Composition and content of glucosinolates in developing Arabidopsis thaliana

The glucosinolate composition and content in various tissues of Arabidopsis thaliana (L.) Heynh. ecotype Columbia during development from seeds to bolting plants were determined in detail by high-performance liquid chromatography. Comparison of the glucosinolate profiles of leaves, roots and stems from mature plants with those of green siliques and mature seeds indicated that a majority of the seed glucosinolates were synthesized de novo in the silique. A comparison of the glucosinolate profile of mature seeds with that of cotyledons indicated that a major part of seed glucosinolates was retained in the cotyledons. Turnover of glucosinolates was studied by germination of seeds containing radiolabelled p-hydroxybenzylglucosinolate (p-OHBG). Approximately 70% of the content of [14C]p-OHBG in the seeds was detected in seedlings at the cotyledon stage and [14C]p-OHBG was barely detectable in young plants with rosettes of six to eight leaves. The turn-over of p-OHBG was found to coincide with the expression of the glucosinolate-degrading enzyme myrosinase, which was detectable at very low levels in seedlings at the cotyledon stage, but which dramatically increased in leaves from plants at later developmental stages. This indicates that there is a continuous turnover of glucosinolates during development and not only upon tissue disruption.     

Stimulation of shoot regeneration from jute cotyledons cultured with non-ionic surfactants and relationship to physico-chemical properties

Summary The effects have been studied of the non-ionic surfactants, Plutonic F-68, Tween 20 or Triton X-100, on shoot regeneration from cultured jute (Corchorus capsularis L.) cotyledons with attached petioles. This group of non-ionic surfactants was selected in order to determine a possible relationship between the physico-chemical properties of individual compounds and their observable effects on plant morphogenesis in cultured jute cotyledons. Supplementation of culture medium with 0.001–0.5% (w/v) Pluronic F-68 increased the mean percentage of cotyledons producing shoots and the mean number of shoots/cotyledon, with maximal responses at 0.5% (w/v). By contrast, Tween 20 produced maximal effects at 0.001% (v/v), with inhibition of shoot formation at 0.5% (v/v). In both cases, phenotypically normal plants were recovered which could be grown to maturity. Culture of cotyledons with 0.001% (v/v) Triton X-100 similarly increased both the percentage of cotyledons producing shoots and the number of shoots/cotyledon. However, these shoots did not develop into mature plants. Additionally, shoots did not regenerate from cotyledons cultured with Triton at 0.01–0.5% (v/v). These results demonstrate mat there is an apparent relationship between the hydrophilic-hydrophobic (HLB) balance of surfactants which determine their cell permeabilising properties and consequently, their effects on morphogenesis.Abbreviations BAP 6-benzylaminopurine - IAA indole-3-acetic acid - MS Murashige and Skoog (1962)     

Root Formation by Detached White Mustard (Sinapis alba) Cotyledons

Rooting is shown to occur in excised cotyledons of Sinapis alba when grown in petri dishes on moist filter paper. Cotyledons were excised at intervals from 6 hours after the start of imbibition, when they were yellow, unexpanded and enclosed within the testa, to 27 days after sowing when the cotyledons were green and fully expanded and on plants possessing up to 3 foliage leaves. Rooting generally began 5 or 6 days after excision and was completed dining the following 5 days. The age of cotyledons at t ho time of excision had three effects on rooting: the lag period be-fore rooting began and the period during which rooting took place both increased with age: but the most marked effect was on the total number of cotyledons which were able to form roots, which increased until cotyledon expansion was almost complete, then decreased as the mature cotyledons became older. Optimal rooting was shown by cotyledons detached 8 days alter sowing, when they were half expanded. At this age S5 % of them formed roots between 6 days and 8 days after excision.     

Senescence progression in a single darkened cotyledon depends on the light status of the other cotyledon in Cucurbita pepo (zucchini) seedlings: potential involvement of cytokinins and cytokinin oxidase/dehydrogenase activity

Darkness mediates different senescence-related responses depending on the targeting of dark treatment (whole plants or individual leaves) and on the organs that perceive the signal (leaves or cotyledons). As no data are available on the potential role of darkness to promote senescence when applied to individual cotyledons, we have investigated how darkness affects the progression of senescence in either a single or both individually darkened cotyledons of young 10-day-old Cucurbita pepo (zucchini) seedlings. Strong acceleration of senescence was observed when both cotyledons were darkened as judged by the damage in their anatomical structure, deterioration of chloroplast ultrastructure in parallel with decreased photosynthetic rate and photochemical quantum efficiency of PSII. In addition, the endogenous levels of cytokinins (CKs) and IAA were strongly reduced. In a single individually darkened cotyledon, the structure and function of the photosynthetic apparatus as well as the contents of endogenous CKs and IAA were much less affected by darkness, thus suggesting inhibitory effect of the illuminated cotyledon on the senescence of the darkened one. Apparently, the effect of darkness to accelerate/delay senescence in a single darkened cotyledon depends on the light status of the other cotyledon from the pair. The close positive correlation between CK content and the activity of CK oxidase/dehydrogenase (CKX; EC 1.4.3.18/1.5.99.12) suggested that CKX was essentially involved in the mechanisms of downregulation of endogenous CK levels. Our results indicated that CKX-regulated CK signaling could be a possible regulatory mechanism controlling senescence in individually darkened cotyledons.     

Timing of cotyledon damage affects growth and flowering in mature plants

Although the effects of herbivory on plant fitness are strongly linked to age, we understand little about how the timing of herbivory at the seedling stage affects growth and reproduction for plants that survive attack. In this study, we subjected six north-western European, dicotyledonous grassland species (Leontodon autumnalis, Leontodon hispidus, Plantago lanceolata, Plantago major, Trifolium pratense and Trifolium repens) to cotyledon removal at 7, 14 and 21 d old. We monitored subsequent growth and flowering (number of inflorescences recorded, and time taken for first flowers to open) over a 107 d period. Cotyledon removal reduced growth during establishment (35 d) for all species, and a further three exhibited reduced growth at maturity. Four species developed fewer inflorescences, or had delayed flowering after cotyledon removal. Although early damage (7 d old) had the greatest long-term effect on plant performance, responses varied according to the age at which the damage occurred and the species involved. Our results illustrate how growth and flowering into the mature phase is affected by cotyledon damage during different stages of seedling ontogeny, and we highlight the ways in which ontogenetic variation in seedling tolerance of tissue loss might impact upon plant fitness in mature plant communities.     

Evaluation of induced responses, insect population growth, and host-plant fitness may change the outcome of tests of the preference-performance hypothesis: a case study

The preference‐performance hypothesis predicts that insect preference should correspond to host suitability for offspring development. We studied the pattern of within‐plant preference in the aphid Sipha flava and its consequences for offspring performance on the host‐plant Sorghum halepense, regarding the role of induced responses of plants to aphid feeding. The consequences of within‐plant preference on aphid population growth and host‐plant traits were also evaluated. Our results showed that winged and wingless aphids preferred to settle on mature rather than young leaves. In contrast, aphid individual growth rate was higher on young leaves when compared with mature leaves, suggesting that the outcome of this test rejected the preference‐performance hypothesis. However, the inclusion of the factor ‘previous aphid infestation’ changed the outcome from a maladaptive choice to a neutral one. Thus, individual growth rates of S. flava increased when aphids developed on leaves that had been previously infested. Interestingly, aphid growth rate on previously infested leaves did not differ between young and mature leaves. On the other hand, aphid population reproductive rate was higher and the percentage of winged aphids lower when infestation occurred on mature rather than young leaves. Aphid infestation reduced plant and shoot biomass, and increased leaf mortality. These negative effects on plant traits related to plant fitness were greater when aphid infestation occurred on young leaves. Likewise, whereas infestation on mature leaves did not cause a significant reduction in the number of flowering plants compared with control plants, aphid infestation on young leaves did reduce the number of plants at the flowering stage. Consequently, if both the reproductive rate of aphids in the mid‐term, and host‐plant fitness are taken into account, the results indicate that aphid preference for mature leaves may be an adaptive choice, thus supporting the preference‐performance hypothesis.     

Changes in a Leaf-growth Substance in Cotyledons and Primary Leaves during the Growth of Dwarf Bean Seedlings

The growth of etiolated dwarf bean leaf disks in darkness wasused to assay leaf-growth substances extracted from plant tissuesand separated on chromato-grams. A leaf-growth substance, with the same Rf value in isopropanol/ammoniaas gibberellic acid, was found in the acidic fraction of extractsfrom dwarf bean primary leaves and cotyledons. Neither neutralnor basic leaf-growth substances were found in primary leafextracts. The amount of leaf-growth substance per cotyledon reached amaximum at the 4th day in cotyledons, whether bean plants weregrown in the light or dark. Primary leaves of dwarf bean plantsgrown in the light reached their maximum content of leaf-growthsubstance later than the cotyledons; the time of maximum contentcoincided with the maximum growth-rate of the primary leaves.Leaf-growth substances did not accumulate in primary leavesof plants grown in the dark.     

Changes in French bean cotyledon composition associated with modulated life-span

The onset of Phaseolus vulgaris L. cotyledon senescence and its characteristics were modulated by irradiance (higher or lower than standard) and by epicotyl decapitation. The cotyledon life-span of 16 d was not influenced by irradiance while decapitation prolonged the life-span to 28 d. The fresh mass of cotyledons, an indicator of organ viability, decreased in a similar manner in all non-decapitated plants, though it was relatively slower in plants grown under a low irradiance (LI). Three days after decapitation the fresh mass of cotyledons increased by one third, a slight decrease was observed on the 21st d, and it lasted until the end of the life span. Deducing from the fall of chlorophyll (Chl) concentration expressed per unit protein, senescence started after the 10th day in non-decapitated plants. Decapitation postponed the onset of senescence until the 21st day. Expression of Chl amount per unit dry mass did not detect any changes in LI plants, hence this parameter can not be used for the assessment of senescence. The measurements of Chl a and b concentrations indicated that the light-harvesting complexes (LHCs) proliferated during ageing and were rapidly destroyed at the onset of senescence. Changes of the concentrations of carotenoids supported the hypothesis of free radicals involvement in senescence. The bean cotyledons responded to free radical production induced under higher irradiance by increased β-carotene synthesis. Oxidative damage to galactolipids during senescence was documented by fluorescence measurements. The changes in cotyledon composition were correlated to morphologic changes observed by electron microscopy.     

Early degradation of photosynthetic membranes in carob and sunflower cotyledons

The assimilatory activity of cotyledons can play an essential role in the survival of seedlings with a slow and delayed development of primary leaves. Changes in the photosynthetic activity of the cotyledon, from the onset of greening through senescence, were studied in two such plants, carob and sunflower, in order to determine its efficiency and duration, also in connection with the achievement of assimilatory autonomy by the plantlet. Chlorophyll analyses showed that the cotyledon's chloroplasts reached maximal greening in plantlets with a pair of expanded leaves. In contrast, the cotyledon's photosynthetic activity, measured as the rate of oxygen release, started to decrease early, before expansion of primary leaves. The decrease was due to the inactivation of a number of photosystem II (PSII) units, as revealed by immunodetection of breackdown products of the reaction centre's D1 and D2 thylakoid proteins. No signals of PSII alteration were noticed in the primary leaf chloroplasts that differentiated under the same environmental conditions. The damage to the cotyledon PSII, occurring in a non-photoinhibitory situation, might be due to a slower rate of turnover of D1 polypeptide than in the leaf thylakoids. The differential turnover of this protein in cotyledons and in leaves might represent an organ-specific regulation of the photosynthetic activity. The peculiarity of the cotyledon thylakoids make these organs useful objects for studying the metabolic cycle of both D1 and D2 proteins in vivo, under non-photoinhibiting conditions.     

Additive effects of herbivory,nectar robbing and seed predation on male and female fitness estimates of the host plant <Emphasis Type="Italic">Ipomopsis aggregata</Emphasis>

Many antagonistic species attack plants and consume specific plant parts. Understanding how these antagonists affect plant fitness individually and in combination is an important research focus in ecology and evolution. We examined the individual and combined effects of herbivory, nectar robbing, and pre-dispersal seed predation on male and female estimates of fitness in the host plant Ipomopsis aggregata. By examining the effects of antagonists on plant traits, we were able to tease apart the direct consumptive effects of antagonists versus the indirect effects mediated through changes in traits important to pollination. In a three-way factorial field experiment, we manipulated herbivory, nectar robbing, and seed predation. Herbivory and seed predation reduced some male and female fitness estimates, whereas plants tolerated the effects of robbing. The effects of herbivory, robbing, and seed predation were primarily additive, and we found little evidence for non-additive effects of multiple antagonists on plant reproduction. Herbivory affected plant reproduction through both direct consumptive effects and indirectly through changes in traits important to pollination (i.e., nectar and phenological traits). Conversely, seed predators primarily had direct consumptive effects on plants. Our results suggest that the effects of multiple antagonists on estimates of plant fitness can be additive, and investigating which traits respond to damage can provide insight into how antagonists shape plant performance.     

Changes in French bean cotyledon composition associated with modulated life-span

The onset of Phaseolus vulgaris L. cotyledon senescence and its characteristics were modulated by irradiance (higher or lower than standard) and by epicotyl decapitation. The cotyledon life-span of 16 d was not influenced by irradiance while decapitation prolonged the life-span to 28 d. The fresh mass of cotyledons, an indicator of organ viability, decreased in a similar manner in all non-decapitated plants, though it was relatively slower in plants grown under a low irradiance (LI). Three days after decapitation the fresh mass of cotyledons increased by one third, a slight decrease was observed on the 21st d, and it lasted until the end of the life span. Deducing from the fall of chlorophyll (Chl) concentration expressed per unit protein, senescence started after the 10th day in non-decapitated plants. Decapitation postponed the onset of senescence until the 21st day. Expression of Chl amount per unit dry mass did not detect any changes in LI plants, hence this parameter can not be used for the assessment of senescence. The measurements of Chl a and b concentrations indicated that the light-harvesting complexes (LHCs) proliferated during ageing and were rapidly destroyed at the onset of senescence. Changes of the concentrations of carotenoids supported the hypothesis of free radicals involvement in senescence. The bean cotyledons responded to free radical production induced under higher irradiance by increased -carotene synthesis. Oxidative damage to galactolipids during senescence was documented by fluorescence measurements. The changes in cotyledon composition were correlated to morphologic changes observed by electron microscopy.     

The notoriously destructive potato stalk borer (<Emphasis Type="Italic">Trichobaris trinotata</Emphasis>) has negligible impact on its native host, <Emphasis Type="Italic">Solanum carolinense</Emphasis> (horsenettle)

While herbivores can have a wide range of impacts on their host plants, instances in which herbivore damage is truly beneficial are rare. Thus, it was surprising that damage by the potato stalk borer (PSB) was associated with increased fitness of its native host plant (horsenettle) in a recent field study, particularly because this insect can have such severe negative effects on potato crops. A controlled experiment with potted horsenettle was conducted to investigate the impact of damage by PSB to see if it has any negative impacts on the plants, or whether horsenettle truly overcompensates for its damage. Damage by PSB had negligible impact on sexual reproduction and potential future vegetative propagation through root production in this experiment. Additionally, PSB damage did not exacerbate the negative fitness impact of heavy leaf damage by the eggplant lace bug. The lack of positive impacts in the potted horsenettle study suggests that selection for decreased resistance to PSB in the field study was due to correlated selection for increased plant vigor, rather than to overcompensation. That is, when given options, PSB females may preferentially oviposit on larger, healthier plants that are likely to be better hosts for their larvae. An important implication of these results is that a wild weed’s high tolerance of a natural herbivore can compound the weed’s potential to serve as a reservoir from which the herbivore can switch to closely related agricultural plants that are not tolerant of its damage.     

Influence of a propagative plant virus on the fitness and wing dimorphism of infected and exposed insect vectors

To maximize fitness, plant pathogenic viruses may manipulate their arthropod vectors through direct and indirect (via the host plant) interactions. For many virus-vector-plant associations, insect feeding does not always lead to virus acquisition. In fact, many plant viruses, especially those that propagate into their vectors, are acquired at low rates. Although the majority of insects colonizing an infected plant escape from viral infection, they are still exposed to the indirect effects (i.e. the effect of plant metabolism modification following virus infection). Little information has been reported on the effects of plant viruses on insects that become infected versus those that do not (here referred to as “exposed”). The effect that the Maize mosaic virus (MMV) (Rhabdoviridae) exerts on the fitness and wing dimorphism of the planthopper vector, Peregrinus maidis (Hemiptera, Delphacidae), that developed on leaves from either young or old corn plants was examined. MMV exerted non-consistent to minimal direct effects on developmental time, longevity, nymphal mortality and fecundity. In addition, some small yet significant fitness costs were encountered by exposed planthoppers to escape MMV infection. Furthermore, a significantly higher proportion of macropters over brachypters were produced on MMV-infected old leaves compared with healthy leaves of a similar age. We conclude that the virus influences the dispersal of the vector, promoting a larger production of macropters at the costs of brachypters at a late stage of the plant infection. Because MMV infection in planthoppers did not segregate by wing morphotype, our results indicate that the dispersal of both infected and exposed planthoppers was a likely consequence of the indirect effects of MMV.     

Herbivore-specific elicitation of photosynthesis by mirid bug salivary secretions in the wild tobacco Nicotiana attenuata

Herbivory is thought to be detrimental to plant fitness and commonly results in a metabolic shift in the plant: photosynthetic processes are typically down-regulated, while resource allocation to defenses is increased in herbivore-attacked plants, resulting in fitness costs of induced plant responses. Wild tobacco, Nicotiana attenuata, attacked by Tupiocoris notatus mirid bugs becomes resistant against more damaging herbivores through mirid-induced direct and indirect defenses. However, mirid-induced resistance and tissue loss do not result in a reduction of plant fitness. These findings suggest induced metabolic responses allowing the plant to compensate for the lost tissue and resources allocated to defenses. While feeding by Manduca sexta larvae results in a strong down-regulation of photosynthesis, we demonstrate a specific induction of elevated photosynthetic activity in N. attenuata leaves by elicitors in mirid salivary secretions. The elevated CO(2) assimilation rate is sufficient to compensate for the loss of photosynthetically active tissue and balances the net photosynthesis of infested leaves. We discuss the observed increase in the plant's primary metabolic activity as a mechanism that allows plants to alleviate negative fitness effects of mirid attack and mediates the vaccination effects that result in a net benefit in environments with multiple herbivores.     

Development of Mitochondrial Activities in Pea Cotyledons: INFLUENCE OF DESICCATION DURING AND FOLLOWING GERMINATION OF THE AXIS

Mitochondria in 4-hour imbibed and desiccated pea cotyledons develop in a similar manner upon rehydration to those in cotyledons hydrated only once. As a consequence of desiccation during imbibition, mitochondria revert to their original state as in the mature dry cotyledon, although limited damage occurs. This damage is more evident when the initial imbibition time before desiccation is longer. The presence of the axis does not protect cotyledonary mitochondria from damage, nor does it influence mitochondrial development upon rehydration of desiccated cotyledons. During the early hours after the start of imbibition mitochondrial development is dependent both upon hydration levels of the cotyledon and upon other metabolic processes, as shown by sensitivity to conditions that prevent ATP synthesis.     

Thermal Inactivation of Plant Growth: Effects on Cotyledon Metabolism

Temperature exposures which normally decrease growth of Pisum sativum seedlings by 50 % were found to be lethal in plants whose cotyledons were removed. Utilization of the two major reserves, starch and protein, decreased at high temperatures. However, the two enzymes responsible for their hydrolysis were thermostable. It appears that the influence of high temperatures on seedling growth is not due to direct effects of temperature on cotyledon metabolism, but rather indirectly through the axis.     

The question of cotyledon homology in angiosperms

The flowering plants (Magnoliophyta) are separated into two large classes distinguished by the morphology of their embryos. The embryos of monocots (class Liliopsida) have a single terminal cotyledon, while the embryos of dicots (class Magnoliopsida) usually have two lateral cotyledons. The cotyledons of monocots and dicots also differ in form, and there are no true intermediates. In addition, the third leaf of Nymphaealean seedlings appears to be identical to the single cotyledon of monocots. From this it is concluded that the cotyledons of monocots and dicots are not homologous. In addition, dissimilarity of cotyledons and succeeding leaves in dicots, together with recent genetic studies, suggests that the two cotyledons of dicots are not homologous with the succeeding leaves of the same plant. This interpretation is consistent with the view that the Nymphaealean embryo’s third leaf is homologous to the first leaf (cotyledon) of monocots. Because dicotyledonous embryos are common among seed plants and are present in the Gnetopsids, the most likely scenario is that the dicots share a widespread seed plant symplesiomorphy and that the monocots have lost this character state. A less parsimonious hypothesis of monocotyledonous embryos as plesiomorphic for angiosperms is also discussed. Genetic analysis of early embryo development in a variety of vascular plants may be the only way to conclusively determine the evolutionary origin of the distinctive difference between monocot and dicot embryos.     

Additive and non-additive effects of simulated leaf and inflorescence damage on survival, growth and reproduction of the perennial herb Arabidopsis lyrata

Herbivores may damage both leaves and reproductive structures, and although such combined damage may affect plant fitness non-additively, this has received little attention. We conducted a 2-year field experiment with a factorial design to examine the effects of simulated leaf (0, 12.5, 25, or 50% of leaf area removed) and inflorescence damage (0 vs. 50% of inflorescences removed) on survival, growth and reproduction in the perennial herb Arabidopsis lyrata. Leaf and inflorescence damage negatively and independently reduced flower, fruit and seed production in the year of damage; leaf damage also reduced rosette size by the end of the first season and flower production in the second year. Leaf damage alone reduced the proportion of flowers forming a fruit and fruit production per plant the second year, but when combined with inflorescence damage no such effect was observed (significant leaf × inflorescence damage interaction). Damage to leaves (sources) caused a greater reduction in future reproduction than did simultaneous damage to leaves and inflorescences (sinks). This demonstrates that a full understanding of the effects of herbivore damage on plant fitness requires that consequences of damage to vegetative and reproductive structures are evaluated over more than 1 year and that non-additive effects are considered.     

Sources of variation in rapidly inducible responses to leaf damage in the mountain birch-insect herbivore system

Summary Studies on rapidly inducible resistance in trees against insect herbivores show substantial variation in the strength of responses. Here we report the results of a study which examined causes of this variation. We bioassayed the quality of leaves of two developmental phases (young vs. mature) of the mountain birch Betula pubescens ssp. tortuosa by measuring the growth of two instars of Epirrita autumnata larvae. We used only short shoot leaves from trees of a natural stand, uniform in size and age. Damage was caused by larvae and artificial tearing of leaf lamina, varying the scale and time. We separated seasonal changes in plants from instar-dependent effects of the animals by testing experimental larvae in two subsequent growth trials. We found that only larval-made damage induced responses in leaves that made the leaves significantly poorer quality for the test larvae. Artificial damage induced only weak responses, and artificial canopy-wide damage even caused slight improvement of leaf quality. Cumulative leaf damage did not strengthen birch responses. Leaves that were in the expansion phase responded to damage while fully-expanded, mature leaves showed no response. The pattern of responses indicated that there might be physiological constraints: small-scale damage induced resistance against the larvae but largescale damage did not. Prevalent weather conditions might have modified these responses. Larvae of two instars and sexes, of low- and high-density populations responded to leaf damage similarly. However, prior experience of larvae with the host plant may have affected subsequent larval performance. Variation in rapidly inducible responses in birches was caused by plant characters rather than by test animals.     

Mechanisms of constraints: the contributions of selection and genetic variance to the maintenance of cotyledon number in wild radish

The evolutionary mechanisms underlying the maintenance of invariant traits are poorly understood, partly because the lack of variance makes these mechanisms difficult to study. Although the number of cotyledons that plant species produce is highly canalized, populations of plants frequently contain individuals with abnormal cotyledon numbers. In a garden study with 1857 wild radish plants from 75 paternal half-sibling families, 89 (almost 5%) had cotyledon numbers less or greater than two. We found evidence for direct selection on cotyledon number, but no evidence for additive genetic variation for cotyledon number. In spite of the very large sample size, our power to detect variation and selection was hampered by the small number of individuals (10) producing more than two cotyledons. Thus, our results provide support for both a lack of genetic variation and selection as reasons for the current lack of variation in wild radish cotyledon number.