Removal Of Apical Meristem Research Articles

Effects of different combinations of pre- and post-grazing heights on herbage mass and nutrient reserves of Leymus chinensis in Northeast China.

The preservation or removal of apical meristem in Leymus chinensis is contingent upon grazing intensity and has a significant impact on above- and belowground biomass, nutritive value, and sustainability of L. chinensis grassland. However, this topic remains understudied. Therefore, a manipulative trial was conducted to induce grazing defoliation through mowing, where two post-grazing heights (preservation or removal of the apical meristem) and four pre-grazing plant heights (i.e., 18, 24, 31, and 35 cm) are combined factorially to create gradients of grazing intensities, resulting in a total of eight treatments. Additionally, two identical control treatments are also incorporated. Our results showed that apical meristem removal at various pre-grazing heights resulted in varying degrees of increased grazing intensities, thereby enhancing the nutritive value of L. chinensis. However, this practice also led to detrimental effects on the plant's carbohydrates reserve as well as herbage mass. The results indicated that although defoliation in treatments involving apical meristem removal resulted in the highest number of frequent cuttings, it did not confer any advantages in terms of herbage mass and nutrient preserves, except for herbage nutritive values when compared to treatments involving apical meristem preservation. The apical meristem preservation treatments demonstrated the highest CP yield over a 2-year period compared to the apical meristem removal treatments. Furthermore, within these apical meristem preservation treatments, only when the pre-grazing height is 35 cm and post-grazing height is 17 cm, there is no significant decrease in above- and belowground biomass. This establishes this specific defoliation regime as an optimal and effective management strategy for L. chinensis grassland.

Brussels Sprout Cultivar Performance and Response to Apical Meristem Removal

We compared the performance of Brussels sprout (Brassica oleracea var. gemmifera) cultivars in New Hampshire and evaluated the effects of topping (apical meristem removal) on marketable yields. A total of 23 cultivars were evaluated in the study, with 8 to 16 cultivars evaluated in any given year. We identified several cultivars that produced moderate to high yields of well-spaced, uniform sprouts that had few Alternaria blight (Alternaria sp.) symptoms, and identified many others, including all red cultivars evaluated, that produced very low yields consistently. In 2013, 2014, and 2015, we used a replicated split-plot experimental design with cultivar as the main plot and topping treatment as the subplot, to evaluate the effects of topping plants. Early and midseason cultivars showed increased yields in response to topping, unless topping was performed too early. Cultivars with sprouts that did not reach marketable size within our growing season generally produced low yields, and topping had no effect on yields. To explore the effects of topping at different dates, we evaluated three cultivars on seven different topping dates plus an untopped control in 2015 and 2017. In addition to reducing stalk height by limiting late-season growth, topping affected marketable yields by affecting the number of sprouts that were either undersized or oversized. The ideal topping date window for minimizing defects and maximizing yields varied slightly for each cultivar, ranging from early to late September.

No evidence of a generalized potential ‘cost’ of apical dominance for species that have strong apical dominance

Abstract When the shoot apical meristem of plants is damaged or removed, fecundity and/or plant growth may suffer (under-compensation), remain unaffected (compensation) or increase (overcompensation). The latter signifies a potential ‘cost’ of apical dominance. Using natural populations of 19 herbaceous angiosperm species with a conspicuously vertical, apically dominant growth form, we removed (clipped) the shoot apical meristem for replicate plants early in the growing season to test for a potential cost of apical dominance. Clipped and unclipped (control) plants had their near neighbours removed, and were harvested after flowering production had finished but before seed dispersal. Dry mass was measured separately for aboveground body size (shoots), leaves, seeds and fruits; and number of leaves, fruits and seeds per plant were counted. We predicted that: (i) our study species (because of their strong apically dominant growth form) would respond to shoot apical meristem removal with greater branching intensity, and thus overcompensation in terms of fecundity and/or biomass; and (ii) overcompensation is particularly enabled for species that produce smaller but more leaves, and hence with a larger bud bank of axillary meristems available for deployment in branching and/or fruit production. Widely variable compensatory capacities were recorded, and with no significant between-species relationship with leaf size or leafing intensity—thus indicating no generalized potential cost of apical dominance. Overall, the results point to species-specific treatment effects on meristem allocation patterns, and suggest importance for effects involving local variation in resource availability, and between-species variation in phenology, life history traits and susceptibility to herbivory.

Methods for vegetative propagation of wild enset (Ensete ventricosum (Welw.) Cheesman) that make genotype conservation possible

The declining trends in crop wild relative genetic resources in many crop centers of origins including Ethiopia require short and long-term conservation strategies. Enset (Ensete ventricosum) is arguably the most important cultivated food security crop of Ethiopia with dwindling wild stocks. The cultivated enset is propagated clonally through adventitious bud sprouting from the corm after the distraction of the apical meristem. Shoot regeneration in the cultivated enset has been induced by humans and has not been observed to occur naturally. The technique of shoot induction has not been extended to the wild enset. To determine whether the capacity for shoot regeneration existed in wild enset and optimize the technique, a series of experiments were conducted. These involved: (i) sucker production from corms of wild enset with and without apical meristem removal; (ii) sprouting capacity of corms ranging 22–49 cm diameter, with removed apical meristem; and (iii) a factorial experiment involving two populations of wild enset (from Shebena and Getiba localities in Sheka zone), two ways of preparing or cutting the corms: tero and tubo, i.e. cutting the pseudostem at the corm junction and cutting it at 25–30 cm height, respectively, and three extents of parting the corm (whole, half, and quarter) using corms with a diameter of 45 ± 2.9 cm. The experiments revealed that wild enset can be successfully propagated vegetatively in the same way as the cultivated enset. It also revealed that the regeneration process involved callus formation and adventurous bud proliferation from corms only after the apical meristem was removed. Corms of different sizes varied in their capacity for regeneration significantly with a linear increase in regeneration frequency with corm size. With a one cm increase in corm diameter, regeneration frequency increased by 3.138 %. The two populations of wild enset showed non-significant differences in regeneration capacity; however, the achieved regeneration was generally analogous to that observed among cultivated enset clones: whole corms resulted in a longer time to emergence and fewer sucker per corm than split corms. Specifically, halved corms emerged significantly (p < 0.05) earlier (71 ± 9 and 75 ± 7 days, for Shebena and Getiba populations, respectively) than whole corms (120 days). Regeneration frequency was higher (75–100%) for split than for whole corms (33–56%). The highest rate of suckering (94 ± 14 per corm) was achieved from quarter corms prepared by cutting the pseudo-stem at the junction. In conclusion, the adventitious bud propagation technique developed by farmers to propagate the cultivated enset can successfully be used for the clonal regeneration of wild enset. We recommend the adoption of this shoot induction to conserve and maintain the rapidly eroding wild enset genetic resources in Ethiopia. In addition, wild enset plants with promising characteristics may be fixed using the method to enrich the gene pool of the cultivated enset.

Anatomy of the main stem of soybean plants submitted to the removal of the stem apical meristem

Some plant species allow the cutting of the apical meristem in order to assist activities of genetic improvement programs, among them is the soybean. The objective was to verify if the removal of the apical meristem of soybean plants induces any alteration in the stem anatomy, since it was verified that the removal of the apical meristem reduces the need for tutoring of the plants cultivated under greenhouse conditions. The experiment was conducted with plants of the BRSMG 752S cultivar and the treatments consisted of sections of the hypocotyl region of plants that had undergone apical meristem removal at the V2 development stage and of plants without apical meristem removal. The permanent slides were processed following the usual methodologies in plant anatomy. Descriptions and measurements of anatomical tissues were made for comparison between treatments. Plants with removal presented epidermis as a covering tissue until 20 days after the V2 development stage, while plants without removal of the apical meristem presented it until 30 days after V2. Periderm was observed only in plants with removal, and this feature was not evident in plants without removal until 30 days after V2. There was formation of secondary vascular tissues in the collections 30 days after removal (V2 stage). Thus, we conclude that the removal of the apical meristem accelerates the secondary development in hypocotyls of soybean plants grown under greenhouse conditions.

Morphogenetic and structural characteristics of Megathyrsus maximus cv. Centenário under defoliation intensities

The effect of defoliation intensities (20, 30, 40 and 50 cm above soil level) on green dry matter (GDM) yield and morphogenetic and structural characteristics of Megathyrsus maximus cv. Centenário were evaluated under field conditions in Roraima´s savannas. The effects of defoliation intensities on the GDM yields, leaf area index and leaf elongation rates was adjusted to the quadratic regression model and maximum values recorded with cutting at 35.8; 44.9 and 30.2 cm above soil level, respectively. The tiller population density, number of leaves tiller-1 and leaf appearance rate was inversely proportional to the intensity of defoliation, while the opposite occurred for to average leaf length and leaf senescence rate. Apical meristem removal percentage was higher with increasing defoliation intensity. Vigor regrowth showed close negative correlation with defoliation intensity level. Pastures of M. maximus cv. Centenário managed under 30 to 35 cm residue provides higher forage productivity, larger efficiency of forage utilization, greater tissue renewal and canopy structure more favorable to grazing.

Temporal patterns of ungulate herbivory and phenology of aspen regeneration and defense.

Ungulate herbivory can create strong top-down effects on forest recruitment, especially after fire. Defense strategies of tree species against ungulate herbivory include escape through vertical growth and resistance through the production of defense compounds. Using afour-way fence design and camera traps we characterized the differential impacts of ungulate herbivores (deer, elk, cattle) on aspen forest recruitment and plant defense responses and how they vary depending on the timing of herbivory. Aspen height growth was greatest between June and August and ungulate use of aspen was highest in July and August. Threeyears after fire, height of aspendiffered among fence treatments with full ungulate exclusion > deer-only plots > native ungulate plots > fenceless plots: 108 ± 4cm, 94 ± 4cm, 89 ± 4cm, and 65 ± 4cm, respectively. Fenceless plots had the highest rates of removal of apical meristems by the end of 2014 and 2015 (61% and 53%, respectively). Native ungulate plots, and deer-only plots both had similar removal of apical meristems in 2014 (37% and 39%, respectively). The highest phenolic glycoside concentrations were associated with an 80% reduction in meristem removal and four-fold greater aspen height by the end of summer. Low nitrogen was associated with an 86% reduction in apical meristem removal and threefold greater aspen height. In conclusion, our study suggests that high ungulate abundance can have detrimental impacts on forest recruitment and that high aspen defense chemistry and lower leaf N deters ungulate herbivory, especially in the late summer.

Differential effects of cattle, mule deer, and elk herbivory on aspen forest regeneration and recruitment

The abundance and composition of ungulate herbivore communities are changing globally, which can impact the resilience and function of Earth’s ecosystems. Impacts from herbivory are compounded in areas where multiple ungulates overlap, which is common in forest ecosystems. The objective of this study was to examine the differential and combined effects of ungulate communities (deer, elk, and cattle) on aspen forest recruitment after fires that occurred in 2012. Eight sets of differential ungulate exclosures, monitored by camera traps, were established across three National Forests in Utah. We identified the differential effect of each of three ungulate species using fencing that allowed for deer-only, native ungulate only (deer and elk), all ungulates and a complete ungulate exclosure. Over a three year period (2013–2016) we quantified ungulate species impacts on aspen height, density, and browse rates using camera trap photos. Ungulate activity was nearly 10-fold higher in two National Forests compared to the third, and gradually decreased over time. Meristem removal by ungulates in unfenced plots across sites averaged 60% which we identified as a critical threshold point for aspen recruitment failure. All three ungulate species had significant and similar effects on aspen regeneration success, but when adjusted for differences in estimated forage intake (animal unit months), differential impacts became apparent (deer > elk > cattle). We estimated that 4 cattle per camera−1 day−1 and 2.5 deer or elk per camera−1 day−1 was sufficient to reach the critical recruitment threshold of 60% removal of apical meristems. We conclude that ungulates species differentially influence aspen regeneration and recruitment, and that ungulate browsing above 30% meristem removal impairs aspen recruitment with recruitment failure occurring above 60% meristem loss.

Early‐Season Lactofen Application Fails to Increase Soybean Yield under Weed‐Free Conditions

In an effort to increase soybean [Glycine max (L.) Merr.] yield, growers may consider non‐traditional use of crop inputs. One non‐traditional input use is the application of lactofen {2‐ethoxy‐1‐methyl‐2‐oxoethyl 5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐2‐nitrobenzoate} herbicide to early‐vegetative soybean to promote increased branch development and ultimately increase seed yield. The purpose of this study was to evaluate the effect of early‐season lactofen application and simulated herbicide injury on stands, plant height, light interception, and seed yield. The experiments were conducted at two locations in Kentucky during the 2013 and 2014 growing seasons. Treatments included lactofen herbicide applied at 240 g a.i. ha−1 and fomesafen {5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐N‐methylsulfonyl‐2‐nitrobenzamide} herbicide applied at 600 g a.i. ha−1. A meristem removal treatment was included, where the apical meristem of each soybean was physically removed, and a leaf removal treatment was also performed. All treatments were applied to soybean at V1, V2, V3, and V4 growth stages. The herbicide application timing had no effect on any of the above mentioned agronomic measurements. The apical meristem removal reduced plant stands and plant height in 2 site‐years while lactofen and leaf removal decreased early‐light interception in all site‐years. Meristem removal and leaf removal reduced seed yield in 1 site‐year, while lactofen, leaf removal, and meristem removal reduced seed yield in another site‐year. None of the treatments increased seed yield compared with the untreated control. Despite a limited number of trials, this study suggests that application of lactofen to soybean for non‐weed control purposes is not a viable strategy to increase soybean yield.Core Ideas Leaf removal and lactofen application decrease early‐season light interception in soybean. Destroying the soybean apical meristem either decreases or does not affect soybean yield. Lactofen application to early vegetative soybean does not increase yield under weed free conditions.

Regrowth patterns and rosette attributes contribute to the differential compensatory responses of Arabidopsis thaliana genotypes to apical damage.

A plant's compensatory performance refers to its ability to maintain or increase its reproductive output following damage. The ability of a plant to compensate depends on numerous factors including the type, severity, frequency and timing of damage, the environmental conditions and the plant's genotype. Upon apical damage, a cascade of hormonal and genetic responses often produces dramatic changes in a plant's growth, development, architecture and physiology. All else being equal, this response is largely dependent on a plant's genotype, with different regrowth patterns displayed by different genotypes of a given species. In this study, we compare the architectural and growth patterns of two Arabidopsis thaliana genotypes following apical damage. Specifically, we characterise regrowth patterns of the genotypes Columbia-4 and Landsberg erecta, which typically differ in their compensation to apical meristem removal. We report that Landsberg erecta suffered reductions in the number of stems produced, maximum elongation rate, a delay in reaching this rate, lower average rosette quality throughout the growing period, and ultimately, less aboveground dry biomass and seed production when damaged compared to undamaged control plants. Columbia-4 had no reductions in any of these measures and maintained larger rosette area when clipped relative to when unclipped. Based on the apparent influence of the rosette on these genotypes' compensatory performances, we performed a rosette removal experiment, which confirmed that the rosette contributes to compensatory performance. This study provides a novel characterisation of regrowth patterns following apical damage, with insights into those measures having the largest effect on plant performance.

Effect of sunn hemp (Crotalaria juncea L.) cutting date and planting density on weed suppression in Georgia, USA

A field study was conducted in 2008 and 2009 at the USDA, ARS, Plant Genetic Resources Conservation Unit in Griffin, GA, to investigate weed suppression by sunn hemp (Crotalaria juncea L). The objectives were to (1) evaluate the effects of apical meristem removal (AMR) at three dates [5, 6, and 7 wks after planting (WAP) on May 14, 2008 and May 21, 2009] and (2) assess the impact of seeding rates (11, 28, and 45 kg ha−1) on weed biomass reduction. Weed species were identified at 4, 8, and 12 wks after sunn hemp planting. Sunn hemp cutting date had no significant effect on weed suppression in 2008 but significant differences for grass weeds at 4, 8, and 12 WAP and for yellow nutsedge at 8 and 12 WAP did occur when compared to the control in 2009. In comparison to the sunn hemp-free control plot in 2009, all three seeding rates had reduced grass weed dry weights at 4, 8, and 12 WAP. The total mass of yellow nutsedge when grown with sunn hemp was reduced compared to the total mass of yellow nutsedge grown in the weedy check for all seeding rates at 8 and 12 WAP. Lower grass weed biomass was observed by 12 WAP for cutting dates and seeding rates during 2008 and 2009. Sunn hemp cutting date and seeding rate reduced branch numbers in both years. The reduction in sunn hemp seeding rates revealed a decrease in weed populations.

入侵植物黄顶菊生长、再生能力对模拟天敌危害的响应

Biological invasion is becoming one of most serious environmental problems in the 21st century.Flaveria bidentis,an exotic plant with the strong invasiveness from South America,has spread over more than 92 counties of Hebei Province and expanded to Tianjin,Shandong,Henan Province in China as well.The wise management on the exotic species is pivotal for the balance of ecosystem and the maintenance of biodiversity.There are many challenges for classical biological control,such as host specificity,biosafety risk,and appropriate applications as well as efficiency assessment.This study aims to mimic the effects of herbivory damage on plant growth and reproduction in invaded habitats and thus to investigate whether herbivory treatment could be used as an effective measure to manage F.bidentis. A field experiment was carried out to clarify the effects of simulated herbivory damage on the growth,reproduction and related physiological characteristics of F.bidentis.We clipped leaves with scissor to simulate different level damage by folivores and removed apical meristems to simulate apical mortality caused by stem borers.Five treatments were designed,three levels of leaf removal(1/4,1/2,and 3/4),apical meristem removal and the undamaged control.Each treatment included 45 replications(individual plant),and each plant is marked by a nameplate. Compared with the control,the overcompensation effect was observed under low level damage and apical removal treatments with increased total biomass,root biomass,stem biomass,plant height,branch numbers,flower bud numbers,net photosynthetic(Pn) and water use efficiency(WUE),while,these parameters were only reduced by severe damage level(3/4) in our study.Initial fluorescence yield(F0) under three leaf damage treatments was significantly higher than that in other treatments,whereas the maximum photochemical efficiency of photosystem Ⅱ(Fv/Fm) and potential activity of photosystem Ⅱ(Fv/F0) were significantly suppressed.Higher phenotypic plasticity were observed in biomass related parameters,indicating these parameters of F.bidentis have high herbivore tolerance,which might make an important acclimation under herbivores regimes for this invasive species. These results suggested that natural enemies may have little impact on fecundity of F.bidentis.In practice,more swift management strategy such as clipping,plant replacement and integrated control measure is required to prevent the reproduction of this weed.

Practical Factors Controlling in vitro Multiplication and Rooting in Empetrum nigrum var. japonicum, an Endangered Woody Species

The plant Empetrum nigrum, valued in the traditional system of medicine, is well known for its antibacterial, antifungal, and antioxidant properties. In the present work, the effect of removal of shoot apical meristem (SAM) on shoot proliferation was studied. It was observed that removal of SAM promoted shoot proliferation whereas intact tip resulted in higher survival percentage. Further, the effect of different concentrations of BA on above was also studied. During root formation the effect of light quality after treatment with IBA was investigated. For rooting, continuous red light without IBA resulted in maximum rooting percentage. The above factors when taken into consideration during micropropagation of this endangered plant can result in healthier plantlets. The results show that the species could be successfully conserved by in vitro propagation system.

Remoção do meristema apical e adensamento em plantas de soja visando sua utilização no método descendente de uma única semente

The objective of this work was to evaluate the effect of removing the apical meristem of soybean plants grown at different densities on branch formation, seed production at the highest density and reduction of plant height in order to find the best greenhouse cultivation strategies to be used in the genetic improvement through the SSD method. The experiment was arranged in a split-plot design, in which densities were randomized in the plots and meristem removal in the subplots, using a randomized block design, with three repetitions, with each plant container being considered as a repetition. The evaluated parameters included height of first pod insertion, number of nodes in the main stem, number of branches per plant, number of pods per plant, number of seeds per plant and weight of 100 seeds. Removal of the apical meristem carried out at the 6 th trifoliate leaf was more efficient, stimulating branching, reducing plant height and height of the first pod insertion. Removal of apical meristem at the density of ten plants/container provided the production of at least one pod/plant, allowing the use of the SSD method in greenhouse conditions.

Nicotine Concentration in Leaves of Flue‐cured Tobacco Plants as Affected by Removal of the Shoot Apex and Lateral Buds

It is believed that the nicotine concentration in tobacco is closely correlated with the amount of nitrogen (N) supplied. On the other hand, N uptake mainly occurs at the early growth stage, whereas nicotine concentration increases at the late growth stage, especially after removing the shoot apex. To identify the causes of the increased nicotine concentration in tobacco plants, and to compare the effects of different ways of mechanical wounding on nicotine concentration, field experiments were carried out in Fuzhou, Fujian Province in 2003 and 2004. Excision of the shoot apex had almost no influence on N content in the plant; however, it caused dramatic increases in nicotine concentration in leaves, especially in the middle and upper leaves. An additional increase of the nicotine concentration was obtained by removal of axillary buds. The wounding caused by routine leaf harvests, however, did not change the leaf nicotine concentration, and neither did reducing leaf harvest times. The present results revealed no direct relationship between N supply and nicotine concentration in tobacco leaves, and indicate that not all kinds of mechanical wounding were capable of stimulating nicotine synthesis in tobacco plants. Since nicotine production is highly dependent on the removal of apical meristems and hence on the major sources of auxin in the plant, and application of 1-naphthylacetic acid onto the cut surface of the stem after removing the shoot apex markedly decreased the nicotine concentration in different leaves and the total nicotine content in the plant, the results suggest that decreased auxin supply caused by removal of the shoot apex as a kind of mechanical wounding might regulate nicotine synthesis in the roots of tobacco plants.

Apical dominance and the importance of clonal integration to apical growth in the seagrass Syringodium filiforme

The existence of apical dominance and the importance of clonal integration to apical growth in the seagrass Syringodium filiforme were examined using field and mesocosm experiments. In the field, apical dominance was observed with proliferative branching resulting from the removal of rhizome apical meristems (RAMs). Rhizome internode length and branching increased when plants grew from a dense meadow into a bare patch, providing further evidence for the existence of apical dominance in S. filiforme. The results of the experiments indicated that growth of the RAM is dependent on the translocation of resources from older ramets. Removing 3 shoots from a rhizome runner lead to a significant reduction in the growth of the RAM, and removing 6 shoots had a greater effect. Apical growth was more significantly affected by cutting the rhizome, with the lowest growth observed in clonal fragments comprised of a RAM and the 4 youngest ramets. We conclude that clonal integration is an important factor regulating the growth form and productivity of S. filiforme. These results have implications for damage assessment and restoration projects, and indicate that future studies of meadow structure and plant production should consider RAM health and branch formation along with individual ramet growth.

Magnitudes and Mechanisms of Shoot-damage Compensation in Annual Species of Linum (Linaceae) in Iowa

ABSTRACT The effect of shoot damage on plant performance depends partly on a plant's ability to recover by growth compensation. Plant populations in tallgrass prairie likely experience, or historically experienced, high risks of damage and therefore might be expected to have evolved significant compensation ability. We investigated shoot damage and subsequent growth compensation in Iowa populations of the annuals Linum rigidum and L. sulcatum. To estimate damage rate and responses to damage under natural conditions, we collected two data sets. The first consisted of over 200 herbarium specimens collected over a 113-y period and the second consisted of field data for four populations in the same growing season. A companion experiment investigated damage responses under controlled greenhouse conditions and identified possible mechanisms of compensation. The study species frequently experience apical meristem removal in nature. Per-individual damage-rate estimates ranged from 33–54% in L. rigidum and from 12...

Nicotine synthesis in Nicotiana tabacum L. induced by mechanical wounding is regulated by auxin

The effects of different kinds of mechanical wounding on nicotine production in tobacco plants were compared, with sand or hydroponics culture under controlled conditions. Both removal of the shoot apex and damage of the youngest unfolded leaves nos 1 and 2 by a comb-like brusher with 720 punctures caused an increase in nicotine concentration in whole plants at day 3, and reached its highest level at day 6. The nicotine concentration induced by excision of the shoot apex was much higher than that induced by leaf wounding. Both treatments also caused an increase in jasmonic acid (JA) concentration within 90 min in the shoot, followed by an increase in the roots (210 min), in which the JA concentration induced by leaf wounding was significantly higher than that induced by excision of the shoot apex. The increase in nicotine concentration occurred throughout the whole plant, especially in the shoot, while the increase in JA concentration in the shoot was restricted to the damaged tissues, and was not observed in the adjacent tissues. Removal of the lateral buds that emerged after excision of the shoot apex caused a further increase in nicotine concentrations in the plant tissues. Removal of mature leaves, however, did not cause any changes in nicotine concentration in the plant, even though the degree of wounding in this case was comparable with that occurring with apex removal. The results suggest that the nicotine production in tobacco plants was not correlated with the degree of wounding (cut-surface or punctures), but was highly dependent on the removal of apical meristems and hence on the major sources of auxin in the plant. Furthermore, immediate application of 1-naphthylacetic acid (NAA) on the cut surface after removing the shoot apex completely inhibited the increase both in nicotine in whole plants and in JA in the damaged stem segment and roots. Application of an auxin transport inhibitor around the stem directly under the shoot apex of intact plants also caused an increase in nicotine concentration in the whole plant. The results strongly suggest that auxin serves as a negative signal to regulate nicotine synthesis in roots of tobacco plants.

Influência da remoção do meristema apical sobre os componentes de produtividade em populações de plantas de soja

The purpose of this work was to check the efficiency of apical meristem removal in different soybean populations plants as for to stimulate branching habit and to verify if this removal contributes to the increase of productivity and decrease the works of staking-out, in greenhouse under growth conditions, with UFV-18 variety (Patos de Minas), in 2001/02 agricultural year. The trials were set up with plant populations of 1 to 6 per vase, 3 heights of apical meristem removal when the plants were with 25, 50 and 75cm of height, and control without removal. The experiment was installed in subdivided plots, being the plots composed by heights and the subplots by different populations in complete randomized design with 6 replications. The following characteristics were evaluated: plant weight pod weight/plant, main stem weight, seeds weight/plant, number of pods/plant, number of seeds/plant, number of seeds/pod, seed production/vase and index of harvest/plant. The apical meristem removal was more efficient to stimulate branching habit in populations of 1 plant per vase. The apical meristem removal when made at 25cm of height increased productivity and decreased work of staking-out in greenhouse under growth conditions

Drought and root herbivory in understorey Parashorea Kurz (Dipterocarpaceae) seedlings in Borneo

The influence of herbivory on dipterocarp seedling growth and survival in Bornean primary lowland forest understorey during and after the 1997–8 El Niño-Southern Oscillation was investigated. During the drought, a coleopteran (Scolytidae) root borer attacked dipterocarp seedlings, primarily of the genus Parashorea. Infestation was spatially heterogeneous on a large (c. 100 m) scale. Attack rate decreased with plant vigour within infested areas. Experiments showed that root damage was fatal under drought conditions, but not after rain. Defoliation and apical meristem removal did not increase mortality. The spatio-temporal heterogeneity of herbivore outbreaks and difficulties involved in experimenting with root herbivores limit the power of such short-term investigations. However, the study shows that herbivores can cause differential mortality between species, and can therefore influence dipterocarp regeneration dynamics. The effect of herbivory depends on the plant organ attacked and interactions with other stresses such as drought. El Niño-related droughts are increasing in frequency in South-East Asian rain forests, which may lead to increased numbers of herbivore outbreaks and greater seedling mortality due to these factors.