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.

Transcriptome analysis provides new insights into plants responses under phosphate starvation in association with chilling stress

Background Chilling temperature reduces the rate of photosynthesis in plants, which is more pronounced in association with phosphate (Pi) starvation. Previous studies showed that Pi resupply improves recovery of the rate of photosynthesis in plants much better under combination of dual stresses than in non-chilled samples. However, the underlying mechanism remains poorly understood. Results In this study, RNA-seq analysis showed the expression level of 41 photosynthetic genes in plant roots increased under phosphate starvation associated with 4 °C (-P 4 °C) compared to -P 23 °C. Moreover, iron uptake increased significantly in the stem cell niche (SCN) of wild type (WT) roots in -P 4 °C. In contrast, lower iron concentrations were found in SCN of aluminum activated malate transporter 1 (almt1) and its transcription factor, sensitive to protein rhizotoxicity 1 (stop1) mutants under -P 4 °C. The Fe content examined by ICP-MS analysis in -P 4 °C treated almt1 was 98.5 ng/µg, which was only 17% of that of seedlings grown under -P 23 °C. Average plastid number in almt1 root cells under -P 4 °C was less than -P 23 °C. Furthermore, stop1 and almt1 single mutants both exhibited increased primary root elongation than WT under combined stresses. In addition, dark treatment blocked the root elongation phenotype of stop1 and almt1. Conclusions Induction of photosynthetic gene expression and increased iron accumulation in roots is required for plant adjustment to chilling in association with phosphate starvation.

Identification and Functional Characterization of Apple MdCKX5.2 in Root Development and Abiotic Stress Tolerance

Cytokinin oxidase/dehydrogenases (CKXs) are the key enzymes in cytokinin degradation and have been widely studied in model plants. Little is known about apple’s (Malus×domestica) CKX genes. Here, using genome-wide analysis, we identified 10 MdCKX genes in apple. The phylogenetics, chromosome locations, and genome structures were then tested. Expression analysis showed that MdCKX genes had different expression profiles in apple, pointing to the different roles. Meanwhile, relative expression analysis showed that these genes have different expression patterns in response to several exogenous cytokinin factors, including trans-zeatin (ZT), thidiazuron (TDZ), and N6-furfuryladenine (KT). Finally, we introduced the MdCKX5.2 gene into Arabidopsis to evaluate its functions, and the results suggested the transgenic Arabidopsis displayed phenotypes related to promoting primary root and lateral root development, response to exogenous ZT, and conferring to drought and salt tolerant. Taken together, our results provide insights on the possible application of the MdCKX5.2 gene for molecular breeding in apples.

Osmoprotection in Salvia hispanica L. seeds under water stress attenuators

Salvia hispanica cultivation is recent in Brazil and occurs in the off-season, when there is lower water availability in the soil. Water deficit is one of the abiotic factors that most limit germination for compromising the sequence of metabolic events that culminate with seedling emergence. Several attenuating substances have been used to mitigate the effects resulting from this stress and give higher tolerance to the species. Thus, the objective of this study was to evaluate the action of different agents as water stress attenuators in the germination and accumulation of organic compounds in S. hispanica seedlings. The treatments consisted of pre-soaking the seeds for 4 hours in salicylic acid (1 mM.L-1), gibberellic acid (0.4 mM.L-1), distilled water and control treatment (without soaking). The seeds were germinated at osmotic potentials of 0.0, -0.1, -0.2, -0.3 and -0.4 MPa, using PEG 6000 as an osmotic agent. The variables germination percentage, germination speed index, shoot and primary root lengths, total dry mass, proline, total soluble sugars and total free amino acids were analyzed. Salicylic acid and gibberellic acid led to the best results among the attenuators tested, increasing germination, length, dry mass and biochemical components of S. hispanica seedlings under water deficit. Therefore, salicylic and gibberellic acids are efficient in mitigating water stress in S. hispanica seeds up to the potential of -0.4 MPa.

Effects of Aluminium Toxicity on Root and Shoot Growth Of Rice and Chickpea Seedlings

Increasing concentrations of aluminium progressively declined primary root length and number of lateral roots in rice and chickpea seedlings grown in rhizobox. It also inhibited the root and shoot length, dry weight of root and shoot of rice and chickpea seedlings grown in solution culture. On the other hand, it enhanced shoot/root length ratio and dry weight ratio for both the genera. Bangladesh J. Bot. 50(4): 1195-1201, 2021 (December)

Seedlings of zea mays l. (poaceae) and pterogyne nitens tul. (fabaceae): Morphoanatomic and terminological considerations / Plântulas de zea mays l. (poaceae) e pterogyne nitens tul. (fabaceae): Considerações morfoanatômicas e terminológicas

Seedlings of Zea mays L. (maize), Poaceae, and Pterogyne nitens Tul. (wild peanut), Leguminosae, are described morphologically and anatomically in order to characterize the species, but particularly to disseminate the terminology about the seedling, which is little known by non-specialist researchers and undergraduate students. Seedlings were obtained in the laboratory, using Petri dishes. Seedling was considered as the initial plant development phase, which comprises the period from germination to formation of the eophyll. Zea mays seedling is hypogeal and cryptocotyledonous, and it consists of coleorhiza, considered the primary root, endogenous embryonic root, commonly considered in the literature as radicle, reduced hypocotyl, and coleoptile, considered here as eophyll. The second seedling leaf of Z. mays is made up of uniseriate epidermis and homogeneous mesophyll. Pterogyne nitens exhibits epigeal and phanerocotyledonous seedling, and consists of primary root, long hypocotyl, two cotyledons, epicotyl, and opposite eophylls difoliolated or trifoliolated. The hypocotyl has root/shoot transition structure and the eophylls are dorsiventral consisting of one cell layer palisade parenchyma and pluriseriate spongy parenchyma. Seedlings of both species show significant morphological and anatomical differences and specific terminology, especially that of Z. mays.

Function of hydroxycinnamoyl spermidines in seedling growth of Arabidopsis

Hydroxycinnamic acid amides (HCAAs) are involved in various developmental processes as well as in biotic and abiotic stress responses. Among them, the presence of spermidine derivatives, such as N1,N8-di(coumaroyl)-spermidine and N1,N8-di(sinapoyl)-spermidine, and their biosynthetic genes have been reported in Arabidopsis, but their functions in plants are still unknown. We chemically synthesized the above mentioned spermidine derivatives to assess their physiological functions in Arabidopsis. We evaluated the growth and development of chemically treated Arabidopsis and demonstrated that these compounds inhibited seed germination, hypocotyl elongation, and primary root growth, which could be due to modulation of plant hormone homeostasis and signaling. The results suggest that these compounds are regulatory metabolites that modulate plant growth and development.

Reactive oxygen species signalling is involved in alkamide-induced altered root development.

Alkamides are alpha unsaturated N-acylamides structurally related to N-acyl ethanolamides (NAEs) and N-acyl-L-homoserine lactones (AHLs). Studies have shown that alkamides induce prominent changes in root architecture, a significant metabolic readjustment, and transcriptional reprogramming. Some alkamide responses have been associated with redox signalling; however, this involvement and ROS sources have not been fully described. We utilized a genetic approach to address ROS signalling in alkamide-induced processes and found that in Arabidopsis, treatment with the alkamide affinin (50μM) increased the in-situ accumulation of H2O2 in lateral root emergence sites and reduced H2O2 accumulation in primary root meristems implying that altered root growth was dependent on endogenous H2O2. Results show that ROS sourced from PRX34, RBOHC and RBOHD were involved in promotion of lateral root emergence by alkamides. RBOHC was required for affinin-induced enhanced root hair expansion. Furthermore, affinin-induced changes in lateral root emergence, but not root hair length, were dependent on a change in extracellular pH. Finally, reverse genetic experiments suggest heterotrimeric G-proteins were involved in plant response to alkamides; nevertheless, further studies with additional higher order G-protein mutants will be required to resolve this question. These results support that alkamides recruit specific ROS signaling programs to mediate alterations in root architecture.

Bradyrhizobium japonicum IRAT FA3 alters Arabidopsis thaliana root architecture via regulation of auxin efflux transporters PIN2, PIN3, PIN7 and ABCB19

Beneficial rhizobacteria can stimulate changes in plant root development. While root system growth is mediated by multiple factors, the regulated distribution of the phytohormone auxin within root tissues plays a principal role. Auxin transport facilitators help to generate the auxin gradients and maxima that determine root structure. Here, we show that the plant growth-promoting rhizobacterial strain Bradyrhizobium japonicum IRAT FA3 influences specific auxin efflux transporters to alter Arabidopsis thaliana root morphology. Gene expression profiling of host transcripts in control and B. japonicum-inoculated roots of the wild type A. thaliana accession Col-0 confirmed upregulation of PIN2, PIN3, PIN7 and ABCB19 with B. japonicum and identified genes potentially contributing to a diverse array of auxin-related responses. Co-cultivation of the bacterium with loss-of-function auxin efflux transport mutants revealed that B. japonicum requires PIN3, PIN7 and ABCB19 to increase lateral root development and utilizes PIN2 to reduce primary root length. Accelerated lateral root primordia production due to B. japonicum was not observed in single pin3, pin7 or abcb19 mutants, suggesting independent roles for PIN3, PIN7 and ABCB19 during the plant-microbe interaction. Our work demonstrates B. japonicum’s influence over host transcriptional reprogramming during plant interaction with this beneficial microbe and the subsequent alterations to root system architecture.

Physiological response of sorghum seeds treated with Arsenicum album submitted to low temperature

Introduction: Temperature is one of the main environmental factors that act on plants, affecting physiological processes such as germination and vigor, growth, photosynthesis, water and nutrients uptake, among others [1]. When seeds are exposed to temperature stress during imbibition process occur dramatic changes in the reorganization and function of the plasma membrane impairing the stability and functional structure of the membrane resulting in the decrease on germination and embryo death [2][3]. In plant, stress triggers wide response that extends from the change of gene expression and cell metabolism to changes in growth rate and productivity. The organism’s reaction is a function of plant capacity to produce effects opposite to the action of stressors [4]. Aim: the purpose of this study was to evaluate high dilution effect of Arsenicum album on physiological variables of germination and growth of sorghum. Material and Methods: The experiment was conducted at the Laboratory of Physiology and Homeopathy at Universidade Estadual de Maringá - UEM. Arsenicum album 6x matrix was acquired in homeopathic laboratory. From matrix, other dilutions were prepared according to Brazilian Homeopathic Pharmacopoeia [5] with the homeopathic remedies prepared in distilled water (1/10) and succussed by 100 times in mechanical arm (50-Denise Model Autic). For cold test, 50 seeds were distributed on germitest paper moistened to 2.5 times the weight of paper under different dilutions of A. album (9, 12, 18, 24 and 30x) with four replications. The control consisted of distilled water. After sowing, the rolls were placed in plastic bags and sealed, and lead in BOD-chamber at 10°C for 7 days. After this period, the rolls were removed from plastic bags and transferred to BOD-chamber at (25 ± 2)°C, arranged at random where they remained for seven days. Germination percentage (GP%) were evaluated according to Rules for Seed Analysis [6]. The length of primary roots (LPR) and length of hypocotyl (LH) were determined only for seedlings. The total length seedlings (TLS) was calculated as the sum of the lengths of hypocotyl (LH) and primary root (LPR). The fresh biomass (FB) of the seedlings were obtained by removing from their cotyledons, and then weighed on an analytical balance. The dry biomass (DB) was obtained after drying at (80 ± 1)°C for 72h. The experimental design was completely randomized. We adopted the double-blind procedure, thereby avoiding possible researcher interference. Data were subjected to analysis of variance and means compared by Scott-Knott (P≤ 0.05). Results: Seed exposure for seven days to cold stress at 10º C inhibited the germination percentage (GP%). Dilutions 9 and 18x showed the lowest germination percentage (Figure 1A). The cold inhibited the total length of hypocotyls (LH) the length of the seedlings (TLS), with the lowest values ​​observed in seeds treated with dilution 24x (Figures 1B and 1C). Fresh biomass production of seedlings (FB) also was reduced the dilutions 9, 12 and 24x (Figure 1D). Seedlings treated with the dilution 24x reduced the dry biomass production (DB) (Figure 1E). Conclusions: We can conclude that homeopathy Arsenicum album 24x reduced the germination percentage, the length, fresh and dry biomass of sorghum. Probably the cause of this reduction is the lower absorption/water content in the system. The reduction in water content can be the cause lower values ​​for the variables mentioned. However, the inhibitory action of the 24x dilution in water content is not yet known and will be one of the goals of future work.