High throughput phenotyping of root growth dynamics, lateral root formation, root architecture and root hair development enabled by PlaRoM

Plant organ phenotyping by non-invasive video imaging techniques provides a powerful tool to assess physiological traits and biomass production. We describe here a range of applications of a recently developed plant root monitoring platform (PlaRoM). PlaRoM consists of an imaging platform and a root extension profiling software application. This platform has been developed for multi parallel recordings of root growth phenotypes of up to 50 individual seedlings over several days, with high spatial and temporal resolution. PlaRoM can investigate root extension profiles of different genotypes in various growth conditions (e. g. light protocol, temperature, growth media). In particular, we present primary root growth kinetics that was collected over several days. Furthermore, addition of 0.01% sucrose to the growth medium provided sufficient carbohydrates to maintain reduced growth rates in extended nights. Further analysis of records obtained from the imaging platform revealed that lateral root development exhibits similar growth kinetics to the primary root, but that root hairs develop in a faster rate. The compatibility of PlaRoM with currently accessible software packages for studying root architecture will be discussed. We are aiming for a global application of our collected root images to analytical tools provided in remote locations

Shoot apex culture of Acacia mearnsii (De wild)

Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.Research into the micropropagation of black wattle in South Africa is important for two reasons. Firstly micropropagation technology allows breeders to select and propagate mature tissue, which in turn allows them to better capture selected traits. Secondly, tissue culture may control the highly invasive nature of black wattle. If triploid black wattle can be developed, foresters will then have to rely on clonal propagation to supply material for their growing operations. This research was part of the Institute for Commercial Forestry’s Acacia mearnsii vegetative propagation programme. The main focus of this research was to overcome various problems associated with direct organogenesis of ex vitro material. The shoot apex region was used as the explant in all studies because this region is thought to harbour relatively few internal microbial contaminants and is of sufficient size to withstand stresses associated with micropropagation. The initial research was focussed on the screening of sterilants, searching for a viable alternative to mercuric chloride. Surface sterilisation is integral to any micropropagation technique. This process should do the least amount of plant damage, whilst reducing microbial contamination to an acceptable level. Explants were cultured on Murashige and Skoog (MS) medium supplemented with 2.0 mg L-1 BA and monitored for signs of contamination and shooting. Household bleach proved an excellent alternative to mercuric chloride because it did significantly less damage to the explants than mercuric chloride and is handled easily. There was no significant effect of sterilant exposure time on explant decontamination levels, whilst the shortest exposure time resulted in significantly higher levels of shoot development than the other two times tested. The results of this initial research was developed into a protocol and utilised in subsequent investigations. Due to a considerable variation in the success of the developed surface sterilisation protocol according to different times of the year, a further investigation into the effects of season and mother plant material on shoot apex culture of Acacia mearnsii was undertaken. The success of any tissue culture technique depends on a large array of ex vitro and in vitro variables. The objective of this research was to determine the ii effect of two ex vitro variables, season and mother plant, on shoot apex culture of Acacia mearnsii. Explants from individual mother plants were cultured on MS medium supplemented with 2.0 mg L-1 BA during four separate seasons and monitored for signs of contamination and shooting. Spring was found to be the best harvesting season because spring explants showed significantly higher decontaminated explant levels and shooting levels than explants harvested in the other three seasons. The effect of mother plant selection on the performance of Acacia mearnsii explants during shoot apex culture was also found to be significant, especially with regard to shooting levels. Finally factors influencing shoot elongation of A. mearnsii during shoot apex culture were investigated. In the past, induction of shoot elongation during micropropagation of A. mearnsii was attained through the addition of plant growth regulators and other supplements to the basal culture medium. However, some micropropagation methods in other species have utilised red light as a means of promoting shoot elongation. The objective of this study was to test the effects of an alternative basal medium, red light and differing concentrations of chemical additions to the culture medium on shoot elongation of Acacia mearnsii during shoot apex culture. Four independent experiments were undertaken comparing: shoot elongation on Woody Plant Medium (WPM) to the MS basal medium control; shoot elongation under a red cellophane box compared to control culture light conditions; shoot elongation on media supplemented with various concentrations of GA3 to the un-supplemented control and shoot elongation on media supplemented with combinations of BA and IBA compared to a control. Although no significant effects were observed, many trends were noted. The results indicated that there was no advantage to using WPM instead of MS medium when attempting to elongate shoots, rejuvenated through shoot apex culture of A. mearnsii, whilst the effect of GA3 showed a negative trend. The effects of red light and some BA and IBA combinations showed positive trends on the elongation of initiated shoots. This research successfully addressed some of the problems associated with micropropagation of A. mearnsii. Shoot apex culture shows promise and further research into this technique should be considered. A viable surface sterilant alternative to mercuric chloride was successfully identified. This alternative is not only iii safer to use but shows a large reduction in phytotoxic effects. The effects of season and mother plant on shoot apex culture was successfully investigated, resulting in a better understanding of mother plant influences on tissue culture as well as the identification of an optimum season for explant selection. Finally two possible shoot elongation promoters were identified for further research and a more affordable alternative to red light sources and screens was identified

Determination of allelopathic potential in mahogany (Swietenia macrophylla King) leaf litter using sandwich method

The sandwich method is a reliable screening bioassay that can be utilized to investigate allelopathic activity of leaf litter leachates. Screening the allelopathic potential of mahogany (Swietenia macrophylla King) leaf litter in plant–plant interaction using the sandwich bioassay method has not been reported. The research objectives were to determine and categorize allelopathic potential of S. macrophylla leaf litter using the sandwich bioassay method, and to determine specific activity (EC550). S. macrophylla leaf litter. The results showed that S. macrophylla leaf litter exhibited strong allelopathic activity when compared with 46 leaf litter species and was included in the top ten of allelopathic leaf litter species. Increasing S. macrophylla leaf litter concentration was concomitant with inhibition of radicle lettuce seedling growth compared with the control. According to the linear regression analysis, the effective concentration (EC50) of S. macrophylla was estimated to be 3.25 mg D.W. eq. mL-1 and was considered to have strong growth-inhibitory activity on lettuce radicle elongation. The results suggest the possibility of allelopathic potential of leaf litter in plant–plant interaction under S. macrophylla trees

Toxicity of manufactured particulate materials on plant root growth

The rapid development of particle technology and the growing use of particulate materials in industries are bringing large amounts of manufactured particles into the environment. Epidemiological studies suggest that fine particles (particles with aerodynamic diameter smaller than 2.5 μm, i.e., PM2.5) have an association with various adverse health effects in humans. Mass studies have been performed on the toxicity and toxicological mechanisms of airborne particles such as PM2.5 and PM10, but there are very few investigations which contribute to the knowledge base on biological implications of manufactured particulate materials. Up to now, the published toxicity studies on manmade particulate materials focus on human health effects. No investigations have addressed to the ecological effects of the particulate materials. Toxicities of manufactured particles are evaluated by means of a root elongation test in this study. The particles studied include 13-nm alumina, 14-nm hydrophilic silica, 21-nm titania, 161.2-nm spherical hydrophilic silica, 1 .0-μm alumina, 667.6-nm spherical hydrophilic silica, and 0.96-μm titania. Six plant species, Zea mays (corn), Cucumis sativus (cucumber), Avena sativa (oat), Glycine max (soybean), Brassica oleracea (cabbage), and Daucus carota (carrot) were used in this study of the phytotoxicity of the commercially available manufactured particles. Physical and chemical characterization techniques of FTIR, SEM/EDS, the BET method, and particle size analysis, as well as liquid phase coating techniques were applied simultaneously to facilitate the study on toxicological mechanisms of these manufactured particles. The results indicate that phytotoxicity of particles does not depend solely on the particle mass concentration, particle chemical composition, particle size, as well as the particle specific surface area. It also depends on particle surface characteristics

ASSESSMENT OF TOXICITY OF INDUSTRIAL WASTES USING CROP PLANT ASSAYS

Environmental pollution has a harmful action on bioresources, including agricultural crops. It is generated through many industrial activities such as mining, coal burning, chemical technology, cement production, pulp and paper industry, etc. The toxicity of different industrial wastes and heavy metals excess was evaluated using crop plant assays (germination and hydroponics seedlings growth tests). Experimental data regarding the germination process of wheat (from two cultivars) and rye seeds in the presence of industrial wastes (thermal power station ash, effluents from a pre-bleaching stage performed on a Kraft cellulose – chlorinated lignin products or chlorolignin), along with use of an excess of some heavy metals (Zn and Cu) are presented here. Relative seed germination, relative root elongation, and germination index (a factor of relative seed germination and relative root elongation) were determined. Relative root elongation and germination index were more sensitive indicators of toxicity than seed germination. The toxic effects were also evaluated in hydroponics experiments, the sensitivity of three crop plant species, namely Triticum aestivum L. (wheat), Secale cereale (rye), and Zea mays (corn) being compared. Physiological aspects, evidenced both by visual observation and biometric measurements (mean root, aerial part and plant length), as well as the cellulose and lignin content were examined

Strategies to design a new generation of biofertilisers for a more sustainable agriculture

Dupré du Boulois, Hervé1UniTN: http://hdl.handle.net/11572/305429openPlant biostimulants (PBs) are an attractive and environmental friendly strategy to mitigate the continuous application of chemical fertilisers which disrupt the environment by degrading soil fertility and contaminating ground water. The research described in this PhD thesis explored strategies to select, characterise and design a new generation of PBs formulations. Numerous parameters are involved in the multistep process of formulating inoculants and add up to an infinite amount of possible approaches. This requires an elaborate and high-throughput screening to narrow down all the possible criteria. Several authors suggest that this is best achieved by using a stepwise screening approach. However, the scientific literature lack of a suitable screening strategy. We addressed this facet by designing a stepwise screening procedure to select the best microbial candidates as promising new active ingredients of PBs products. Furthermore, this screening was validated by using a case study: plant growth-promoting rhizobacteria (PGPR) combined with humic acids (HA) to be applied on tomato plants. This validation led us to select two PGPR, Pantoea agglomerans MVC 21 and Pseudomonas (Ps.) putida MVC 17 as potential candidates for PBs formulations. Recently, co-inoculation of two or multiple PGPR is used to achieve prominent multifactorial effects on crop productivity. To develop a PGPR consortium, we evaluated how P. agglomerans MVC 21 and Ps. putida MVC 17 interact together and the effect of this interaction on tomato seedlings. Compatibility studies revealed that both strains may be combined in a biostimulant product. Experiments testing the effect of the PGPR interaction indicated that both PGPR interact together and with tomato seedlings mainly by volatile organic compounds (VOCs) produced by P. agglomerans MVC 21. Metabolomic studies pinpointed VOCs belonging to the family of alcohols, ketones and sulfide as the main VOCs released by P. agglomerans MVC 21. Moreover, the identification of the main VOC responsible of the effects of P. agglomerans MVC 21 VOCs deciphered new ecological roles of VOCs as chemical signals able to modulate behaviour of PGPR as well as the interaction between plants and PGPR. Another promising area of PBs formulations is the use of HA combined with PGPR which have shown to better benefit plant growth. Our study, conducted under in vitro conditions, showed that HA synergistically modulate plant growth-promoting activities of P. agglomerans MVC 21. Whole genome sequencing analysis of P. agglomerans MVC 21 will be subject of future studies. Moreover, transcriptomic analysis will be carried out to better understand the effect of HA on P. agglomerans MVC 21 genes related to plant growth-promoting activitiesopenVASSEUR CORONADO, M.F

South African plants as a source of herbicides : identification of a compound with phytotoxic activity from artemisia afra jacq. ex willd.

Master of Science in Chemistry. University of KwaZulu-Natal, Pietermaritzburg 2017.Abstract available in PDF file