Identification of Sorbitol Transporters Expressed in the Phloem of Apple Source Leaves

Sorbitol is a major photosynthetic product and a major phloem-translocated component in Rosaceae (e.g. apple, pear, peach, and cherry). We isolated the three cDNAs, MdSOT3, MdSOT4, and MdSOT5 from apple (Malus domestica) source leaves, which are homologous to plant polyol transporters. Yeasts transformed with the MdSOTs took up sorbitol significantly. MdSOT3- and MdSOT5-dependent sorbitol uptake was strongly inhibited by xylitol and myo-inositol, but not or only weakly by mannitol and dulcitol. Apparent Km values of MdSOT3 and MdSOT5 for sorbitol were estimated to be 0.71mM and 3.2mM, respectively. The protonophore, carbonyl cyanide m-chlorophenylhydrazone (CCCP), strongly inhibited the sorbitol transport. MdSOT3 was expressed specifically in source leaves, whereas MdSOT4 and MdSOT5 were expressed in source leaves and also in some sink organs. MdSOT4 and MdSOT5 expressions were highest in flowers. Fruits showed no or only weak MdSOT expression. Although MdSOT4 and MdSOT5 were also expressed in immature leaves, MdSOT expressions increased with leaf maturation. In addition, in situ hybridization revealed that all MdSOTs were expressed to high levels in phloem of minor veins in source leaves. These results suggest that these MdSOTs are involved in sorbitol loading in Rosacea

α-Tomatine gradient across artificial roots recreates the recruitment of tomato root-associated Sphingobium

α-Tomatine is a major saponin that accumulates in tomatoes (Solanum lycopersicum). We previously reported that α-tomatine secreted from tomato roots modulates root-associated bacterial communities, particularly by enriching the abundance of Sphingobium belonging to the family Sphingomonadaceae. To further characterize the α-tomatine-mediated interactions between tomato plants and soil bacterial microbiota, we first cultivated tomato plants in pots containing different microbial inoculants originating from three field soils. Four bacterial genera, namely, Sphingobium, Bradyrhizobium, Cupriavidus, and Rhizobacter, were found to be commonly enriched in tomato root-associated bacterial communities. We constructed a pseudo-rhizosphere system using a mullite ceramic tube as an artificial root to investigate the influence of α-tomatine in modifying bacterial communities. The addition of α-tomatine from the artificial root resulted in the formation of a concentration gradient of α-tomatine that mimicked the tomato rhizosphere, and distinctive bacterial communities were observed in the soil close to the artificial root. Sphingobium was enriched according to the α-tomatine concentration gradient, whereas Bradyrhizobium, Cupriavidus, and Rhizobacter were not enriched in α-tomatine-treated soil. The tomato root-associated bacterial communities were similar to the soil bacterial communities in the vicinity of artificial root-secreting exudates; however, hierarchical cluster analysis revealed a distinction between root-associated and pseudo-rhizosphere bacterial communities. These results suggest that the pseudo-rhizosphere device at least partially creates a rhizosphere environment in which α-tomatine enhances the abundance of Sphingobium in the vicinity of the root. Enrichment of Sphingobium in the tomato rhizosphere was also apparent in publicly available microbiota data, further supporting the tight association between tomato roots and Sphingobium mediated by α-tomatine

Comparison of effect of salt stress on the cell death in seminal root and lateral root of rye seedlings by the modified TUNEL method

Abstract: Cell death in the lateral root tip of rye seedlings under salt stress conditions was analyzed quantitatively by the modified terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) method and the frequency of cell death was compared in the seminal root tip. There were no significant differences in total root length and the number of root tips among control, 10 mM and 100 mM NaCl treatments, although the root elongation and initiation was inhibited in the 250 mM NaCl treatment. The frequency of cell death was increased in 100 mM and 250 mM NaCl treatments compared with the control, significantly. There was no significant difference in the frequency of cell death between seminal root and lateral root in all stress treatments. Moreover, technical advantage of the modified TUNEL method was discussed by comparing with the classical TUNEL method

Quantitative Analysis of Cell Division and Cell Death in Seminal Root of Rye under Salt Stress

Cell division and cell death in the cell division zone of the roots of rye seedlings under salt stress were analyzed quantitatively. Cell division was examined by immunological staining with anti-5-bromo-2'-deoxyuridine (BrdU) and cell death by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL). In the 0-700 µm portion from the root tip, which is the cell division zone, the frequency of cell division increased linearly during BrdU treatment. Therefore, the frequency of cell division under salt stress was compared with that in the control at 7 hours after application of BrdU. In the 250 mM NaCl solution (salt stress), the frequency of cell division was decreased and that of cell death was increased as compared with the control resulting in the inhibition of root elongation. In the presence of 50 and 100 mM NaCl, the frequency of cell division was also significantly increased and cell death was hardly detected, and root growth was unchanged as compared with the control. These results suggested that the increase of cell division complemented the decrease of cell elongation due to salt stress, and consequently maintained root growth under mild salt stress conditions

Expression of α-Amylase Isoforms and the RAmylA Gene in Rice (Oryza sativa L.) during Seed Germination, and its Relationship with Coleoptile Length in Submerged Soil

A significant difference in the seed germinability was observed between the two rice cultivars, ‘Nipponbare’ and ‘Suweon 287’, under anoxia (i.e., during germination in submerged soil at 18°C), although little difference was seen under aerobic (in air) or hypoxic (in water) conditions. The number of α-amylase isoforms synthesized in germinating seeds was inversely proportional to the O2 concentrations at the early germination stage. The formation of isoform B was promoted by oxygen supply, while isoform H was undetectable if the seeds were unable to germinate. The activity of isoform H was highly correlated with the coleoptile length in the submerged soil at 18°C, indicating that isoform H is a critical factor for seed germination under anoxia. The expression of the rice α-amylase RAmylA gene was repressed when the seeds germinated under hypoxia or anoxia. The interactions between oxygen stress, gibberel-lin, and carbon metabolites on the expression of α-amylase in rice are discussed

Sucrose Metabolism for the Development of Seminal Root in Maize Seedlings

The objective of this study was to elucidate the roles of sugar in the formation of root systems. Several parts of theseminal root were investigated to determine their sucrose, glucose and fructose contents, and the activity and the in situ localization of the activities of two kinds of metabolic enzymes, invertase and sucrose synthase, whichhydrolyze sucrose. The sucrose, glucose and fructose concentrations in the 0-1 cm section from the root apex were three to five times those in the other sections. The invertase and sucrose synthase activities were also higher in the apical section. The in situ localization of invertase activity was detected in the cell elongation zone of the seminal root using histochemical method. The sucrose synthase activity was detected in the cell elongation zone of the seminal root and the root apices of lateral roots. These results suggested that sucrose is transported to the root elongation zone and the surrounding tissue of the lateral root primordia, and is cleaved into glucose, fructose, and UDP-glucose by invertase or sucrose synthase. This suggested that sucrose contributes to root formation by serving as the energy source, the carbon source for cell wall synthesis, and as a compatible solute for cell elongation

Osmotic Stress Leads to Significant Changes in Rice Root Metabolic Profiles between Tolerant and Sensitive Genotypes

To breed osmotic stress-tolerant rice, the mechanisms involved in maintaining root growth under osmotic stress is important to elucidate. In this study, two rice (Oryza sativa L.) cultivars, IR 58 (stress-tolerant cultivar) and Basilanon (stress-sensitive cultivar), were used. After 1, 3, and 7 days of −0.42 MPa osmotic stress treatment induced by polyethylene glycol (PEG) 6000, root metabolomes were analyzed, yielding 276 detected compounds. Among 276 metabolites, 102 metabolites increased with the duration of the stress treatment in IR 58 roots, and only nine metabolites decreased. In contrast, 51 metabolites increased, and 45 metabolites decreased in Basilanon roots. Principal component analysis (PCA) scores clearly indicated differences between the cultivars and the treatments. Pathway analysis showed that the metabolites exhibiting stress-induced increases in IR 58 were those involved in sugar metabolism (such as sucrose 6’-phosphate, glucose 1-phosphate), polyamine and phenylpropanoid metabolisms (such as spermine, spermidine, gamma-aminobutyric acid (GABA)), and glutathione metabolism (such as glutathione, cysteine, cadaverine). IR 58 roots showed an increase in the most proteinogenic amino acids such as proline, serine, glutamine and asparagine. It was also maintained or increased the tricarboxylic acid (TCA) cycle intermediates (citric acid, cis-Aconitic acid, isocitric acid, fumaric acid, malic acid) under osmotic stress compared with that under control. Therefore, IR 58 actively synthesized various metabolites, and the increase in these metabolites contributed to the maintenance of important biological functions such as energy production and antioxidant defense to promote root development under osmotic stress