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Chen Lin and Margret Sauter

Drought and flooding are environmental extremes and major threats to crop production. Water uptake is achieved by plant roots which have to explore new soil spaces to alleviate water deficit during drought or to cope with water excess during flooding. Adaptation of the root system architecture helps plants cope with such extreme conditions and is crucial for plant health and survival. While for dicot plants the well studied model plant Arabidopsis thaliana has provided insight into the genetic and molecular regulation of the root system, less information is available for monocot species, which include the agronomically important cereal crops. Rice (Oryza sativa L.) is a semi-aquatic monocot plant that develops strong tolerance to flooding. Flooding tolerance of rice is closely linked to its adaptive root system. The functional root system of rice is mainly composed of crown roots and is shifted to nodal adventitious roots during flooding which allows rice to maintain oxygen supply to the roots and to survive longer periods of partial submergence as compared with other crops. Likewise, a number of drought-tolerance traits of rice are the result of an altered root system architecture. Hence, the structure of the root system adapts to, both, flooding and drought. Understanding the regulatory mechanisms that control root system adaptation to extreme environments is a key task for scientists to accelerate the breeding efforts for stress-tolerant crops. This review summarizes recently identified genes and molecular mechanisms that regulate root system architecture in rice in response to drought and flooding.

Johnatan Vilasboa, Cibele Tesser da Costa, Hélio Nitta Matsuura and Arthur Germano Fett-Neto

Passiflora suberosa L. (Passifloraceae) can be found throughout the Americas, and has several medicinal properties, including antioxidant, antibacterial, anti-hemolytic, hypolipidemic, and hypoglycemic activities. Germination rates of P. suberosa are low, even with dormancy breaking treatments, posing an obstacle for its multiplication. Vegetative propagation is a valuable approach to produce clones of elite individuals with important pharmacological characteristics, affording fast genetic improvement of biomass source for both phytomedicine manufacturing and bioactive compound isolation. Understanding the rooting process of this species is an important step to exploit its full potential in a sustainable way. We investigated adventitious rooting (AR) in absence or presence of exogenous auxin in P. suberosa cuttings, using a non-aerated hydroponic system. Changes in concentration of flavonoids, phenolics, hexoses, starch, and auxin, as well as peroxidase activity, were monitored along AR. Cuttings showed spontaneous rooting, although the application of exogenous indole-3-butyric acid (IBA) yielded higher number of shorter roots. Biochemical parameters, mainly concentration of carbohydrates and total phenolics, as well as peroxidase activity, varied along the course of the experiments. Based on these results, attempts were made to up- or down-modulate rooting responses by applying putative regulators to the growth solution at different time points. It was possible to block the positive effect of auxin on root development, with only minor positive impacts on the modulated control devoid of auxin. Overall analyses suggested that the rooting system proved effective and specific peroxidase activity showed partial correlation with AR, being able to suffer modulation by culture solution factors.

Avi Eliyahu, Zvi Duman, Sara Sherf, Olga Genin, Yuval Cinnamon, Mohamad Abu-Abied, Roy Weinstain, Arnon Dag and Einat Sadot

Summer and autumn in Israel are highly arid with not enough plants in bloom offering nectar and pollen to support the local apiary. This leads to decline in colony health and honey production. To increase food sources for honeybees, we initiated a project to clone elite Eucalyptus trees exhibiting constant and rich blooming from late summer to early winter. We induced adventitious roots from cuttings of two mature Eucalyptus trees of which nectar production and honeybees’ attraction was measured: Eucalyptus brachyphylla and Eucalyptus x trabutii. During the rooting process, a high frequency of cylindrical callus formation instead of roots was obtained. To shed light on the inner anatomy of the callus chunks, we compared their cell organization and cell-wall composition to those of roots. Whereas in the root, cells were organized in circumferential symmetry, no symmetry was found in the callus. Instead, a more chaotic accumulation of meristematic-like cells with sporadic clusters of tracheary elements laid in different directions were observed. The outer cell layer of the callus often included swollen cells with thin cell walls. Most callus cells stained more strongly for cellulose and lignin than cells in the root meristem. In addition, specific antibodies to methylesterified and de-methylesterified pectin showed differential staining of callus vs. root cells indicating cell wall differences. Strikingly, roots were seen to differentiate from the chaotic cell organization of the callus, albeit at low rates. Further investigation of the cellular and molecular mechanisms underlying callus formation, are required.

Barbara Ghislain, Julien Engel and Bruno Clair

Edited by Lloyd Donaldson and Pieter Baas

ABSTRACT

Angiosperm trees produce tension wood to actively control their vertical position. Tension wood has often been characterised by the presence of an unlignified inner fibre wall layer called the G-layer. Using this definition, previous reports indicate that only one-third of all tree species have tension wood with G-layers. Here we aim to (i) describe the large diversity of tension wood anatomy in tropical tree species, taking advantage of the recent understanding of tension wood anatomy and (ii) explore any link between this diversity and other ecological traits of the species. We sampled tension wood and normal wood in 432 trees from 242 species in French Guiana. The samples were observed using safranin and astra blue staining combined with optical microscopy. Species were assigned to four anatomical groups depending on the presence/absence of G-layers, and their degree of lignification. The groups were analysed for functional traits including wood density and light preferences. Eighty-six % of the species had G-layers in their tension wood which was lignified in most species, with various patterns of lignification. Only a few species did not have G-layers. We found significantly more species with lignified G-layers among shade-tolerant and shade-demanding species as well as species with a high wood density. Our results bring up-to-date the incidence of species with/without G-layers in the tropical lowland forest where lignified G-layers are the most common anatomy of tension wood. Species without G-layers may share a common mechanism with the bark motor taking over the wood motor. We discuss the functional role of lignin in the G-layer.

I. Verstraeten, H. Buyle, S. Werbrouck, M.C. Van Labeke and D. Geelen

In vitro propagation of the ornamentally interesting species Wikstroemia gemmata is limited by the recalcitrance to form adventitious roots. In this article, two strategies to improve the rooting capacity of in vitro microcuttings are presented. Firstly, the effect of exogenous auxin was evaluated in both light and dark cultivated stem segments and also the sucrose-content of the medium was varied in order to determine better rooting conditions. Secondly, different spectral lights were evaluated and the effect on shoot growth and root induction demonstrated that the exact spectral composition of light is important for successful in vitro growth and development of Wikstroemia gemmata. We show that exogenous auxin cannot compensate for the poor rooting under unfavorable light conditions. Adapting the culture conditions is therefore paramount for successful industrial propagation of Wikstroemia gemmata.

Adya P. Singh, Yoon Soo Kim and Ramesh R. Chavan

Edited by Lloyd A. Donaldson

ABSTRACT

This review presents information on the relationship of ultrastructure and composition of wood cell walls, in order to understand how wood degrading bacteria utilise cell wall components for their nutrition. A brief outline of the structure and composition of plant cell walls and the degradation patterns associated with bacterial degradation of wood cell walls precedes the description of the relationship of cell wall micro- and ultrastructure to bacterial degradation of the cell wall. The main topics covered are cell wall structure and composition, patterns of cell wall degradation by erosion and tunnelling bacteria, and the relationship of cell wall ultrastructure and composition to wood degradation by erosion and tunnelling bacteria. Finally, pertinent information from select recent studies employing molecular approaches to identify bacteria which can degrade lignin and other wood cell wall components is presented, and prospects for future investigations on wood degrading bacteria are explored.

J. Efrain Ramirez-Benitez, Ibis Vargas Paredes, Luis F. Cuevas Glory, Enrique Sauri Duch, Victor M. Moo Huchin, Sara Solis Pereira and Gabriel Lizama Uc

Plant-essential oils have been considered as an important source of bioactive molecules like antimicrobials, analgesics, anti-inflammatory and anti-carcinogen agents. Biological functions of plant extracts from the genus Capsicum are unknown. In the present work, non-polar fractions of ripe and unripe fruits of Capsicum chinense Jacq. Cultivar (cv.) Jaguar and Criollo were obtained by hexane-batch extraction and tested for antimicrobial activity against Gram-negative bacterial strain Escherichia coli (ATCC 25922), Gram-positive bacterial strains Enterococcus faecalis (ATCC 29212), Staphylococcus aureus (ATCC 25923) and Staphylococcus epidermidis (ATCC 12228), and yeast Candida albicans (ATCC 90028). Non-polar fractions from ripe fruits for both cv. exhibited greater antimicrobial activity compared to unripe fruits. Implication of numbered FFA’s on observed antimicrobial activity are discussed.

Mast Ram Dhiman, Siddharth Moudgil, Chander Parkash, Raj Kumar, Sandeep Kumar, S.S. Sindhu and Arun Agarwal

Interploidy crosses between Lilium lancifolium (3x) and Asiatic lily cultivar ‘Brunello’ (4x) were attempted for creating genetic variability and to analyse the progenies for different ploidy levels. Experimental results revealed that most of the crosses attempted were developed into fruits, confirming that male-sterile triploid lilies can be used as the female parent for crossing with a suitable male parent. Wide variation in chromosome numbers (28 to 38) was obtained in different plant progenies, indicating that aneuploidy is generated by 3x × 4x crosses. The nuclear DNA content analysis of 13 plant progenies showed that the 2C nuclear DNA content has increased (range = 32.60 pg to 41.32 pg) as compared to Lilium lancifolium, while it was found lower than the cultivar ‘Brunello. Further, morphological characterization of different plant progenies revealed significant differences among themselves, which confirmed the dependence of these traits on cultivars ploidy level. Therefore, present findings will be instrumental for development of new Lilium cultivars with high aesthetic value and utility.

D.R. Bhardwaj, Sharmistha Pal and Pankaj Panwar

In this paper we investigated how succession has altered soil properties in relation to plant biomass and litter characteristics in mid Himalayan region of India. The natural forest with four succession phases were identified. The early stages are (1) pure Pinus roxburghii forest of coniferous shade intolerant species (2) middle stage is a Pinus roxburghii + Quercus leucotricophora (60: 40) forest with combination of coniferous and deciduous species (3) later stage is a Quercus leucotricophora + Pinus roxburghii (60: 40) and (4) climax stage is a Pure Quercus leucotricophora forest of shade tolerant deciduous broadleaf species. The soil samples were collected from surface (0–15 cm) and subsurface (15–30 cm and 30–45 cm) levels. The soil properties showed gradual improvement with progress in succession phases. Our study shows that, there was a substantial increase in level of soil organic carbon and nitrogen from early to climax phase. Soil pH was significantly lower in early succession phase. The highest available nitrogen was under climax (pure oak) and least in early phase (pure pine) (402 and 347 Kg ha–1 in surface soil, respectively). The concentration of very labile carbon (fraction 1) was highest in climax and least in early stage. The highest biomass accumulation was in climax (pure oak, 420.6 Mgha–1), followed by oak + pine (348.7 Mgha–1) and least in pine + oak (299.3 Mgha–1). Out of 4 stages, shrub biomass was maximum in early (pure pine) (20.5 M Mgha–1), being 6.57% of total biomass and least in climax (pure oak) (10.7 Mgha–1), being 2.54% of total biomass. Further, the labile carbon pools showed a strong positive correlation with total biomass at different succession stages. The recalcitrant carbon pool had significant negative correlation with biomass. Hence, the study suggests that, this increase in soil organic carbon, nitrogen and soil fertility parameters are in accordance to changes in biomass and litter fall characteristics with progress in forest succession.

Ahmet Pişkin

This study was carried out in the Konya Experiment Station experimental plots of the Directorate of Sugar Research Institute of the Turkish Sugar Factories Corporation from 2005 to 2010, with first two years being the transition period, for the purpose of investigating the effect of manure on sugar beet yield and quality in production of organic sugar beet (Beta vulgaris L.). Trials were organized into a randomized block design with 4 replications in the same plot. The experiments evaluated manure application, chemical fertilizer application and control (growing plants with no fertilizer). The study investigated sugar beet root yield, sugar concentration, white sugar concentration and white sugar yield. According to the 3 year experimental results, 69.8–83.3% of the white sugar in chemical fertilizer treatment achieved by sheep manure treatment. Despite some reduction in sugar beet yield values, it is evident that manure may be used effectively in the production of organic sugar beet in accordance with an organic production system.