Yasunori Koda

The Role of Jasmonic Acid and Related Compounds in the Regulation of Plant Development

Publisher Summary This chapter reviews the roles of jasmonic acid (JA) and related compounds in the regulation of plant development. JA-related compounds are widely distributed among higher plants and are potent inducers of expression of several genes, such as the genes of proteinase inhibitor in tomato plants and the genes of vegetative storage proteins in soybean plants. JA is synthesized from linolenic acid by a series of enzymes. The initial reaction in JA synthesis is catalyzed by lipoxygenase, which is a common enzyme in plant tissues. JA-related compounds are easily extracted from plant materials by methanol, ethanol, or acetone. The material should be homogenized immediately after harvest with sufficient solvent to prevent the enzymatic changes of the compounds. JA has four stereoisomers because of the presence of two chiral carbons at the C-1 and C-2 positions of a cyclopentane ring. Maslenkova et al. examined the effect of JA on the oxygen-evolving activity of chloroplasts isolated from barley leaves. The kinetics characteristics of oxygen evolution indicated that JA decreased the value of the total number of oxygen-evolving centers. JA affects the degree of structuring of the granal region or the structural integrity of the electron transport chain in barley chloroplasts.

Potato tuber-inducing activities of jasmonic acid and related compounds

Salicylic acid (SA) induced potato tuberization in vitro at concentrations greater than 10−5 M. A comparison of the tuber-inducing activities of various related compounds suggested that derivatives of benzoic acid with a free carboxyl group and a substituent at the C-2 position of the benzene ring have this activity. Although SA had the strongest activity among the compounds tested, the activity was about one thousandth of that of natural jasmonic acid (1R,2S-jasmonic acid) in terms of the threshold concentration for activity. Spraying SA to leaves of plants grown under tuber-noninducing conditions (long days) induced tuberization. However, the natural occurrence of SA was not detected in the leaves of potato plants that had been grown under tuber-inducing conditions (short days) and had begun to form tubers. The results seem to exclude the possibility of the involvement of SA in the natural tuberization of potato plants.

Comparisons of various biological activities of stereoisomers of methyl jasmonate

Abstract Stereoisomers of methyl jasmonate (JA-Me) showed different biological activities in four bioassay systems. Growth of soybean callus was inhibited strongly by (1R,2S)- and (1R,2R)-JA-Me. By contrast, (1S,2R)- and (1S,2S)-JA-Me had very low inhibitory effect on it, suggesting that the activity is dependent largely on the (1R)-configuration. With regard to potato tuber-induction and the senescence-promotion of oat leaves, although the highest activities were found in (1R,2S)-JA-Me, isomers which have the (1S)-configuration showed considerable activities. (1R,2S)- and (1S,2R)-JA-Me equally inhibited straight growth of oat coleoptiles. These results suggest that requirements of the absolute configurations of the two side chains with respect to the plane of the cyclopentanone ring for each activity are different, and that there are different receptors which trigger reactions leading to the individual activity.

Somatic embryogenesis induced by the simple application of abscisic acid to carrot (Daucus carota L.) seedlings in culture.

Abstract. Seedlings of carrot (Daucus carota L. cv. Red Cored Chantenay) formed somatic embryos when cultured on medium containing abscisic acid (ABA) as the sole source of growth regulator. The number of embryos per number of seedlings changed depending on the concentration of ABA added to the medium, with a maximum embryo number at 1 × 10−4 M ABA. Seedling age was critical for response to exogenous ABA; no seedling with a hypocotyl longer than 3.0 cm was able to form an embryo. Removal of shoot apices from seedlings completely inhibited the embryogenesis induced by application of exogenous ABA, suggesting that the action of ABA requires some substance(s) that is translocated basipetally from shoot apices through hypocotyls. Histologically, somatic embryos shared common epidermal cells and differentiated not through the formation of embryogenic cell clumps, but directly from epidermal cells. These morphological traits are distinct from those of embryogenesis via formation of embryogenic cell clumps, which has been found in embryogenic carrot cultures established using 2,4-dichlorophenoxyacetic acid or other auxins. These results suggest that ABA acts as a signal substance in stress-induced carrot seedling somatic embryogenesis.

Similarities of the biological activities of coronatine and coronafacic acid to those of jasmonic acid

Coronatine, a phytotoxin produced by Pseudomonas syringae pv. atropurpurea and an amide of coronafacic acid and coronamic acid, is known to induce the expansion of cells in potato tubers just as jasmonic acid (JA) does. Furthermore, the chemical structure of coronafacic acid resembles that of JA to some extent. These observations led us to postulate that coronatine and related compounds might have biological activities similar to those of JA. We compared the biological activities of coronatine and coronafacic acid to those of JA in four jasmonate-responsive assay systems, namely, in assays for tuber-inducing activity (with single-node segments of potato stems), for cell expansion-inducing activity (with cells of potato tubers), for cell division-inhibiting activity (with soybean callus) and for senescence-promoting activity (with oat leaves). Coronatine had a positive effect in all these assays and its activity was 100 to 10 000 times higher than that of JA in terms of the threshold concentration for activity. Coronafacic acid also gave a positive result in all the assays, but its activity was slightly weaker than that of JA in two assay systems. These results suggest that the special configuration of side chains with respect to the plane of the cyclopentanone ring, namely, the 1R, 2S configuration in JA and the 3aS, 7aR configuration in coronatine and coronafacic acid, is necessary for these various biological activities.

Expansion of potato cells in response to jasmonic acid

Abstract Since jasmonic acid (JA) has strong potato tuber-inducing activity and tuberization of potato plants is initiated mainly by expansion of cells, it is highly likely that JA is capable of inducing expansion of potato cells. When disks cut from potato tubers were cultured on medium that contained JA, the disks began to swell markedly after 1 day in culture. Within 5 days in culture, the fresh weight of the disks doubled in the presence of JA at 3 × 10 −5 M. Light microscopy revealed that the swelling was due to the expansion and not the division of cells. JA exhibited this expansion-inducing activity at concentrations above 10 −5 M. Air-borne methyl jasmonate (JA-Me) also exhibited this activity. The cells that expanded in response to JA in the medium or to airborne JA-Me were localized on the lower side of each disk. The localization seemed to be a result of the greater availability of water. Sucrose in the culture medium was not necessary for the expansion of cells. The expansion-inducing activity appeared to be specific to JA and related compounds, since various plant hormones and a precursor of ethylene had no appreciable effects on the size of cells. Abscisic acid at concentrations above 10 −5 M and benzyl adenine at concentrations above 10 −4 M markedly inhibited the JA-induced expansion of cells. The expansion-inducing activities of JA and JA-Me seem to be associated with their tuber-inducing activities.

Potato micro-tuber inducing substances from Lasiodiplodia theobromae

Abstract Three potato-tuber inducing substances were isolated from Lasiodiplodia theobromae IFO 31059, and their structures identified as mellein, jasmonic acid and a previously unrecorded cyclohexene named theobroxide.

Micropropagation of Cypripedium macranthos var. rebunense through Protocorm-like Bodies Derived from Mature Seeds

Cypripedium macranthos var. rebunense is the most famous terrestrial orchid in Japan, since the variety has large beautiful yellowish-white flowers and is threatened with extinction. Establishment of an efficient method for micropropagation is urgently needed. When imbibed mature seeds of the orchid, that had been pre-chilled at 4°C for 3 months, were sown onto Hyponex-peptone medium that contained both α-naphthaleneacetic acid (NAA) and cytokinin, protocorm-like bodies (PLBs) were formed from germinated seeds. Although the growth of PLBs was very slow, plantlets were easily regenerated from the PLBs on hormone-free medium. The PLBs were subcultured eight times along 2 years without loss of ability to regenerate plantlets, and one aggregate of PLBs (ca. 5 mm in diameter) produced ca. 10 plants within a year. A reduction of commercial value through a large-scale micropropagation by this method will be able to prevent illegal collection from the wild populations.

Characterization of mycorrhizal fungi isolated from the threatened Cypripedium macranthos in a northern island of Japan: two phylogenetically distinct fungi associated with the orchid

We isolated Rhizoctonia-like fungi from populations of the threatened orchid Cypripedium macranthos. In ultrastructural observations of the septa, the isolates had a flattened imperforate parenthesome consisting of two electron-dense membranes bordered by an internal electron-lucent zone, identical to the septal ultrastructure of Rhizoctonia repens (teleomorph Tulasnella), a mycorrhizal fungus of many orchid species. However, hyphae of the isolates did not fuse with those of known tester strains of R. repens and grew less than half as fast as those of R. repens. In phylogenetic analyses, sequences for rDNA and internal transcribed spacer (ITS) regions of the isolates were distinct from those of the taxonomically identified species of Tulasnella. On the basis of the ITS sequences, the isolates clustered into two groups that corresponded exactly with the clades demonstrated for other Cypripedium spp. from Eurasia and North America despite the geographical separation, suggesting high specificity in the Cypripedium–fungus association. In addition, the two phylogenetic groups corresponded to two different plant clones at different developmental stages. The fungi from one clone constituted one group and did not belong to the other fungal group isolated from the other clone. The possibility of switching to a new mycorrhizal partner during the orchid’s lifetime is discussed.

Involvement of the accumulation of sucrose and the synthesis of cell wall polysaccharides in the expansion of potato cells in response to jasmonic acid

Jasmonic acid (JA) is capable of inducing the expansion of cells in potato tubers. Changes in the levels of soluble sugars and starch, as well as changes in the levels of cell wall polysaccharides, during the JA-induced expansion of cells were studied. JA caused a considerable increase in the level of sucrose in the cells, while it did not affect levels of glucose and fructose. JA also increased the levels of cell wall polysaccharides. An inhibitor of cellulose synthesis, 2,6-dichlorobenzonitrile (DCB), almost completely inhibited the JA-induced expansion of cells. The results suggest that the cellulose synthesis is necessary for the JA-induced expansion of cells. Cytoskeletal inhibitors also strongly inhibited the JA-induced expansion of cells, suggesting the involvement of cytoskeletal structures, namely, microtubules and microfilaments, in the JA-induced expansion of cells.