A method for continuously monitoring the quality of Masson pine seedlings

Root growth potential (RGP) is a popular physiological indicator used to evaluate seedling vigor. However, the time scale used in the RGP test is the order of days, which leads to poor performance of the RGP method. We propose an optical interference method, called statistical interferometry, to measure minute root elongation at a sub-nanometer scale, which can decrease the time used in measuring RGP. The time scale of this method is also 104 times less than that of the RGP method. Because we can measure the length of root elongation continuously, we can compute the root elongation rate (RER), which is the variety of the length of root elongation per second. Continuous monitoring can help determine the quality of Masson pine seedling as soon as possible. To show the effectiveness of our proposed method, we designed an experiment, in which we applied different water stresses to our collected Masson pine seedlings and acquired two groups of pines, representing two different qualities: one stressed by water and one not. After measuring the RER of the groups in our experiments, we found that RER is interrelated with the quality of seedlings.

Alleviation of Al toxicity by Si is associated with the formation of Al-Si complexes in root tissues of sorghum

Silicon is reported to reduce the toxic effects of Al on root elongation but the in planta mechanism by which this occurs remains unclear. Using seedlings of soybean (Glycine max) and sorghum (Sorghum bicolor), we examined the effect of up to 2 mM Si on root elongation rate (RER) in Al-toxic nutrient solutions. Synchrotron-based low energy X-ray fluorescence (LEXRF) was then used for the in situ examination of the distribution of Al and Si within cross-sections cut from the apical tissues of sorghum roots. The addition of Si potentially increased RER in Al-toxic solutions, with RER being up to ca. 0.3 mm h−1 (14 %) higher for soybean and ca. 0.2 mm h−1 (17 %) higher for sorghum relative to solutions without added Si. This improvement in RER could not be attributed to a change in Al-chemistry of the bulk nutrient solution, nor was it due to a change in the concentration of Al within the apical (0-10 mm) root tissues. Using LEXRF to examine sorghum, it was demonstrated that in roots exposed to both Al and Si, much of the Al was co-located with Si in the mucigel and outer apoplast. These observations suggest that Si reduces the toxicity of Al in planta through formation of Al-Si complexes in mucigel and outer cellular tissues, thereby decreasing the binding of Al to the cell wall where it is known to inhibit wall loosening as required for cell elongation.

Soil strength and rate of root elongation alter the accumulation of Pseudomonas spp. and other bacteria in the rhizosphere of wheat

Results from a controlled environment system and the field showed that slow root elongation rate was associated with accumulation of Pseudomonas spp. in the rhizosphere; fast root elongation avoided accumulation. In the controlled environment system, total bacteria and bacteria belonging to the genus Pseudomonas were quantified along wheat (Triticum aestivum L. cv. Janz) seminal roots elongating at rates of 2.4 or 0.8 cm d–1 in loose and compacted field soil, respectively. Although total numbers of bacteria were similar for both rates of elongation, more Pseudomonas spp. accumulated on the slow-growing roots and their numbers were greatest 0.5–1 cm from the root tips. A reduced rate of root elongation in compacted soil accelerated the differentiation of root hairs, branch roots and adhesion of rhizosheath soil. Elongation rate and distance between the root tip and the zone of root hair development were positively correlated (r=0.9), providing a morphological indicator of root elongation rate in the field. Slow-growing roots from the field had 20 times more Pseudomonas spp. per unit root length than fast-growing field roots, while total bacteria were 8-fold higher; differences were greatest 0–1 cm from the tips. These results may explain how soil structure and Pseudomonas spp. interact in conservation farming. Rapid root elongation is identified as a desirable trait for avoiding accumulations of bacteria.