Plant growth acceleration using a transparent Eu3+-painted UV-to-red conversion film.

The stimulation of photosynthesis is a strategy for achieving sustainable plant production. Red light is useful for plant growth because it is absorbed by chlorophyll pigments, which initiate natural photosynthetic processes. Ultraviolet (UV)-to-red wavelength-converting materials are promising candidates for eco-friendly plant cultures that do not require electric power. In this study, transparent films equipped with a UV-to-red wavelength-converting luminophore, the Eu3+ complex, were prepared on commercially available plastic films for plant growth experiments. The present Eu3+-based films absorb UV light and exhibit strong red luminescence under sunlight. Eu3+-painted films provide significant growth acceleration with size increment and biomass production for vegetal crops and trees in a northern region. The plants cultured with Eu3+-painted films had a 1.2-fold height and 1.4-fold total body biomass than those cultures without the Eu3+ luminophores. The present film can promote the plant production in fields of agriculture and forestry.

Functional characterization and vacuolar localization of fructan exohydrolase derived from onion (Allium cepa).

Fructans such as inulin and levan accumulate in certain taxonomic groups of plants and are a reserve carbohydrate alternative to starch. Onion (Allium cepa L.) is a typical plant species that accumulates fructans, and it synthesizes inulin-type and inulin neoseries-type fructans in the bulb. Although genes for fructan biosynthesis in onion have been identified so far, no genes for fructan degradation had been found. In this study, phylogenetic analysis predicted that we isolated a putative vacuolar invertase gene (AcpVI1), but our functional analyses demonstrated that it encoded a fructan 1-exohydrolase (1-FEH) instead. Assessments of recombinant proteins and purified native protein showed that the protein had 1-FEH activity, hydrolyzing the ß-(2,1)-fructosyl linkage in inulin-type fructans. Interestingly, AcpVI1 had an amino acid sequence close to those of vacuolar invertases and fructosyltransferases, unlike all other FEHs previously found in plants. We showed that AcpVI1 was localized in the vacuole, as are onion fructosyltransferases Ac1-SST and Ac6G-FFT. These results indicate that fructan-synthesizing and -degrading enzymes are both localized in the vacuole. In contrast to previously reported FEHs, our data suggest that onion 1-FEH evolved from a vacuolar invertase and not from a cell wall invertase. This demonstrates that classic phylogenetic analysis on its own is insufficient to discriminate between invertases and FEHs, highlighting the importance of functional markers in the nearby active site residues.

Freezing resistance and behavior of winter buds and canes of wine grapes cultivated in northern Japan.

In high-latitude regions, the cold hardiness of buds and canes of grapevine is important for budburst time and yield in the next season. The freezing resistance of buds and canes sampled from six wine grapes currently cultivated in Hokkaido, Japan, all of them grown from autumn to winter, was investigated. A significant difference between the cultivars in their freezing resistance was detected in the buds harvested in winter. In addition, outstanding differences in the lower temperature exotherms (LTE) related to the supercooling ability of tissue cells happened in the winter buds, and there is a close relationship between freezing resistance and LTE detected in the winter buds. This suggests that the supercooling ability of tissue cells in winter buds is strongly related to the freezing resistance. However, detailed electron microscopy exposed that the differences in freezing resistance among cultivars appeared in freezing behavior of leaf primordium rather than apical meristem. This indicated that as the water mobility from the bud apical meristem to the spaces around the cane phloem progressed, the slightly dehydrated cells improved the supercooling ability and increased the freezing resistance.

Structural features of the aleurone layer of the seed coat associated with imbibition injury in soybean.

Soybean (Glycine max) seeds are prone to imbibition injury caused by a rapid uptake of water. Genetic variation in imbibition injury tolerance is well documented, but the underlying mechanisms remain unclear. The aim of this study was to clarify the role of the aleurone layer of seed coat in the tolerance and its structural differences between tolerant and susceptible cultivars. Imbibition injury tolerance was closely related to the water absorption rate of seeds, which was regulated by the aleurone layer of the seed coat. Cryo-scanning electron microscopy analysis revealed that water absorbed in seed coats entered the seed preferentially through the aleurone layer of the top area above the raphe. In susceptible cultivars, the cell walls of the aleurone layer facing the cotyledon in this area were thin and the surface showed shallow depression-like structures, a distinct structure different from those of the tolerant cultivars, which had aleurone cells with thick outer cell walls and smooth and stripe-like deposits. The differences in the structural features of the cell walls and surfaces of aleurone cells in the top area of the seed may be responsible for the difference in the extent of imbibition injury between susceptible and tolerant cultivars.

Visualization of soluble carbohydrate distribution in apple fruit flesh utilizing MALDI-TOF MS imaging.

To confirm availability of Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry imaging (MSI) for visualizing distribution of soluble carbohydrates in apple (Malus domestica) fruits a horizontal fruit flesh specimen was cut from a matured 'Fuji' fruit, mounted on a glass slide, lyophilized and then ion intensities of individual soluble carbohydrates were probed around the specimen using a MALDI-TOF MSI apparatus automatically. Contents of soluble carbohydrates in adjacent tissue of the same fruit were also determined using HPLC to compare the distribution of individual carbohydrate based on the ion intensities from MALDI-TOF MSI with those from HPLC. Positive correlation (P < 0.001, R2 > 0.95) was confirmed between the concentration of each standard carbohydrate and the relative ion intensity of MALDI-TOF mass spectrometry (MS), and thus it seems possible to use the ion intensity of MALDI-TOF MS for determining the relative concentration of carbohydrates in a sample. Singly charged ions attached with a potassium ion only were detected from the apple fruit specimen when DHB was used as a matrix for MALDI-TOF MSI. Graded increase of sucrose content from center to cortex side of the fruit flesh was confirmed by both MALDI-TOF MSI and HPLC. When pseudo color images on the distribution of individual carbohydrates based on the results from MALDI-TOF MSI were compared with the content of carbohydrates in the adjacent 16 tissue blocks quantified using HPLC, strong (P < 0.001, R2 = 0.6222) and weak (P < 0.10, R2 = 0.2123) correlation was confirmed between the brightness and the content of sucrose and sorbitol, respectively. These facts indicate that distribution of sucrose and sorbitol in apple fruit tissue can be visualized using MALDI-TOF MSI. Thus, MALDI-TOF MSI will be useful for examining carbohydrate metabolism during the maturing of apple fruit.

A Single-Nucleotide Polymorphism in an Endo-1,4-ß-Glucanase Gene Controls Seed Coat Permeability in Soybean.

Physical dormancy, a structural feature of the seed coat known as hard seededness, is an important characteristic for adaptation of plants against unstable and unpredictable environments. To dissect the molecular basis of qHS1, a quantitative trait locus for hard seededness in soybean (Glycine max (L) Merr.), we developed a near-isogenic line (NIL) of a permeable (soft-seeded) cultivar, Tachinagaha, containing a hard-seed allele from wild soybean (G. soja) introduced by successive backcrossings. The hard-seed allele made the seed coat of Tachinagaha more rigid by increasing the amount of ß-1,4-glucans in the outer layer of palisade cells of the seed coat on the dorsal side of seeds, known to be a point of entrance of water. Fine-mapping and subsequent expression and sequencing analyses revealed that qHS1 encodes an endo-1,4-ß-glucanase. A single-nucleotide polymorphism (SNP) introduced an amino acid substitution in a substrate-binding cleft of the enzyme, possibly reducing or eliminating its affinity for substrates in permeable cultivars. Introduction of the genomic region of qHS1 from the impermeable (hard-seeded) NIL into the permeable cultivar Kariyutaka resulted in accumulation of ß-1,4-glucan in the outer layer of palisade cells and production of hard seeds. The SNP allele found in the NIL was further associated with the occurrence of hard seeds in soybean cultivars of various origins. The findings of this and previous studies may indicate that qHS1 is involved in the accumulation of ß-1,4-glucan derivatives such as xyloglucan and/or ß-(1,3)(1,4)-glucan that reinforce the impermeability of seed coats in soybean.

Roles of the plasma membrane and the cell wall in the responses of plant cells to freezing.

In an effort to clarify the responses of a wide range of plant cells to freezing, we examined the responses to freezing of the cells of chilling-sensitive and chilling-resistant tropical and subtropical plants. Among the cells of the plants that we examined, those of African violet ( Saintpaulia grotei Engl.) leaves were most chilling-sensitive, those of hypocotyls in mungbean [ Vigna radiata (L.) R. Wilcz.] seedlings were moderately chilling-sensitive, and those of orchid [ Paphiopedilum insigne (Wallich ex Lindl.) Pfitz.] leaves were chilling-resistant, when all were chilled at -2 degrees C. By contrast, all these plant cells were freezing-sensitive and suffered extensive damage when they were frozen at -2 degrees C. Cryo-scanning electron microscopy (Cryo-SEM) confirmed that, upon chilling at -2 degrees C, both chilling-sensitive and chilling-resistant plant cells were supercooled. Upon freezing at -2 degrees C, by contrast, intracellular freezing occurred in Saintpaulia leaf cells, frost plasmolysis followed by intracellular freezing occurred in mungbean seedling cells, and extracellular freezing (cytorrhysis) occurred in orchid leaf cells. We postulate that chilling-related destabilization of membranes might result in the loss of the ability of the plasma membrane to act as a barrier against the propagation of extracellular ice in chilling-sensitive plant cells. We also examined the role of cell walls in the response to freezing using cells in which the plasma membrane had been disrupted by repeated freezing and thawing. In chilling-sensitive Saintpaulia and mungbean cells, the cells with a disrupted plasma membrane responded to freezing at -2 degrees C by intracellular freezing. By contrast, in chilling-resistant orchid cells, as well as in other cells of chilling-resistant and freezing-resistant plant tissues, including leaves of orchard grass ( Dactylis glomerata L.), leaves of Arabidopsis thaliana (L.) Heynh. and cortical tissues of mulberry ( Morus bombycis Koids.), cells with a disrupted plasma membrane responded to freezing by extracellular freezing. Our results indicate that, in the chilling-sensitive plants cells that we examined, not only the plasma membrane but also the cell wall lacked the ability to serve as a barrier against the propagation of extracellular ice, whereas in the chilling-resistant plant cells that we examined, not only the plasma membrane but also the cell wall acted as a barrier against the propagation of extracellular ice. It appears, therefore, that not only the plasma membrane but also the cell wall greatly influences the freezing behavior of plant cells.