On the improvement of the podophyllotoxin production by phenylpropanoid precursor feeding to cell cultures of Podophyllum hexandrum Royle

In order to improve the production of the cytotoxic lignan podophyllotoxin, seven precursors from the phenylpropanoid-routing and one related compound were fed to cell suspension cultures derived from the rhizomes of Podophyllum hexandrum Royle. These cell cultures were able to convert only coniferin into podophyllotoxin, maximally a 12.8 fold increase in content was found. Permeabilization using isopropanol, in combination with coniferin as a substrate, did not result in an extra increase in podophyllotoxin accumulation. Concentrations of isopropanol exceeding 0.5% (v/v) were found to be rather toxic for suspension growth cells of P. hexandrum. When coniferin was fed in presence of such isopropanol concentrations, -glucosidase activity was still present, resulting in the formation of the aglucon coniferyl alcohol. In addition, podophyllotoxin was released into the medium under these permeabilization conditions. Entrapment of P. hexandrum cells in calcium-alginate as such or in combination with the feeding of biosynthetic precursors, did not improve the podophyllotoxin production. Cell-free medium from suspension cultures at later growth stages incubated with coniferin, resulted in the synthesis of the lignan pinoresinol.     

GA3 induced flowering in Podophyllum hexandrum Royle: A rare alpine medicinal herb

Podophyllum hexandrum Royle, an important alpine herb, is the source of highly valued podophyllotoxin. The effect of some plant growth substances (GA₃, BAP & ABA), uniconazole (an inhibitor of GA biosynthesis), and a combination of GA₃ and uniconazole were examined in respect to influence on sprouting in rhizomes of P. hexandrum and on induction of flowering at a lower altitude. Amongst the various chemicals tested, GA₃ had a marked effect resulting in uniform sprouting and also induced flowering in about half of the treated rhizomes. While BAP also promoted early sprouting, delayed sprouting was seen in rhizomes treated with ABA. Uniconazole treatment, either alone or with GA₃ was found to inhibit flowering and also resulted in reduced plant height. GA₃ treatment of rhizomes from plants that was maintained for up to 30 months at a lower altitude also induced flowering thus replacing the normal chilling requirement of plants. These results suggest that treatment of GA₃ could be effectively used for inducing uniform sprouting and flowering in rhizomes of P. hexandrum grown at lower altitudes.     

Production of podophyllotoxin from Podophyllum hexandrum: a potential natural product for clinically useful anticancer drugs

Podophyllum hexandrum Royle of family Berberidaceae is an endangered medicinal plant. Rhizome ofP.hexandrum contains several lignans which posses antitumor activity. Podphyllotoxin is the most active cytotoxic natural product. It is used as starting compound for the synthesis of anticancer drug etoposide and teniposide. Podophyllotoxin acts as an inhibitor of microtubule assembly. These drugs are used for lung cancer, testicular cancer, neuroblastoma, hepatoma and other tumors. Besides this, it also shows antiviral activities by interfering with some critical viral processes. Availabilityof podophyllotoxin from plants has its limitations because of its intense collection from nature and lack of organized cultivation. The chemical synthesis of podophyllotoxin is considered to be very complicated as yet. The use of biotechnological approaches for the production of podophyllotoxin using cell cultures, organ cultures, and biotransformation route or by manipulating biosynthetic pathway proves to be an attractive alternative for production of podophyllotoxin. The present paper discusses the current status of research, limitations and future prospects for theproduction of podophyllotoxinin vitro.     

Podophyllum hexandrum modulates gamma radiation-induced immunosuppression in Balb/c mice: Implications in radioprotection

Aqueous extract of Podophyllum hexandrum (RP-1), which has been reported to render more than 82% survival against whole body lethal (10 Gy) gamma-irradiation in mice, was further investigated for its immunomodulatory potential. In this study, no significant change could be scored in peritoneal macrophages survival up to 8th day after whole body irradiation. RP-1 treatment (200 mg/kg body weight, i.p.) alone or 2 h before whole body irradiation enhanced macrophage survival significantly (p < 0.05) as compared to irradiated control mice. In irradiated animals, there was significant (p < 0.01) reduction in splenocyte survival and proliferation as revealed by 3H-TdR method. RP-1 treatment (200 mg/kg) alone or 2 h before irradiation countered the decrease in survival of splenocytes and proliferation significantly (p < 0.05) as compared to irradiated control group. Whole body irradiation also significantly (p < 0.05) reduced the population of CD4+ and CD8+ T cells and bone marrow GM-CFU at 24 h and 72 h post-irradiation intervals, respectively, as compared to unirradiated control. RP-1 treatment 2 h before whole body irradiation countered the decrease in CD4+ and CD8+ T cells populations and CGM-CFU. Nitric oxide free radicals generation was enhanced significantly (p < 0.05) in the supernatant of peritoneal macrophage cultures exposed to 2 Gy gamma radiation ex vivo in comparison to unirradiated control, which was reduced by pre-irradiation (−2 h) administration of RP-1. Whole body irradiation (10 Gy) also reduced the serum titres of IL-3, IL-1 and various IgG isotypes observed at different post-irradiation time interval. RP-1 treatment alone or before whole body irradiation countered radiation induced decrease in the titre of IL-1, IL-3 and IgG’s in the serum of mice. These findings indicate immunostimulatory potential of RP-1.     

Podophyllotoxin content in <Emphasis Type="Italic">Podophyllum hexandrum</Emphasis> Royle plants of known age of seed origin and grown at a lower altitude

Podophyllum hexandrum Royle, an important alpine herb, and a source of the highly valued aryltetralin-type lignan, podophyllotoxin, has been subjected to heavy collection from the wild due to ever increasing demand. The present study deals with an attempt to bring this plant under cultivation at a relatively lower altitude and to evaluate (1) various growth parameters including above and below ground biomass accumulation, net assimilation rate and relative growth rate, etc., and (2) podophyllotoxin content from the resulting above and below ground biomass in seed raised plants of a known age series of 1–5 years. The podophyllotoxin content was estimated on the basis of HPLC analyses. The levels were found to increase with the plant age and the maximum amount was found in 5-year old plants. This study demonstrates that (1) seeds can be conveniently used for raising healthy propagules in easily approachable locations at a relatively lower altitude, and that the plants can be maintained in such sites over long periods, and (2) this approach of “conservation through cultivation” can be suggested as an effective tool for the management of this “critically endangered status” species.     

Assessment of genetic diversity through RAPD,ISSR and AFLP markers in Podophyllum hexandrum: a medicinal herb from the Northwestern Himalayan region

Total synthesis of podophyllotoxin is an expensive process and availability of the compound from the natural resources is an important issue for pharmaceutical companies that manufacture anticancer drugs. In order to facilitate reasoned scientific decisions on its management and conservation for selective breeding programme, genetic analysis of 28 populations was done with 19 random primers, 11 ISSR primers and 13 AFLP primer pairs. A total of 92.37 %, 83.82 % and 84.40 % genetic polymorphism among the populations of Podophyllum were detected using RAPD, ISSR and AFLP makers, respectively. Similarly the mean coefficient of gene differentiation (Gst) were 0.69, 0.63 and 0.51, indicating that 33.77 %, 29.44 % and 26 % of the genetic diversity resided within the population. Analysis of molecular variance (AMOVA) indicated that 53 %, 62 % and 64 % of the genetic diversity among the studied populations was attributed to geographical location while 47 %, 38 % and 36 % was attributed to differences in their habitats using RAPD, ISSR and AFLP markers. An overall value of mean estimated number of gene flow (Nm) were 0.110, 0.147 and 0.24 from RAPD, ISSR and AFLP markers indicating that there was limited gene flow among the sampled populations.     

Antioxidant activity of fractionated extracts of rhizomes of high-altitude Podophyllum hexandrum: Role in radiation protection

Whole extract of rhizomes of Podophyllum hexandrum has been reported earlier by our group to render whole-body radioprotection. High-altitude P. hexandrum (HAPH) was therefore fractionated using solvents of varying polarity (non-polar to polar) and the different fractions were designated as, n-hexane (HE), chloroform (CE), alcohol (AE), hydro-alcohol (HA) and water (WE). The total polyphenolic content (mg% of quercetin) was determined spectrophotometrically, while. The major constituents present in each fraction were identified and characterized using LC-APCI/MS/MS. In vitro screening of the individual fractions, rich in polyphenols and lignans, revealed several bioactivities of direct relevance to radioprotection e.g. metal-chelation activity, antioxidant activity, DNA protection, inhibition of radiation (250 Gy) and iron/ascorbate-induced lipid peroxidation (LPO). CE exhibited maximum protection to plasmid (pBR322) DNA in the plasmid relaxation assay (68.09% of SC form retention). It also showed maximal metal chelation activity (41.59%), evaluated using 2,2-bipyridyl assay, followed by AE (31.25%), which exhibited maximum antioxidant potential (lowest absorption unit value: 0.0389± 0.00717) in the reducing power assay. AE also maximally inhibited iron/ascorbate-induced and radiation-induced LPO (99.76 and 92.249%, respectively, at 2000 g/ml) in mouse liver homogenate. Under conditions of combined stress (radiation (250 Gy) + iron/ascorbate), at a concentration of 2000 g/ml, HA exhibited higher percentage of inhibition (93.05%) of LPO activity. HA was found to be effective in significantly (p < 0.05) lowering LPO activity over a wide range of concentrations as compared to AE. The present comparative study indicated that alcoholic (AE) and hydro-alcoholic (HA) fractions are the most promising fractions, which can effectively tackle radiation-induced oxidative stress.     

Protein turnover in the attached leaves of non-stressed and stressed barley seedlings

Protein turnover was examined, using tritiated water, in various 2-cm regions of 7-11-d-old, first leaves of barley (Hordeum vulgare). Differences were found between the regions in their protein turnover and their responses to stress. The rate constant for degradation for total protein was the same throughout the leaf and the average half-life (t_1/2) of protein=approx. 220 h. Only in the older regions did a 24-h pulse of³H₂O preferentially label protein with a t_1/2 (90 h) considerably shorter than the t_1/2 for total protein. Soluble protein was degraded faster than insoluble protein and contained an appreciable short-lived protein component observable by short-pulse labelling. The rate of protein synthesis was greatest in the cells of the youngest region and declined as each region aged. The mean rate of protein synthesis over the 4-d period was 4 and 7 nmol h^-1 of amino-N with respect to the regions 1–3 and 7–9 cm from the leaf tip. Seedlings, stressed by adding polyethylene glycol (2.0 MPa) to the roots, showed a marked loss of protein from the older leaf regions with only small losses in the younger regions. Amino acids accumulated in the younger region continuously whereas in the older region little accumulation occurred until day 3 of stress when proline levels increased. Protein synthesis was decreased by between 30% and 50% in all leaf regions. In the region 1–3 cm from the leaf tip, the rate of protein degradation of total protein was enhanced and equalled the rate of degradation of 24-h-pulse-labelled protein which was not itself significantly affected by stress (t_1/2=approx. 90 h). In the region 3–5 cm, the degradation of both 4-d and 24-h-labelled protein was enhanced by stress to rates similar to those found in the region 1–3 cm. This was largely through increases in the degradation of the insoluble protein, but the degradation of soluble protein was also raised. Protein degradation in the region 7–9 cm was not affected by stress.Abbreviations t_1/2 average half-life - PEG polyethylene glycol     

Plant growth in relation to ontogenetic changes in productive characteristics of individual leaves I. growth and productive characteristics ofHelianthus annuus andZinnia elegans leaves

Growth and productive characteristics of successive leaves were ontogenetically examined using sunflower and zinnia plants grown in the field. For the purpose of more advanced comprehension, ontogenetic behavior of productive characteristics was formulated with the schematic leaf growth model. The largest leaf in zinnia appeared around the middle leaf order, but did not show the highest photosythetic rate. The decreasing pattern of relative leaf area expansion rate did not significantly differ among individual leaves, and seemed inherent to species. The ontogenetic changes in net photosynthetic rate per unit leaf area showed convex curves, while those in dark respiratory rate per unit leaf area rapidly decreased with leaf development and then became constant. In part, the rapid increase of photosynthetic rate in young leaves was supported by enhancement of light utilization efficiency, along with increase of chlorophyll content. The approach of leaf angle to the horizontal was more or less accompanied by photosynthetic development and leaf expansion. It was suggested that photosynthetic maturation in leaves of the sun-leaf type appears at leaf age equivalent to 0.35 to 0.46 of leaf life span. Ontogenetic pattern of all productive characteristics basically differed little among successive leaves.     

Effects of seed phosphorus concentration on the emergence and growth of subterranean clover (Trifolium subterraneum)

Subterranean clover seed (Trifolium subterraneum cv. Dalkeith) with phosphorus concentrations of 0.75% (high P seed) and 0.48% (low P seed) and of uniform size (2.0–2.4 mm diameter) was used to measure the effect of seed P concentrations on seedling emergence and growth.Seedling emergence numbers were 35% greater for the high P seed, and this effect was independent of external P supply. High P seed also emerged more quickly than low P seed.Leaf emergence was faster and shoot dry weight was greater for seedlings grown from high compared with low P seed, but only when external P supply was deficient for plant growth. Phosphorus concentrations in the shoots of two-week old seedlings were 32–51% higher for high P seed, although by four weeks plants grown from high and low P seed had similar concentrations of P in their shoots. We suggest that establishing pastures using high P seed would improve both early and late season pasture production.     

Pretreatment in thidiazuron improves the in vitro shoot induction from leaves in Curculigo orchioides Gaertn., an endangered medicinal plant

Leaf regeneration via direct induction of adventitious shoots obtained from an endangered medicinal plant, Curculigo orchioides Gaertn. by pretreating with thidiazuron. C. orchioides is an endangered medicinal herb belonging to the family Hypoxidaceae. Direct inoculation of leaf pieces on MS medium supplemented with various concentrations of BAP (2–8 μM) or TDZ (2–8 μM) alone or in combination with NAA (0.5 and 1.0 μM) produced low shoot induction both in terms of % response and number of shoots per explant. Hence, leaf explants were pretreated with 15, 25 or 50 μM thidiazuron (TDZ), for 6, 24 or 48 h with the aim of improving shoot regeneration from cultured explants. After pretreatment, explants were transferred to an agar solidified MS medium that was supplemented with BAP (4 μM), TDZ (6 μM), BAP (4 μM) + NAA (1.0 μM), TDZ (6 μM) + NAA (0.5 μM). Control explants were incubated directly on the medium without any pretreatment. The pretreatment of explants with 15 μM TDZ for 24 h significantly promoted the formation of adventitious shoots and the maximum response was observed on MS medium supplemented with 6 μM TDZ. In this medium, 96 % cultures responded with an average number of 16.2 adventitious shoots per explant. The percentage of leaf explants producing shoots and the average number of shoots per explant were significantly improved when TDZ pretreated leaves were cultured onto MS medium supplemented with BAP or TDZ alone or in combination with NAA. The rooted plantlets were successfully transplanted to soil with 90% success. The present investigation indicated the stimulatory role of TDZ pretreatment in regulating shoot regeneration from leaf explants of C. orchioides.     

Effects of Chironomus tentans larval growth retardation on adult emergence and ovipositing success: implications for interpreting freshwater sediment bioassays

A laboratory study was conducted with Chironomus tentans to assess the significance of growth retardation of third-to fourth-instar larvae over a 10-d test period on long-term survival, adult emergence, and ovipositing success. Data were intended to provide interpretive guidance for the commonly used growth endpoint in 10-d sediment bioassays with C. tentans. Larval growth was controlled by using six feeding levels ranging from 0.2 to 5.9 mg dry weight Tetrafin® fish food per day. Mean 10-d survival was 88% at all feeding levels, but larval growth decreased significantly (p<0.05) with each decrease in feeding level. Cumulative successful emergence of adult C. tentans decreased significantly with decreasing larval growth. Mean times to emergence always increased with decreasing growth rates and effects were generally more pronounced for females than males. At the lowest 10-d mean growth where successful emergence occurred (0.27 mg), the times to emergence doubled relative to the times observed at the highest 10-d mean growth (1.03 mg). Ten-day larval growth retardation was strongly correlated with reduction in adult emergence success (r ² = 0.96). Growth retardations 64% resulted in 86–100% reductions in adult emergence. Growth retardation in the range of 35 to 50% equated with comparable percent reductions in adult emergence success. Although fewer females successfully emerged at 10-d growths of 0.37 and 0.74 mg relative to the highest 10-d growth (1.03 mg), ovipositing success of these females did not appear to be adversely affected by either their slower growth rates or their lower mean dry weights (0.62 and 0.99 mg, respectively). Growth of second generation larvae did not appear to be affected by maternal growth rate, but rather appeared to be solely correlated with their own feeding level.     

Effects of emergence characteristics on longevity and maturation in the dragonflySympetrum danae (Anisoptera : Libellulidae)

Size, sex-ratio and mean abdomen length of an emergingSympetrum danae population showed significant yearly variations. It is argued that weather plays a major role. A consistent female-excess at emergence existed.Longevity estimates in the field were highly biased by emigration, especially at an early age, and seemingly more so in females than males. The larger, early emerging individuals emigrated more readily immediately after emergence and lived longer if they stayed in the area, than the smaller, late-emerging ones. This relation was especially clear in males.The shorter maturation in males found in the field was attributed to a sex-specific bias in the field. Maturation-time was found to be inversely related with emergence-data. No effects of abdomen length, weather or density could be demonstrated.     

Salinity effect on plant growth and leaf demography of the mangrove, Avicennia germinans L.

We assessed the effect of salinity on plant growth and leaf expansion rates, as well as the leaf life span and the dynamics of leaf production and mortality in seedlings of Avicennia germinans L. grown at 0, 170, 430, 680, and 940 mol m⁻³ NaCl. The relative growth rates (RGR) after 27 weeks reached a maximum (10.4 mg g⁻¹ d⁻¹) in 170 mol m⁻³ NaCl and decreased by 47 and 44% in plants grown at 680 and 940 mol m⁻³ NaCl. The relative leaf expansion rate (RLER) was maximal at 170 mol m⁻³ NaCl (120 cm m⁻² d⁻¹) and decreased by 57 and 52% in plants grown at 680 and 940 mol m⁻³ NaCl, respectively. In the same manner as RGR and RLER, the leaf production (P) and leaf death (D) decreased in 81 and 67% when salinity increased from 170 to 940 mol m⁻³ NaCl, respectively. Since the decrease in P with salinity was more pronounced than the decrease in D, the net accumulation of leaves per plant decreased with salinity. Additionally, an evident increase in annual mortality rates (λ) and death probability was observed with salinity. Leaf half-life (t _0.5) was 425 days in plants grown at 0 mol m⁻³ NaCl, and decreased to 75 days at 940 mol m⁻³ NaCl. Thus, increasing salinity caused an increase in mortality rate whereas production of new leaves and leaf longevity decreased and, finally, the leaf area was reduced.     

The adaptive value of functional and life-history traits across fertility treatments in an annual plant

Background and Aims

Plant functional traits are assumed to be adaptive. As selection acts on individuals and not on traits, interpreting the adaptive value of a trait not may be straightforward. For example, productive leaves are associated with fertile environments. However, it is not clear if productive leaves confer an advantage in these habitats, or if they are an advantage as part of a suite of coordinated traits.

Methods

Genotypes of Arabidopsis thaliana were grown in high and low nutrient treatments and low, neutral and high pH treatments. Nutrient availability is reduced in acidic or basic soils relative to neutral pH soils. pH treatments were used to alter the availability of resources rather than the amount of resources.

Key Results

Leaf function (specific leaf area, SLA) and life history (size at reproduction, age at reproduction) were variable across genotypes and were plastic. High nutrient availability induced higher SLA and larger size at reproduction. Genotypes that reproduced at large size in high nutrient conditions at neutral pH had the greatest fruit production. SLA was only indirectly related to fruit production through a causal relationship with rosette size; in high nutrient conditions, plants with high SLA were large at reproduction and had higher fruit production. In high nutrient and high pH treatments, plants were large at reproduction, but large size at reproduction was associated with low fecundity. This suggests that large size is adaptive under high nutrient availability.

Conclusions

Interpreting the adaptive value of functional traits will sometimes only be possible when these traits are considered as a suite of correlated and coordinated traits. Leaf functional traits may be important in defining adaptive strategies in A. thaliana but only through how they affect plant life history. Finally, manipulating soil pH can be a valuable tool in assessing adaptive plasticity on nutrient gradients.     

Development of leaf water deficits in detached green and lime-chlorotic leaves of seedlings from populations ofEucalyptus obliqua L'Hérit

Summary The water relations of three populations ofEucalyptus obliqua affected by limechlorosis were studied by monitoring water loss of leaves detached from seedlings. Water was lost faster from chlorotic leaves than from green leaves of the same population; the rate of water loss was inversely propotional to the chlorophyll content. Although chlorophyll content may affect stomatal behaviour, the water loss curves were interpreted as indicating that cuticular aspects of leaf water retention were severely affected.These findings concur with recent observations of severe water stress in chlorotic plants growing on calcareous soils in the Cape Otway region. Moreover, it appears that the greater susceptibility of the acidic population to lime-chlorosis compared with that of the calcareous population would be a considerable disadvantage when growing on a calcareous site subjected to periodic droughts.     

A new life table of leaves ofPhaseolus vulgris L. in relation to their position within the canopy and plant density

In order to demonstrate in detail the relationship between the longevity and productivity of leaves within a canopy, a new life table approach, the ‘bioeconomic life table’, was applied to the leaves of kidney bean plants (Phaseolus vulgaris L.) in relation to planting density and their position within the canopy. The net photosynthetic rate for upper leaves under full daylight tended to decline gradually due to leaf senescence from about 20 days after leaf emergence, and for the lower leaves the decrease was very rapid due to both shading and senescence about 10 days after emergence. Analysis of the survivorship curves and daily surplus production of leaves suggested that the lower and middle leaves, especially the latter, survived without surplus production of dry matter after they had reached mean longevity, and while the upper leaves at high density had a much shorter mean longevity, they had very large values of daily surplus production throughout the survival period. For the total foliage, the summed value of accumulated surplus production during the survival period was about five times as large as the summed value of the dry weight of the dead leaves, regardless of planting density. The daily rate of canopy leaf respiration was almost proportional to that of canopy gross photosynthesis for the various leaf area indices of the canopy, so that there was no optimum leaf area index that maximized canopy daily surplus production.     

Role of the host cell cycle in theAgrobacterium-mediated genetic transformation ofPetunia: Evidence of an S-phase control mechanism for T-DNA transfer

Chimeric -glucuronidase (GUS) gene expression in an efficientAgrobacterium-mediated transformation system utilising mesophyll cells ofPetunia hybrida synchronized with cell cycle phase-specific inhibitors (mimosine and colchicine) was used to show the absolute requirement of S-phase for transfer and/or integration of the transferred DNA (T-DNA). Flow-cytometric analysis of nuclear DNA content and immunohistological detection of bromodeoxyuridine (BrdUrd) incorporation showed that, prior to phytohormone treatment, most (98%) mesophyll cells were at GO-Gl-phase (quiescent phase) and no cell division was occurring. After 48 h and 72 h of phytohormone treatment, there was a rapid increase in S-G2-M-phase populations (> 75%) and a concomitant decrease (down to 24%) in G0–-G1-phase cells. Assays of GUS showed that maximum transformation (> 95% of explants) also occurred after this period. Our data showed that mimosine and colchicine blocked the mesophyll cells at late Gl-phase and M-phase, respectively. No transformation (= GUS expression) was observed in phytohormone-treated cells inhibited in late G1 by mimosine. However, after removal of mimosine, 82% of the explants were transformed, indicating the non-toxic and reversible effect of the inhibitor. On the other hand, a relatively high transformation frequency (65% of explants) was observed after blocking the cell cycle at M-phase with colchicine. However, only transient, but no stable, gene expression (= kanamycin-resistant callus formation) was observed in colchicine-treated M-phase-arrested cells. Similarly, endoreduplication of nuclear DNA, which occurred during the 48 h of phytohormone treatment in some mesophyll cells and cells located along the minor veins in the leaf explants, resulted in transient GUS expression only. These observations indicate a direct correlation between endoreduplication and transient GUS gene expression. Obviously, for stable GUS gene expression, cell division and proliferation are required, indicating that both DNA duplication (S-phase) and cell division (M-phase) are strongly related to stable transformation. We propose that the present system should facilitate further dissection of the process of T-DNA integration in the host genome and therefore should aid in developing new strategies for transformation of recalcitrant plants.Abbreviations BAP 6-benzylaminopurine - BM basal medium - BrdUrd bromodeoxyuridine - GUS -glucuronidase - Km^R kanamycin resistant - T-DNA transferred DNA     

The effects of light on foliar chemistry,growth and susceptibility of seedlings of a canopy tree to an attine ant

Summary Seedlings of Inga oerstediana Benth. (Mimosaceae) growing in three different light environments (the understory, tree-fall gaps and full sun) were tested for differences in chemistry (nutrients and tannins), wound-induced increases in tannins, growth, and susceptibility to leaf-cutter ants, Atta cephalotes (L.) (Formicidae: Attini). I hypothesized that seedlings of I. oerstediana would contain higher concentrations of tannins when growing in high light conditions and, therefore, would be less susceptible to leaf-cutter ants.Foliar concentrations of condensed tannins were much higher in plants growing in full sun compared to those growing in the understory. The concentrations of condensed tannins did not increase following damage. Despite higher concentrations of condensed tannins in sun foliage, leaf-cutter ants found these leaves more acceptable. The preference for sun leaves was consistent with higher concentrations of foliar nutrients. I suggest that the magnitude of the increase in condensed tannins was not great enough to override the benefits of increased concentrations of foliar nutrients. Finally, based on these results and those of others, I suggest that foraging by leaf-cutter ants may be an important factor determining patterns of succession in early successional habitats.     

Pastoralism, plant conservation, and conflicts on proliferation of Himalayan knotweed in high altitude protected areas of the Western Himalaya, India

The conservation policy of banning pastoral grazing, and subsequently emerging conflicts between conservationists and pastoral communities regarding the proliferation of Himalayan knotweed (Polygonum polystachyum), was studied in the Valley of Flowers National Park, a high altitude protected area of the Western Himalaya, India. A total of 10 habitat types identified in the study area were sampled using quadrats along an altitudinal gradient between 3000 and 4500 m. Plant species richness decreases with altitude and also varies across habitat types. The highest density of P. polystachyum and its associated species, Impatiens sulcata, was found between 3300 and 3500 m in the disturbed habitat types, viz., bouldery areas, fragmented treeline zone, avalanche-prone areas and eroded slopes. Eradication of P. polystachyum from the national park by managers is not going to serve any meaningful purpose to the long-term conservation; rather it initiates soil erosion and instability, hindering the establishment of natural plant communities.