the ‘Afin’ and ‘Bouquet de Fleur’ varieties of Citrus aurantium L. from Spain are the best choices. A preliminary study indicated that the high flavanone contents resulted from the genetic characteristics of the cultivars, rather than from climatic effects.

BIOPRODUCTION OF DIOSGENIN IN CALLUS CULTURES OF TRIGONELLA FOENUM-GRAECUM L

The production of the steroidal sapogenin, diosgenin, by callus cultures of Trigonella foenum-graecum L. (fenugreek) is described. The levels of this secondary compound were examined by high performance liquid chromatography with a diode-array detector, and its identity was confirmed by mass spectrometry. The levels of diosgenin detected in leaf callus exceeded the levels detected in stem and root calli. The diosgenin levels accumulated in leaf, stem and root calli at 45 days (maximum production) represent 22, 10 and 27%, respectively, of the levels detected in the corresponding organs of the mother plant at 45 days.

Tylose formation and changes in phenolic compounds of grape roots infected with Phaeomoniella chlamydospora and Phaeoacremonium species.

The role of phenolic compounds in strengthening resistance of grapevine to young grapevine decline was analysed. The formation of tyloses has also been associated with this disease. A microscopic study showed that tyloses originated in parenchyma cells associated with the xylem and from there invaded the xylem lumen. As tyloses formed, there were changes in the cell wall, associated with the accumulation of crystalline structures. The cells surrounding the blocked xylem contained more polyphenolic compounds than the cells of intact xylem. Changes in the level and composition of polyphenolic compounds occurred in relation to the severity of infection. Tannin concentrations also increased with increasing numbers of xylem vessels containing tyloses. Root extracts added to fungal culture media inhibited mycelial growth of Phaeomoniella chlamydospora, Phaeoacremonium aleophilum and Pm. inflatipes. Inhibition was greater with extracts from roots with tyloses, and was also correlated with polyphenol content. Extracts of the leaves, stems and berries of vines treated with Brotomax, which increases the biosynthesis of phenolic compounds, inhibited mycelial growth of the fungi compared to untreated control plants.

Lateral diffusion of polarly transported indoleacetic acid and its role in the growth of Lupinus albus L. hypocotyls.

The transport and metabolism of indole-3-acetic acid (IAA) was studied in etiolated lupin (Lupinus albus L, cv. Multolupa) hypocotyls, following application of dual-isotope-labelled indole-3-acetic acid, [5-3H]IAA plus [1-14C]IAA, to decapitated plants. To study the radial distribution of the transported and metabolized IAA, experiments were carried out with plants in which the stele was separated from the cortex by a glass capillary. After local application of labelled IAA to the cortex, radioactivity remained immobilized in the cortex, near the application point, showing that polar transport cannot occur in the outer tissues. However, following application of IAA to the stele, radioactivity appeared in the cortex in those hypocotyl sections below the first 1 cm (in which the capillary was inserted), and the basipetal IAA movement was similar to that observed after application of IAA to the complete cut surface. In both assays, longitudinal distribution of 14C and 3H in the stele outside the first 1 cm was positively correlated with that of cortex, indicating that there was a lateral migration of IAA from the transport pathway (in the stele) to the outer tissues and that this migration depended on the amount of IAA in the stele. Both tissues (stele and cortex) exhibited intensive IAA metabolism, decarboxylation being higher in the stele than in the cortex while IAA conjugation was the opposite. Decapitation of the seedlings caused a drastic reduction of hypocotyl growth in the 24 h following decapitation, unless the hypocotyls were treated apically with IAA. Thus, exogenous IAA, polarly transported, was able to substitute the endogenous source of auxin (cotyledons plus meristem) to permit hypocotyl growth. It is proposed that IAA escapes from the transporting cells (in the stele) to the outer tissues in order to reach the growth-responsive cells. The IAA metabolism in the outer tissues could generate the IAA gradient necessary for the maintenance of its lateral flow, and consequently the auxin-induced cell elongation.

Distribution and changes of diosgenin during development of Trigonella foenum-graecum plants. Modulation by benzylaminopurine

The distribution and evolution of diosgenin levels in the different organs of Trigonella foenum-graecum were investigated. The results revealed that the maximum levels of this secondary compound are reached in the young leaves (20mg g−1 dry weight). A considerable increase in the levels of this sapogenin was observed after treatment of seeds with benzylaminopurine. These results open up new perspectives for the possible development of plants with high concentrations of this compound.

Influence of 2,3,5-triiodobenzoic acid on the transport and metabolism of IAA in lupin hypocotyls

The influence of 2,3,5-triiodobenzoic acid (TIBA) on the transport and metabolism of indolyl-3-acetic acid (IAA) was studied in etiolated lupin (Lupinus albus L) hypocotyls. Double isotope-labeled IAA [(5-3H)-IAA plus (1-14C)-IAA] was applied to the cut surface of decapitated seedlings. This confirmed that the species mobilized was unaltered IAA and permitted us to measure the in vivo decarboxylation of applied IAA. A pretreatment with TIBA applied to the cut surface produced a partial or drastic inhibition in the basipetal IAA movement at 0.5 or 100 μM, respectively. Since TIBA inhibits auxin polar transport by interfering with the efflux carrier, the above results suggest that 100 μM TIBA is sufficient to saturate the binding sites in the transporting cells. Compared to the control plants, in vivo decarboxylation of IAA was enhanced in 0.5 μM TIBA-treated plants, while no decarboxylation was detected after treatment with 100 μM TIBA. The in vitro decarboxylation of (1-14C)-IAA catalyzed by purified peroxidase was moderately activated by 100 μM and unaffected by 0.5 μM TIBA. The paradoxical effect of TIBA in vivo vs in vitro assays suggests that the in vivo effect of TIBA on IAA oxidation might be the consequence of the action of TIBA on the auxin transport system. Thus, transport reduction by 0.5 μM TIBA caused a temporary accumulation of IAA in that apical region of the hypocotyl which has the highest capacity to decarboxylate IAA. In the presence of 100 μM TIBA, a concentration which presumably saturates the efflux carriers, most of the added IAA can be expected to be located in the transporting cells where, according to the present data, IAA decarboxylation cannot take place.

Regulation of the diosgenin expression in Trigonella foenum-graecum plants by different plant growth regulators

Abstract The effect of indole-3-acetic acid (10−4 and 10−5 M), gibberellic acid (10−4 and 10−5 M) and ethephon (50 ppm) as an ethylene releasing compound, on the diosgenin synthesis and/or accumulation process and their effects on the growth of Trigonella foenum-graecum plants were investigated. Treatment with 10−5 and 10−4 M gibberellic acid led to 43 and 19% increases, respectively, of diosgenin in 30-day-old whole plants. These increases might be associated with the action that this growth regulator has in stimulating plant growth and the biosynthetic pathway of this sapogenin. A smaller increase was obtained with the 10−5 M indole-3-acetic acid treatment (6%, in 30 day-old plants), probably due to a stimulation of the biosynthetic pathway, alone, since no effect on growth was observed. Treatment with 50 ppm ethephon increased the diosgenin levels observed in the leaves of 15- and 30-day-old plants, growth of the whole plant being substantially reduced at 30 days in comparison with the growth observed in control plants. These figures reflect a 77% increase in diosgenin levels in 15-day-old plants and a decrease of 68% in 30-day-old plants.

Uptake and decarboxylation of indole-3-acetic acid during auxin-induced growth in lupin hypocotyl segments

The elongation growth of etiolated hypocotyl segments of lupin (Lupinus albus L.) was stimulated by acid pH (4.6 versus 6.5) and by IAA for periods of up to 4 h. After this time, the segments were unable to grow further. In the presence of an optimal IAA concentration (10 μM), acid pH increased the growth rate but had no effect on final growth. With suboptimal IAA (0.1 μM), however, acid pH increased growth in a more than additive way, suggesting a synergistic action between the two factors. This synergism may be explained by the increased IAA uptake and decarboxylation seen at an acid pH. These results reinforce the view that the effects of low pH and IAA on growth are not independent. Vanadate inhibited growth and also IAA uptake and decarboxylation. This inhibitor, therefore, probably inhibits growth not only by decreasing ATPase-mediated acidification but also by decreasing H+-dependent IAA uptake from the apoplasm. This dependence of IAA uptake on ATPase may be mediated by apoplasmic acidification. The amount of IAA decarboxylated increased when the assay conditions favored the growth of segments, indicating that IAA could be destroyed by decarboxylation during the auxin-induced growth.