Multiple shoot induction and leaf and flower bud abscission of Annonacultures as affected by types of ventilation

Nodal explants of Annona squamosa L. and Annona muricata L. were cultured in vitro under various types of ventilation: airtight vessel (sealed condition; number of air exchange 0.1 h^–1), natural ventilation (via a polypropylene membrane; number of air exchange 1.5 h^–1), and forced ventilation (5.0 cm³ min^–1 in a 60 cm³ vessel; number of air exchange 5.0 h^–1). In both species, numbers of leaves, leaf areas and numbers of nodes per shoot increased with improving standards of ventilation, while leaf abscissions were substantially reduced; all the leaves had abscised in the airtight vessels after 12–15 days, but none had done so with forced ventilation. Flower-bud abscission in A. muricatashowed a similar trend after 21 days. These effects were associated with reductions in the accumulation of ethylene within the culture vessels, produced by increasing the efficiency of ventilation; ethylene was not detected in those fitted with a forced ventilation system. CO₂ concentrations in culture headspaces and the net photosynthetic rates of the plantlets were also evaluated. CO₂ concentrations decreased well below the ambient in the natural and airtight vessels; however, under forced ventilation, CO₂ concentrations were significantly higher during the photoperiod, compared to those of the natural ventilation and airtight vessel treatments. In general, net photosynthetic rates per unit leaf area increased with increasing photosynthetic photon flux (PPF) and rates were highest in plantlets grown under forced ventilation, intermediate under natural ventilation and lowest in the airtight vessels.Eighteen different media were investigated for their effects on multiple shoot induction in both species. The best medium for multiple shoot induction and growth in A. squamosa was Murashige and Skoog medium (MS) + 6-benzylaminopurine (BA; 1.5 mg l^–1) + casein hydrolysate (1.0 g l^–1) and for A. muricata MS + BA (1.0 mg l^–1) + naphthaleneacetic acid (NAA; 0.1 mg l^–1).     

Intercellular chitinase and peroxidase activities associated with resistance conferred by geneLr35to leaf rust of wheat

The effect of leaf rust (Puccinia triticina) infection on intercellular chitinase (EC 3.2.1.14) and peroxidase (EC 1.11.1.7) activities was studied in resistant [RL 6082 (Thatcher/Lr35)] and susceptible (Thatcher) near isogenic wheat (Triticum aestivum L.) lines at seedling, stem elongation and flag leaf stages of plant growth. The levels of activity of these enzymes were low during the seedling and stem elongation stages. Resistant plants at the flag leaf stage, during which the Lr35 resistance gene was maximally expressed, exhibited high constitutive levels of chitinase and peroxidase activities, in contrast to the lower constitutive levels of susceptible plants. The results suggest that chitinase and peroxidase, constitutively present in the intercellular spaces of Thatcher/Lr35 wheat leaves, may play a role in Lr35 mediated resistance to leaf rust.     

Sink Effect of Cytokinin in Detached Leaves Is Not Caused by Structural Rearrangements of Phloem

The sink effect of cytokinin is manifested as a decrease in source capacity and the induction of sink activity in the phytohormone-treated region of a mature excised leaf. In order to find out whether this effect was due to the direct action of cytokinin on the phloem structure, two types of phloem terminals were examined. In pumpkin (Cucurbita pepo L.) leaves, the phloem terminals are open; i.e., they are linked to mesophyll by numerous symplastic connections, which are located in narrow areas called plasmodesmal pit fields. In broad bean (Vicia faba L.) leaves, the phloem terminals belong to the closed type and have no symplastic links with mesophyll. The electron microscopic study of terminal phloem did not reveal any structural changes in the companion cells, which could account for the suppression of assimilate export. The treatment of leaves with cytokinin neither disturbed the structure of plasmodesmal pit fields in pumpkin leaves nor eliminated the wall protuberances (the ingrowths promoting phloem loading) in bean leaves. No evidence was obtained that the cytokinin-induced import of assimilates in mature leaves is caused by the recovery of meristematic activity, i.e., by either formation of new phloem terminals having immature sieve elements capable of unloading or by the development of new sieve elements within the existing veins. Cytokinin did not induce de novo formation of phloem elements. Structural characteristics of the leaf phloem, such as the number of branching orders in the venation pattern, the number of vein endings per areole, the number of areoles per leaf, the area of one areole, and the number of sieve elements per bundle remained unaltered. It is concluded that the sink effect of cytokinin in excised leaves cannot be determined by alteration of the phloem structure.     

The Role of Hormones in Fast Growth Responses of Wheat Plants to Osmotic and Cold Shocks

The effects of nutrient-solution cooling and PEG addition to the nutrient solution on the phytohormone content, the rate of leaf growth, leaf extensibility under the influence of external mechanical action, osmotic potential, and transpiration were studied in seven-day-old wheat plants. Leaf growth rapidly ceased, and the transpiration rate was reduced in both treatments. Growth cessation induced by PEG was transient, and growth resumption was preceded by an increase in the leaf extensibility. The functional role of auxin accumulation in plant shoots in the control of extensibility as well as the relationship between the ABA accumulation and a decrease in the cytokinin content, on the one hand, and reduced transpiration, on the other hand, under stress conditions are discussed.     

New Data on the Cenozoic History of the Underwater Yamato Rise,Sea of Japan

The Miocene terrestrial plant assemblage (in macro- and microfossils) from the underwater Yamato Rise (Sea of Japan) is examined. A fossil leaf found in the tuffogenic–sedimentary strata is identified as belonging to the beech tree. Data on the Paleogene–Neogene history of the underwater rise are given. Against the background of its general subsidence, positive relief features (volcanoes and their formations) were formed. During the Cenozoic, the entire Sea of Japan depression experienced a submergence.     

Expression of the tobacco mosaic virus movement protein alters starch accumulation inNicotiana benthamiana

Nicotiana benthamiana plants were transformed with the movement protein (MP) gene of tobacco mosaic virus (TMV), usingAgrobacterium-mediated transformation. Plants regenerated from the transformed cells accumulated 30-kDa MP and complemented the activity of TMV MP when infected with chimeric TMVs containing defective MR These transgenic plants displayed stunting, pale-green leaves, and starch accumulations, indicating that TMV MP altered the carbon partitioning for leaves involved in TMV cell-to-cell movement.     

Estimating mixtures of leaf functional types using continental-scale satellite and climatic data

Aim Recent research has shown that much of the variability in leaf gas exchange and leaf longevity can be related to variations in the surface : volume ratio of leaves. The aim of this paper was to develop a theoretical framework and a practical method to extend that result to the vegetation at the continental scale. Location The study was conducted in Australia. Methods We propose that vegetation is composed of a mixture of three basic leaf types, ‘turgor’ (T), ‘mesic’ (M) and ‘sclerophyll’ (S) leaves. Changes in the relative proportions of T, M and S leaves within a vegetation type are visualized using a ternary diagram and differences in vegetation structure are shown to be easily mapped onto the ternary diagram. We estimate the proportions of T, M and S leaves using readily available data. The total amount of PAR absorbed by the vegetation (fPAR) is estimated using continental‐scale satellite observations. The total fPAR is then decomposed into that absorbed by T, M and S leaves. The relative absorption of PAR by T leaves is estimated from the temporal dynamics in the satellite signal, while the relative proportions of M and S leaves are estimated using climatic (solar radiation, rainfall) data. Results When the availability of light, nutrients and water were near‐optimal, the vegetation was composed of predominantly M leaves. In low nutrient environments S leaves predominated. T leaves were dominant in disturbed environments. Conclusions The theoretical framework is used to predict that elevated atmospheric CO₂ would tend to increase the proportion of M and S leaves in an ecosystem and the resulting change means that the proportion of T leaves would decrease. In terms of the TMS scheme, this implies that elevated CO₂ has the same net effect on the vegetation as a decrease in disturbance.     

Choleretic activity and biliary elimination of lipids and bile acids induced by an artichoke leaf extract in rats

The therapeutic properties of artichoke (Cynara scolymus L.) preparations have been known since ancient times. The traditional use of artichoke leaf extract (ALE) in gastroenterology is mainly based upon its strong antidyspeptic actions which are mediated by its choleretic activity. The aim of this study was to investigate the effects of ALE on bile flow and the formation of bile compounds in anaesthetised Wistar rats after acute and repeated (twice a day for 7 consecutive days) oral administration. A significant increase in bile flow was observed after acute treatment with ALE as well as after repeated administration. The choleretic effects of ALE were similar to those of the reference compound dehydrocholic acid (DHCA). Total bile acids, cholesterol and phospholipid were determined by enzymatic assays. There was a strong ALE-induced increase in total bile acid concentration over the entire experiment. With the highest dose (400 mg/kg), a significant increase was obtained after single and repeated administration. The bile acids-increased effects of ALE were much more pronounced than those of reference (DHCA). No significant differences in cholesterol and phospholipid content could be found.