The content of the depside 4-O-demethylbarbatic acid in the mycobiont isolated from Ramalina siliquosa was examined under various controlled culture conditions. The content of the depside was similar regardless of the growth stage of the mycobiont colonies, whose weight increased linearly in a logarithmic scale for 11 months. Both the growth rate and the depside content of the mycobiont colonies were highest when the pH of the medium was 6.5. The growth rate of the mycobiont colonies increased with elevation of temperature until 250C. But the content of the depside changed greatly with differing temperature, and was highest at 150C. These results obtained from the isolated lichen mycobiont are compared with those from the whole lichen. In my previous studies, some interesting results were obtained concerning the content of lichen substances in the whole lichen. The content of salazinic acid, a depsidone, was similar regardless of the developmental stages of the lichen (Hamada 1982a). Moreover, the content of salazinic and divaricatic acids in Ramalina species increased with elevation of the temperature of the habitat, but was independent of any other environmental factors; for example, light (Hamada 1982b, 1983). However, for these previous assessments on lichen substances, lichens grown under natural conditions were used as the experimental materials instead of lichens under artificial conditions. Though lichens occurring on rocks in nature were cultivated in the growth cabinet for 7 months, no growth in thallus was recognized (Hamada 1984). On the other hand, I succeeded in the production of the depside 4-O-demethylbarbatic acid by cultivating lichen mycobionts isolated from some species of Ramalina, which produce salazinic acid or protocetraric acid in the lichenized condition (Hamada 1988; Hamada & Ueno 1987). In my preliminary experiment, the content of depside in lichen mycobionts was recognized to vary with differing culture conditions, especially temperature. Examining the effect of various culture conditions on depside production was thought to be useful for investigating the physiology of lichen mycobionts. In this paper, the results from an investigation of the growth and depside content of the isolated mycobiont from R. siliquosa under controlled culture conditions of various medium pH and temperatures are reported. Study of the isolated lichen mycobiont is thought to be also significant for the whole lichen. MATERIALS AND METHODS A thallus of R. siliquosa was collected as experimental material in Ohshima Island of Wakayama Prefecture (33030'N, 135050'E), Japan, on 17 September 1987. This thallus consisted of 12 ramuli with 23 mature apothecia. After collection, the thallus was dried in room temperature for one day. Ten selected apothecia were cut from the ramuli for use as the experimental materials. After being soaked in distilled water for about 15 minutes and blotted to remove excess water, each apothecium was kept on the lid of an upside down petri dish with a layer of 1.5% agar at the bottom for 5 hours. More than 100 spores discharged from each apothecium, spouted 1.5 cm high, and attached to the agar surface. Spores obtained by this method were diluted with 10 ml of sterile water, and separated and mixed uniformly by shaking. One hundred dl of the spore suspension were placed in a slant tube containing a modified malt-yeast extract medium (malt extract, 10 g; yeast extract, 4 g; sugar, 4 g; and agar, 15 g; in water, 1 liter) for culture. In my preliminary experiment, in which the content of 4-O-demethylbarbatic acid in the lichen mycobiont was affected by the pH and temperature of the medium, the optimal conditions for depside production were found to be pH 6.5 and 150C. This study was performed in the dark to examine the effect of temperature without interference by light. For examining the growth rate of the lichen mycobiont, it was cultured at pH 6.5 and 150C for 3, 5, 7, 9, and 11 months (Fig. 1, Table 1). For examining the effect of pH of the medium, the mycobiont was cultured at 150C for 11 months in slant tubes adjusted to pH 5.0, 6.0, 6.5, 7.0, 8.0, and 9.0, respectively, with HC1 or KOH, after sterilization by autoclave (Fig. 2). For examining the effect of temperature, slant tubes with pH 6.5 were kept in the phytotron at controlled temperatures of 5, 10, 15, 20, and 250C, respectively, for 11 months (Fig. 3). To maintain the cultures on a slightly wet medium, the mycelia, with a small segment of agar, were transplanted to a new medium every 3 months and cultured at 15, 20, and 25*C; those cultured at 109C were transplanted every 6 months, but the mycelia cultured at 50C were not transplanted at all. Because mycobiont spores kept at 50C from the start 0007-2745/89/310-313$0.55/0 This content downloaded from 157.55.39.242 on Thu, 21 Apr 2016 07:03:32 UTC All use subject to http://about.jstor.org/terms 1989] HAMADA: DEPSIDES IN ISOLATED MYCOBIONTS 311
Read full abstract
Apr 16, 2022
Maonian Xu + 19
Open Access
