Artificial Defoliation Induces Trichome Production in the Tropical Shrub Cnidoscolus aconitifolius (Euphorbiaceae)1

Induction of plant defenses and their spatial variability are key subjects in the field of ecology and evolution of defensive traits in plants. Nevertheless, induction has been more commonly studied under controlled environments, ignoring other factors that might influence this process in natural settings. The main goal of this study was to determine if artificial defoliation induces trichome production in three natural populations of the tropical shrub Cnidoscolus aconitifolius. First, we performed trichome counts for each population before imposing artificial defoliation to assess differences in trichome loads between populations. Trichome densities (trichomes/cm²) were quantified for leaf blades, petioles, and flower stalks. To determine if defoliation induced trichome production, three defoliation treatments (0% leaves defoliated or controls, 50% of total leaves defoliated, and 100% defoliation) were applied once at the beginning of the reproductive season. Trichome counts were performed on each structure every ～20 d during a 3‐mo period after the application of treatments. Trichome counts showed significant differences in trichome densities between populations for all three structures. In turn, artificial defoliation increased trichome density. Significant differences among treatments were found for trichome densities on leaf blades and petioles. In both these structures, the 100 percent defoliation treatment differed significantly from control plants, presenting higher trichome densities. In addition, the treatment × population interaction was not significant for leaf blades and petioles, indicating that induction is a generalized response in this species, at least at the study sites. These results indicate that trichomes in C. aconitifolius are inducible due to defoliation.     

INDUCED DIMORPHIC LIFE CYCLE OF A COCCOLITHOPHORID,CALYPTROSPHAERA SPHAEROIDEA (PRYMNESIOPHYCEAE,HAPTOPHYTA)1

The holococcolith Calyptrosphaera sphaeroidea Schiller was collected at Miyake‐jima Island, Japan and unialgal cultures established. Alternation of the holococcolith and heterococcolith phases was induced using new culture media (MNK, TR, and LO). Cells synchronized in the holococcolith phase were transferred into TR medium to induce a life cycle change. The heterococcolith phase, which has never been reported before, appeared after more than 40 days. The heterococcoliths were very small elliptical discs, about 0.5 μm wide and 1 μm long. Typical diploid‐type organic scales on the cell surface were observed. This phase was very stable in culture and was tolerant of unfavorable conditions. To reverse the life phase, cells in the heterococcolith phase were transferred into cold LO medium and exposed to low temperature (4°C) and low light (2 μmol photons·m^?2·s^?1) for 30 min before culturing at normal conditions (22.5°C and 20 μmol photons· m^?2·s^?1). The swimming behavior of the holococcolith cells seemed to be an indicator of the life cycle phase transition. This article reports for the first time a set of conditions that could control the transition of a coccolithophorid from one life phase to the other. Selected vitamins and trace metals induced the heterococcolith phase, whereas a slightly higher concentration of components in the basic medium along with concomitant stresses of light and temperature induced the holococcolith phase. Based on the results, we propose a hypothesis that the alternation of coccolithophorid life phases is regulated by changes between pelagic and coastal environments coupled with changes in seasonal conditions.     

EVIDENCE FOR METHYL JASMONATE-INDUCED PHLOROTANNIN PRODUCTION IN FUCUS VESICULOSUS (PHAEOPHYCEAE)

The plant growth regulators jasmonic acid and methyl jasmonate (MeJA) have recently been identified in a variety of marine algae; however, their role in these organisms is currently unknown. Here we report that exposure to MeJA, during periods of tidal emergence causes the induction of polyphenolic chemical defenses (the phlorotannins) in two populations of the common rockweed Fucus vesiculosus (Linnaeus). Phlorotannin concentrations were up to 1.6 times higher in the growing apices of F. vesiculosus from both Avery Point (Connecticut, USA) and Roosevelt Inlet (Delaware, USA) within 10–14 days after a single brief exposure to airborne MeJA at concentrations ranging from 5.42 to 542 nM. The timing and magnitude of this induced increase in phlorotannin concentration are similar to that caused by real and simulated herbivory, raising the question of whether jasmonates, or their oxylipin relatives, are natural elements of antiherbivore responses in Fucus , as they are in vascular plants.     

CIRCANNUAL GROWTH RHYTHM AND PHOTOPERIODIC SORUS INDUCTION IN THE KELP LAMINARIA SETCHELLII (PHAEOPHYTA)1

Growth and reproduction of laboratory-grown sporophytes of Laminaria setchellii Silva were investigated in a tank system with controlled conditions of daylength, temperature, and nutrients (N and P). A circannual growth rhythm of the frond was detected under constant laboratory conditions. In continuous long-day and night-break conditions the period τ of the free-running rhythm varied between 11.3 and 17.3 months; in short-day conditions the frond grew indefinitely. The growth rhythm of individual plants could be synchronized by a simulated annual cycle of day-length with a period of T = 12 months. The four seasons of the year were simultaneously simulated by phase shifting the annual cycle of daylength by 3, 6, or 9 months in three out of four tanks. The annual growth cycle followed these phase shifts, and initiation of the new blade always started just after the winter daylength minimum. The formation of sori was induced by a genuine photoperiodic short-day reaction in 1- to 2-year-old plants. Sori became, visible 9–14 weeks after transfer of individual plants from long-day to short-day conditions, whereas plants cultured in continuous long-day or night-break conditions remained sterile. Sporophytes with or without blades were able to continue growth or produce new blades in continuous darkness.     

Seed dormancy patterns in Epipactis palustris (Orchidaceae): Requirements for germination and establishment of mycorrhiza

Some terrestrial orchid species, including Epipactis palustris (L.) Crantz, are considered extremely difficult to germinate and cultivate in vitro. Observations of orchids germinating in nature are very few, and the timing and requirements for seedling establishment are unknown for most species. Seeds of E. palustris were incubated in vitro with an appropriate fungus, but germination was poor unless several other conditions were also met: scarification of the testa in Ca(OCL)₂, an initial incubation for several weeks at 27°C, and a subsequent cold stratification for 8–12 weeks at 4–8°C, With these pretreatments, germnation responses exceeded 50% after incubation for 4 weeks at 20°C. Healthy protocorms with normal organ development were only produced by symbiotic culture following this lengthy seed preparation. The findings suggest that under natural conditions the seeds need some after-ripening, and the testa needs to be partially decomposed before germination. The requirement for chilling suggests that germination of seeds in situ occurs in spring.     

NMR imaging of roots: effects after root freezing of containerised conifer seedlings

Seedlings of Scots pine ( Pinus sylvestris L.) and Norway spruce [ Picea abies (L) Karst.] were subjected to low root temperatures, and 10 days later the roots were examined by NMR imaging. The amount of NMR detectable roots decreased with decreasing temperature, with the signal from the younger roots at the bottom of the container being the first to disappear. The origin of the loss of NMR signal is unclear but may be due to changes in the NMR properties of root water after cold damage. A recent method is discussed for obtaining unbiased estimates of root lengths from a series of total vertical projections; the method is particularly suited to evaluating NMR projection images. Since NMR imaging methods can apparently distinguish between control and cold damaged roots, it may be possible to design more routine applications using low resolution NMR methods.     

抗寒锻炼对冬小麦幼苗质膜Ca^2＋—ATPase的稳定作用

通过氯化铈（ＣｅＣｌ３）沉淀的电镜细胞化学方法,观察了抗寒锻炼对冬小麦（ＴｒｉｔｉｃｕｍａｅｓｔｉｖｕｍＬ．）幼苗质膜Ｃａ２＋ＡＴＰａｓｅ的稳定作用,主要结果是：（１）正常温度（２０℃）下生长的冬小麦幼苗（未经抗寒锻炼）,其质膜上有很强的Ｃａ２＋ＡＴＰａｓｅ活性反应;当经过－９℃３ｈ的低温处理后,质膜的Ｃａ２＋ＡＴＰａｓｅ活性明显降低;在处理１２ｈ后,质膜的Ｃａ２＋ＡＴＰａｓｅ活性进一步降低;当处理时间延长到２４ｈ,质膜的Ｃａ２＋ＡＴＰａｓｅ完全失活,同时细胞的超微结构受到破坏。（２）冬小麦幼苗在２℃低温下锻炼１５ｄ后,其质膜的Ｃａ２＋ＡＴＰａｓｅ活性高于未经抗寒锻炼的小麦幼苗。抗寒锻炼后的小麦幼苗在－９℃处理３ｈ后,质膜的Ｃａ２＋ＡＴＰａｓｅ活性与低温处理前相比无明显降低;经低温处理１２ｈ,质膜仍保持较高的Ｃａ２＋ＡＴＰａｓｅ活性,较同样低温处理（－９℃,１２ｈ）但未经抗寒锻炼的幼苗高;当－９℃低温处理２４ｈ后,质膜上仍可观察到Ｃａ２＋ＡＴＰａｓｅ的活性反应,而且细胞的超微结构也未受到破坏。结果表明,抗寒锻炼可提高冬小麦幼苗质膜Ｃａ２＋ＡＴＰａｓｅ在低温下的稳定性     

Conditioned medium from cultured rat hepatocytes completely blocks induction of glutamine synthetase by dexamethasone in several rat liver epithelial cell lines

A variant RL-ET-1G of a rat liver epithelial cell line (RL-ET-1) characterized by a very high inducibility for glutamine synthetase (GS) in response to dexamethasone was established by cultivation in glutamine-free, glutamate-supplemented culture medium. Using this cell line, conditioned medium produced by periportal hepatocytes in primary culture was found to suppress this induction, acting with a lag-phase of about 8 h irrespective whether the GS activity was basal or preinduced. Analysis of the response of several epithelial cell lines to the conditioned medium showed a reciprocal relationship between the dexamethasone-dependent induction and the residual activity after exposure to the conditioned medium, indicating that a hypothetical factor in the conditioned medium was interfering with the induction process but not with the basal GS level of these cells. Careful analysis revealed that the effect of the conditioned medium was neither due to deficiency of a component used up by the hepatocytes, nor due to glutamine or ammonia, both of which affected GS activity at concentrations above 0.5 mmol/L. The hypothetical factor was found to be quite small (molecular mass range 100–500 Da), heat and acid stable, as well as highly water soluble. Most interestingly, the conditioned medium did not suppress GS induction in astroglial cells and in the two hepatoma cell lines C2 and FAO, but strongly diminished the spontaneous induction of GS in cocultured pig hepatocytes, suggesting that the hypothetical factor acts primarily on normal nontransformed liver-derived cell populations.