Aspects Of Root Growth Research Articles

A mechanism coordinating root elongation, endodermal differentiation, redox homeostasis and stress response.

Root growth relies on both cell division and cell elongation, which occur in the meristem and elongation zones, respectively. SCARECROW (SCR) and SHORT-ROOT (SHR) are GRAS family genes essential for root growth and radial patterning in the Arabidopsis root. Previous studies showed that SCR and SHR promote root growth by suppressing cytokinin response in the meristem, but there is evidence that SCR expressed beyond the meristem is also required for root growth. Here we report a previously unknown role for SCR in promoting cell elongation. Consistent with this, we found that the scr mutant accumulated a higher level of reactive oxygen species (ROS) in the elongation zone, which is probably due to decreased expression of peroxidase gene 3, which consumes hydrogen peroxide in a reaction leading to Casparian strip formation. When the oxidative stress response was blocked in the scr mutant by mutation in ABSCISIC ACID 2 (ABA2) or when the redox status was ameliorated by the upbeat 1 (upb1) mutant, the root became significantly longer, with longer cells and a larger and more mitotically active meristem. Remarkably, however, the stem cell and radial patterning defects in the double mutants still persisted. Since ROS and peroxidases are essential for endodermal differentiation, these results suggest that SCR plays a role in coordinating cell elongation, endodermal differentiation, redox homeostasis and oxidative stress response in the root. We also provide evidence that this role of SCR is independent of SHR, even though they function similarly in other aspects of root growth and development.

Auxin is Involved in Lateral Root Formation Induced by Drought Stress in Tobacco Seedlings

Drought stress is a common abiotic stress that affects plant root development. The goal of this study was to identify the role of auxin on aspects of root growth under water-deficient conditions in Nicotiana tabacum L. In this study, time-course development of lateral root (LR) growth in response to water deficiency (2.5% polyethylene glycol 6000, PEG) was analyzed in tobacco seedlings. LR formation in tobacco plants in response to drought stress depended on the experimental duration. First- and second-order LR formation was induced, respectively, by 43 and 28% on day 5 and by 57 and 40% on day 7 relative to control treatment. Thereafter, PEG-induced LR formation was not observed, and a decrease of 16% was recorded in first-order LR formation on day 11. A root pruning study suggested that PEG-induced LR formation plays a pivotal role in maintaining tobacco plant growth during drought stress. The change in the indole-3-acetic acid (IAA) concentration in leaves and roots was consistent with that of LR formation. This was corroborated by elevated DR5::GUS expression levels on day 5 and by decreased expression levels on day 9. Application of N-1-naphthylphthalamic acid (NPA) to PEG-treated seedlings reduced LR formation to levels similar to those of the control treatment; DR5::GUS expression was also similar between these treatments after NPA application. Results were similar following α-naphthylacetic acid application to control-treated seedlings. Measurement of [3H]IAA transport indicated that polar auxin transport from shoots to roots was increased by 43% under PEG application. Quantitative reverse transcription PCR revealed higher expression of YUC and PIN genes in PEG-treated plants, indicating that they play key roles in auxin synthesis and transport regulation in drought stress. Overall, these suggest that drought stress regulates LR formation in tobacco seedlings via modification of auxin synthesis and polar transport depending on the experimental stage.

Nitrogen nutrition and aspects of root growth and function of two wheat cultivars under elevated [CO2

Nitrogen (N) input into food production is environmentally sensitive and economically significant, making efficient N use an important goal in agricultural practice and in plant breeding. In cereals, grain N concentration [N] is an important component of grain quality and nutritional value. Increasing atmospheric CO2 concentration [CO2] will not only stimulate growth and yield but also diminish grain [N], raising concerns about product quality and nutritional value.In this study we investigated how differences in root structure and function and agronomic properties between two bread wheat (Triticum aestivum L.) cultivars affect N uptake and allocation to grains in a low rainfall environment, and whether such differences can indicate strategies to mitigate grain [N] decreases under increased [CO2]. Two cultivars (‘Silverstar’ and ‘Yitpi’) were chosen for their similar phenology and yields, but ‘Silverstar’ often has lower grain [N]. A glasshouse experiment showed contrasting root structure and function strategies between the two cultivars in response to soil N: ‘Yitpi’ but not ‘Silverstar’ responded to lower soil N with increased root growth, whereas ‘Silverstar’ but not ‘Yitpi’ showed increased N uptake per unit root mass in response to lower N.When grown in the Australian Grains Free Air CO2 Enrichment facility over multiple seasons both cultivars produced similar yields, but ‘Silverstar’ had consistently lower grain [N], smaller grains and greater harvest index. In situ N uptake measurements with 15N label showed that wheat roots can take up nitrate, ammonium and glutamine, and also confirmed differences in uptake strategies between cultivars: ‘Silverstar’ roots had significantly greater uptake capacity than ‘Yitpi’ roots for ammonium. Whilst these results suggest that different strategies in response to variations in soil N supply could be related to grain N outcomes at this field site, there was no interaction with atmospheric [CO2] for any of the measured parameters. Regardless of cultivar, elevated [CO2] (550μmolmol−1) increased yields and decreased grain [N], but did not affect root uptake capacities for either N form. Contrasting root uptake strategies seem unrelated to grain [N] decrease under elevated [CO2], at least for this site.

The interaction between glucose and cytokinin signaling in controlling Arabidopsis thaliana seedling root growth and development

ABSTRACTCytokinin (CK) and glucose (GLC) control several common responses in plants. There is an extensive overlap between CK and GLC signal transduction pathways in Arabidopsis. Physiologically, both GLC and CK could regulate root length in light. CK interacts with GLC via HXK1 dependent pathway for root length control. Wild-type (WT) roots cannot elongate in the GLC free medium while CK-receptor mutant ARABIDOPSIS HISTIDINE KINASE4 (ahk4) and type B ARR triple mutant ARABIDOPSIS RESPONSE REGULATOR1, 10,11 (arr1, 10,11) roots could elongate even in the absence of GLC as compared with the WT. The root hair initiation was also found defective in CK signaling mutants ahk4, arr1,10,11 and arr3,4,5,6,8,9 on increasing GLC concentration (up to 3%); and lesser number of root hairs were visible even at 5% GLC as compared with the WT. Out of 941 BAP regulated genes, 103 (11%) genes were involved in root growth and development. Out of these 103 genes, 60 (58%) genes were also regulated by GLC. GLC could regulate 5736 genes, which include 327 (6%) genes involved in root growth and development. Out of these 327 genes, 60 (18%) genes were also regulated by BAP. Both GLC and CK signaling cannot alter root length in light in auxin signaling mutant AUXIN RESPONSE3/INDOLE-3-ACETIC ACID17 (axr3/iaa17) suggesting that they may involve auxin signaling component as a nodal point. Therefore CK- and GLC- signaling are involved in controlling different aspects of root growth and development such as root length, with auxin signaling components working as downstream target.

From leaf explants to rooted plantlets in a mist reactor

The medicinally important plant Artemisia annua was used as an example to study the effect of mist reactor conditions on shooting, rooting, and in vitro acclimatization. During all three stages, plants grown in the mist reactor yielded more shoot biomass than corresponding gelled medium controls. During shoot development, shooting percentage and shoot multiplication increased with increased light intensity and CO2. Shooting percentage and shoot multiplication were also better under a once vs. twice per hour misting frequency. Hyperhydricity was lowest under light and CO2 enrichment and with less frequent misting. Compared to unhyperhydric shoots, hyperhydric shoots showed significantly greater water content. Hyperhydric shoots also produced fewer glandular trichomes and artemisinin and flavonoids were 3 and 14.5%, respectively, compared to unhyperhydric shoots. During root development, all aspects of root growth, including rooting percentage, number of primary roots and secondary roots, and length of the latter, improved with more frequent misting cycles and light and CO2 enrichment. Although plants grown in the mist reactor did not yield a better rooting percentage than gelled medium controls, new roots formed in the reactor were thicker than those grown on gelled medium. During in vitro acclimatization, reducing the relative humidity of the ventilating air from ~50 to ~10% improved stomatal closure and subsequent ex vitro survival. Plantlets acclimatized in unventilated reactors had broken stems with less lignin. Together, these results showed that compared to traditional methods using gelled medium, the mist reactor can be used to improve micropropagation.

Analysis of movement in primary maize roots

Studying plant root kinematics is important for understanding certain aspects of root growth and movement, which are strictly correlated in plants. However, there is little available data on autonomous movements in plant roots, such as nutations, and the data that are available are poorly described. We investigated the autonomous movements during growth in primary maize roots by estimating the main kinematic parameters of nutations (i.e., the period of duration and amplitude) and the growth rate. The estimations of nutation parameters were performed by developing dedicated methods, which are based on the analysis of root tip displacement and tip velocity. The data relative to the tip displacements were obtained using tip tracing software developed by our team specifically for this purpose. The results confirmed that the nutational phenomenon covers the continuous range of periods and amplitudes, with certain dominant period-amplitude types, which we clustered into three groups: i) amplitudes less than 0.1 mm and 4–16 min periods, ii) amplitudes less than 0.1 mm and 20–120 min periods, and iii) amplitudes greater than 0.1 mm and 24–120 min periods.

Identification of QTL controlling root growth response to phosphate starvation in Arabidopsis thaliana

One of the responses of plants to low sources of external phosphorus (P) is to modify root architecture. In Arabidopsis thaliana plantlets grown on low P, the primary root length (PRL) is reduced whereas lateral root growth is promoted. By using the Bay-0 x Shahdara recombinant inbred line (RIL) population, we have mapped three quantitative trait loci (QTL) involved in the root growth response to low P. The Shahdara alleles at these three QTL promote the response of the primary root to low P (i.e., root length reduction). One of these QTL, LPR1, located in a 2.8 Mb region at the top of chromosome 1, explains 52% of the variance of the PRL. We also detected a single QTL associated with primary root cell elongation in response to low P which colocalizes with LPR1. LPR1 does not seem to be involved in other typical P-starvation responses such as growth and density of root hairs, excretion of acid phosphatases, anthocyanin accumulation or the transcriptional induction of the P transporter Phtl;4. LPR1 might highlight new aspects of root growth that are revealed specifically under low P conditions.

Gasparikova O., Ciamporova M., Mistrik I., Baluska F. Recent advances of plant root structure and function. Developments in plant and soil sciences, volume 90.

This slim book presents selections of the proceedings of the 5th International Symposium on Structure and Function of Roots held in Stara Lensna, Slovakia, in 1998. The quality of the print and the majority of the illustrations are very good. The content will be of interest primarily to lecturers looking for brief reviews of specific topics for teaching purposes, and to researchers studying roots at the tissue, organ and whole plant levels. With the exception of one article, the book does not deal with molecular aspects of root structure and function; researchers interested in this area of plant biology will need to consult primary literature articles in several major journals. The book is divided into three sections, namely: ‘Structural and molecular aspects of root growth and development’ with eight contributions, ‘Physiology of water and ion uptake’ with eight contributions, and ‘Root [sic] under stress conditions’ with six contributions. In the latter section, the stresses include chilling, drought, lead and aluminium. The contributions are between five and 12 pages in length, and present a coherent description of the subjects. The somewhat eclectic mix of topics was evidently dictated by the individuals who chose to attend the conference. The style of the articles varies from mini‐reviews, mini‐reviews with a small amount of new information, to primary literature articles. Approximately half the contributions have already been published in Plant and Soil [volume 226 (1), 2000]. After the illustrious beginning of the series, the book as a whole disappoints on several fronts. Publication 3 years after the conference makes it less current than it should be. Perhaps more importantly, rather few new and original ideas are to be found within its covers. The need for better English language editing is apparent in some articles, as well as in the title of the book itself (which would have been better named ‘Recent advances in . . .’). Nevertheless, the book contains articles by some of the leaders in the field of root structure and function, and provides several useful reviews of current thinking.