Chemical and physical defence in early and late leaves in three heterophyllous birch species native to northern Japan

BACKGROUND AND AIMS: Betula ermanii, B. maximowicziana and B. platyphylla var. japonica have heterophyllous leaves (i.e. early leaves and late leaves) and are typical pioneer species in northern Japan. Chemical and physical defences against herbivores in early and late leaves of these species were studied. METHODS: Two-year-old seedlings were grown under full sunlight in a single growing season. Three-week-old leaves of each seedling were harvested three times (May, July and October). Total phenolics and condensed tannin content were determined for chemical defence and leaf toughness and trichome density were assessed for physical defence. Defoliation of early leaves in May was also performed to study the contribution of early leaves to subsequent growth. KEY RESULTS: Chemical and physical defences were greater in early than late leaves in B. platyphylla and B. ermanii, whereas the reverse was true in B. maximowicziana. In contrast to its weak chemical defences, the trichome density in B. maximowicziana was very high. In B. platyphylla and B. ermanii, the relative growth rates (RGR) were greater early in the growing season. Negative effects on growth of removal of early leaves were significant only in B. platyphylla. CONCLUSIONS: B. platyphylla and B. ermanii invest in defence in early rather than late leaves, since early leaves are crucial to subsequent growth. In contrast, B. maximowicziana more strongly defends its late leaves, since its RGR is maintained at the same level throughout the growing season.     

Stature of sub-arctic birch in relation to growth rate, lifespan and tree form

BACKGROUND AND AIMS: Sub-arctic mountain birch Betula pubescens var. pumila communities in the North Atlantic region are of variable stature, ranging from prostrate scrubs to forests with trees up to 12 m high. Four hypotheses were tested, relating growth and population characteristics of sub-arctic birch woodland and scrub to tree stature; i.e. the variable stature of birch woods is due to differences in (1) the mean growth rate; (2) the age-related patterns of growth rate; (3) the life expectancy of stems; or (4) the tree form. Methods: A stratified random sample of 300 birch trees was drawn from the total population of indigenous birch woodlands and scrub in Iceland, yielding 286 valid sample genets. The population was divided into three sub-populations with dominant trees 0-2, 2-4 and 4-12 m tall, referred to as birch scrub, birch scrub-woodland and birch forest, respectively. KEY RESULTS: Trees in the scrub population were of more contorted growth form than birch in the scrub-woodland and forest populations. Mean growth rates, mean age and median life expectancies increased significantly with sub-population of greater tree stature. At the population level, annual increment and longevity of birch stems was apparently interrelated as the stems in vigorously growing birch sub-populations had a longer life expectancy than those of slower growth. However, no difference was observed between sub-populations in age-related patterns of extension growth rate. CONCLUSIONS: The results were consistent with hypotheses (1), (3) and (4), but hypothesis (2) was rejected. Hence, mountain birch of more vigorous growth attains a greater stature than birch of lesser increment due to faster extension growth rate and a longer lifespan. In addition, the more contorted stem form of scrub populations contributes to their low stature.     

Diprenylated chalcones and other constituents from the twigs of Dorstenia barteri var. subtriangularis

The twigs of Dorstenia barteri var. subtriangularis yielded three diprenylated chalcones: (-)-3-(3,3-dimethylallyl)-5'-(2-hydroxy-3-methylbut-3-enyl)-4,2',4'-trihydroxychalcone, (+)-3-(3,3-dimethylallyl)-4',5'-[2'-(1-hydroxy-1-methylethyl)-dihydrofurano]-4,2'-dihydroxychalcone and 3,4-(6",6"-dimethyldihydropyrano)-4',5'-[2',-(1-hydroxy-1-methylethyl)-dihydrofurano]-2'-hydroxychalcone for which the names bartericins A, B and C, respectively, are proposed. Stipulin, beta-sitosterol and its 3-beta-D-glucopyranosyl derivative were also isolated. The structures of these secondary metabolites were determined on the basis of spectroscopic analysis, especially, NMR spectra in conjunction with 2D experiments, COSY, HMQC and HMBC. The structural relationship of bartericins B and C was further established by the chemical cyclization of one to the other.     

In vitro assay and light regulation of nitrate reductase in red alga Gracilaria chilensis

Nitrate reductase (NR) is the first enzyme in the nitrogen assimilation pathway. The in vitro NR activity of Gracilaria chilensis was assayed under different conditions to reveal its stability and biochemical characteristics, and an optimized in vitro assay is described. Maximal NR activities were observed at pH 8.0 and 15 degrees C. The apparent Km value for NADH was 8 microM and for nitrate 680 microM. Crude extracts of G. chilensis stored at 4 degrees C showed a 50% decrease of NR activity after 24 h. The highest NR activity value (253.20+/-2.60 x 10(-3) U g(-1)) was obtained when 100% von Stosch medium (500 microM NO3-) was added before extraction of apical parts. Algae under light:dark cycles of 12:12h exhibited circadian fluctuation of NR activity and photosynthesis with more than 2 times higher levels in the light phase. No evidence of endogenous diel rhythm controlling NR activity or photosynthesis was observed. Light pulses lasting 10 or 60 min during the darkness increased the NR activity by 30% and 45%, respectively. The results indicate that NR and photosynthesis are regulated mainly by light and not by a biological clock.     

野牛草幼穗愈伤组织的诱导及植株再生

以野牛草[Buchloe dactyloides(Nutt．)Engelm．]幼穗为外植体,建立了愈伤组织诱导、继代培养和植株再生体系。结果表明,雌穗比雄穗难以脱分化形成愈伤组织;小于8mm雄幼穗在2mg／L2,4-D培养基上的愈伤组织诱导率为80．0％～86．8％;添加10mg／L AgNO3对愈伤组织诱导率影响不明显,但可改善愈伤组织质量。2mg／L 2,4-D结合0．1mg／L 6-BA的培养基有利于愈伤组织的继代培养;继代超过3次、继代间隔超过3周,愈伤组织分化能力明显下降。雄穗愈伤组织在含1．0mg／L 6-BA培养基上,弱光条件下分化出芽的频率较高,达31．8％～35．0％;附加3％麦芽糖既可减轻褐化程度,又利于丛生芽的分化。分化苗在1/2MS 0．3mg／L IBA培养基上的生根率为62．5％。     

传统中药白芍原植物分类鉴定及根形态解剖研究

对我国主产地的白芍(Radix Paeonia alba)原植物10个居群进行调查及标本采集,植物鉴定结果为：川白芍原植物粉红花居群为原变种芍药Paeonia lactiflora Pall,白花居群为芍药变种毛果芍药P.lactiflora var.trichocarpa(Bunge)Stern;毫白芍原植物线条居群和蒲棒居群均为芍药;杭白芍原植物红花、白花、粉红花居群均为毛果芍药;陕西韩城、江苏东海、山东荷泽白芍均为芍药,各居群在花色及形态上有明显而稳定的变异。根横切面解剖结构显示,按木质部的排列方式可将白芍原植物10个居群分为两大类：第一类为有呈两个不相连的扇形中央导管群,并且有狭长、具分枝的从形成层到根中央部分连续排列的木质部,基本上是原植物芍药的植物特征,其中毫白芍线条居群兼有毛果芍药和芍药的特征;第二类为具有不明显的根中央扇形导管束,导管束呈环状围绕中央排列,并且有粗短不分枝的靠近形成层处成群的导管,与原植物毛果芍药的特征基本一致,其中杭白芍红花居群与川白芍白花居群根中央导管群呈现较明显的2个分离扇形排列,类似芍药。白芍原植物的种分类定位与花色无密切关联,但由于性状的稳定,可以考虑作为变种或变型定位。     

EXAFS study on arsenic species and transformation in arsenic hyperaccumulator

Synchrotron radiation extended X-ray absorption fine structure (SR EXAFS) was employed to study the transformation of coordination environment and the redox speciation of arsenic in a newly discovered arsenic hyperaccumulator, Cretan brake (Pteris cretica L. var nervosa Thunb). It showed that the arsenic in the plant mainly coordinated with oxygen, except that some arsenic coordinated with S as As-GSH in root. The complexation of arsenic with GSH might not be the predominant detoxification mechanism in Cretan brake. Although some arsenic in root presented as As(V) in Na₂HAsO₄ treatments, most of arsenic in plant presented as As(III)-O in both treatments, indicating that As(V) tended to be reduced to As(III) after it was taken up into the root, and arsenic was kept as As(III) when it was transported to the above-ground tissues. The reduction of As(V) primarily proceeded in the root.     

Growth and architecture of small honey mesquites under jackrabbit browsing: overcoming the disadvantage of being eaten

Browsing is an important mortality factor in seedlings and small plants. However, the induced changes in the architecture of plant survivors may influence subsequent browsing, opening the possibility of compensating for the damage done. How jackrabbit (Lepus californicus) browsing affects the growth and architecture of small individuals of honey mesquite, Prosopis glandulosa var. torreyana, a tree/shrub that produces spines at every node, was explored. Naturally established mesquites of unknown age were selected in one site, and 2-year-old mesquites were transplanted in another site. In both cases, half of them were exposed to jackrabbits and the other half were excluded as controls. After 4 years, shoot production (height, length and number of derived shoots) and plant growth (height and cover) increased 1.4-2.5-fold in naturally established controls relative to exposed plants, depending on the measured variable. In the transplant experiment, the increases were 2.8-7.1-fold in controls relative to exposed plants 2 years after initiation of the experiment. The net loss of biomass in treatment vs. control plants in these experiments suggests a negative response to browsing which has been defined as under-compensation. Alternative architectures in honey mesquites were evident at the end of the exclusion experiments: controls had long branches and an extended crown cover, while exposed plants had short branches and a compact crown cover. Results indicated that mesquites were able to grow under browser pressure by packing many stems in a compact matrix armed with spines and producing one or more shoots tall and wide enough to escape from jackrabbits.     

Variation in DNA-ploidy Levels of Reynoutria Taxa in the Czech Republic

The genus Reynoutria is represented by four taxa in the Czech Republic: Reynoutria japonica var. japonica, R. japonica var. compacta, R. sachalinensis and R. xbohemica. By using flow cytometry, cytological variability within the genus is described based on 257 Reynoutria samples. The varieties of R. japonica are cytologically uniform, var. japonica is exclusively octoploid (2n = 8x = 88) and var. compacta occurs only as a tetraploid (2n = 4x = 44), but R. sachalinensis and R. xbohemica exhibit some variation in chromosome numbers. Reynoutria sachalinensis is predominantly tetraploid (2n = 4 x = 44), but also occurs occasionally as hexaploid and octoploid cytotypes. The most common ploidy level in R. xbohemica is hexaploid (2n = 6x = 66), but tetraploid and octoploid clones were also found. The four taxa occurring in the Czech Republic are described briefly and the possible origins of the cytotypes discussed.