Biotin is a member of the vitamin B-complex family that acts as a cofactor of carboxylases and is essential in the metabolism of all organisms. In addition to its essential metabolic functions, biotin has been suggested to play a critical role in regulating gene expression in plants and animals. However, all studies in plants have been conducted under biotin deficiency. Therefore, we hypothesized that exogenously supplied biotin also exerts non-enzymological functions similar to those reported in animals, regulating root growth and development in Arabidopsis thaliana. To test this hypothesis, we evaluated the effects of the biotin supply on seedlings and analyzed the root architecture. Biotin supplementation inhibited root elongation and promoted lateral root formation in a concentration-dependent manner. Inhibited primary root elongation was correlated with decreased expression of the cell cycle genes CycB1;1:uidA and cell expansion gene pAtExp7::uidA, and depended on the concentration of biotin. Viability tests with AtHisH2B:YFP showed that the meristem was depleted. However, biotin supplementation did not affect the concentration of chlorophyll but had a slight inhibitory effect on foliage growth and increased the production of reactive oxygen species (ROS) at the apex of primary roots. Our study provides the first evidence of functions of biotin supplementation in plants in addition to its catalytic role as an enzyme cofactor, likely advancing our understanding of the biological functions of biotin.
The mechanical harvesting of processing spinach (spinach used in production of processed food) is potentially becoming a common practice in Japan. Root distribution affects water and nutrient absorption, but how the roots spread in the soil profile during the regrowth period of spinach remains unknown. In this study, we investigate the root systems of processing spinach in topsoil (5 and 15 cm deep) and deeper soil layers (25, 35, 45, and 55 cm deep) cultivated using ratoon harvesting system. The total root length densities (calculated using the average of the densities at 0 and 15 cm horizontal distance from the row for each depth) in the second harvest were more than two-fold greater than those in the first harvest. The root length percentage in the topsoil and root depth indexes indicate that root systems are in shallower soil layers at the second harvest than at first harvest.
Synthetic auxins are currently used to promote adventitious root formation and thereby propagation by cutttage of plants in horticulture. In the present study, we tested commercial products, named NSC-Base® and NSC-Pro®, which are alkaline hydrolysis products of soy oil and pine seed oil, respectively, for possible use as agents to promote adventitious root formation. The commercial products were found to stimulate adventitious root formation in cut stems of ornamental cabbage, and in root-cut seedlings of mung bean, cucumber, sweet pepper, tomato, melon and pumpkin. Their root-forming activity was further characterized using NSC-Base® and mung bean seedlings. NSC-Base® is mainly composed of sodium salts of long chain fatty acids. NSC-Base® diluted to 104 to 102 times and sodium linoleate, the major ingredient of NSC-B®, at 0.1 and 1.0 mM, significantly increased adventitious root formation, when judged by the total root length and number of roots. Among sodium salts of long chain fatty acids included in NSC-Base®, sodium salts of unsaturated fatty acids, linoleic acid, linolenic acid and probably oleic acid at 1 mM, were active in promoting adventitious root formation, but those of saturated fatty acids were not. Simultaneous application of NSC-Base® with 3-pyridinecarboxylic acid, a stimulator of root elongation, exerted a synergistic effect on root elongation in root-cut mung bean seedlings.
Non-isotopic strontium (Sr) is a non-essential element found in the environment but its effect on plants is unknown. Sr amount may reach even several thousands of ppm at near roads with heavy traffic. The effect of high Sr concentration on vegetative plants has not been investigated. Here, the effect of Sr on the growth of Solanum lycopersicum was studied. The fresh weights of the shoots and roots were reduced by addition of Sr in a dose-dependent manner, suggesting that a high Sr concentration is toxic to the tomato plant. The Sr concentration in the shoots and roots increased in a dose-dependent manner. The Sr concentration in the shoots was 2 to 4 fold higher than that in the roots. Shoots treated with 10 mM Sr had a higher accumulation of Mg, and Ca ions than those in the control shoots. Roots treated with 10 mM Sr only had a higher Ca accumulation than that in the control. The tomato roots were stained by Fluorol Yellow 088 to observe the formation of suberin. In the mature zone of roots, the fluorescence of suberin was increased by 10 mM Sr treatment, indicating that suberin induction caused higher Ca accumulation.
Heterogeneity of individual root traits (heterorhizy) is thought to be one of the most important mechanisms that maintain the functional gradients in fine root systems. It is necessary to know heterorhizy and its relation to the root system architecture in seedlings, because it is the initial form of fine root development. Herein, we investigated individual root traits and the root system architecture of blueberry seedlings by using the protoxylem grouping. Most individual roots were diarch but some laterals were monarch. Compared to the monarch, the diarch roots had significantly larger diameters and tissues, and over half of them exhibited secondary growth. In other words, frameworks of the blueberry seedlings were diarch, although those of cuttings had been at least triarch as seen in our previous study. The employment of diarch frameworks may optimize investment for root system expansion of blueberry seedlings. Our results imply ontogenetic dynamics of heterorhizy in blueberries.