Sweetpotato is a globally important food crop that plays a crucial role in food security in developing countries where it is often grown under marginal conditions. Sweetpotato yield is determined by the number of adventitious roots (ARs) that forms storage roots (SRs). Recent information indicates that sweetpotato root system architecture (RSA) is related to the competency of an AR to undergo SR formation (SRF). It has also been found that local nitrogen presence influenced sweetpotato RSA development which in turn influenced the uptake of mobile and non-mobile nutrients from the growth substrate. We considered this information in examining a LSQUOGeorgia JetRSQUO root transcriptome dataset to search for genes that are related to SRF, on one hand, and are responsive to nutrient availability, on the other. Using this approach, we found that putative nitrate (NO3-) and ammonium transporters were down-regulated in initiating SRs, while a putative potassium transporter was up-regulated. In addition, we found that a homologue of the Arabidopsis ANR1 gene, a component of the signalling pathway that links external NO3- to RSA development, shows up-regulated expression in initiating SRs. The same gene sequence exhibits homology to IbMADS1, shown previously to act as positive regulators of cell proliferation in root vascular tissue leading to SRF. Taken together, the evidence suggests that RSA provides an important link between environmental signals (nutrient availability) and gene networks previously associated with SRF in sweetpotatoes. This information can be useful for efficiently identifying gene-based markers in breeding programs, especially for low-input environments.
Exposure to higher-than-optimal temperatures reduces crop yield and quality, mainly due to sensitivity of developing pollen grains. The mechanisms maintaining high pollen quality under heat-stress conditions are poorly understood. Our recently published data indicate high heat-stress-induced expression of ethylene-responsive genes in tomato pollen, indicating ethylene involvement in the pollen heat-stress response. Here we elucidated ethylene's involvement in pollen heat-stress response and thermotolerance by assessing the effects of interfering with the ethylene signalling pathway and altering ethylene levels on tomato pollen functioning under heat stress.Plants of the ethylene-insensitive mutant Never ripe (Nr)-defective in an ethylene response sensor (ERS)-like ethylene receptor-and the corresponding wild type were exposed to control or heat-stress growing conditions, and pollen quality was determined. Starch and carbohydrates were measured in isolated pollen grains from these plants. The effect of pretreating cv. Micro-Tom tomato plants, prior to heat-stress exposure, with an ethylene releaser or inhibitor of ethylene biosynthesis on pollen quality was assessed.Never ripe pollen grains exhibited higher heat-stress sensitivity, manifested by a significant reduction in the total number of pollen grains, reduction in the number of viable pollen and elevation of the number of non-viable pollen, compared with wild-type plants. Mature Nr pollen grains accumulated only 40 % of the sucrose level accumulated by the wild type. Pretreatment of tomato plants with an ethylene releaser increased pollen quality under heat stress, with an over 5-fold increase in the number of germinating pollen grains per flower. Pretreatment with an ethylene biosynthesis inhibitor reduced the number of germinating pollen grains following heat-stress exposure over 5-fold compared with non-treated controls.Ethylene plays a significant role in tomato pollen thermotolerance. Interfering with the ethylene signalling pathway or reducing ethylene levels increased tomato pollen sensitivity to heat stress, whereas increasing ethylene levels prior to heat-stress exposure increased pollen quality.
• Premise of the study: Yield in sweetpotato is determined by the number of storage roots produced per plant. Storage roots develop from adventitious roots (ARs) present in stem cuttings that serve as propagation material. Data on the origin of sweetpotato ARs and the effect of nodal position on AR establishment and further development are limited. • Methods: We anatomically described root primordium initiation using stem sections and measured number of root primordia formed at different nodal positions using light microscopy and correlated nodal positions with AR number and length 14 d after planting (DAP). • Key results: Primordia for ARs initiate at the junction of the stem pith ray and the cambium, on both sides of the leaf gap, and they are well developed before emerging from the stem. The number of ARs that develop from isolated stem nodes 14 DAP corresponded to the number of AR primordia detected inside the stem. The total length of established roots at nodes 9–13 from the apex is about 2‐fold longer than at nodes 5–8. • Conclusions: Nodal position (age) has a significant effect on the developmental status and number of root primordia inside the stem, determining the number and length of ARs that have developed by 14 DAP. Adventitious roots originating from nodes 9–13 possess similar AR systems and develop better than those originating from younger nodes 3–8. The mechanism regulating AR initiation in nodes is discussed. This system can serve for studying the effect of environmental conditions on AR initiation, development, and capacity to form storage roots.
Exposing pepper ( Capsicum annuum ) plants to extremely high day temperatures (HDT) (day/night temperatures of 36 ± 2/10 ± 2°C), obtained by keeping the greenhouse closed during the day to exploit solar heating, prevented the development of low night temperature (LNT) symptoms. Plants of cultivars Fiesta and Selica grown under LNTs (10 ± 2°C) and moderate day temperatures (25 ± 2°C) during winter exhibited retarded growth, reduced leaf numbers, and deformed fruits with few or no seeds. LNT caused a reduction in the number and quality of pollen grains: the reduction in pollen quality was associated with reduced starch accumulation in pollen grains at 3 days before anthesis (DBA) and a decrease of more than two‐fold in total soluble sugars in the mature pollen grains. This inhibitory effect was associated with more than 50% reduction in the enzymatic activities of the cell wall‐bound and soluble acid invertases that catalyze the hydrolysis of incoming sucrose molecules. All these symptoms were prevented by HDT treatment which matched the vegetative and reproductive performance of the plants to those of plants grown under optimal night temperature (ONT) conditions (day/night temperatures of 23 ± 2/18 ± 2°C). HDT also prevented the inhibitory effect of LNT on enzymatic activities of both invertases in pollen at 5 DBA and brought about the accumulation of high levels of starch in pollen at 3 DBA. The results presented could support the development of a novel procedure for producing greenhouse crops with minimum or even with no fuel consumption for heating during the winter nights in regions with bright and sunny days.
We measured the mannose-specific adherence of radiolabeled Escherichia coli, carrying type 1 fimbriae, to monolayers of wild-type baby hamster kidney (BHK) cells and to 3 ricin-resistant mutants defective in the synthesis of complex N-linked oligosaccharide units. RicR14, a mutant accumulating N-linked oligomannose units in its glycoproteins at the expense of complex (N-acetyllactosamine) units, bound the largest number of bacteria, about 4 times more than the wild-type cells. The mutant cells in suspension were also readily agglutinated by the bacteria, while no agglutination of wild-type cells occurred under the conditions used. RicR21, a mutant which accumulates hybrid structures, bound about twice as many bacteria as wild-type cells, and was agglutinated by the bacteria to a lesser extent than RicR14. Binding and agglutination of RicR19, also presumed to accumulate hybrid structures, were the same as those of RicR14. These results provide evidence that oligomannose and hybrid units of cell surface glycoproteins serve as preferred receptors for mannose-specific E. coli. Lectin-resistant mutants are therefore useful for the investigation of sugar-specific adherence.
We measured the mannose-specific adherence of radiolabeled Escherichia coli, carrying type 1 fimbriae, to monolayers of wild-type baby hamster kidney (BHK) cells and to 3 ricin-resistant mutants defective in the synthesis of complex N-linked oligosaccharide units. RicR14, a mutant accumulating N-linked oligomannose units in its glycoproteins at the expense of complex (N-acetyllactosamine) units, bound the largest number of bacteria, about 4 times more than the wild-type cells. The mutant cells in suspension were also readily agglutinated by the bacteria, while no agglutination of wild-type cells occurred under the conditions used. RicR21, a mutant which accumulates hybrid structures, bound about twice as many bacteria as wild-type cells, and was agglutinated by the bacteria to a lesser extent than RicR14. Binding and agglutination of RicR19, also presumed to accumulate hybrid structures, were the same as those of RicR14. These results provide evidence that oligomannose and hybrid units of cell surface glycoproteins serve as preferred receptors for mannose-specific E. coli. Lectin-resistant mutants are therefore useful for the investigation of sugar-specific adherence.
Exposure to higher than optimal temperatures - heat-stress (HS) - is becoming increasingly common to all crop plants worldwide. Heat stress coinciding with microgametogenesis, especially during the post-meiotic phase that is marked by starch biosynthesis, is often associated with starch-deficient pollen and male sterility and ultimately, greatly reduced crop yields. The molecular basis for the high sensitivity of developing pollen grains, on one hand, and factors involved in pollen heat-tolerance, on the other, is poorly understood. The long-term goal of this project is to provide a better understanding of the genes that control pollen quality under heat-stress conditions. The specific objectives of this project were: (1) Determination of the threshold heat stress temperature(s) that affects tomato and sorghum pollen quality whether: a) Chronic mild heat stress conditions (CMHS), or b) Acute heat stress (AHS). (2) Isolation of heat-responsive, microgametogenesis-specific sequences. During our one-year feasibility project, we have accomplished the proposed objectives as follows: Objectrive 1: We have determined the threshold HS conditions in tomato and sorghum. This was essential for achieving the 2nd objective, since our accumulated experience (both Israeli and US labs) indicate that when temperature is raised too high above "threshold HS levels" it may cause massive death of the developing pollen grains. Above-threshold conditions have additional major disadvantages including the "noise" caused by induced expression of genes involved in cell death and masking of the differences between heatsensitive and heat-tolerant pollen grains. Two different types of HS conditions were determined: a) Season-long CMHS conditions: 32/26°C day/night temperatures confirmed in tomato and 36/26°C day maximum/night minimum temperatures in sorghum. b) Short-term AHS: In tomato, 2 hour exposure to 42-45°C (at 7 to 3 days before anthesis) followed by transfer to 28/22±2oC day/night temperatures until flower opening and pollen maturation, caused 50% reduced germinating pollen in the heat-sensitive 3017 cv.. In sorghum, 36/26°C day/night temperatures 10 to 5 days prior to panicle emergence, occurring at 35 days after sowing (DAS) in cv. DeKalb28E, produced starch-deficient and sterile pollen. Objective 2: We have established protocols for the high throughput transcriptomic approach, cDNA-AFLP, for identifying and isolating genes exhibiting differential expression in developing microspores exposed to either ambient or HS conditions and created a databank of HS-responsivemicrogametogenesis-expressed genes. A subset of differentially displayed Transcript-Derived Fragments (TDFs) that were cloned and sequenced (35 & 23 TDFs in tomato and sorghum, respectively) show close sequence similarities with metabolic genes, genes involved in regulation of carbohydrate metabolism, genes implicated in thermotolerance (heat shock proteins), genes involved in long chain fatty acids elongation, genes involved in proteolysis, in oxidation-reduction, vesicle-mediated transport, cell division and transcription factors. T-DNA-tagged Arabidopsis mutants for part of these genes were obtained to be used for their functional analysis. These studies are planned for a continuation project. Following functional analyses of these genes under HS – a valuable resource of genes, engaged in the HS-response of developing pollen grains, that could be modulated for the improvement of pollen quality under HS in both dicots and monocots and/or used to look for natural variability of such genes for selecting heat-tolerant germplasm - is expected.
This study characterized lateral root (LR) development attributes during the onset of storage root (SR) initiation stage in ‘Beauregard’ sweetpotato. SR initiation has been defined as the appearance of cambia around the protoxylem and secondary xylem elements. Our results showed that 20-day-old adventitious roots (ARs) classified as SRs had 53% and 85% greater mean LR count than pencil roots (PRs) and lignified roots (LGs), respectively. SRs had 53% and 78% greater mean LR density relative to PRs and LGs, respectively. SRs had 66% and 130% greater mean total LR length than PRs and LGs, respectively. SRs had lower mean main root (MR)/LR length ratio compared with PRs (–38%) and LGs (–60%). SRs had 70% and 134% greater mean surface area than PRs and LGs, respectively. SRs had lower mean MR/LR surface area ratio compared with PRs (–42%) and LGs (–62%). The plot of the first and second principal components revealed the presence of a gradient between extreme LG and SR clusters, suggesting a developmental transition between LGs and SRs with PRs representing an intermediate developmental stage. Although AR architecture is not the sole determinant of SR formation, our data help provide a basis for integrating AR architecture attributes with other factors that are known to influence SR initiation. Growth substrate moisture variability influenced LR development during the critical SR initiation period. Relative to the control treatments, water deprivation 10 to 20 days after transplanting (DAT) reduced mean LR count, length, and surface area by 49%, 103%, and 94%, respectively. Saturated conditions 10 to 20 DAT reduced mean LR count, length, and surface area by 75%, 81%, and 77%, respectively. These results represent the first evidence for the association between anatomical cues of SR initiation and root architecture and provide corroborating data that soil moisture variability 10 to 20 DAT directly influences SR yield potential through AR architecture modifications that are associated with diminished SR formation. This information can be used to further optimize SR yield by identifying agroclimatic and management variables that are associated with desirable LR development during the critical SR initiation stage.
Heat stress is a major cause for yield loss in many crops, including vegetable crops. Even short waves of high temperature, becoming more frequent during recent years, can be detrimental. Pollen development is most heat-sensitive, being the main cause for reduced productivity under heat-stress across a wide range of crops. The molecular mechanisms involved in pollen heat-stress response and thermotolerance are however not fully understood. Recently, we have demonstrated that ethylene, a gaseous plant hormone, plays a role in tomato (Solanum lycopersicum) pollen thermotolerance. These results were substantiated in the current work showing that increasing ethylene levels by using an ethylene-releasing substance, ethephon, prior to heat-stress exposure, increased pollen quality. A proteomic approach was undertaken, to unravel the mechanisms underlying pollen heat-stress response and ethylene-mediated pollen thermotolerance in developing pollen grains. Proteins were extracted and analyzed by means of a gel LC-MS fractionation protocol, and a total of 1355 proteins were identified. A dataset of 721 proteins, detected in three biological replicates of at least one of the applied treatments, was used for all analyses. Quantitative analysis was performed based on peptide count. The analysis revealed that heat-stress affected the developmental program of pollen, including protein homeostasis (components of the translational and degradation machinery), carbohydrate and energy metabolism. Ethephon-pretreatment shifted the heat-stressed pollen proteome closer to the proteome under non-stressful conditions, namely, by showing higher abundance of proteins involved in protein synthesis, degradation, tricarboxylic acid cycle and RNA regulation. Furthermore, up-regulation of protective mechanisms against oxidative stress was observed following ethephon-treatment (including higher abundance of glutathione-disulfide reductase, glutaredoxin and protein disulfide isomerase). Taken together, the findings identified systemic and fundamental components of pollen thermotolerance, and serve as a valuable quantitative protein database for further research.
