Interaction of jasmonic acid and blue light in the regulation of arabidopsis morphogenesis

The effects of blue light (BL) and jasmonic acid (JA) on morphogenesis of Arabidopsis thaliana (L.) Heynh seedlings of genotypes Col and Ler and their mutants, namely, axr1-3 and jar1-1 mutants resistant to IAA and JA, respectively, and a CRY1 photoreceptor-deficient mutant hy4 were studied. Both 1 μM JA and BL exposure retarded hypocotyl growth of Ler, Col, and jar1-1 seedlings, whereas JA had no effect on hypocotyl growth of axr1-3, but the suppression of hypocotyl growth of this mutant by BL was even more noticeable than that of Ler, Col, and jar1-1. JA and BL applied simultaneously inhibited hypocotyl growth of axr1-3 and especially of Ler, Col, and jar1-1 more than either of factors applied separately. The hy4 mutant did not respond to BL, whereas JA stimulated its hypocotyl growth. JA did not change the cotyledon size of Col, axr1-3, and jar1-1 and reduced the cotyledon size of Ler and hy4. BL enhanced the cotyledon growth of all wild-type and mutant plants used in the study. The cotyledon sizes of all plants except Ler were also increased when JA and BL were applied together. Some of the growth responses correlated with the endogenous IAA and ABA contents. Thus, for example, the hypocotyl and cotyledon growth retardation of Ler seedlings in the presence of JA correlated with a reduced level of free IAA and a considerable increase in the free ABA level in plants grown both in darkness and in BL. Under other growth conditions, no correlation between the endogenous IAA and ABA levels and A. thaliana seedling growth was noted. The interaction between the signal transduction pathways triggered by BL and JA at the early stages of arabidopsis morphogenesis is discussed on the basis of Col, Ler, axr1-3, and jar1-1 hypocotyl growth responses.     

The Role of Cryptochrome 1 and Phytochromes in the Control of Plant Photomorphogenetic Responses to Green Light

We studied the role of cryptochrome 1 (CRY1) and phytochromes in the photomorphogenetic responses of plants to the middle-wavelength region of photosynthetically active radiation. A comparison was performed of green light (GL) action on growth, GA activity and IAA and ABA contents during seedling deetiolation of two Arabidopsis thaliana (L.) Heynh lines of Landsnerg erecta ecotype (wild type Ler and mutant hy4) and of Phaseolus vulgaris L. It was shown that a growth responses of Ler hypocotyls to GL of 515 nm and Ler cotyledons to GL of 542 nm were weaker than those of the hy4 mutant defected in the CRY1 synthesis. Far-red light (730 nm) neutralized the effect of GL (533 nm) on the phytohormone balance in the primary kidney bean leaves. The data obtained permit a supposition that plants possess several photoregulatory systems functioning under GL of higher (515 nm) and lower emission energy (542–553 nm). A possible operation of GL receptors, other than cryptochrome 1 and phytochromes, is discussed.     

The Effect of Epibrassinolide on Arabidopsis Seedling Morphogenesis and Hormonal Balance under Green Light

We studied the effect of 24-epibrassinolide (EB) on the levels of endogenous hormones and photomorphogenesis of Arabidopsis thaliana (L.) Heynh wild-type (Ler) and mutant (hy4) seedlings. This mutant is deficient in the cryptochrome 1 (CRY1) synthesis. CRY1, which is a product of the HY4 gene, is a blue light photoreceptor in wild-type plants, but is sensitive to green light as well. In dark-grown seven-day-old mutant seedlings, the ABA/zeatin ratio differed from this ratio in wild-type seedlings. Thehy4 mutant exhibited a lower zeatin and higher free-ABA contents, which could retard its hypocotyl growth in darkness. EB retarded the growth of hypocotyls in etiolated hy4 seedlings and enlarged their cotyledons more efficiently than in wild-type seedlings. Green light (GL) did not affect the growth of hypocotyls but enlarged cotyledons of hy4 seedlings, which might be associated with some increase in the level of free IAA and a considerable decrease in free ABA and also with a decrease in the cytokinin level in seedlings. The hy4 cotyledon response to GL depended evidently on photoreceptors other than CRY1. GL enhanced the effects of EB on the morphogenesis of both Ler and hy4 seedlings, which was coupled with changes in the balance of endogenous IAA, ABA, and cytokinins. We may suppose that EB is involved in the control of photomorphogenesis by interaction with endogenous hormones, which are involved in the transduction of a light signal absorbed by the GL photoreceptors.     

Identification of Quantitative Trait Loci Controlling High Calcium Response in Arabidopsis thaliana

Natural variation for primary root growth response to high Ca stress in Arabidopsis thaliana was studied by screening a series of accessions (ecotypes) under high Calcium (40 mM CaCl₂ ) conditions. The genetic basis of this variation was further investigated by QTL analysis using recombinant inbred lines from Landsberg erecta (Ler)×Cape Verde Islands (Cvi) cross. Four QTLs were identified in chromosome 1, 2 and 5,and named response to high Calcium (RHCA) 1–4. The three QTLs (RHCA1, RHCA2 and RHCA4) were further confirmed by analysis of near isogenic lines harboring Cvi introgression fragments in Ler background. Real-time PCR analysis showed that several genes associated with high Ca response including SMT1 and XHT25 have changed expression pattern between Ler and near isogenic lines. These results were useful for detecting molecular mechanisms of plants for high Ca adaption.     

Conditional Synergism between Cryptochrome 1 and Phytochrome B Is Shown by the Analysis of phyA, phyB, and hy4 Simple, Double, and Triple Mutants in Arabidopsis

Wild-type or phyA, phyB, or hy4 mutant Arabidopsis seedlings lacking phytochrome A (phyA), phytochrome B (phyB), or cryptochrome 1 (cry1), respectively, and the double and triple mutants were used in combination with blue-light treatments given simultaneously with red or far-red light. We investigated the interaction between phytochromes and cry1 in the control of hypocotyl growth and cotyledon unfolding. Under conditions deficient for cry1 (short exposures to blue light) or phyB (far-red background), these photoreceptors acted synergistically: Under short exposures to blue light (3 h/d) added to a red-light background, cry1 activity required phyB (e.g. the hy4 mutant was taller than the wild type but the phyBhy4 mutant was not taller than the phyB mutant). Under prolonged exposures to blue light (24 h/d) added to a far-red light background, phyB activity required cry1 (e.g. the phyAphyB mutant was taller than the phyA mutant but the phyAphyBhy4 mutant was not taller than the phyAhy4 mutant). Under more favorable light inputs, i.e. prolonged exposures to blue light added to a red-light background, the effects of cry1 and phyB were independent. Thus, the synergism between phyB and cry1 is conditional. The effect of cry1 was not reduced by the phyA mutation under any tested light condition. Under continuous blue light the triple mutant phyAphyBhy4 showed reduced hypocotyl growth inhibition and cotyledon unfolding compared with the phyAphyB mutant. The action of cry1 in the phyAphyB double mutant was higher under the red-light than the far-red-light background, indicating a synergistic interaction between cry1 and phytochromes C, D, or E; however, a residual action of cry1 independent of any phytochrome is likely to occur.     

Analysis of a Plant Complex Resistance Gene Locus Underlying Immune-Related Hybrid Incompatibility and Its Occurrence in Nature

Mechanisms underlying speciation in plants include detrimental (incompatible) genetic interactions between parental alleles that incur a fitness cost in hybrids. We reported on recessive hybrid incompatibility between an Arabidopsis thaliana strain from Poland, Landsberg erecta (Ler), and many Central Asian A. thaliana strains. The incompatible interaction is determined by a polymorphic cluster of Toll/interleukin-1 receptor-nucleotide binding-leucine rich repeat (TNL) RPP1 (Recognition of Peronospora parasitica1)-like genes in Ler and alleles of the receptor-like kinase Strubbelig Receptor Family 3 (SRF3) in Central Asian strains Kas-2 or Kond, causing temperature-dependent autoimmunity and loss of growth and reproductive fitness. Here, we genetically dissected the RPP1-like Ler locus to determine contributions of individual RPP1-like Ler (R1–R8) genes to the incompatibility. In a neutral background, expression of most RPP1-like Ler genes, except R3, has no effect on growth or pathogen resistance. Incompatibility involves increased R3 expression and engineered R3 overexpression in a neutral background induces dwarfism and sterility. However, no individual RPP1-like Ler gene is sufficient for incompatibility between Ler and Kas-2 or Kond, suggesting that co-action of at least two RPP1-like members underlies this epistatic interaction. We find that the RPP1-like Ler haplotype is frequent and occurs with other Ler RPP1-like alleles in a local population in Gorzów Wielkopolski (Poland). Only Gorzów individuals carrying the RPP1-like Ler haplotype are incompatible with Kas-2 and Kond, whereas other RPP1-like alleles in the population are compatible. Therefore, the RPP1-like Ler haplotype has been maintained in genetically different individuals at a single site, allowing exploration of forces shaping the evolution of RPP1-like genes at local and regional population scales.     

The role of low intensity red luminescent radiation in the control of Arabidopsis thaliana morphogenesis and hormonal balance

The effects of low intensity red luminescent radiation emitted by the polyethylene light-correcting film due to the conversion of UV-A radiation on Arabidopsis thaliana (L.) Heynh. morphogenesis and hormonal balance were studied. Wild-type Ler plants and two mutants, hy3 and hy4, displaying disturbances in the synthesis of phytochrome B and cryptochrome 1, respectively, were compared. In wild-type and hy4 plants grown under the light-correcting film, growth and development were substantially accelerated, whereas, in hy3 plants, they were retarded. These changes were correlated with changes in the levels of endogenous hormones, both growth activators and inhibitors. We concluded that low intensity red luminescent radiation affected the plant hormonal balance. In its turn, the changes in the hormone ratios, growth stimulators and inhibitors, affected the rate of plant growth and their productivity.     

Wound-Induced Endogenous Jasmonates Stunt Plant Growth by Inhibiting Mitosis

When plants are repeatedly injured their growth is stunted and the size of organs such as leaves is greatly reduced. The basis of this effect is not well-understood however, even though it reduces yield of crops injured by herbivory, and produces dramatic effects exemplified in ornamental bonsai plants. We have investigated the genetic and physiological basis of this “bonsai effect” by repeatedly wounding leaves of the model plant Arabidopsis. This treatment stunted growth by 50% and increased the endogenous content of jasmonate (JA), a growth inhibitor, by seven-fold. Significantly, repeated wounding did not stunt the growth of the leaves of mutants unable to synthesise JA, or unable to respond to JA including coi1, jai3, myc2, but not jar1. The stunted growth did not result from reduced cell size, but resulted instead from reduced cell number, and was associated with reduced expression of CycB1;2. Wounding caused systemic disappearance of constitutively expressed JAZ1::GUS. Wounding also activates plant immunity. We show that a gene, 12-oxo-phytodienoate reductase, which catalyses a step in JA biosynthesis, and which we confirm is not required for defence, is however required for wound-induced stunting. Our data suggest that intermediates in the JA biosynthetic pathway activate defence, but a primary function of wound-induced JA is to stunt growth through the suppression of mitosis.     

Physiological basis of QTLs for boron efficiency in Arabidopsis thaliana

Boron (B) is an essential micronutrient for higher plants, but the adaptability of plants to B deficiency varies widely both between and within species. On the basis of quantitative trait loci (QTL) analysis of the B efficiency coefficient (BEC) detected in an Arabidopsis thaliana Ler × Col recombinant inbred (RI) population, B efficiency was evaluated in the original parents (Ler and Col-4) and two F₈ lines (1938 and 1961), both of which were selected on the basis of phenotype and genotype of the RI population. The parent Ler and F₈ progeny 1938 had higher BEC and B utilization efficiency (BUE) values than those calculated for parent Col-4 and F₈ progeny 1961, respectively, when grown in nutrient solutions containing three different concentrations of B. The magnitude of the BEC and BUE-values was correlated closely with the combined phenotypic effect of the corresponding QTLs among the four genotypes. The F₈ line, 1938, inherited all four B-efficient QTLs, AtBE1-1, AtBE1-2, AtBE2 and AtBE5, from its two original parents. The four QTLs accounted for 65.2% of the total variation in BEC and 1938 showed the highest BEC (0.74) and BUE (10.5) values among the four genotypes when grown in nutrient solution that contained 0.324 μM B. Only one minor-effect QTL (AtBE1-1) was found in the parent, Col-4. This QTL accounted only for 8.8% of total BEC variation and resulted in the lowest BEC (0.39) and BUE (0.76) in Col-4 when it was grown in nutrient solution that contained 0.324 μM B. Phenotypic profile analysis showed that 1938 not only inherited the B utilization and distribution characteristics found in the silique of Ler, but also acquired the low-B requirement for root and shoot growth from Col-4. As a result, this genotype displayed the strongest tolerance to B deficiency. In addition, both B-efficient genotypes, 1938 and Ler, possessed the QTL (AtBE1-2) and both plants had high-seed yields and high-B distributions in their siliques. Therefore, we hypothesize that QTL AtBE1-2 plays a role in the utilization and/or the distribution of B to the silique when plants suffer from B deficiency. A close correlation between the B-efficient phenotype and the corresponding QTLs indicated that phenotypic differences depend on the genetic variation. Responsible Editor: Richard W. Bell.     

Accession-dependent action potentials in Arabidopsis

Plant excitability, as measured by the appearance and circulation of action potentials (APs) after biotic and abiotic stress treatments, is a far lesser and more versatile phenomenon than in animals. To examine the genetic basis of plant excitability we used different Arabidopsis thaliana accessions. APs were induced by wounding (W) with a subsequent deposition (D) of 5 μL of 1 M KCl onto adult leaves. This treatment elicited transient voltage responses (APs) that were detected by 2 extracellular electrodes placed at a distance from the wounding location over an experimental time of 150 min. The first electrode (e1) was placed at the end of the petiole and the beginning of the leaf, and the second (e2) electrode was placed on the petiole near the center of the rosette. All accessions (Columbia (Col), Wassilewskija (Ws) and Landsberg erecta (Ler)) responded to the W & D treatment. After W & D treatment was performed on 100 plants for each accession, the number of APs ranged from 0 to 37 (median 8, total 940), 0 to 16 (median 5, total 528) and 0 to 18 (median 2, total 296) in Col, Ws and Ler, respectively. Responding plants (>0 APs) showed significantly different behaviors depending on their accessions of origin (i.e., Col 91, Ws 83 and Ler 76%). Some AP characteristics, such as amplitude and speed of propagation from e1 to e2 (1.28 mm s⁻¹), were the same for all accessions, whereas the average duration of APs was similar in Col and Ws, but different in Ler. Self-sustained oscillations were observed more frequently in Col than Ws and least often in Ler, and the mean oscillation frequency was more rapid in Col, followed by Ws, and was slowest in Ler. In general, Col was the most excitable accession, followed by Ws, and Ler was the least excitable; this corresponded well with voltage elicited action potentials. In conclusion, part of Arabidopsis excitability in AP responses is genetically pre-determined.     

Photosystem II Function and Dynamics in Three Widely Used Arabidopsis thaliana Accessions

Columbia-0 (Col-0), Wassilewskija-4 (Ws-4), and Landsberg erecta-0 (Ler-0) are used as background lines for many public Arabidopsis mutant collections, and for investigation in laboratory conditions of plant processes, including photosynthesis and response to high-intensity light (HL). The photosystem II (PSII) complex is sensitive to HL and requires repair to sustain its function. PSII repair is a multistep process controlled by numerous factors, including protein phosphorylation and thylakoid membrane stacking. Here we have characterized the function and dynamics of PSII complex under growth-light and HL conditions. Ws-4 displayed 30% more thylakoid lipids per chlorophyll and 40% less chlorophyll per carotenoid than Col-0 and Ler-0. There were no large differences in thylakoid stacking, photoprotection and relative levels of photosynthetic complexes among the three accessions. An increased efficiency of PSII closure was found in Ws-4 following illumination with saturation flashes or continuous light. Phosphorylation of the PSII D1/D2 proteins was reduced by 50% in Ws-4 as compared to Col-0 and Ler-0. An increase in abundance of the responsible STN8 kinase in response to HL treatment was found in all three accessions, but Ws-4 displayed 50% lower levels than Col-0 and Ler-0. Despite this, the HL treatment caused in Ws-4 the lagest extent of PSII inactivation, disassembly, D1 protein degradation, and the largest decrease in the size of stacked thylakoids. The dilution of chlorophyll-protein complexes with additional lipids and carotenoids in Ws-4 may represent a mechanism to facilitate lateral protein traffic in the membrane, thus compensating for the lack of a full complement of STN8 kinase. Nevertheless, additional PSII damage occurs in Ws-4, which exceeds the D1 protein synthesis capacity, thus leading to enhanced photoinhibition. Our findings are valuable for selection of appropriate background line for PSII characterization in Arabidopsis mutants, and also provide the first insights into natural variation of PSII protein phosphorylation.     

Effect of gibberellin on <Emphasis Type="Italic">Arabidopsis</Emphasis> growth,development, and hormonal balance under green and blue light

The role of gibberellins in plant morphology under selective light was studied. A comparison of the effects of green and blue light on growth, development, and hormonal balance was performed for two Arabidopsis thaliana (L.) Heynh. (ecotype Landsberg erecta lines: wild type Ler and its ga4-1 mutant with suppressed GA_4/1 synthesis. The absence of active GA_4/1 from ga4-1 mutant determined its retarded growth, slowed passing through developmental phases, suppressed apical dominance, and reduced seed productivity. The retarded growth and development of the mutant was related to changed hormonal balance in them as compared to wild-type line: IAA content and the IAA/ABA ratio were declined, zeatin riboside and ABA accumulated. Green light retarded stem elongation and branching, reduced leaf specific surface density and plant seed productivity, and retarded plant transition to reproduction to a greater degree at GA_4/1 deficit (ga4-1) than at its normal content (Ler).     

Interaction of gibberellic acid and 24-epibrassinolide in the regulation of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> seedling scotomorphogenesis

The effects of GA₃, 24-epibrassinolide (EBL), and their combination on morphogenesis of Arabidopsis thaliana (L.) Heynh seven-day-old seedlings were studied. Four plant lines were analyzed: wild type Ler and ga4-1 mutant, belonging to the Landsberg erecta ecotype and wild type Col and det2 mutant, both of the Columbia ecotype. In ga4-1 and det2, GA_4/1-and brassinosteroid-deficient mutants, the highest hypocotyl growth response to the lack of hormones was noted. The cotyledon shape and size were dependent on EBL, and the root length was both GA₃-and EBL-regulated, indicating organ specificities in the responses to these hormones. Simultaneous treatment of dark-grown plants with GA₃ and EBL exerted an additive stimulatory effect on the root growth of det2, reduced the inhibitory effect of EBL on hypocotyl elongation of ga4-1, and enhanced the effect of EBL on hypocotyl and cotyledon elongation of det2.     

Phototropin 1 and cryptochrome action in response to green light in combination with other wavelengths

Genetic studies have shown the effects of various photoreceptors on early photomorphogenic processes, defining the precise time course of red (RL), far-red (FrL) and blue light (BL) action. In this study, the effect of green wavebands in conjunction with these responses is examined. Longer-term (end point; 24–96 h) analysis of hypocotyl elongation in enriched green environments shows an increase in growth compared to seedlings under blue, red or both together. The effect was only observed at lower fluence rates (<10 μmol/m² s). Genetic analyses demonstrate that cryptochromes are required for this GL effect, consistent with earlier findings, and that the phy receptors have no influence. However, analysis of early (minutes to hours) stem growth kinetics indicates that GL cannot reverse the cryptochrome-mediated BL effect during early stem growth inhibition, and instead acts additively with BL to drive cryptochrome-mediated inhibition. Green light (GL) treatments antagonize RL and FrL-mediated hypocotyl inhibition. The GL opposition of RL responses persists in phyA, phyB, cry1cry2 and phot2 mutants. The response requires phot1 and NPH3, suggesting that this is not a GL response, but instead a response to extremely low-fluence rate BL. Tests with dim BL (<0.1 μmol/m² s) confirm a previously uncharacterized phot1-dependent promotion of stem growth, opposing the effects of RL. These findings demonstrate how enriched green environments may adjust RL and BL photomorphogenic responses through both the crys and phot1 receptors, and define a new role for phot1 in stem growth promotion.     

Regulation of jasmonic acid biosynthesis by silicon application during physical injury to Oryza sativa L.

We investigated the effects of silicon (Si) application on rice plants (Oryza sativa L.) and its responses in the regulation of jasmonic acid (JA) during wounding stress. Endogenous JA was significantly higher in wounded rice plants than in non-wounded. In contrast, Si treatment significantly reduced JA synthesis as compared to non-Si applications under wounding stress. mRNA expression of O. sativa genes showed down-regulation of lipoxygenase, allene oxide synthase 1, allene oxide synthase 2, 12-oxophytodienoate reductase 3, and allene oxide cyclase upon Si application and wounding stress as compared to non-Si-treated wounded rice plants. The physical injury-induced-oxidative stress was modulated by Si treatments, which resulted in higher catalase, peroxidase, and polyphenol oxidase activities as compared with non-Si-treated plants under wounding stress. The higher Si accumulation in rice plants also reduced the level of lipid peroxidation, which helped the rice plants to protect it from wounding stress. In conclusion, Si accumulation in rice plants mitigated the adverse effects of wounding through regulation of antioxidants and JA.     

Jasmonic acid inhibition of in vitro shoot organogenesis in Pinus radiata cotyledons

The effect of jasmonic acid (JA) onde novo shoot formation in excised cotyledons of radiata pine (Pinus radiata D. Don), was examined. JA had no effect on shoot-forming (SF) tissues at concentrations up to 10⁻⁶ mol · L⁻¹. At concentrations greater than that, JA caused a reduction in the number of shoots formed, as well as the lengths of the shoots and fresh and dry masses of the tissues. Reciprocal transfer of excised radiata pine cotyledons from a SF medium with 10⁻⁵ mol · L⁻¹ JA to a SF medium without JA and vice versa showed that any exposure of the cotyledons to JA either during the shoot induction phase (days 0-21) or the shoot development phase (beyond day 21) led to a reduction in shoot formation. However, the JA effect was significantly less if the cotyledons were not exposed to JA during the initial 10 days in culture; indicating that the JA effect was mainly during shoot primordia formation and the subsequent development into shoots.     

Relationships between endogenous hormonal content and direct somatic embryogenesis in Prunus persica L. Batsch cotyledons

Cotyledons of peach (Prunus persica L. Batsch cv. ZiseMay^®) were cultured in vitro on medium deprived of plant growth regulators. Two different lines varying in their embryogenic capacity were studied after 90 days in culture media. Endogenous levels of abscisic acid (ABA), indole-3-acetic acid (IAA), trans-zeatin (Z), trans-zeatin riboside (ZR), the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), salicylic acid (SA), and jasmonic acid (JA) were analyzed in embryogenic and non-embryogenic cotyledons. No significant differences were observed in total ABA, IAA, ZR, SA and JA concentrations between the embryogenic and non-embryogenic cotyledons. On the contrary, lower Z and ACC contents, and also a reduced balance between Z and IAA levels were related with the embryogenic capacity of the cotyledons. These results suggest that the difference in somatic embryo formation capacity observed between embryogenic and non-embryogenic cotyledons is related to their endogenous Z contents, and that the endogenous hormonal balance between Z and IAA is an important index defining the embryogenic potential in peach cotyledons.     

Source-to-sink relationship between green leaves and green petals of different ages of the CAM orchid <Emphasis Type="Italic">Dendrobium</Emphasis> cv. Burana Jade

Photosynthetic capacities of green leaves (GL) and green flower petals (GFP) of different ages of the CAM plant Dendrobium cv. Burana Jade were studied through chlorophyll (Chl) content, Chl fluorescence characteristic F_v/F_m, maximal photosynthetic O₂ evolution rates (P _max), and CAM acidities [dawn/dusk fluctuations in titratable acidity (TA)]. All these photosynthetic parameters were higher in GL than in GFP. Among the different ages of GFP, the young GFP had significant higher readings of all photosynthetic parameters than the oldest GFP, indicating that reduced photosynthesis occurred in the senesced GFP. The source-to-sink relationship between GL and GFP was also studied by comparing the diurnal changes in contents of total soluble and insoluble sugars and TA between the fully irradiated (FI) control (with both irradiated GL and GFP) and GL-darkened plants (covering all GL with aluminium foils, leaving only the GFP exposed to radiation). CAM acidities were much lower in GL darkened with aluminium foils compared to those of FI-GL while there were no differences in CAM acidities of their GFP. The contents of total soluble and insoluble sugars and the CAM acidities of GL towards the end of the day were lower in GL-darkened plants compared to that of FI-plants. Hence CAM acidities of GL depended on their saccharide contents. However, diurnal changes of TA in GFP were similar in all GFP regardless of their ages, with or without GL photosynthetic sources. Thus CAM acidities of GFP are independent of GL saccharides. However, lower saccharide content in GFP (especially the oldest GFP) of GL-darkened plants implies that GFP function as sinks and depend on saccharides exported from GL for its development and growth.     

The role of jasmonic acid and ethylene crosstalk in direct defense of Nicotiana attenuata plants against chewing herbivores

We examined performance of herbivores on plants lacking either jasmonate (JA, asLOX3) or ethylene (ET, mETR1) signaling or both (mETR1asLOX3). Plant defenses against Manduca sexta caterpillars were strongly impaired in JA-deficient asLOX3 plants; however, making asLOX3 plants ethylene insensitive did not further increase the performance of the larvae on a mETR1asLOX3 genetic cross. This result demonstrates the dominant role of JA over ET in the regulation of plant defenses against herbivores. However, ET-insensitivity combined with otherwise normal levels of JA in mETR1 plants promoted faster caterpillar growth, which correlated with reduced accumulation of the alkaloidal direct defense nicotine in mETR1 compared to WT plants. Our data points to an important accessory function of ET in the activation of JA-regulated plant defenses against herbivores at the level of alkaloid biosynthesis in the roots and/or accumulation in the leaves.Key words: herbivory, jasmonic acid and ethylene crosstalk, Nicotiana attenuata, nicotine, trypsin proteinase inhibitors (TPIs)