Seedling Elongation Research Articles

Over-expression of GhDWF4 gene improved tomato fruit quality and accelerated fruit ripening

Brassinosteroids (BRs), a class of steroidal phytohormones are essential for many biological processes in plant. However, little is known about their roles in fruit development. Tomato is a highly valuable vegetable and has been adopted as the model species for studying fruit growth, development, and ripening. To understand the role of endogenous BRs in the development of tomato fruit, the expression patterns of three homologues of DWF4 gene were investigated and the transgenic tomato plants were generated in which the GhDWF4 gene from upland cotton (Gossypium hirsutum L.) was ectopically expressed. The contents of main quality components were analyzed in fruits of transgenic tomato line and non-transgenic line (control plant, CP) when the fruit was mature. SlCYP90B3 that possesses high homology with GhDWF4 preferentially expressed in mature fruit. Significantly higher contents of soluble sugar, soluble proteins, and vitamin C were obtained in fruit of transgenic tomato lines compared with those in the CP. Furthermore, overexpressing GhDWF4 promoted fruit growth and ripening. The weight per fruit was increased by about 23% in transgenic lines. In addition, overexpressing GhDWF4 promoted the germination of transgenic tomato seeds and hypocotyl elongation of seedlings. These results indicated that overexpressing GhDWF4 gene in tomato could increase the contents of many nutrients in fruit and accelerate fruit ripening. It is suggested that increased endogenous BRs in fruit affect the growth and development of tomato fruit and therefore improved the nutrient quality of tomato.

The Effect of Halopriming and Salicylic Acid on the Germination of Fenugreek (<i>Trigonella foenum-graecum</i>) under Different Cadmium Concentrations

The hereby study was based on a factorial experiment conducted in a completely randomized design with four replications, at Agriculture College, Shahrekord University, Iran, in 2014. The role of salicylic acid (SA), potassium nitrate (KNO3) and potassium chloride (KCl) was evaluated on seed germination of fenugreek (Trigonella foenum-graecum L.) under different cadmium concentrations. Treatments included four levels of seed priming (no priming, potassium chloride, potassium nitrate, salicylic acid) and four levels of cadmium concentration (0, 10, 20, 30 mg/L). Cadmium chloride caused a significant inhibition in germination percentage, root elongation, shoot elongation and seedling dry weight. The shoot length was more sensitive to cadmium concentrations than the root length. Primed seeds with SA (100 mg/L) proved protection against Cd stress and increased the germination percentage, root elongation, shoot elongation and dry weight of seedlings compared to the control treatment. Seeds treated with SA alleviated the Cd negative effect on germination parameters. In conclusion, using seed priming with salicylic acid can be recommended as a good technique for fenugreek crop on fields exposed to high cadmium toxicity.

Patatin-related phospholipase A, pPLAIIIα, modulates the longitudinal growth of vegetative tissues and seeds in rice.

Patatin-related phospholipase A (pPLA) hydrolyses glycerolipids to produce fatty acids and lysoglycerolipids. The Oryza sativa genome has 21 putative pPLAs that are grouped into five subfamilies. Overexpression of OspPLAIIIα resulted in a dwarf phenotype with decreased length of rice stems, roots, leaves, seeds, panicles, and seeds, whereas OspPLAIIIα-knockout plants had longer panicles and seeds. OspPLAIIIα-overexpressing plants were less sensitive than wild-type and knockout plants to gibberellin-promoted seedling elongation. OspPLAIIIα overexpression and knockout had an opposite effect on the expression of the growth repressor SLENDER1 in the gibberellin signalling process. OspPLAIIIα-overexpressing plants had decreased mechanical strength and cellulose content, but exhibited increases in the expression of several cellulose synthase genes. These results indicate that OspPLAIIIα plays a role in rice vegetative and reproductive growth and that the constitutive, high activity of OspPLAIIIα suppresses cell elongation. The decreased gibberellin response in overexpressing plants is probably a result of the decreased ability to make cellulose for anisotropic cell expansion.

Minimizing ammonia volatilization from urea, improving lowland rice (cv. MR219) seed germination, plant growth variables, nutrient uptake, and nutrient recovery using clinoptilolite zeolite

The anionic nature and high cation exchange capacity (CEC) of clinoptilolite zeolite can be exploited to reduce ammonia (NH3) loss from urea and to improve soil chemical properties to increase nutrient utilization efficiency in lowland rice cultivation. A closed-dynamic airflow system was used to determine NH3 loss from treatments (20, 40, and 60 g clinoptilolite zeolite pot−1). Seed germination study was conducted to evaluate the effects of clinoptilolite zeolite on rice seed germination. A pot study was conducted to determine the effects of clinoptilolite zeolite on rice plant growth variables, nutrient uptake, nutrient recovery, and soil chemical properties. Standard procedures were used to determine NH3 loss, rice plant height, number of leaves, number of tillers, dry matter production, nutrient uptake, nutrient recovery, and soil chemical properties. Application of clinoptilolite zeolite (15%) increased shoot elongation of seedlings and significantly reduced NH3 loss (up to 26% with 60 g zeolite pot−1), and increased number of leaves, total dry matter, nutrient uptake, nutrient recovery, soil pH, CEC, and exchangeable Na+. Amending acid soils with clinoptilolite zeolite can significantly minimize NH3 loss and improve rice plant growth variables, nutrient uptake, nutrient recovery, and soil chemical properties. These findings are being validated in our ongoing field trials.

Studies on the Effects of Vermicompost on Physicochemical Properties and Growth of Two Tomato Varieties under Greenhouse Conditions

This research was conducted to investigate effects of different vermicompost rates on breeding quality and growth of two tomato varieties. Six treatments were applied, combining vermicompost (VC) with rice husk ash (RHS) and coconut fiber (CF) with the following proportions: 3/3 VC (control treatment, T1), 2/3 VC + 1/3 RHS (T2), 2/3 VC + 1/3 CF (T3), 1/3 VC + 2/3 RHS (T4), 1/3 VC + 2/3 CF (T5), and 1/3 VC + 1/3 RHS + 1/3 CF (T6). The results demonstrated that there was significant difference between combining VC, RHS, and CF into EC and combining those into macronutrients of substrates with increasing VC mixture proportion; however, water-holding capacity (WHC), zinc (Zn), manganese (Mn), and iron (Fe) contents were significantly increased with reduced VC mixture proportion. A mixture of VC with RHS and CF made with the rate of 1:1:1 significantly influenced emergence and elongation of seedlings of both varieties. Biomass allocation was affected by VC amendments for two varieties in seedling stage and one field-grown tomato variety. The VC amendment did not affect the phosphorous (P), Fe, and Zn contents but significantly influenced nitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), and Mn concentrations in the shoots. The mixture of VC with RHS and CF made with the rate of 1:1:1 was found to provide optimum conditions for seedling performance of the two tomato varieties.

Identification of Octanal as Plant Growth Inhibitory Volatile Compound Released from Heracleum sosnowskyi Fruit

Heracleum sosnowskyi Manden of the Apiaceae family is a malignant invasive plant in Eastern Europe, Belarus and Russia. The species is known for its prolific seed production, which has been linked to the plant's invasive success. The fruit also has a strong aroma, but the contribution of the fruit's volatile constituent to out-compete neighboring plants has not been fully established. In this study, fruit volatiles of H. sosnowskyi and conspecifics (i.e. H. asperum, H. lescovii, H. dissectum, H. hirtum) were identified by headspace gas chromatography-mass spectrometry (HS-GC-MS). Octyl acetate, octanol, octanal, hexyl isobutyrate, and hexyl-2-methyl butyrate were found to be the principal volatiles. Using authentic standards, the growth-inhibitory property of the individual compounds was assayed by the novel Cotton swab method. Assay results with lettuce (Lactuca sativa) showed that octanal strongly inhibited seed germination and radicle elongation of seedlings. The results suggest that octanal may be the main contributor to the allelopathic activity of H. sosnowksyi fruits. Furthermore, the mixture of fruit volatiles from the invasive H. sosnowskyi more strongly delayed lettuce seedling elongation than the volatiles from fruits of the non-invasive H. asperum, H. lescovii, H. dissectum and H. hirtum. Thus, the present study is the first to demonstrate the possible involvement of fruit volatiles of Heracleum species in plant-plant interaction.

Shade avoidance components and pathways in adult plants revealed by phenotypic profiling.

Shade from neighboring plants limits light for photosynthesis; as a consequence, plants have a variety of strategies to avoid canopy shade and compete with their neighbors for light. Collectively the response to foliar shade is called the shade avoidance syndrome (SAS). The SAS includes elongation of a variety of organs, acceleration of flowering time, and additional physiological responses, which are seen throughout the plant life cycle. However, current mechanistic knowledge is mainly limited to shade-induced elongation of seedlings. Here we use phenotypic profiling of seedling, leaf, and flowering time traits to untangle complex SAS networks. We used over-representation analysis (ORA) of shade-responsive genes, combined with previous annotation, to logically select 59 known and candidate novel mutants for phenotyping. Our analysis reveals shared and separate pathways for each shade avoidance response. In particular, auxin pathway components were required for shade avoidance responses in hypocotyl, petiole, and flowering time, whereas jasmonic acid pathway components were only required for petiole and flowering time responses. Our phenotypic profiling allowed discovery of seventeen novel shade avoidance mutants. Our results demonstrate that logical selection of mutants increased success of phenotypic profiling to dissect complex traits and discover novel components.

Growth-limiting proteins in maize coleoptiles and the auxin-brassinosteroid hypothesis of mesocotyl elongation.

The shoot of grass coleoptiles consists of the mesocotyl, the node, and the coleoptile (with enclosed primary leaf). Since the 1930s, it is known that auxin (indole-3-acetic acid, IAA), produced in the tip of the coleoptile, is the central regulator of turgor-driven organ growth. Fifty years ago, it was discovered that antibiotics that suppress protein biosynthesis, such as cycloheximide, inhibit auxin (IAA)-induced cell elongation in excised sections of coleoptiles and stems. Based on such inhibitor studies, the concept of "growth-limiting proteins (GLPs)" emerged that was subsequently elaborated and modified. Here, we summarize the history of this idea with reference to IAA-mediated shoot elongation in maize (Zea mays) seedlings and recent studies on the molecular mechanism underlying auxin action in Arabidopsis thaliana. In addition, the analysis of light-induced inhibition of shoot elongation in intact corn seedlings is discussed. We propose a concept to account for the GLP-mediated epidermal wall-loosening process in coleoptile segments and present a more general model of growth regulation in intact maize seedlings. Quantitative proteomic and genomic studies led to a refinement of the classic "GLP concept" to explain phytohormone-mediated cell elongation at the molecular level (i.e., the recently proposed theory of a "central growth regulation network," CGRN). Novel data show that mesocotyl elongation not only depends on auxin but also on brassinosteroids (BRs). However, the biochemical key processes that regulate the IAA/BR-mediated loosening of the expansion-limiting epidermal wall(s) have not yet been elucidated.

Effects of the size and morphology of zinc oxide nanoparticles on the germination of Chinese cabbage seeds.

The toxicity of four zinc oxide nanoparticles (i.e., spheric ZnO-30, spheric ZnO-50, columnar ZnO-90, and hexagon rod-like ZnO-150) to the seed germination of Chinese cabbage (Brassica pekinensis L.) was investigated in this study. The results showed that zinc oxide nanoparticles (nano-ZnOs) did not affect germination rates at concentrations of 1-80 mg/L but significantly inhibited the root and shoot elongation of Chinese cabbage seedlings, with the roots being more sensitive. The inhibition was evident mainly during seed incubation rather than the seed soaking process. Both the production of free hydroxyl groups (·OH) and the Zn bioaccumulation in roots or shoots resulted in toxicity of nano-ZnOs to Chinese cabbage seedlings. The toxicity of nano-ZnOs was affected significantly by their primary particle sizes in the minimum dimensionality, but large columnar ZnO-90 and small spherical ZnO-50 had comparable toxicities. Therefore, both the particle size and morphology affected the toxicity of nano-ZnOs.

Mechanism of artemisinin phytotoxicity action: Induction of reactive oxygen species and cell death in lettuce seedlings

Artemisinin has been recognized as an allelochemical that inhibits growth of several plant species. However, its mode of action is not well clarified. In this study, the mechanism of artemisinin phytotoxicity on lettuce seedlings was investigated. Root and shoot elongation of lettuce seedlings were inhibited by artemisinin in a concentration-dependent manner. The compound effectively arrested cell division and caused loss of cell viability in root tips of lettuce. Overproduction of reactive oxygen species (ROS) was induced by artemisinin. Lipid peroxidation, proline overproduction and reduction of chlorophyll content in lettuce seedlings were found after treatments. These results suggested that artemisinin could induce ROS overproduction, which caused membrane lipids peroxidation and cell death, and impacted mitosis and physiological processes, resulting in growth inhibition of receptor plants.

Involvement of nitrate reductase in the ameliorating effect of 5-aminolevulinic acid on NaCl-stressed barley seedlings

Exogenous application of 5-aminolevulinic acid (ALA) is widely used to decrease the effect of different abiotic stresses in various crops while the nitrogen metabolism is a possible target of ALA in plants. We investigated the effect of exogenous ALA on growth, activity of nitrate reductase (NR; EC 1.6.6.1), synthesis of proline and ROS generation in seedlings of the salt-sensitive barley cultivar (Hordeum vulgare L. cv. Gonar). Obtained data indicated that the ALA (20, 40 and 80 mg L−1) increased elongation and leaf blade expansion of barley seedlings exposed to 150 mM NaCl as compared to control plants, which were not treated by ALA. NR gene (Nar1) expression, NR protein content and enzymatic activities increased in ALA-treated plants. ALA also induced accumulation of free proline and decreased generation of superoxide anion radicals. Overall, this study demonstrates that ALA effects on salt-stressed barley involves changes of NR activities both at transcriptional and translational levels and leads to complex physiological modifications, such as improvement of growth and antiradical defense.

Arabidopsis DET1 Represses Photomorphogenesis in Part by Negatively Regulating DELLA Protein Abundance in Darkness

Arabidopsis De-etiolated 1 (DET1) is one of the key repressors that maintain the etiolated state of seedlings in darkness. The plant hormone gibberellic acid (GA) also participates in this process, and plants deficient in GA synthesis or signaling show a partially de-etiolated phenotype in darkness. However, how DET1 and the GA pathway work in concert in repressing photomorphogenesis remains largely unknown. In this study, we found that the abundance of DELLA proteins in det1-1 was increased in comparison with that in the wild-type plants. Mutation in DET1 changed the sensitivity of hypocotyl elongation of mutant seedlings to GA and paclobutrazol (PAC), an inhibitor of GA synthesis. However, we did not find obvious differences between det1-1 and wild-type plants with regard to the bioactive GA content or the GA signaling upstream of DELLAs. Genetic data showed that removal of several DELLA proteins suppressed the det1-1 mutant phenotype more obviously than GA treatment, indicating that DET1 can regulate DELLA proteins via some other mechanisms. In addition, a large-scale transcriptomic analysis revealed that DET1 and DELLAs play antagonistic roles in regulating expression of photosynthetic and cell elongation-related genes in etiolated seedlings. Taken together, our results show that DET1 represses photomorphogenesis in darkness in part by reducing the abundance of DELLA proteins.

MPK6 controls H2 O2-induced root elongation by mediating Ca2+ influx across the plasma membrane of root cells in Arabidopsis seedlings.

Mitogen-activated protein kinases (MPKs) play critical roles in signalling and growth, and Ca(2+) and H2 O2 control plant growth processes associated with abscisic acid (ABA). However, it remains unclear how MPKs are involved in H2 O2 - and Ca(2+) -mediated root elongation. Root elongation in seedlings of the loss-of-function mutant Atmpk6 (Arabidopsis thaliana MPK6) was less sensitive to moderate H2 O2 or ABA than that in wild-type (WT) plants. The enhanced elongation was a result of root cell expansion. This effect disappeared when ABA-induced H2 O2 accumulation or the cytosolic Ca(2+) increase were defective. Molecular and biochemical evidence showed that increased expression of the cell wall peroxidase PRX34 in Atmpk6 root cells enhanced apoplastic H2 O2 generation; this promoted a cytosolic Ca(2+) increase and Ca(2+) influx across the plasma membrane. The plasma membrane damage caused by high levels of H2 O2 was ameliorated in a Ca(2+) -dependent manner. These results suggested that there was intensified PRX34-mediated H2 O2 generation in the apoplast and increased Ca(2+) flux into the cytosol of Atmpk6 root cells; that is, the spatial separation of apoplastic H2 O2 from cytosolic Ca(2+) in root cells prevented H2 O2 -induced inhibition of root elongation in Atmpk6 seedlings.

Diversity and characterization of culturable bacterial endophytes from Zea mays and their potential as plant growth-promoting agents in metal-degraded soils.

In this study, we evaluated the phylogenetic diversity of culturable bacterial endophytes of Zea mays plants growing in an agricultural soil contaminated with Zn and Cd. Endophytic bacterial counts were determined in roots and shoots, and isolates were grouped by random amplified polymorphic DNA and identified by 16S ribosomal RNA (rRNA) gene sequencing. Endophytes were further characterized for the production of plant growth-promoting (PGP) substances, such as NH3, siderophores, indol-3-acetic acid (IAA), hydrogen cyanide and extracellular enzymes, and for the capacity to solubilize phosphate. The endophytes producing higher amounts of IAA were screened for their tolerance to Zn and Cd and used as bioinoculants for maize seedlings grown in the Zn/Cd-contaminated soil. The counts of endophytes varied between plant tissues, being higher in roots (6.48 log10 g(-1) fresh weight) when compared to shoots (5.77 log10 g(-1) fresh weight). Phylogenetic analysis showed that endophytes belong to three major groups: α-Proteobacteria (31 %), γ-Proteobacteria (26 %) and Actinobacteria (26 %). Pseudomonas, Agrobacterium, Variovorax and Curtobacterium were among the most represented genera. Endophytes were well-adapted to high Zn/Cd concentrations (up to 300 mg Cd l(-1) and 1,000 mg Zn l(-1)) and showed ability to produce several PGP traits. Strains Ochrobactrum haematophilum ZR 3-5, Acidovorax oryzae ZS 1-7, Frigoribacterium faeni ZS 3-5 and Pantoea allii ZS 3-6 increased root elongation and biomass of maize seedlings grown in soil contaminated with Cd and Zn. The endophytes isolated in this study have potential to be used in bioremediation/phytoremediation strategies.

Sesquiterpenes from the saprotrophic fungus Granulobasidium vellereum (Ellis & Cragin) Jülich

Twelve sesquiterpenes comprising either the protoilludane or the rare cerapicane carbon skeletons were obtained from the saprotrophic wood decomposing fungus Granulobasidium vellereum; 2a-hydroxycoprinolone (1), 3-hydroxycoprinolone (2), coprinolone diol B (3), granulodiene A (4), granulodiene B (5), granulone A (6), 8-deoxy-4a-hydroxytsugicoline B (7), granulone B (8), demethylgranulone (9), cerapicolene (10), as well as the known compounds radudiol and Δ6-coprinolone. The structures were determined using spectroscopic methods and biosynthetic considerations. Granulone A had growth stimulating effect on the total elongation of lettuce seedlings. None of the isolated compounds showed any antifungal effect.

Osmotic adjustment and maintenance of the redox balance in root tissue may be key points to overcome a mild water deficit during the early growth of wheat

In this investigation we analyzed in detail the consequences of water deficit during the first 4 days of wheat development, focusing on root growth as affected by eventual changes in cell cycle regulation and oxidative processes. Root elongation decreased under water restriction in correlation with the intensity of this limitation, but the total number of cells between the quiescent center and the start of the rapid elongation zone in the root apex did not vary. Neither lipid peroxidation nor protein carbonylation increased in the roots of water-starved seedlings (ψw: −0.6 MPa); accordingly, catalase activity increased, and transcript levels of cat2 gene were enhanced. Superoxide dismutase activity rose at day 2 and 3 and, unlike catalase, displayed quite similar levels on comparing roots and coleoptiles. Proline and total soluble carbohydrates increased in the roots of water-starved seedling. Total conductivity and osmolality were also augmented. No changes in the transcript levels of the markers related to G1-S transition phase of cell cycle could be detected. However, two expansin genes (TaEXPB8 and TaEXPA5) were up-regulated in roots under water deficit. We conclude that wheat root elongation in water-deprived seedlings was simply hampered by lack of water income to cells. The enhanced expression of two root expansin genes is probably related to the eventual need of a quick cell wall expansion to allow the existing root cells to recover normal turgor, in case of sudden rewatering. Maintenance of redox balance, osmotic adjustment and modification of cell wall plasticity may be key points for wheat seedlings to overcome a water restriction during early growth.

Bioinformatic and phylogenetic analysis of the CLAVATA3/EMBRYO-SURROUNDING REGION (CLE) and the CLE-LIKE signal peptide genes in the Pinophyta.

BackgroundThere is a rapidly growing awareness that plant peptide signalling molecules are numerous and varied and they are known to play fundamental roles in angiosperm plant growth and development. Two closely related peptide signalling molecule families are the CLAVATA3-EMBRYO-SURROUNDING REGION (CLE) and CLE-LIKE (CLEL) genes, which encode precursors of secreted peptide ligands that have roles in meristem maintenance and root gravitropism. Progress in peptide signalling molecule research in gymnosperms has lagged behind that of angiosperms. We therefore sought to identify CLE and CLEL genes in gymnosperms and conduct a comparative analysis of these gene families with angiosperms.ResultsWe undertook a meta-analysis of the GenBank/EMBL/DDBJ gymnosperm EST database and the Picea abies and P. glauca genomes and identified 93 putative CLE genes and 11 CLEL genes among eight Pinophyta species, in the genera Cryptomeria, Pinus and Picea. The predicted conifer CLE and CLEL protein sequences had close phylogenetic relationships with their homologues in Arabidopsis. Notably, perfect conservation of the active CLE dodecapeptide in presumed orthologues of the Arabidopsis CLE41/44-TRACHEARY ELEMENT DIFFERENTIATION (TDIF) protein, an inhibitor of tracheary element (xylem) differentiation, was seen in all eight conifer species. We cloned the Pinus radiata CLE41/44-TDIF orthologues. These genes were preferentially expressed in phloem in planta as expected, but unexpectedly, also in differentiating tracheary element (TE) cultures. Surprisingly, transcript abundances of these TE differentiation-inhibitors sharply increased during early TE differentiation, suggesting that some cells differentiate into phloem cells in addition to TEs in these cultures. Applied CLE13 and CLE41/44 peptides inhibited root elongation in Pinus radiata seedlings. We show evidence that two CLEL genes are alternatively spliced via 3′-terminal acceptor exons encoding separate CLEL peptides.ConclusionsThe CLE and CLEL genes are found in conifers and they exhibit at least as much sequence diversity in these species as they do in other plant species. Only one CLE peptide sequence has been 100% conserved between gymnosperms and angiosperms over 300 million years of evolutionary history, the CLE41/44-TDIF peptide and its likely conifer orthologues. The preferential expression of these vascular development-regulating genes in phloem in conifers, as they are in dicot species, suggests close parallels in the regulation of secondary growth and wood formation in gymnosperm and dicot plants. Based on our bioinformatic analysis, we predict a novel mechanism of regulation of the expression of several conifer CLEL peptides, via alternative splicing resulting in the selection of alternative C-terminal exons encoding separate CLEL peptides.

Transcription ofST2AEncoding A Sulfotransferase Family Protein That Is Involved in Jasmonic Acid Metabolism Is Controlled According to the Circadian Clock- and PIF4/PIF5-Mediated External Coincidence Mechanism inArabidopsis thaliana

Plant elongation growth on a day-to-day basis is enhanced under specific photoperiod and temperature conditions. Circadian clock is involved in the temperature adaptive photoperiodic control of plant architecture, including hypocotyl elongation in Arabidopsis thaliana. In this regulation, phytochrome interacting transcriptional factors, PIF4 and PIF5, are activated at the end of night under short photoperiod or high temperature conditions, due to the coincidence between internal (circadian rhythm of the transcripts) and external (length of dark period) time cues. It is previously found that biosynthesis or metabolism of phytohormones including auxin, and their signal transduction-related genes are downstream targets of circadian clock and PIF4/PIF5 mediated external coincidence mechanism. Brassinosteroid and gibberellic acid played a positive role in the hypocotyl elongation of seedlings under light and dark cycle conditions. On the other hand, cytokinin and jasmonic acid played an opposite role. In this study, diurnal expression profile of a gene encoding a sulfotransferase family protein that is involved in the jasmonic acid metabolism, ST2A, was examined. It was found that transcription of ST2A is induced at the end of night under LD/22 °C and SD/28 °C conditions according to the external coincidence mechanism. The results of this study support the idea that the circadian clock orchestrates a variety of hormone-signaling pathways to regulate the photoperiod and temperature-dependent morphogenesis in A. thaliana.

Mitogen-activated protein kinase 6 controls root growth in Arabidopsis by modulating Ca2+-based Na+ flux in root cell under salt stress

Little is known about the role of mitogen-activated protein kinase 6 (MPK6) in Na+ toxicity and inhibition of root growth in Arabidopsis under NaCl stress. In this study, we found that root elongation in seedlings of the loss-of-function mutants mpk6-2 and mpk6-3 was less sensitive to NaCl or Na-glutamate, but not to KCl or mannitol, as compared with that of wild-type (WT) seedlings. The less sensitive characteristic was eliminated by adding the Ca2+ chelator EGTA or the Ca2+ channel inhibitor LaCl3, but not the Ca2+ ionophore A23187. This suggested that the tolerance of mpk6 to Na+ toxicity was Ca2+-dependent. We measured plasma membrane (PM) Na+-conducted currents (NCCs) in root cells. Increased concentrations of NaCl increased the inward NCCs while decreased the outward NCCs in WT root cells, attended by a positive shift in membrane potential. In mpk6 root cells, NaCl significantly increased outward but not inward NCCs, accompanied by a negative shift in membrane potential. That is, mpk6 decreased NaCl-induced the Na+ accumulation by modifying PM Na+ flux in root cells. Observations of aequorin luminescence revealed a NaCl-induced increase of cytosolic Ca2+ in mpk6 root cells, resulting from PM Ca2+ influx. An increase of cytosolic Ca2+ was required to alleviate the NaCl-increased Na+ content and Na+/K+ ratio in mpk6 roots. Together, these results show that mpk6 accumulated less Na+ in response to NaCl because of the increased cytosolic Ca2+ level in root cells; thus, its root elongation was less inhibited than that of WT by NaCl.

A xyloglucan-induced increase in lettuce germination and seedling elongation is not related to the degradation of the exogenous xyloglucan

Xyloglucans are the main hemicellulosic polysaccharides found in the primary cell walls of dicots and nongraminaceous monocots. Although xyloglucans are building blocks used in plant cell wall assembly, the function of these molecules in the structure and growth of the primary cell wall remains poorly understood. In this study, we demonstrate that treatment of lettuce seeds with a xyloglucan extracted from cotyledons of Hymenaea courbaril L. (Leguminosae (Fabaceae) – Caesalpinioideae) in the 0.1 to 10 nmol·L−1 range resulted in significantly increased germination percentage. In addition, lettuce seedlings grown in the presence of 500 nmol·L−1 xyloglucan presented a significantly larger length compared with seedlings grown in the absence of xyloglucan. Furthermore, the H. courbaril xyloglucan was not able to reverse a 2,4-dichlorophenoxy acetic acid induced inhibition of seedling elongation. High performance size exclusion chromatography (HPSEC) and high-performance liquid chromatography (HPLC) analyses indicated that the xyloglucan-induced enhancement of germination percentage and seedling elongation in lettuce does not rely on the release of monomers, i.e., glucose, xylose, and galactose from the exogenous xyloglucan.