The phytohormones auxin and cytokinin control plant development through a complex network of interactions which include synergistic, additive, and opposite effects whose mechanisms are unknown. The auxin-insensitive diageotropica (dgt) mutant provided a tool to dissect the relationship between auxin- and cytokinin-induced responses in tomato. Morphological, physiological, and molecular data support the proposal that auxin and cytokinins control a common set of developmental processes through separate signal transduction pathways which interact downstream from the DGT gene product. Morphological traits of dgt plants, such as reduced root and shoot growth, reduced leaf complexity, and reduced apical dominance were phenocopied by exogenous cytokinin application to wild-type plants, demonstrating that cytokinins and the DGT-mediated auxin response control a common set of phenotypic characteristics. Because the dgt mutation had no detectable effects on the levels of endogenous cytokinins or on the cytokinin sensitivity of whole plants, cytokinins were hypothesized to cause dgt-like effects on plant development through inhibiting auxin-induced responses. This hypothesis was supported by physiological experiments showing that auxin-induced elongation and ethylene synthesis were inhibited in cytokinin-treated wild-type and in untreated dgt hypocotyls. Differences between the effects of cytokinins and the dgt mutation on auxin responses became apparent at the molecular level. Experiments on the auxin-induced accumulation of transcripts for two ACC-synthase genes and one SAUR gene demonstrated that cytokinin treatment selectively reduced the auxin-induced expression of only one ACC-synthase gene, while the dgt mutation inhibited the auxin-inducibility of all three genes. The effects of the dgt mutation were thus more pleiotropic than the cytokinin effects, suggesting that cytokinins inhibit auxin-responses downstream from the DGT gene product. In vitro culture of dgt hypocotyl explants and calli demonstrated shared or interacting signal transduction pathways for auxin and cytokinin in the stimulation of cell division, and independent pathways for the control of organ regeneration and vascular differentiation. / Graduation date: 1997

Pepper plants (Capsicum annuum L.) were grown in field and a greenhouse in Arizona to determine the effects of water stress, root temperature, and exogenously applied growth regulators on cytokinin production and the resulting growth. Research showed that vegetative plants were significantly higher in cytokinin activity and growth parameters than fruiting plants. Also, in root-pruned fruiting plants, cytokinin activity was less than that of intact fruiting plants. In vegetative plants, the competition between removed sinks and the rest of the shoot was reduced and, hence, more cytokinin came from the roots to the shoots. Besides, additional carbohydrates were available and recycled to the roots. In respect to temperature effect, elevating temperature from 15 to 30°C had a pronounced effect of increasing the growth rate and cytokinin activity. The measured parameters declined when temperature exceeded 30°C. Temperatures between 25 and 30°C were found to be optimum. Under experimental conditions, growth regulators (Cytex® and Burst®) applied to the soil or foliage had no significant effect on growth rates or cytokinin activity in roots. Also, applying Burst® or kinetin to the nutrient medium had inconsistent and statistically nonsignificant effects on photosynthesis and transpiration.

A review of the literature revealed that there is a lack of depth in our knowledge of gymnospermous seeds with regard to the development and germination processes. The phytohormones, particularly the cytokinins have been implicated in these processes. The seeds of Podocarpus henkelii were thus selected as experimental material for studying the biochemical and cytokinin-like changes associated with development and germination. The development of these seeds was also followed at the ultrastructural level. These studies revealed that cellular detail within the female gametophyte only began .to form in December (early summer), approximately six weeks after fertilization had taken place. At this time some reserve protein was evident and the embryo sporophyte consisted of only a few pro-suspensor and pro-embryo cells. Concurrently, the cytokinin levels were fairly high in the female gametophyte but low in the epimatium. In both seed components two cytokinin- like compounds predominated which co-chromatographed with the free base cytokinin zeatin and its ribonucleoside. The second sample was taken in late January (mid-summer) by which time the embryo sporophyte had developed rapidly into a readily distinguishable seed component. The cellular detail indicated that much cell division had recently taken place and that the cells were currently increasing in size and accumulating starch and lipid. In the female gametophyte the soluble sugars were at the maximum level recorded during these experiments and the level of starch was increasing. The extractable cytokinin content of the seed was high at this time, particularly in the embryo sporophyte. In all three seed components cytokinin-like compounds which co-chromatographed with zeatin and ribosylzeatin were present. These high levels of cytokinin coincided with the rapid increase in both fresh and dry mass of the embryo sporophyte and female gametophyte. Ultrastructural studies of the third sample collected in mid-March (early autumn) showed that cellular changes were associated mainly with increases in cell size and the accumulation of food reserves, particularly starch. The cytokinin levels had decreased in all three seed components at this time. There was an increase in the cytokinin which co-chromatographed with glucosylzeatin in the female gametophyte. The seeds matured in late April (autumn) and had the unusual features of not drying out during maturation. Fresh seeds collected from the ground had a moisture content of ca. 62 per cent. The main food reserve was starch with relatively small amounts of protein and lipid also present. The seeds of Podocarpus henkelii germinated readily after scarification in the absence of water provided that their moisture content remained ca. 60 per cent. Seeds in which the moisture content had fallen below ca. 54 per cent required additional water for germination. The moisture content of the seeds fell rapidly under natural conditions and viability was lost below a moisture content of ca. 34 per cent. Unscarified seeds of 52 per cent moisture content placed under moist conditions at a constant 25°C took 23 weeks to achieve 68 per cent germination. These experiments showed that although the epimatium limited water uptake by the seeds it did not prevent moisture loss to the atmosphere. This appears to be the main factor contributing to the seed's inefficiency as a propagule. A small degree of after-ripening was recorded with the embryo sporophyte increasing in size with storage. This appeared to contribute to the increased rate of germination of the scarified seeds. An interesting feature of the seeds of Podocarpus henkelii is that they have the ability to fix atmospheric carbon, which is subsequently translocated from the epimatium to the female gametophyte and embryo sporophyte. The mature seeds were stored at 4°C for six weeks during which time little change had occurred at the ultrastructural level. Protein vacuoles in the embryo sporophyte had disappeared and in all three seed components cytokinin levels were low. Three days after scarification and the start of incubation, little change in cellular detail was apparent as limited rehydration was necessary due to the high moisture content. The cytokinin levels in the embryo sporophyte and epimatium had increased, whilst the levels in the female gametophyte had decreased at this time. In the embryo sporophyte lipid mobilization had commenced with these reserves apparently being metabolized within vacuoles. The rate of respiration measured in terms of increases in CO[2] evolution, increased 60 hours after the start of the incubation period, just 12 hours before ten per cent germination was recorded. Germination was accompanied by a large increase in the levels of cytokinins in the female gametophyte and embryo sporophyte. The cytokinins detected co-chromatographed with the free base cytokinin zeatin and its riboside, ribosylzeatin. Concurrently, marked ultrastructural changes were recorded with increases in the amounts of dictyosomes, endoplasmic reticulum and the formation of polyribosomes, all of which are indicative of increased metabolic activity. Similar increases in the female gametophyte were ofa lower order and occurred only after nine days of incubation. By this time the levels of cytokinins had decreased considerably. After 12 days of incubation 65 per cent of the seeds had germinated. As much of the food reserves in the female gametophyte and embryo sporophyte remained, it is suggested that these reserves are utilized for subsequent seedling establishment rather than for germination. The actual role that cytokinins play in the development and germination of these seeds is not clear. High levels of this phytohormone coincide with periods of food deposition and mobilization suggesting that they play an important part in these processes. The results of the biochemical, cytokinin and ultrastructural studies are discussed in relation to the developmental and germination processes and are compared to the data of other seeds. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1981.

A review of the literature established that there were areas of cytokinin transport which needed further investigation, in order to determine the function and/or mode of action of cytokinins during certain stages of plant development. Radioactive zeatin was applied to plant systems suitable for determining more about specific problems of cytokinin transport. The metabolism of the radioactive zeatin was monitored in relation to transport. The metabolism in, and possible export of, radioactive zeatin out of immature, mature and senescing Ginkgo biloba leaves was monitored using explants. The results showed that approximately the same percentage radioactivity was exported from the leaves at all three stages of their development. This indicates that these deciduous leaves could potentially export cytokinins, but the results were not regarded as being significant. Cytokinins would not have been expected to be transported out of expanding leaves, which rapidly utilize cytokinins, and in comparison greater cytokinin export would have been expected to occur from senescing leaves, but this did not occur. The resuIts could indicate that cytokinin glucosides in deciduous leaves are primarily inactivation products rather than storage compounds. The metabolism and transport of radioactive zeatin, applied to the leaves of Citrus sinesis trees, was monitored during the flush of new growth following a dormant period. Some of the radioactive zeatin applied to these leaves appeared to be utilized in the new shoot growth. This could imply that accumulated cytokinin glucosides in these evergreen leaves are exported out of the leaves and reutilized, and thus fulfil a storage function; although the extent to which export occurred as opposed to interconversion and/or catabolic metabolism in the leaves could not be determined. The distribution of radioactive zeatin applied to the xylem and phloem of Phaseolus vulgaris plants at three stages of development was also monitored. There appeared to be preferential transport of cytokinins in the transpiration stream, that is, applied to the xylem. The vegetative apices, buds and flowers appeared to be the major sinks for radioactive compounds in the vegetative and flowering plants, and the leaves were the most important sink in the fruiting plants. Radioactive zeatin in the phloem appeared to move passively with the assimilate stream. The transport of radioactive zeatin applied to the primary leaves appeared to confirm that cytokinins in the phloem were transported along with the assimilate stream. The results also indicated that the accumulated cytokinin glucosides in these annual leaves were primarily inactivation products, involved in regulating leaf metabolism, although some re-utilization of these cytokinins could potentially take place. could have reflected normal cytokinin transport occurring in the tissues. The main metabolic pathway, oxidation, did not, however, appear to be the main metabolic pathway in the plant tissues and may have been the result of the exogenous application of zeatin. The fact that metabolism did not appear to be the normal metabolism of the tissues, could potentially have affected transport. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1982.

Diss. (sammanfattning). Umeå : Sveriges lantbruksuniv. / Härtill 4 uppsatser.

Thesis (M.Sc.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references: leaf 115-122.

Made available in DSpace on 2014-06-11T19:32:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-08-03Bitstream added on 2014-06-13T18:43:11Z : No. of bitstreams: 1 garbelini_rcbs_dr_botib.pdf: 487851 bytes, checksum: d58b1e0c9d0eba6f910c42755bfed845 (MD5) / O estudo objetivou avaliar os efeitos de reguladores vegetais na emergência e no desenvolvimento de plantas de macadâmia (Macadamia integrifolia Maiden & Betche). Para o estudo da emergência de plântulas de macadâmia, as sementes foram tratadas com: T1- água (testemunha) sob Sombrite®; T2- GA4+7 + N-(fenilmetil)- aminopurina (Promalin®) a 200 mg L-1 sob Sombrite®; T3- GA4+7 + N-(fenilmetil)- aminopurina (Promalin®) a 400 mg L-1 sob Sombrite®; T4- GA3 + IBA + Kt (Stimulate®) a 5 mL kg-1 sementes sob Sombrite®; T5- GA3 + IBA + Kt (Stimulate®) a 10 mL kg-1 sementes sob Sombrite® e T6-água (testemunha) sem Sombrite®. Os efeitos dos reguladores vegetais foram avaliados pelo número e porcentagem de emergência de plântulas de cada tratamento. Foram utilizados 6 tratamentos com 450 sementes cada. Os resultados permitiram concluir que o tratamento que promoveu os melhores resultados na emergência de plântulas foi com GA4+7 + N-(fenilmetil)-aminopurina (Promalin®) a 400 mg L-1 sob Sombrite®. Sete meses após o transplantio das plantas jovens de macadâmia, estas foram tratadas com os seguintes tratamentos através de pulverização foliar: Testemunha (água); T2- GA4+7 + N-(fenilmetil)-aminopurina (Promalin®) a 200 mg L-1 em 1, 2 e 3 aplicações; GA4+7 + N-(fenilmetil)-aminopurina (Promalin®) a 400 mg L-1 em 1, 2 e 3 aplicações; GA3 + IBA + Kt (Stimulate®) a 2,5 mL L-1 em 1, 2 e 3 aplicações; GA3 + IBA + Kt (Stimulate®) a 5,0 mL L-1 em 1, 2 e 3 aplicações. Nos tratamentos com 2 ou 3 aplicações, foram realizadas a intervalo de 21 dias. As características avaliadas foram comprimento de caule, diâmetro do caule, teor de clorofila, taxa de assimilação de CO2 (A), condutância estomática (gs), transpiração (E) e concentração interna de CO2 na câmara subestomática (Ci). As avaliações de comprimento e diâmetro do caule foram realizadas antes da aplicação... / This study aimed to evaluate the effect of plant growth regulators on seed germination and development of macadamia nut trees (Macadamia integrifolia Maiden & Betche). For germination, seeds were treated with: T1- water (control) under shading screen; T2- GA4+7 + N-(phenylmethyl)-1H-purine-6-amine at 200 mg L-1 under shading screen; T3- GA4+7 + N-(phenylmethyl)-1H-purine-6-amine at 400 mg L-1 under shading screen; T4- GA3 + IBA + Kt at 5 mL kg-1 seeds under shading screen; T5- GA3 + IBA + Kt at 10 mL kg-1 seeds under shading screen, and T6-water (control) without shading screen. The effect of plant growth regulators was evaluated based on the number and percentage of emerged seedlings under each treatment. Experimental design was completely randomized, including 5 treatments with 450 seeds each. The greatest seedling emergence was detected with GA4+7 + N-(phenylmethyl)-1H-purine-6- amine at 400 mg L-1 under shading screen. At seven months after transplanting, young macadamia nut trees were subjected to 1, 2 and 3 leaf applications of: water (control); T2- GA4+7 + N-(phenylmethyl)-1H-purine-6-amine at 200 mg L-1; GA4+7 + N- (phenylmethyl)-1H-purine-6-amine at 400 mg L-1; GA3 + IBA + Kt at 2.5 mL L-1; GA3 + IBA + Kt at 5.0 mL L-1. The second and the third applications were performed at 21- days intervals. Shoot length, stem diameter, chlorophyll levels, net CO2 assimilation rate (A), stomatal conductance (gs), transpiration (E), and CO2 concentration inside the substomatal chamber (Ci) were evaluated. Plant height and stem diameter were measured before application of treatments and at 21-day intervals, considering the difference among evaluations. Gas exchange evaluations were performed at the 1st and at the 150th days after application of plant growth regulators. Experimental design was in completely randomized blocks, in the factorial arrangement 4 (4 treatments) x 3 (frequency of ... (Complete abstract click electronic access below)

Orientador: Elizabeth Orika Ono / Banca: João Domingos Rodrigues / Banca: Sarita Leonel / Banca: Elisangela Clarete Camili / Banca: Leonardo Ferreira / Resumo: O estudo objetivou avaliar os efeitos de reguladores vegetais na emergência e no desenvolvimento de plantas de macadâmia (Macadamia integrifolia Maiden & Betche). Para o estudo da emergência de plântulas de macadâmia, as sementes foram tratadas com: T1- água (testemunha) sob Sombrite®; T2- GA4+7 + N-(fenilmetil)- aminopurina (Promalin®) a 200 mg L-1 sob Sombrite®; T3- GA4+7 + N-(fenilmetil)- aminopurina (Promalin®) a 400 mg L-1 sob Sombrite®; T4- GA3 + IBA + Kt (Stimulate®) a 5 mL kg-1 sementes sob Sombrite®; T5- GA3 + IBA + Kt (Stimulate®) a 10 mL kg-1 sementes sob Sombrite® e T6-água (testemunha) sem Sombrite®. Os efeitos dos reguladores vegetais foram avaliados pelo número e porcentagem de emergência de plântulas de cada tratamento. Foram utilizados 6 tratamentos com 450 sementes cada. Os resultados permitiram concluir que o tratamento que promoveu os melhores resultados na emergência de plântulas foi com GA4+7 + N-(fenilmetil)-aminopurina (Promalin®) a 400 mg L-1 sob Sombrite®. Sete meses após o transplantio das plantas jovens de macadâmia, estas foram tratadas com os seguintes tratamentos através de pulverização foliar: Testemunha (água); T2- GA4+7 + N-(fenilmetil)-aminopurina (Promalin®) a 200 mg L-1 em 1, 2 e 3 aplicações; GA4+7 + N-(fenilmetil)-aminopurina (Promalin®) a 400 mg L-1 em 1, 2 e 3 aplicações; GA3 + IBA + Kt (Stimulate®) a 2,5 mL L-1 em 1, 2 e 3 aplicações; GA3 + IBA + Kt (Stimulate®) a 5,0 mL L-1 em 1, 2 e 3 aplicações. Nos tratamentos com 2 ou 3 aplicações, foram realizadas a intervalo de 21 dias. As características avaliadas foram comprimento de caule, diâmetro do caule, teor de clorofila, taxa de assimilação de CO2 (A), condutância estomática (gs), transpiração (E) e concentração interna de CO2 na câmara subestomática (Ci). As avaliações de comprimento e diâmetro do caule foram realizadas antes da aplicação ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This study aimed to evaluate the effect of plant growth regulators on seed germination and development of macadamia nut trees (Macadamia integrifolia Maiden & Betche). For germination, seeds were treated with: T1- water (control) under shading screen; T2- GA4+7 + N-(phenylmethyl)-1H-purine-6-amine at 200 mg L-1 under shading screen; T3- GA4+7 + N-(phenylmethyl)-1H-purine-6-amine at 400 mg L-1 under shading screen; T4- GA3 + IBA + Kt at 5 mL kg-1 seeds under shading screen; T5- GA3 + IBA + Kt at 10 mL kg-1 seeds under shading screen, and T6-water (control) without shading screen. The effect of plant growth regulators was evaluated based on the number and percentage of emerged seedlings under each treatment. Experimental design was completely randomized, including 5 treatments with 450 seeds each. The greatest seedling emergence was detected with GA4+7 + N-(phenylmethyl)-1H-purine-6- amine at 400 mg L-1 under shading screen. At seven months after transplanting, young macadamia nut trees were subjected to 1, 2 and 3 leaf applications of: water (control); T2- GA4+7 + N-(phenylmethyl)-1H-purine-6-amine at 200 mg L-1; GA4+7 + N- (phenylmethyl)-1H-purine-6-amine at 400 mg L-1; GA3 + IBA + Kt at 2.5 mL L-1; GA3 + IBA + Kt at 5.0 mL L-1. The second and the third applications were performed at 21- days intervals. Shoot length, stem diameter, chlorophyll levels, net CO2 assimilation rate (A), stomatal conductance (gs), transpiration (E), and CO2 concentration inside the substomatal chamber (Ci) were evaluated. Plant height and stem diameter were measured before application of treatments and at 21-day intervals, considering the difference among evaluations. Gas exchange evaluations were performed at the 1st and at the 150th days after application of plant growth regulators. Experimental design was in completely randomized blocks, in the factorial arrangement 4 (4 treatments) x 3 (frequency of ... (Complete abstract click electronic access below) / Doutor

Magnaporthe oryzae est un champignon filamenteux responsable de la principale maladie du riz, la pyriculariose. Ce pathosystème est très étudié, notamment dans le but de contribuer à l’identification de facteurs pouvant permettre le développement de résistances efficaces. Si certaines hormones végétales, comme l’acide salycilique, sont requises pour la mise en place des défenses de la plante, d’autres sont impliquées dans des processus développementaux. Parmi elles, les cytokinines (CKs) sont des dérivés d’adénine décrites pour participer à la croissance et la différenciation de l’appareil aérien et racinaire. Elles contribuent à la répartition des nutriments et impactent également la viabilité des cellules, en retardant la senescence ou en induisant la mort cellulaire. Des études précédentes ont montré que les CKs pouvaient perturber la résistance de la plante hôte dans différents pathosystèmes. Chez le riz, les CKs agissent en synergie avec l’acide salicylique pour induire l’expression des gènes marqueurs des défenses. Cependant aucun phénotype de résistance associé aux CKs n’a été observé in planta. Mes travaux montrent qu’un apport exogène de CKs (kinétine, BAP) affecte la résistance du riz à Magnaporthe avant infection, de manière dose dépendante. Le phénotype de résistance observé est corrélé avec une plus forte expression des défenses pendant infection, limitant la pénétration et l’invasion du champignon. Des plantes de riz mutées pour une probable cytokinine UDP-glucosyl transferase (CK-UGT) ont été obtenues. Ces mutants ck-ugt sont affectés dans le métabolisme des CKs et sont également plus résistants à M. oryzae. Hors infection, une plus forte expression des gènes de défense a été mesurée chez les plantes mutantes, confirmant que les CKs endogènes affectent directement ou indirectement les défenses de l’hôte. En parallèle de ces analyses sur la plante, mes travaux ont aussi porté sur le rôle des CKs produites par M.oryzae. En effet, leur rôle dans l’interaction ainsi que la voie de leur biosynthèse chez le champignon n’était pas caractérisé. Conservées au sein des différents organismes, les tRNA-IPT (isopentenyl transferase) sont décrites pour participer à la biosynthèse de CKs. Un seul gène homologue a été identifié chez M. oryzae et nommé CKS1 car sa délétion abolit la production de CKs. Le mutant de Magnaporthe cks1 est moins virulent (pénétration et invasion in planta réduites) que la souche témoin complémentée. Il induit une plus forte accumulation des espèces actives de l’oxygène et une plus forte expression des défenses chez la plante. Les dosages des acides aminés et des sucres pendant infection ont montré que les concentrations de ces nutriments étaient différemment perturbées par la souche déficiente en CKs. Ces résultats suggèrent que les CKs fongiques pourraient être requises pour affecter la répartition des acides aminés et contribuer une accumulation progressive de sucres au cours de l’infection. Ainsi, chez un champignon qui n’induit pas de tumeurs, les CKs pourraient agir comme des effecteurs qui auraient une double fonction d’inhibition des défenses et de drainage des nutriments. Chez les champignons, ces hormones induisent également des réponses physiologiques comme la résistance à certains stress, les processus de nutrition et la reproduction sexuée. Ces effets ont été étudiés chez Magnaporthe dans différentes conditions de croissance in vitro plus ou moins stressantes. Les résultats indiquent que les CKs augmentent la tolérance au stress osmotique et oxydatif et suggèrent qu’elles affecteraient aussi l’absorption des nutriments ainsi que la reproduction sexuée. Comme le gène CKS1 est conservé, cette mutation peut être caractérisée chez d’autres organismes fongiques présentant des modes de vie différents de manière à mieux comprendre le rôle de ces hormones dans les interactions plante-microorganisme mais également au sein des interactions microbiennes. / The blast disease caused by Magnaporthe oryzae is one of the most devastating diseases on rice leading to important yield loss. Plant hormones, like salicylic acid, play a central role in plant resistance establishment. Among these hormones, cytokinins (CKs) are adenine derivatives well described to modulate root/shoot growth and differentiation, cell viability and nutrient distribution. Previous studies have shown that these hormonal compounds can also affect plant host resistance in different pathosystems involving monocot or dicot host plants and microbes (bacteria, oomycetes or fungi). In rice, CKs were described to act synergistically with the salicylic acid pathway to induce defense marker genes expression. However, no resistance phenotype associated with CKs was observed and the way that CKs could act in planta during infection is still unknown. In this work, a resistance phenotype induced by exogenous application of the CK kinetin was characterized and the role of endogenous CKs in rice resistance was investigated by phenotyping plant CK mutants. An exogenous supply of kinetin before infection led to a higher induction of defense marker genes that was associated with limited fungal penetration and invasion, suggesting. However the way CKs affected resistance or susceptibility (or virulence see below) depended on the timing at which they were applied (before or after inoculation). Rice lines mutated for a putative cytokinin- UDP-glycosyl transferase (CK-UGT) were produced. The ck-ugt mutants were more resistant, suggesting that endogenous CKs can also contribute to resistance. Defense marker genes were expressed higher in the absence of infection in the ck-ugt rice mutants, compared to the WT plants. In parallel of these analyses of CK on the plant side, we studied the possible role of CK produced by Magnaporthe. Indeed M.oryzae produces and secretes CKs. However, the way fungal CKs are involved in the rice blast disease development as well as the biosynthesis pathway in M.oryzae were not established. A putative tRNA-IPT (isopentenyl transferase) conserved across organisms was identified in M.oryzae. Mutant analysis of this gene confirmed that this enzyme, thus named CKS1, is required for CK production. Knock-out cks1 fungal mutants were less virulent on rice, affected in penetration and invasion compared to the control complemented strain. They triggered a stronger accumulation of reactive oxygen species and a higher expression of defense marker genes. Aspartate and glutamate, two amino acids important for M.oryzae growth, were differently affected at and around the infected zone by cks1 strain suggesting that fungal CKs could contribute to drain/consume nutrients during infection. Similarly, sugar accumulation was also differently disturbed, indicating that fungal-derived CKs may be required for maintaining a progressive sugar production during host invasion, probably by affecting photosynthesis process. Our results show that fungal CKs, in a non-gall forming fungal pathogen, could act as dual effectors by inhibiting defense and modifying nutrient fluxes. Furthermore, CKs are known to affect some physiological processes in fungi, like stress resistance, nutrition or sexual reproduction. In order to test whether CKs modulate Magnaporthe stress tolerance, the effect of CKs on the mycelial growth in different stressful conditions in vitro was tested. The results indicate that CKs increased osmotic and oxidative stress tolerance and suggest that they also affected nutrient acquisition as well as sexual reproduction. Since the CKS1 gene is highly conserved, the effect of the cks1 mutation could be studied in other fungi showing different lifestyles for improving our knowledge on the role these hormonal compounds play among microbes or in plant-microbe interactions.

Cytokinin levels were determined by bioassay on a seasonal basis, for two species of dwarf mistletoes (Arceuthobium douglasii and Arceuthobium tsugense) and their respective hosts, Douglas-fir (pseudotsuga menziesii) and western hemlock (Tsuga heterophylla). The highest cytokinin levels occurred in early Spring for all of the samples studied. However, with the exception of the first growth segments of Douglas-fir, the levels of cytokinins detected were significantly greater in infected tissue and aerial shoots of the mistletoe than in the healthy tissue. Further studies were carried out on Spring and Winter samples to determine the kinds of cytokinins present. High performance thin layer chromatography and gas liquid chromatography results showed that zeatin riboside (ZR) was the only detectable cytokinin in Winter samples. ZR was also detected in all Spring samples excepting the aerial shoots of A. douglasii. Two other cytokinins were also detectable in Spring samples. Zeatin was present in aerial shoots from both dwarf mistletoes and in the infected fifth growth segments from Douglas-fir and in infected western hemlock tissue. Zeatin occurred in the healthy tissue only in first growth segments of Douglas-fir. The 2iPA was detectable in the aerial shoots of the dwarf mistletoe, in the fifth grmvth segments of Douglas-fir, and in the infected tissue from western hemlock. These results are discussed with particular reference to the role of cytokinins in the physiological interactions between the host and the parasite.