Nursery and Field Development of Cordia Trichotoma Seedlings Subjected to Hardening Practices

Behr M., Lutts S., Hausman J., Guerriero G.

The application of jasmonic acid results in an increased secondary growth, as well as additional secondary phloem fibres and higher lignin content in the hypocotyl of textile hemp (Cannabis sativa L.). Secondary growth provides most of the wood in lignocellulosic biomass. Textile hemp (Cannabis sativa L.) is cultivated for its phloem fibres, whose secondary cell wall is rich in crystalline cellulose with a limited amount of lignin. Mature hemp stems and older hypocotyls are characterised by large blocks of secondary phloem fibres which originate from the cambium. This study aims at investigating the role of exogenously applied jasmonic acid on the differentiation of secondary phloem fibres. We show indeed that the exogenous application of this plant growth regulator on young hemp plantlets promotes secondary growth, differentiation of secondary phloem fibres, expression of lignin-related genes, and lignification of the hypocotyl. This work paves the way to future investigations focusing on the molecular network underlying phloem fibre development.

Meents M.J., Watanabe Y., Samuels A.L.

Secondary cell walls (SCWs) form the architecture of terrestrial plant biomass. They reinforce tracheary elements and strengthen fibres to permit upright growth and the formation of forest canopies. The cells that synthesize a strong, thick SCW around their protoplast must undergo a dramatic commitment to cellulose, hemicellulose and lignin production.This review puts SCW biosynthesis in a cellular context, with the aim of integrating molecular biology and biochemistry with plant cell biology. While SCWs are deposited in diverse tissue and cellular contexts including in sclerenchyma (fibres and sclereids), phloem (fibres) and xylem (tracheids, fibres and vessels), the focus of this review reflects the fact that protoxylem tracheary elements have proven to be the most amenable experimental system in which to study the cell biology of SCWs.SCW biosynthesis requires the co-ordination of plasma membrane cellulose synthases, hemicellulose production in the Golgi and lignin polymer deposition in the apoplast. At the plasma membrane where the SCW is deposited under the guidance of cortical microtubules, there is a high density of SCW cellulose synthase complexes producing cellulose microfibrils consisting of 18-24 glucan chains. These microfibrils are extruded into a cell wall matrix rich in SCW-specific hemicelluloses, typically xylan and mannan. The biosynthesis of eudicot SCW glucuronoxylan is taken as an example to illustrate the emerging importance of protein-protein complexes in the Golgi. From the trans-Golgi, trafficking of vesicles carrying hemicelluloses, cellulose synthases and oxidative enzymes is crucial for exocytosis of SCW components at the microtubule-rich cell membrane domains, producing characteristic SCW patterns. The final step of SCW biosynthesis is lignification, with monolignols secreted by the lignifying cell and, in some cases, by neighbouring cells as well. Oxidative enzymes such as laccases and peroxidases, embedded in the polysaccharide cell wall matrix, determine where lignin is deposited.

Per T.S., Khan M.I., Anjum N.A., Masood A., Hussain S.J., Khan N.A.

Jasmonates (JAs) are naturally occurring plant growth regulators and ubiquitous in plant kingdom. JAs are involved in the improvement of crop performance under natural and changing environmental conditions. Additionally, JAs are also known to interact with other phytohormones and thereby, modulate growth and development of plants and their abiotic stress responses. This review aimed to dissect available information on the role and underlying mechanisms of JAs in plant developmental responses and plant tolerance to major abiotic stresses, and its crosstalk with other major phytohormones in regulating the process. The major points potentially important for future research in the current direction are also summarized. The adoption of exhaustive approaches is advocated to unveil mechanisms underlying abiotic stress-mediated control of up-regulation of JA biosynthesis pathway and its genetic regulation and hormone homeostasis.

Malavasi U.C., Davis A.S., Malavasi M.D.

ABSTRACT Under tropical and sub-tropical conditions, perennial woody plants most often encounter drought stress due to erratic rainfall, which has become compounded as result of recent climatic changes. Control of the efficiency and safety of water transport from roots to shoots is fundamental for plant survival under water stressed conditions. Lignin plays an important role in the life of terrestrial plants. Depending upon the stress, lignin plays protective, sustaining and disruptive roles in addition to its involvement in plant growth, development and defense responses. This review aims to present and summarize reported evidence on the possible role of lignin of plant tissue (in special woody species) in response to water limiting condition which is expected to increase because of environment changes.

Dranski J.A., Malavasi U.C., Malavasi M.D.

ABSTRACT The essay objective was to correlate lignin content resulting from tigmomorphogenesis induced by stem swaying with survival and post-planting growth of P. taeda seedlings. Seedlings were subjected to daily frequencies (0, 5, 10, 20 and 40 movements) of stem swaying for 60 days. By the end of the treatments, we determined lignin content of below and aboveground seedling tissues. Four replicates per treatment were planted in a area cultivated with pines. Ninety days after planting, survival and increments of seedling height, stem diameter and stem volume were quantified. Application of 20 stem swayings increased lignin in both below and aboveground plant tissues. Outplanted seedling survival was reduced with 40 stem swayings while growth increments were increased with both 10 and 20 stem swayings. Lignin content from belowground plant tissues was positively correlated with outplanted seedling survival while lignin from aboveground tissues correlated with height and stem volume increments. P. taeda seedlings with higher lignin content have higher survival chances after planting.

Herbette S., Bouchet B., Brunel N., Bonnin E., Cochard H., Guillon F.

The efficiency and safety functions of xylem hydraulics are strongly dependent on the pits that connect the xylem vessels. However, little is known about their biochemical composition and thus about their hydraulic properties. In this study, the distribution of the epitopes of different wall components (cellulose, hemicelluloses, pectins and lignins) was analysed in intervessel pits of hybrid poplar (Populus tremula × alba).Immunogold labelling with transmission electron microscopy was carried out with a set of antibodies raised against different epitopes for each wall polysaccharide type and for lignins. Analyses were performed on both immature and mature vessels. The effect of sap ionic strength on xylem conductance was also tested.In mature vessels, the pit membrane (PM) was composed of crystalline cellulose and lignins. None of the hemicellulose epitopes were found in the PM. Pectin epitopes in mature vessels were highly concentrated in the annulus, a restricted area of the PM, whereas they were initially found in the whole PM in immature vessels. The pit border also showed a specific labelling pattern, with higher cellulose labelling compared with the secondary wall of the vessel. Ion-mediated variation of 24 % was found for hydraulic conductance.Cellulose microfibrils, lignins and annulus-restricted pectins have different physicochemical properties (rigidity, hydrophobicity, porosity) that have different effects on the hydraulic functions of the PM, and these influence both the hydraulic efficiency and vulnerability to cavitation of the pits, including ion-mediated control of hydraulic conductance. Impregnation of the cellulose microfibrils of the PM with lignins, which have low wettability, may result in lower cavitation pressure for a given pore size and thus help to explain the vulnerability of this species to cavitation.

Volkweis C.R., Dranski J.A., Oro P., Malavasi U.C., Malavasi M.D.

http://dx.doi.org/10.5902/1980509814571O presente estudo objetivou quantificar alterações morfológicas decorrentes de estímulos mecânicos por flexões caulinares na fase de rustificação de mudas de espinheira-santa [Maytenus ilicifolia (Schrad.) Planch.]. O experimento foi conduzido em casa de sombra sob delineamento experimental inteiramente ao acaso em arranjo fatorial 2 x 5, formado por mudas divididas em duas classes quanto à altura da parte aérea e cinco intensidades de flexões caulinares (0, 5, 10, 20 e 40) efetuadas diariamente durante trinta dias, em quatro repetições de dez mudas. O efeito dos estímulos mecânicos foi quantificado pelos incrementos na altura, no diâmetro do coleto, assim como pela mensuração da biomassa de raiz e da parte aérea com os quais se determinou a taxa de crescimento absoluto. Complementarmente, foi mensurada a perda de eletrólitos de raízes. Os dados foram submetidos à análise de regressão a 5%. Os resultados indicaram que o aumento do número de flexões caulinares induziu a redução no incremento em altura, no extravasamento de eletrólitos dos tecidos radiculares e, no aumento do incremento no diâmetro do coleto e na biomassa de raízes em mudas classificadas por altura. A biomassa da parte aérea de mudas com maiores dimensões aumentou com até 20 flexões mesmo com a redução linear na altura e, consequentemente, elevou a taxa de crescimento. Estímulos mecânicos por meio de flexões caulinares é uma opção para promover alterações morfológicas em mudas de Maytenus ilicifolia elevando a rusticidade e a qualidade das mudas aptas ao plantio.

Novaes A.B., Silva H.F., Sousa G.T., De Azevedo G.B.

A presente pesquisa teve como objetivo avaliar a qualidade morfofisiológica de mudas de nim indiano (Azadirachta indica A. Juss) em diferentes recipientes, visando alcançar maior produtividade no campo. Estabeleceram-se quatro tratamentos: T1 - sacola plástica (382 cm³); T2 - sacola plástica (165 cm³); T3 - tubete (288 cm³); T4 - tubete (55 cm³). O experimento foi desenvolvido em três etapas distintas. A primeira consistiu na produção e avaliação morfológica das mudas, visando avaliar as variáveis altura da parte aérea (H), diâmetro de colo (D), relação H/D e pesos de matéria fresca e seca das partes aérea, radicial e total. A segunda etapa objetivou a avaliação do potencial de regeneração de raízes (PRR) das mudas e a terceira fase foi desenvolvida no campo com o intuito de avaliar a sobrevivência das mudas após o plantio e o seu desempenho inicial, por meio da medição da altura e do diâmetro ao nível do solo. As mudas de nim indiano produzidas em sacolas plásticas (382 cm³) apresentaram valores superiores em todas as características morfológicas avaliadas e melhor desempenho no campo aos 15 meses após o plantio. O PRR se mostrou uma característica confiável quanto ao desempenho no campo de mudas produzidas em tubetes de 288 cm³.Palavras-chave: Potencial de regeneração de raízes; sacolas plásticas; tubetes. AbstractQuality of Indian Lilac seedlings produced in different containers and their performance in field.  The present research aims to evaluate the quality of Indian Lilac (Azadirachta indica A. Juss) seedlings in different containers in order to obtain higher productivity in the field. It was established four treatments: T1 - Plastic bags (382 cm³); T2 - Plastic bags (165 cm³); T3 - Tubes (288 cm³) and T4 - Tubes (55 cm³). The experiment was developed in three different stages. The first one consisted on the production and morphological evaluation of the seedlings, seeking to evaluate the variables: stem height (H), root-collar diameter (D), ratio H/D and weights of fresh and dry matter of the stem, root and total. The second stage aimed at evaluation of root regeneration potential (RRP) of seedlings, and the third phase was developed in the field in order to evaluate seedlings survival after planting and their performance by measurement of the height and diameter at the soil level. The seedlings of Indian Lilac produced in plastic bags (382 cm³) presented superior values in all evaluated morphological parameters and improved performance in the field, 15 months after the planting. The RRP has proved a reliable parameter on the field performance of seedlings produced in tubes of 288 cm³.Keywords: Root regeneration potential; plastic bags; tubes.

Andrade C.C., Resende R.S., Rodrigues F.A., Silveira P.R., Rios J.A., Oliveira J.R., Mariano R.L.

Ramos P., Le Provost G., Gantz C., Plomion C., Herrera R.

The gravitropic response in trees is a widely studied phenomenon, however understanding of the molecular mechanism involved remains unclear. The purpose of this work was to identify differentially expressed genes in response to inclination using a comparative approach for two conifer species. Young seedlings were subjected to inclination and samples were collected at four different times points. First, suppression subtractive hybridisation (SSH) was used to identify differentially regulated genes in radiata pine (Pinus radiata D. Don). cDNA libraries were constructed from the upper and lower part of inclined stems in a time course experiment, ranging from 2.5 h to 1 month. From a total of 3092 sequences obtained, 2203 elements were assembled, displaying homology to a public database. A total of 942 unigene elements were identified using bioinformatic tools after redundancy analysis. Of these, 614 corresponded to known function genes and 328 to unknown function genes, including hypothetical proteins. Comparative analysis between radiata pine and maritime pine (Pinus pinaster Ait.) was performed to validate the differential expression of relevant candidate genes using qPCR. Selected genes were involved in several functional categories: hormone regulation, phenylpropanoid pathway and signal transduction. This comparative approach for the two conifer species helped determine the molecular gene pattern generated by inclination, providing a set of Pinus gene signatures that may be involved in the gravitropic stress response. These genes may also represent relevant candidate genes involved in the gravitropic response and potentially in wood formation.

VOELKER S.L., LACHENBRUCH B., MEINZER F.C., KITIN P., STRAUSS S.H.

We studied xylem anatomy and hydraulic architecture in 14 transgenic insertion events and a control line of hybrid poplar (Populus spp.) that varied in lignin content. Transgenic events had different levels of down-regulation of two genes encoding 4-coumarate:coenzyme A ligase (4CL). Two-year-old trees were characterized after growing either as free-standing trees in the field or as supported by stakes in a greenhouse. In free-standing trees, a 20 to 40% reduction in lignin content was associated with increased xylem vulnerability to embolism, shoot dieback and mortality. In staked trees, the decreased biomechanical demands on the xylem was associated with increases in the leaf area to sapwood area ratio and wood specific conductivity (k(s)), and with decreased leaf-specific conductivity (k(l)). These shifts in hydraulic architecture suggest that the bending stresses perceived during growth can affect traits important for xylem water transport. Severe 4CL-downregulation resulted in the patchy formation of discoloured, brown wood with irregular vessels in which water transport was strongly impeded. These severely 4CL-downregulated trees had significantly lower growth efficiency (biomass/leaf area). These results underscore the necessity of adequate lignification for mechanical support of the stem, water transport, tree growth and survival.

del Campo A.D., Navarro R.M., Ceacero C.J.

Holm oak is the hardwood most used for reforestation in Mediterranean Spain, which makes the development of stock quality standards in order to improve establishment success, a priority. However, its nursery culture is characterized by a wide range of practices resulting in stock heterogeneity and a potentially varied outplanting performance. Previous research has focused on specific seedling quality attributes, obviating the integral effect of nursery culture on overall quality. We studied growing regime, seedling quality, and field performance in nine holm oak stocklots produced in commercial nurseries during two consecutive growing years. Results proved variations in field performance were related to stocklot quality and, hence, to the growing regime practised. This dependence on stock quality may vary with planting site weather: in the drier year, survival was related to attributes like height, water status and K concentration, while, in the second, milder year, only growth performance was related to nutrient concentrations, plant size and water status. Results indicated the following quality standards for height: 12–17 cm, diameter: 3.5–4.8 mm, shoot and root weights: 1.3–1.6 and 2.8–4.7 g, respectively, N–P–K foliar concentrations: over 10–0.9–3.7 mg g−1, respectively and in water status parameters: EMX < 5 MPa and SWDTL > 15%. These attributes can be adjusted using nursery cultural practices in order to meet seedling quality standards for holm oak for planting across similar sites.

Peltier A.J., Hatfield R.D., Grau C.R.

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is an economically important disease of soybean (Glycine max) in the north-central United States and other temperate regions throughout the world. The occurrence and severity of Sclerotinia stem rot in the field is highly dependent upon prevailing environmental conditions, which can prove problematic when evaluating soybean accessions for resistance. The identification of an environmentally stable plant trait associated with resistance to S. sclerotiorum could be used to indirectly screen for resistance and would prove useful in the identification and development of resistant germplasm. Observations of the soybean–S. sclerotiorum interaction suggest a role for preformed stem lignin content in disease resistance. Although S. sclerotiorum produces numerous enzymes that degrade plant cell wall components, no lignin-degrading enzymes have been reported. Despite a hypothesized direct relationship between preformed lignin content and disease resistance, previous studies on soybean have correlated lignin content to nutritional value and not to disease resistance. We hypothesized that plants with low stem lignin are more susceptible and exhibit greater Sclerotinia stem rot severity than plants with high lignin concentrations. Six soybean accessions that varied in response to S. sclerotiorum were selected for study in a series of field experiments. Soybean stems were sampled at reproductive developmental stages that correspond to specific events in both soybean plant development and the Sclerotinia stem rot disease cycle. The lignin concentration of stem component samples was quantified. Soybean accessions expressed statistically different disease phenotypes in both 2004 and 2006. Lignin concentrations differed among accessions, growth stages, and plant parts. Results were contrary to our hypothesis, with positively ranked correlations observed between accession Sclerotinia stem rot severity and lignin concentration for all nodes and internodes assayed. For the R3 growth stage, lignin concentration of the internode between the fourth and fifth trifoliate leaves correlated best with disease severity data from each year (P = 0.005). These results indicate that resistance is related to low stem lignin concentration and that soybean stem lignin concentration can be used as a biological marker to select for resistance to S. sclerotiorum.

Coleman H.D., Samuels A.L., Guy R.D., Mansfield S.D.

The effects of reductions in cell wall lignin content, manifested by RNA interference suppression of coumaroyl 3'-hydroxylase, on plant growth, water transport, gas exchange, and photosynthesis were evaluated in hybrid poplar trees (Populus alba x grandidentata). The growth characteristics of the reduced lignin trees were significantly impaired, resulting in smaller stems and reduced root biomass when compared to wild-type trees, as well as altered leaf morphology and architecture. The severe inhibition of cell wall lignification produced trees with a collapsed xylem phenotype, resulting in compromised vascular integrity, and displayed reduced hydraulic conductivity and a greater susceptibility to wall failure and cavitation. In the reduced lignin trees, photosynthetic carbon assimilation and stomatal conductance were also greatly reduced, however, shoot xylem pressure potential and carbon isotope discrimination were higher and water-use efficiency was lower, inconsistent with water stress. Reductions in assimilation rate could not be ascribed to increased stomatal limitation. Starch and soluble sugars analysis of leaves revealed that photosynthate was accumulating to high levels, suggesting that the trees with substantially reduced cell wall lignin were not carbon limited and that reductions in sink strength were, instead, limiting photosynthesis.

Kern K.A., Ewers F.W., Telewski F.W., Koehler L.

Xylem development in trees is affected by dynamic mechanical stresses imposed on stems by wind. To assess clonal differences in response to mechanical perturbation (MP), we subjected seven greenhouse-grown F1 hybrids of Populus trichocarpa Torr. and A. Gray. x P. deltoides Bartr. ex Marsh. to a standard MP treatment consisting of 20 manually imposed stem flexures per day for 70-90 days. Effects of MP on aboveground biomass, hydraulic conductivity (k(h)), specific conductivity (k(s)), flexural stiffness (EI), modulus of elasticity (MOE) and modulus of rupture (MOR) were determined. Treatment increased stem radial growth and decreased height growth, leaf area and total aboveground biomass. It also significantly decreased k(s), MOE and MOR, but significantly increased EI and wood specific gravity in most clones. Mechanical perturbation caused greater stem rigidity, without having a significant effect on whole-stem k(h) or percent loss of conductivity due to embolism. Maximum k(h) was positively correlated with EI in both control (r(2) = 0.54, P < 0.0001) and MP-treated (r(2) = 0.61, P < 0.0001) plants, and k(s) and MOE were positively correlated with percent vessel lumen area (r(2) = 0.45, P < 0.0001 and r(2) = 0.28, P = 0.002, respectively). Thus, contrary to our expectation of a trade-off between conductivity and wood strength, there may be an opportunity to select clones for woody biomass production that are superior in both mechanical strength and hydraulic conductivity, as is the triploid Clone 19-61.