Brassinosteroids Mitigate Cadmium Effects in Arabidopsis Root System without Any Cooperation with Nitric Oxide

The heavy metal cadmium (Cd) affects root system development and quiescent center (QC)-definition in Arabidopsis root-apices. The brassinosteroids-(BRs)-mediated tolerance to heavy metals has been reported to occur by a modulation of nitric oxide (NO) and root auxin-localization. However, how BRs counteract Cd-action in different root types is unknown. This research aimed to find correlations between BRs and NO in response to Cd in Arabidopsis’s root system, monitoring their effects on QC-definition and auxin localization in root-apices. To this aim, root system developmental changes induced by low levels of 24-epibrassinolide (eBL) or by the BR-biosynthesis inhibitor brassinazole (Brz), combined or not with CdSO4, and/or with the NO-donor nitroprusside (SNP), were investigated using morpho-anatomical and NO-epifluorescence analyses, and monitoring auxin-localization by the DR5::GUS system. Results show that eBL, alone or combined with Cd, enhances lateral (LR) and adventitious (AR) root formation and counteracts QC-disruption and auxin-delocalization caused by Cd in primary root/LR/AR apices. Exogenous NO enhances LR and AR formation in Cd-presence, without synergism with eBL. The NO-signal is positively affected by eBL, but not in Cd-presence, and BR-biosynthesis inhibition does not change the low NO-signal caused by Cd. Collectively, results show that BRs ameliorate Cd-effects on all root types acting independently from NO.

Effects of Elevated Temperature on Root System Development of Two Lupine Species

The aim of this study was to assess the effect of elevated temperature on the growth, morphology and spatial orientation of lupine roots at the initial stages of development and on the formation of lupine root architecture at later stages. Two lupine species were studied—the invasive Lupinus polyphyllus Lindl. and the non-invasive L. luteus L. The plants were grown in climate chambers under 25 °C and simulated warming at 30 °C conditions. The angle of root curvature towards the vector of gravity was measured at the 48th hour of growth, and during a 4-h period after 90° reorientation. Root biometrical, histological measurements were carried out on 7-day-old and 30-day-old plants. The elevation of 5 °C affected root formation of the two lupine species differently. The initial roots of L. polyphyllus were characterized by worse spatial orientation, reduced growth and reduced mitotic index of root apical meristem at 30 °C compared with 25 °C. The length of primary roots of 30-day-old lupines and the number of lateral roots decreased by 14% and 16%, respectively. More intense root development and formation were observed in non-invasive L. luteus at 30 °C. Our results provide important information on the effect of elevated temperature on the formation of root architecture in two lupine species and suggest that global warming may impact the invasiveness of these species.

ROOT PENETRATION INDEX 3, a major quantitative trait locus (QTL) associated with root system penetrability in Arabidopsis.

Soil mechanical impedance precludes root penetration, confining root system development to shallow soil horizons where mobile nutrients are scarce. Using a two-phase-agar system, we characterized Arabidopsis thaliana responses to low and high mechanical impedance at three root penetration stages. We found that seedlings whose roots fail to penetrate agar barriers show drastic changes in shoot and root morphology, while those capable of penetrating have only minor morphological effects. The assessment of 21 Arabidopsis accessions revealed that primary root penetrability (PRP) varies widely among accessions. To search for quantitative trait loci (QTLs) associated to root system penetrability, we evaluated a recombinant inbred population (RIL) derived from Landsberg erecta (Ler-0, with a high PRP) and Shahdara (Sha, with a low PRP) accessions. QTL analysis revealed a major-effect QTL localized in chromosome 3 (q-RPI3), which accounted for 29.98% (LOD = 8.82) of the total phenotypic variation. Employing an introgression line (IL-321), with a homozygous q-RPI3 region from Sha in the Ler-0 genetic background, we demonstrated that q-RPI3 plays a crucial role in root penetrability. This multiscale study revels new insights into root plasticity during the penetration process in hard agar layers, natural variation and genetic architecture behind primary root penetrability in Arabidopsis.

Plant Growth Promotion by Two Volatile Organic Compounds Emitted From the Fungus Cladosporium halotolerans NGPF1

Microbial volatiles have beneficial roles in the agricultural ecological system, enhancing plant growth and inducing systemic resistance against plant pathogens without being hazardous to the environment. The interactions of plant and fungal volatiles have been extensively studied, but there is limited research specifically elucidating the effects of distinct volatile organic compounds (VOCs) on plant growth promotion. The current study was conducted to investigate the impact of VOCs from Cladosporium halotolerans NGPF1 on plant growth, and to elucidate the mechanisms for the plant growth-promoting (PGP) activity of these VOCs. The VOCs from C. halotolerans NGPF1 significantly promoted plant growth compared with the control, and this PGP activity of the VOCs was culture medium-dependent. Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography–mass spectrometry (GC–MS) identified two VOC structures with profiles that differed depending on the culture medium. The two compounds that were only produced in potato dextrose (PD) medium were identified as 2-methyl-butanal and 3-methyl-butanal, and both modulated plant growth promotion and root system development. The PGP effects of the identified synthetic compounds were analyzed individually and in blends using N. benthamiana plants. A blend of the two VOCs enhanced growth promotion and root system development compared with the individual compounds. Furthermore, real-time PCR revealed markedly increased expression of genes involved in auxin, expansin, and gibberellin biosynthesis and metabolism in plant leaves exposed to the two volatile blends, while cytokinin and ethylene expression levels were decreased or similar in comparison with the control. These findings demonstrate that naturally occurring fungal VOCs can induce plant growth promotion and provide new insights into the mechanism of PGP activity. The application of stimulatory volatiles for growth enhancement could be used in the agricultural industry to increase crop yield.

Co-fertilization of sulfur and struvite-phosphorus in a slow-release fertilizer improves soybean cultivation

In face of the alarming world population growth predictions and its threat to food security, the development of sustainable fertilizer alternatives is urgent. Moreover, fertilizer performance should be assessed not only in terms of yield but also root system development, as it impacts soil fertility and crop productivity. Fertilizers containing a polysulfide matrix (PS) with dispersed struvite (St) were studied for S and P nutrition due to their controlled-release behavior. Soybean cultivation with St/PS composites provided superior biomass compared to a reference of triple superphosphate (TSP) with ammonium sulfate (AS), with up to 3 and 10 times higher mass of shoots and roots, respectively. Additionally, St/PS achieved a 22% sulfur use efficiency against only 8% from TSP/AS. Root system architectural changes may explain these results, with higher proliferation of second order lateral roots in response to struvite ongoing P delivery. Overall, the composites showed great potential as efficient controlled-release fertilizers for enhanced soybean productivity.

Blue light promotes vascular reconnection, while red light boosts the physiological response and quality of grafted watermelon seedlings

The wound inflicted during grafting of watermelon seedlings requires rapid and sufficient vascular development which is affected by light quality. Our objective was to investigate the effect of light spectra emitted by light-emitting diodes (LEDs) during healing of grafted watermelon (Citrullus lanatus) seedlings on their vascular development, physiological and phytohormonal profile, and root architecture. Three LEDs emitting red (R), blue (B), and RB with 12% blue (12B) were tested in a healing chamber. During the first three days, the photosynthetic apparatus portrayed by PIABS, φP0, ψE0, and ΔVIP was less damaged and faster repaired in B-treated seedlings. B and 12B promoted vascular reconnection and root development (length, surface area and volume). This was the result of signaling cascade between phytohormones such as indole-3-acetic acid and others. After vascular reconnection the seedlings switched lights for 3 more days and the picture was reversed. Seedlings treated with B for the first 3 days and R for days 4 to 6 had better photosynthetic characteristics, root system development, morphological, shoot and root biomass, and quality (i.e. Dickson’s quality index) characteristics. We concluded that blue light is important during the first 3 days of healing, while the presence of red is necessary after vascular reconnection.

Ifluenţa fosforului si tulpinilor rizobacteriene asupra dezvoltării sistemului radicular la plante de soia (Glycine max L. MERR.) în condiţii deficitului de fosfor si umidiate

Drought and nutrient deficiency are major abiotic factors that limits crop production. This study determined the effect of phosphorus (P) and rhizobacteria application on root system development of soybean plants subjected to P deficiency and drought. The P application alone or in combination with bacteria strains (Pseudomonas fluorescence and Azotobacter chroococcum) increased total roots length irrespective of soil moisture. Root growth of cultivar Horboveanca responded more evidently to treatment with rhizobacteria than cultivar Zodiac under P deficiency. Thus, the experimental results demonstrated that the effectiveness of integrated use of P and rhizobacteria (Pseudomonas fluorescence and Azotobacter chroococcum) promotes roots development of soybean plants under normal soil moisture as well as under temporary drought.

Features of the root system of pear trees on different rootstocks in Crimea

В статье представлены результаты исследований состояния насаждений шести сортов груши (Изумрудная, Изюминка Крыма, Мария, Мрия, Отечественная, Таврическая), привитых на три подвоя крымской селекции (КА 53, КА 86, КА 92) в сравнении с контролем (Бере Арданпон /ВА 29) в зависимости от архитектоники корневой системы. Анализ полученных данных дает возможность классифицировать деревья по силе роста в зависимости от подвоя и сорта. Наиболее рослыми являются комбинации сортов Изумрудная, Бере Арданпон, Отечественная на подвоях ВА 29, КА 53 и КА 86. Сорта Изюминка Крыма и Мария, а также подвой КА 92, относятся к группе слаборослых, что подтверждается биометрическими показателями. Площадь сечения штамба 11-летних деревьев в группе сильнорослых сорто-подвойных комбинаций составляет 79,2-81,1 см, у слаборослых - 64,2-68.8 см. На силу роста, помимо указанных факторов, влияет также развитие корневой системы. Цель исследований - установление зависимости роста и развития деревьев груши на разных подвоях от состояния корневой системы. Основным отличием подвоев крымской селекции является хорошо развитая корневая система. Результаты раскопки корней всех сортов на ВА 29 показывают, что основная их масса расположена на глубине 10-40см. Отдельные корни уходят вглубь до 1,7-2,0 м. Основная корневая система подвоев серии КА занимает почвенные горизонты 20-65 см, проникая в глубину до 2,5 м. Более развитая корневая система деревьев груши повышает также засухо- и хлорозоустойчивость деревьев, увеличивает их якорность и повышает продуктивность. Следовательно, при закладке интенсивного сада груши необходимо подбирать сорто-подвойные комбинации, устойчивые к био- и абиотическим условиям произрастания и обладающие умеренной силой роста. Выбор перспективных подвоев для интенсивного садоводства предусматривает необходимость изучения структурно-морфологических особенностей корневой системы. The article presents the study results of stand condition of plantings of six pear varieties (‘Izumrudnaya’, ‘Izyuminka Kryma’, ‘Maria’, ‘Mriya’, ‘Otechestvennaya’, ‘Tavricheskaya’), grafted on three rootstocks of Crimean selection (KA 53, KA 86, KA 92) in comparison with the control (‘Bere Ardanpon’ / BA 29) depending on the root system architectonics. Analysis of the data obtained makes it possible to classify trees according to the growth power depending on the rootstock and variety. The most strongly-grown are combinations of varieties ‘Izumrudnaya’, ‘Bere Ardanpon’, ‘Otechestvennaya’ on rootstocks BA 29, KA 53 and KA 86. The varieties ‘Izyuminka Kryma’ and ‘Maria’, as well as KA 92, belong to the group of weakly-grown, as confirmed by biometric indicators. Basal area of the trunk of 11-year-old trees in the group of strongly-grown variety-rootstock combinations is 79.2-81.1 cm, in the weakly-grown group - 64.2-68.8 cm. The strength of growth, in addition to above mentioned factors, is also influenced by the root system development. The aim of the research is to establish the dependence of growth and development of pear trees using different rootstocks on the root system condition. The main difference of Crimean rootstocks is a well-developed root system. The results of digging up the roots of all varieties on BA 29 show that their basic weight is located at a depth of 10-40 cm. Separate roots go down to 1.7-2.0 m. Basic root system of KA-series rootstocks occupies soil layer of 20-65 cm, penetrating to a depth of 2.5 m. A more developed root system of pear trees also increases the drought and chlorosis resistance of trees, improves their anchoring and productivity. Consequently, when starting an intensive pear garden, it is necessary to select variety-rootstock combinations, resistant to biotic and abiotic growing conditions and having a moderate growth power. The choice of promising rootstocks for intensive gardening involves the necessity to study structural and morphological features of the root system.