Methyl jasmonate-induced nicotine production in Nicotiana attenuata: inducing defenses in the field without wounding

The functional significance of herbivore-induced plant traits known to directly or indirectly influence herbivore performance remains largely untested under field conditions due to the difficulty of uncoupling the response to herbivory from the act of herbivory. The signals that activate many of the induced responses in plants are endogenously produced in response to wounding, unlike many of the predator-induced responses found in aquatic invertebrates (which are activated by exogenous cues derived from predators). Jasmonates, endogenously-produced damage signals, activate diverse wound-induced responses in plants including induced nicotine production in Nicotiana sylvestris. The results presented here are from two experiments which illustrate the use of jasmonates to uncouple induced nicotine production in Nicotiana attenuata (Torrey ex. Watson) from wounding. The exogenous addition of methyl jasmonate (MJ) in small quantities (11 g for a 1.4 g dry mass plant) to roots of hydroponically-grown plants induces de novo nicotine synthesis and increases whole-plant nicotine concentrations just as wounding does. The MJ-induced changes were proportional to the quantity of MJ given. Moreover, the effects of MJ were additive to the effects of damage. Applications of MJ to shoots were less effective. Root treatments also worked with plants growing in a field plot. The application of MJ represents a promising tool for examining the functional significance of induced nicotine responses in plants growing in their native environments.     

Swords into plowshares? Nicotiana sylvestris does not use nicotine as a nitrogen source under nitrogen-limited growth

Whether or not a plant can recover its investment of resources in a chemical defense is central to the mobile-immobile metabolite dichotomy of the resource availability theory. Biochemical measures of metabolite turnover have been used to estimate this trait, but they do not address the ecological question of resource recovery. Numerous studies have found that many Nicotiana species, which normally produce the nitrogen-intensive defense metabolite, nicotine, can rapidly take up and metabolize exogenously administered nicotine from hydroponic solutions. However, Baldwin et al. (1994) found no evidence for turnover of endogenously produced nicotine in pulse-chase experiments using ¹⁵NO₃ as the biosynthetic precursor in N. sylvestris. Given that the capacity to metabolize nicotine exists, we asked (1) whether N. sylvestris could metabolize exogenously fed nicotine and sustain growth under nitrogen-limited conditions and (2) whether leaf damage alters the plants' ability to use nicotine as a nitrogen source. We fed plants with sufficient nicotine in hydroponic culture to increase their nitrogen pools by 70% at the time of nicotine feeding; in 6–10 consecutive harvests over 28–35 days, we measured the biomass of roots, leaves and stems, and the total nitrogen pools of these plant parts as well as the pools of nicotine, nornicotine and myosmine of these plant parts in undamaged nicotinefed and control plants and finally, in a separate experiment, in nicotine-fed damaged and undamaged plants. Nicotine feeding increased nicotine pools by 1.2 times, which was not sufficient to significantly increase total nitrogen pools at the end of the experiment. Nicotine-fed plants rapidly demethylated their acquired nicotine pools to nornicotine, but did not process the alkaloid pool further than myosmine over the duration of the experiment. Leaf damage significantly increased the nicotine pool, but did not significantly alter the processing of the exogenously acquired nicotine. We conclude that N. sylvestris does not recover the nitrogen invested in nicotine even under nitrogen-limited growth, that the rapid metabolism of exogenously introduced nicotine is likely a detoxification pathway, and that these plants are homeostatic with regard to their nicotine pools.     

Tobacco plants can use nitrogen taken up before mechanical wounding to synthesize nicotine afterwards

Mechanical wounding stimulates nicotine synthesis in tobacco plants. In the practice of tobacco production, most nitrogen (N) is taken up before removal of the shoot apex, while nicotine is mainly synthesized afterwards. Since N is required for nicotine synthesis, it is interesting to know whether plants can use N taken up before removal of the shoot apex to synthesize nicotine after wounding. To address this question, a hydroponics culture experiment was carried out, in which N was supplied as NH₄NO₃ at two levels (1 mM and 6 mM) in pre-culture, and N was either withdrawn or replaced by ¹⁵N after removing the shoot apex for the next seven days. Removal of the shoot apex caused a marked increase in nicotine concentration in various organs, also when plants grew under low-N conditions and showed symptoms of N deficiency. Increased nicotine accumulation even occurred when N was withdrawn from the growth medium before the apex was removed, indicating that tobacco plants can use N taken up previously to synthesize nicotine after mechanical wounding. The amount of N used for nicotine synthesis accounted for 5–6% of the total N, irrespective of treatment. Although most of the nicotine in intact plants and plants with the apex removed was synthesized de novo, as evidenced by the data when N was replaced by ¹⁵N-labeled NH₄NO₃, a large amount of the N absorbed before the N replacement was incorporated into the newly formed nicotine. The proportion of nicotine-¹⁵N to total nicotine-N was almost the same as that of ¹⁵N to total N in various organs. The results show the utilization of remobilized N taken up before excision of the shoot apex for nicotine synthesis afterwards, and highlight the importance of N cycling within plants, both when grown under N-sufficient and N-deficient conditions.Key words: ¹⁵N-isotope nitrogen, mechanical wounding, nicotine concentration, nicotine synthesis, nitrogen deficiency, removal of the shoot apex, tobacco (Nicotiana tabacum L.)     

Plasticity in relative growth rate and its components following a change in irradiance

A total of 244 plants from two species, Lythrum salicaria and Epilobium glandulosum, were grown individually in hydroponic sand culture from seed for 36 d. Until day 27 all plants experienced an irradiance of 550 μmol m^?2 s^?1 PFD and on day 27 half of the plants were subjected to a neutral shade treatment in which irradiance was reduced to 100 μmol m^?2 s^?1 photon fluy density (PFD). Measures of relative growth rate, net assimilation rate, specific leaf area, biomass partitioning to leaves, roots, structural tissues (i.e. stems, petioles and inflorescences) and tissue density were obtained from intensive harvests three or four times per day. The shade treatment caused an immediate decrease in relative growth rate and net assimilation rate. Within hours the specific leaf area of the shaded plants increased and leaf tissue density decreased, thus partially offsetting the decrease in relative growth rate. Biomass partitioning was not affected.     

Modulation of carbon and nitrogen metabolism, and of nitrate reductase, in untransformed and transformed Nicotiana plumbaginifolia during CO2 enrichment of plants grown in pots and in hydroponic culture

Transformed plants of Nicotiana plumbaginifolia Viv. constitutively expressing nitrate reductase (35S-NR) or β-glucuronidase (35S-GUS) and untransformed controls were grown for two weeks in a CO₂-enriched atmosphere. Whereas CO₂ enrichment (1000 μl · l⁻¹) resulted in an increase in the carbon (C) to nitrogen (N) ratio of both the tobacco lines grown in pots with vermiculite, the C/N ratio was only slightly modified when plants were grown in hydroponic culture in high CO₂ compared to those grown in air. Constitutive nitrate reductase (NR) expression per se did not change the C/N ratio of the shoots or roots. Biomass accumulation was similar in both types of plant when hydroponic or pot-grown material, grown in air or high CO₂, were compared. Shoot dry matter accumulation was primarily related to the presence of stored carbohydrate (starch and sucrose) in the leaves. In the pot-grown tobacco, growth at elevated CO₂ levels caused a concomitant decrease in the N content of the leaves involving losses in NO⁻ ₃ and amino acid levels. In contrast, the N content and composition were similar in all plants grown in hydroponic culture. The 35S-NR plants grown in air had higher foliar maximum extractable NR activities and increased glutamine levels (on a chlorophyll or protein basis) than the untransformed controls. These increases were maintained following CO₂ enrichment when the plants were grown in hydroponic culture, suggesting that an increased flux through nitrogen assimilation was possible in the 35S-NR plants. Under CO₂ enrichment the NR activation state in the leaves was similar in all plants. When the 35S-NR plants were grown in pots, however, foliar NR activity and glutamine content fell in the 35S-NR transformants to levels similar to those of the untransformed controls. The differences in NR activity between untransformed and 35S-NR leaves were much less pronounced in the hydroponic than in the pot-grown material but the difference in total extractable NR activity was more marked following CO₂ enrichment. Foliar NR message levels were decreased by CO₂ enrichment in all growth conditions but this was much more pronounced in pot-grown material than in that grown hydroponically. Since β-glucuronidase (GUS) activity and message levels in 35S-GUS plants grown under the same conditions of CO₂ enrichment (to test the effects of CO₂ enrichment on the activity of the 35S promoter) were found to be constant, we conclude that NR message turnover was specifically accelerated in the 35S-NR plants as well as in the untransformed controls as a result of CO₂ enrichment. The molecular and metabolic signals involved in increased NR message and protein turnover are not known but possible effectors include NO₃ ⁻, glutamine and asparagine. We conclude that plants grown in hydroponic culture have greater access to N than those grown in pots. Regardless of the culture method, CO₂ enrichment has a direct effect on NR mRNA stability. Received: 17 October 1996 / Accepted: 11 February 1997     

Costs of jasmonate-induced responses in plants competing for limited resources

We present a design to quantify fitness consequences of jasmonate-induced responses in plants that are competing for limited resources with a conspecific. Under both high and low nitrogen supply rates, uninduced (control) Nicotiana attenuata plants growing next to a plant induced with 250 μg methyl jasmonate (MJ) yielded more seed capsules than control plants competing with another control plant. We conclude that there is a opportunity benefit for control plants growing next to an induced plant. Initially, MJ-induced plants grew more slowly, but by senescence they had produced the same number of seed capsules as control plants that had competed with another control plant. Replacement series showed that the fitness of MJ-induced plants is not influenced by the competitive status of their neighbour plant. We argue that competitive designs are useful tools for evaluating the phenotypic costs of ecologically important traits.     

Effects of irradiance on growth and flowering in the shade plant, cineraria

Effects of total irradiance on growth and flowering were studied in cineraria cv. Cindy Blue grown under warm (mean 21°C) glasshouse conditions. Efficiency of light conversion for leaf and shoot dry weight increase were reduced from 0.08 to 0.02 as the mean daily light integral increased from 0.9 to 4.4 MJ m^-2 day^-1 but no significant difference in leaf area were associated with this. Specific leaf area decreased exponentially from 0.07 to 0.02 m²g¹ over the cumulative irradiance range 23 to 127 MJ m^-2 after the start of treatments and thereafter remained stable. A light integral of 19.2 MJ m^-2 were required for initiation of one leaf in plants grown under a daily integral of 4.4 MJ m^-2 day^-1, as compared with only 5.1 MJ m^-2day^-1 required per leaf in plants grown at less than 0.9 MJ m^-2day^-1. Neither chronological duration of juvenile development nor leaf number below the flower was affected by irradiance. However, as the rate of leaf initiation increased with irradiance up to 2.4 MJ m^-2day^-1 so the rate of progress to flower visibility increased linearly with irradiance over the same range. This rate then remained constant from 2.4 to 4.4 MJ m^-2day^-1. Length of the main flowering shoot decreased and the number of flowering shoots increased as irradiance increased from 0.9 to 2.4 MJ m^-2 day^-1 and then remained unchanged by further increases in irradiance.     

ENHANCEMENT OF INBREEDING DEPRESSION BY DOMINANCE AND SUPPRESSION IN IMPATIENS CAPENSIS

We investigated the effect of intraspecific competition on the magnitude of inbreeding depression in Impatiens capensis by planting seeds from chasmogamous (CH) and cleistogamous (CL) flowers in three experimental greenhouse treatments: in individual pots, in flats in dense pure stands according to seed type, and in flats with the two seed types intermixed in a checkerboard array. The size distributions of plants grown in flats were significantly more hierarchical than those of plants grown individually, indicating that larger plants competitively suppressed smaller plants in the high-density treatments. The magnitude of inbreeding depression at high density depended upon the planting arrangement of CL and CH seeds. CH advantage was greatest when CH and CL seedlings were grown in competition with one another, suggesting that fitness differences between outcrossed and inbred individuals were intensified by dominance and suppression. For plants grown individually, the effects of maternal parent, seed weight, and emergence date on seedling size disappeared with plant age, whereas at high density these effects remained at the final harvest. Thus, plant density may influence patterns of natural selection both on mating system and on juvenile traits in natural Impatiens populations.     

Growth and reproduction of Arabidopsis thaliana in relation to storage of starch and nitrate in the wild-type and in starch-deficient and nitrate-uptake-deficient mutants

We have investigated the interactions between resource assimilation and storage in rosette leaves, and their impact on the growth and reproduction of the annual species Arabidopsis thaliana. The resource balance was experimentally perturbed by changing (i) the external nutrition, by varying the nitrogen supply; (ii) the assimilation and reallocation of resources from rosette leaves to reproductive organs, by cutting or covering rosette leaves at the time of early flower bud formation, and (iii) the internal carbon and nitrogen balance of the plants, by using isogenic mutants either lacking starch formation (PGM mutant) or with reduced nitrate uptake (NU mutant). When plants were grown on high nitrogen, they had higher concentrations of carbohydrates and nitrate in their leaves during the rosette phase than during flowering. However, these storage pools did not significantly contribute to the bulk flow of resources to seeds. The pool size of stored resources in rosette leaves at the onset of seed filling was very low compared to the total amount of carbon and nitrogen needed for seed formation. Instead, the rosette leaves had an important function in the continued assimilation of resources during seed ripening, as shown by the low seed yield of plants whose leaves were covered or cut off. When a key resource became limiting, such as nitrogen in the NU mutants and in plants grown on a low nitrogen supply, stored resources in the rosette leaves (e.g. nitrogen) were remobilized, and made a larger contribution to seed biomass. A change in nutrition resulted in a complete reversal of the plant response: plants shifted from high to low nutrition exhibited a seed yield similar to that of plants grown continuously on a low nitrogen supply, and vice versa. This demonstrates that resource assimilation during the reproductive phase determines seed production. The PGM mutant had a reduced growth rate and a smaller biomass during the rosette phase as a result of changes in respiration caused by a high turnover of soluble sugars ( Caspar et al. 1986 ; W. Schulze et al. 1991 ). During flowering, however, the vegetative growth rate in the PGM mutant increased, and exceeded that of the wild-type. By the end of the flowering stage, the biomass of the PGM mutant did not differ from that of the wild-type. However, in contrast to the wild-type, the PGM mutant maintained a high vegetative growth rate during seed formation, but had a low rate of seed production. These differences in allocation in the PGM mutant result in a significantly lower seed yield in the starchless mutants. This indicates that starch formation is not only an important factor during growth in the rosette phase, but is also important for whole plant allocation during seed formation. The NU mutant resembled the wild-type grown on a low nitrogen supply, except that it unexpectedly showed symptoms of carbohydrate shortage as well as nitrogen deficiency. In all genotypes and treatments, there was a striking correlation between the concentrations of nitrate and organic nitrogen and shoot growth on the one hand, and sucrose concentration and root growth on the other. In addition, nitrate reductase activity (NRA) was correlated with the total carbohydrate concentration: low carbohydrate levels in starchless mutants led to low NRA even at high nitrate supply. Thus the concentrations of stored carbohydrates and nitrate are directly or indirectly involved in regulating allocation.     

Effects of nitrogen supply and irradiance on growth and nitrogen status in the moss Dicranum majus from differently polluted areas

Abstract

A growth experiment was undertaken to study the effects of nitrogen supply and irradiance on growth and nitrogen status in the moss Dicranum majus Sm. from two areas receiving different amounts of atmospheric nitrogen deposition. Intact samples of D. majus carpets were taken from two Picea abies forests, one located in southern Norway (high-N site) and the other in central Norway (low-N site). The moss carpets were grown for 120 days at three irradiance levels (PPFD: 20,40 or 80 μmol m^?2 s^?l) and sprayed daily with equal amounts of a nutrient solution containing 30, 180 or 330 μM nitrogen as NO₃ - and NH₄ +. Concentrations and total amounts of nitrogen, soluble proteins and chlorophyll were highest in moss plants from the high-N site, both at the start and the end of the experiment. The elongation growth was highest at the lowest irradiance level. As total biomass production did not differ between nitrogen and light treatments, moss growth was presumably limited by other factors, even at the lowest supply rates. Concentrations and total amounts of nitrogen increased with increasing nitrogen supply in moss plants from both sites. Accumulated nitrogen was partly stored as protein and chlorophyll. Recycling of nitrogen from old to young tissues is discussed as a possible explanation for the rather low nitrogen demand in D. majus and the persistently higher nitrogen contents in moss plants from the high-N site.     

A physiological and molecular study of the effects of nickel deficiency and phenylphosphorodiamidate (PPD) application on urea metabolism in oilseed rape (Brassica napus L.)

Background and aims

Urea is the major nitrogen (N) form supplied as fertilizer in agriculture. However, urease, a nickel-dependent enzyme, allows plants to use external or internally generated urea as a nitrogen source. Since a urease inhibitor is frequently applied in conjunction with urea fertilizer, the N-metabolism of plants may be affected. The aim of this study was to determine physiological and molecular effects of nickel deficiency and a urease inhibitor on urea uptake and assimilation in oilseed rape.

Methods

Plants were grown on hydroponic solution with urea as the sole N source under three treatments: plants treated with nickel (+Ni) as a control, without nickel (?Ni) and with nickel and phenylphosphorodiamidate (+Ni+PPD). Urea transport and assimilation were investigated.

Results

The results show that Ni-deficiency or PPD supply led to reduced growth and reduced ¹⁵N-uptake from urea. This effect was more pronounced in PPD-treated plants, which accumulated high amounts of urea and ammonium. Thus, Ni-deficiency or addition of PPD, limit the availability of N and decreased shoot and root amino acid content. The up-regulation of BnDUR3 in roots indicated that this gene is a component of the stress response to nitrogen-deficiency. A general decline of glutamine synthetase (GS) activity and activation of glutamate dehydrogenase (GDH) and increases in its expression level were observed in control plants. At the same time, in (?N) or (+Ni+PPD) treated plants, no increases in GS or GDH activities and expression level were found.

Conclusions

Overall results showed that plants require Ni as a nutrient (while most widely used nutrient solutions are devoid of Ni), whether they are grown with or without a urea supply, and that urease inhibitors may have deleterious effects at least in hydroponic grown oilseed rape.     

Sagebrush and grasshopper responses to atmospheric carbon dioxide concentration

Summary Seed- and clonally-propagated plants of Big Sagebrush (Artemisia tridentata var.tridentata) were grown under atmospheric carbon dioxide regimes of 270, 350 and 650 μl l⁻¹ and fed toMelanoplus differentialis andM. sanguinipes grasshoppers. Total shrub biomass significantly increased as carbon dioxide levels increased, as did the weight and area of individual leaves. Plants grown from seed collected in a single population exhibited a 3–5 fold variation in the concentration of leaf volatile mono- and sesquiterpenes, guaianolide sesquiterpene lactones, coumarins and flavones within each CO₂ treatment. The concentration of leaf allelochemicals did not differ significantly among CO₂ treatments for these seed-propagated plants. Further, when genotypic variation was controlled by vegetative propagation, allelochemical concentrations also did not differ among carbon dioxide treatments. On the other hand, overall leaf nitrogen concentration declined significantly with elevated CO₂. Carbon accumulation was seen to dilute leaf nitrogen as the balance of leaf carbon versus nitrogen progressively increased as CO₂ growth concentration increased. Grasshopper feeding was highest on sagebrush leaves grown under 270 and 650 μl l⁻¹ CO₂, but varied widely within treatments. Leaf nitrogen concentration was an important positive factor in grasshopper relative growth but had no overall effect on consumption. Potential compensatory consumption by these generalist grasshoppers was apparently limited by the sagebrush allelochemicals. Insects with a greater ability to feed on chemically defended host plants under carbon dioxide enrichment may ultimately consume leaves with a lower nitrogen concentration but the same concentration of allelochemicals. Compensatory feeding may potentially increase the amount of dietary allelochemicals ingested for each unit of nitrogen consumed.     

The effect of fire on nutrients in a pine forest soil

The effect of a hot summer fire on soil nutrient contents in the upper 2 cm of Aleppo pine forest with a dense woody understory was studied from September 1985 to May 1986. In comparison with the adjacent unburned forest, total nitrogen decreased by 25% but available forms of nitrogen were much higher. In burned and unburned soils there was a similar trend to increase and decrease in NH ₄ ⁺ −N, However, while (NO ₂ ⁻ +NO ₃ ⁻ −N decreased in the unburned soil it rose rapidly in the burned ash soil. Total phosphorus increased by 300% after the fire but decreased again 2 months later. Also water-soluble P increased up to November and then decreased to the levels of the unburned soils. The same was true for electrical conductivity and pH, increasing immediately after the fire and then leveling off again. This increase in nutrient levels in the “ash soil” was reflected in the striking increase in shoot and root biomass and in the content of N, P, Mg, K, Ca, Zn and Fe in wheat and clover plants grown in pots in these soils. These nutrient levels were much higher in the wheat plants, which also produced 12 times more seeds in the “ash soil.” It seems that fire in these pine forests causes a short-term flush of the mineral elements in the upper “ash soil” layer which is reverted gradually via the herbaceous post-fire to the ecosystem.     

Effects of the mineral composition and water content of intact plants on the fitness of the African armyworm

The effects of organic nitrogen, nitrate, phosphorus, potassium and water content of leaves of intact maize plants, grown in a gravel culture system, on the fitness of the African armyworm, Spodoptera exempta (Walker)(Lepidoptera: Noctuidae) were studied. Organic nitrogen concentrations ranged from 1.3% to 3.7% over four treatments differing only in nitrate supply to the plants. Water content and other mineral levels were all positively correlated with the organic nitrogen level. Feeding damage by the caterpillars was most severe on the lowest nitrate treatments, where it could be least well compensated for by new leaf growth. Larval and pupal fitness variables were not affected by treatment, except for larval development on the lowest nitrate treatment which was delayed by just 1 day. The large compensatory capacity of the larvae was underlined by a similar mineral composition of the pupae in all treatments. Adult fitness variables hardly differed between the upper three nitrate treatments, but revealed a trend over all treatments: the higher the organic nitrogen content of the leaves, the shorter the pre-oviposition period and the higher the fecundity. This trend, however, might have been due to differences in available food quantity rather than in food quality. It is concluded that fitness of the African armyworm is only slightly affected over a wide range of nitrogen concentrations in its food. Though effects might be larger under field conditions, the large differences in outbreak development between years seem not to be attributable to observed differences in nitrogen levels in host plants between years in primary outbreak areas. Other environmental factors appear to be of greater importance.     

Quantification, correlations and manipulations of wound-induced changes in jasmonic acid and nicotine in Nicotiana sylvestris

Jasmonic acid (JA) is thought to be part of a signal-transduction pathway which dramatically increases de-novo nicotine synthesis in the roots and increases whole-plant (WP) nicotine pools in response to the wounding of the leaves in Nicotiana sylvestrisSpegazzini and Comes (Solanaceae). We report the synthesis of a doubly labeled JA ([1, 2-¹³C]JA) and use it as an internal standard to quantify by gas chromatography-mass spectrometry the changes in root and shoot JA pools in plants subjected to differing amounts of standardized leaf wounding. Wounding increased JA pools 10-fold locally in damaged leaves within 90 min and systemically in the roots (3.5-fold) 180 min after wounding. If JA functions as an intermediary between stimulus and response, quantitative relationships among the stimulus, JA, and the response should exist. To examine these relationships, we varied the number of punctures in four leaves and quantified both the resulting JA in damaged leaves after 90 min and the resulting WP nicotine concentration after 5 d. We found statistically significant, positive relationships among number of leaf punctures, endogenous JA, and WP nicotine accumulation. We used two inhibitors of wound-induced nicotine production, methyl salicylate and indole-3-acetic acid, to manipulate the relationships between wound-induced changes in JA and WP nicotine accumulation. Since wounding and the response to wounding occur in widely separated tissues, we applied inhibitors to different plant parts to examine their effects on the local and systemic components of this response. In all experiments, inhibition of the wound-induced increase in leaf JA 90 min after wounding was associated with the inhibition of the nicotine response 5 d after wounding. We conclude that wound-induced increases in leaf JA are an important component of this long-distance signal-transduction pathway. Received: 24 April 1996 / Accepted: 18 July 1996     

Maternally-induced modification of progeny phenotypes in the C4 weed Echinochloa crus-galli: An analysis of seed constituents and performance

To clarify the physiological basis of maternal inheritance we examined the effect of the thermal environment of mother plants of Echinochloa crus-galli on subsequent seed mass, content and quality. The same plants were grown in a warm and a cold environment until seeds were produced and, since E. crus-galli is a highly inbred species, the observed variation in seed production was a purely plastic response to the environment. When mother plants were grown at high temperature, average seed mass, variance and germinability were low. Cold maturation led to the production of more large seeds than warm maturing temperature. The latter seeds were deprived of reserve constituents. Seeds matured at high temperature had high concentrations of K⁺ and Mn²⁺ but lower concentrations of starch and protein.     

Growth and development of soyabean cv. TK5 as affected by tropical daylengths, day/night temperatures and nitrogen nutrition

Two experiments were done in Saxcil growth cabinets in order to investigate the effects of climatic factors and nitrogen nutrition on the growth, reproductive development and seed yield of soyabean cv. TK5. In the first, plants were grown to maturity in eight environments comprising all combinations of two short daylengths (11 h 40 min and 13 h 20 min), two day (27 and 33^oC) and two night (19 and 24^oC) temperatures. In the second, day temperature was kept at 33^oC but the night temperature was varied (19 and 24^oC) as was the mineral nitrogen supply (20 and 197 ppm N) to plants which were either inoculated or not with an effective single strain of Rhizobium. Taller, more branched, later flowering plants were produced in the longer daylength but seed yield was hardly affected because the components of yield did not all respond similarly. In the higher day temperature treatments seed yield per plant was reduced by half because all yield components were adversely affected - pods per plant by 34 %, mean seed dry weight by 24 % and seeds per pod just slightly. There was a marked effect of the higher night temperature which promoted early vegetative growth, induced early flowering and although the number of pods per plant was, overall, reduced by 48 %, seed yield per plant was little affected as mean seed dry weight was increased by 37 % and the number of seeds per pod was also increased slightly. Prior to flowering, nodulated plants obtained about two thirds of their total nitrogen requirement via direct uptake and one third through the symbiotic system. Vegetative dry weight and plant nitrogen content were increased by the higher mineral nitrogen level and, although height was slightly diminished, more branches were produced. Seed yield, however, was only slightly increased. These experiments have shown that night temperature is an environmental factor of major importance for the growth of this soyabean cultivar. They have provided, also, a more rational basis for interpreting seasonal variations in growth and seed yield of soyabean in the tropics where, clearly, day and night temperature effects can override those of daylength and nitrogen nutrition.     

Beta and habitat diversity in marine systems: a new approach to measurement, scaling and interpretation

Specialist herbivores are known to alter their host's wound-induced responses but the beneficiaries of these alterations are unknown. Nicotiana attenuata plants release a burst of ethylene specifically in response to feeding by Manduca sexta larvae, which is known to suppress wound- and methyl jasmonate (MeJA)-inducible nicotine accumulation. The ethylene burst may be a mechanism by which M. sexta larvae feed "stealthily" on their host plants or, alternatively, it may allow the plant to optimize its defense response against this specialist herbivore by reducing costs of induction. We examined the impact of the ethylene burst on defense-related fitness costs that are readily observed when plants are treated with MeJA and grown in competition with untreated plants. We elicited nicotine induction (with MeJA), the ethylene burst (with the ethylene releasing compound, ethephon) and inhibited the plant's ability to perceive ethylene (with applications of an antagonist of ethylene receptors, 1-methylcyclopropene, 1-MCP). By simultaneously applying MeJA and ethephon we mimicked the plant's hormonal response to larval attack. We hypothesized that if the ethylene burst benefited the plant, the fitness costs of MeJA induction should be reduced by ethephon and restored if the plants were additionally treated with 1-MCP. In a second experiment, we applied larval oral secretion (OS) to elicit endogenous hormone production and predicted that the 1-MCP treatment should reduce the fitness of OS-treated plants. Our measures of plant fitness, namely the rate of stalk elongation and lifetime capsule production, supported these predictions. We conclude that the ethylene burst elicited by this specialist herbivore can reduce MeJA-induced fitness costs and increase the competitive strength of OS-treated plants. Suppressed nicotine production is likely to contribute to, but is not sufficient to explain, the observed fitness outcomes. The intensity of intra-specific competition and herbivore attack will likely determine the adaptive value of the M. sexta-elicited ethylene response.     

Methyl jasmonate stimulates polyamines biosynthesisand resistance against leaf rust in wheat plants

Abstract

Leaf rust of wheat (Triticum aestivum L.), incited by Puccinia recondita ex Desm. f. sp. tritici Eriks, is one of the most important wheat diseases in Egypt. Methyl jasmonate (MJ) is a potential plant elicitor which induces a wide range of chemical and anatomical defense reactions in conifers and might be used to increase systemic resistance against biotic damage. In the greenhouse, different concentrations of MJ (10, 20 and 30 mM) were applied as seed soaking plus foliar spray or only as foliar spray to control leaf rust and induction of secondary compound production in leaves of wheat plants. Foliar spray was applied after 30 and 50 days of sowing. Results indicated that all concentrations and treatments reduced the severity of rust disease caused by P. recondita f. sp. tritici in wheat leaves during 45 days of inoculations. Disease incidence was decreased significantly in MJ-treated plants as seed soaking plus foliar spray with 20 and 30 mM when compared to 10 mM MJ or control plants. The study revealed that, with increasing concentrations of MJ, the secondary metabolites were greatly increased. Endogenous levels of both free and conjugated putrescine, spermidine and spermine increased in response to the elicitor. Activities of polyamine biosynthetic enzymes of ornithine decarboxylase (ODC) and polyamine oxidase (PAO) displayed up to threefold increases relative to untreated control. Moreover, significant increases in activities of plant defense-related protein, enzymes as peroxidase and chitinase as well as free and conjugated phenols contents were recorded in treated plants compared with untreated and infected plants. Furthermore, MJ treatment increased the chlorophyll-a, chlorophyll-b and carotenoids pigments contents, the higher increase was obtained with combined treatment between seeds soaking plus foliar spray at 20 and 30 mM of MJ. Under field conditions, three concentrations of MJ, i.e. 10, 20 and 30 mM as combined treatment between seeds soaking plus foliar spray or only as foliar spray were applied to study their effect against rust disease. Foliar spray was applied after 30 and 80 days of sowing. Results showed that the high reduction in disease severity was obtained with combined treatments between seeds soaking plus foliar spray with MJ at 20 and 30 mM compared with other treatments and control. At the same time, all treatments increased the growth and grain yield of wheat plants. It could be suggested that combination treatment between seeds soaking plus foliar spray with methyl jasmonate might be used commercially for controlling rust disease of wheat plants under field conditions.     

Enriched rhizosphere CO2 concentrations can ameliorate the influence of salinity on hydroponically grown tomato plants

Our previous work indicated that salinity caused a shift in the predominant site of nitrate reduction and assimilation from the shoot to the root in tomato plants. In the present work we tested whether an enhanced supply of dissolved inorganic carbon (DIC, CO₂+ HCO₃) to the root solution could increase anaplerotic provision of carbon compounds for the increased nitrogen assimilation in the root of salinity-stressed Lycopersicon esculentum (L.) Mill. cv. F144. The seedlings were grown in hydroponic culture with 0 or 100mM NaCl and aeration of the root solution with either ambient or CO₂-enriched air (5000 μmol mol^?1). The salinity-treated plants accumulated more dry weight and higher total N when the roots were supplied with CO₂-enriched aeration than when aerated with ambient air. Plants grown with salinity and enriched DIC also had higher rates of NO^?₃ uptake and translocated more NO^?₃ and reduced N in the xylem sap than did equivalent plants grown with ambient DIC. Incorporation of DIC was measured by supplying a 1 -h pulse of H¹⁴CO^?₃ to the roots followed by extraction with 80% ethanol. Enriched DIC increased root incorporation of DIC 10-fold in both salinized and non-salinized plants. In salinity-stressed plants, the products of dissolved inorganic ¹⁴C were preferentially diverted into amino acid synthesis to a greater extent than in non-salinized plants in which label was accumulated in organic acids. It was concluded that enriched DIC can increase the supply of N and anaplerotic carbon for amino acid synthesis in roots of salinized plants. Thus enriched DIC could relieve the limitation of carbon supply for ammonium assimilation and thus ameliorate the influence of salinity on NO^?₃ uptake and assimilation as well as on plant growth.