Thermo Condition Determines the Uptake of Autumn and Winter Applied Nitrogen and Subsequent Utilization in Spring Tea (Camellia sinensis L.)

The effect of thermal condition on the uptake of autumn and winter applied N and its subsequent utilization in spring tea (Camellia sinensis) was investigated by applying 15N enriched urea as single or split applications between October and February in two commercial plantations at Xingyang of Henan province and Yongchuan of Chongqing with different thermal conditions. The proportion of N derived from 15N-labeled urea (Ndff%) in fibrous root and mature leaves 15 days after application at Xingyang and the Ndff% of mature leaves on the day of the first spring tea harvest at both sites were the highest in the single October application. The Ndff% of the following spring tea was also the highest in the single October application at both sites. The results showed that application of N fertilizer in October relative to other later months most significantly improves the accumulation of plant N reserves and consequently contributes more significantly to the early spring tea. Such timing effect was related to the thermal condition, i.e., the growing degree days (°C•d, T > 8 °C) between the dates of fertilization and harvest of young shoots, which represents the combining effect of the temperature and the residence time of N fertilizer in the soil.

Genome-Wide Identification and Expression Analysis of the MADS-Box Gene Family in Sweet Potato [Ipomoea batatas (L.) Lam]

MADS-box gene, one of the largest transcription factor families in plants, is a class of transcription factors widely present in eukaryotes. It plays an important role in plant growth and development and participates in the growth and development of flowers and fruits. Sweet potato is the seventh most important food crop in the world. Its tuberous roots, stems, and leaves contain a large number of proteins, lipids, carotenoids, anthocyanins, conjugated phenolic acids, and minerals, which have high edible, forage, and medicinal value, and is also an important energy crop. At present, MADS-box genes in sweet potato have rarely been reported, and there has been no study on the genome-wide identification and classification of MADS-box genes in Ipomoea batatas. This study provided the first comprehensive analysis of sweet potato MADS-box genes. We identified 95 MADS-box genes, analyzed the structure and protein of sweet potato MADS-box genes, and categorized them based on phylogenetic analysis with Arabidopsis MADS-box proteins. Chromosomal localization indicated an unequal number of MADS-box genes in all 14 chromosomes except LG3, with more than 10 MADS-box genes located on chromosomes LG7, LG11, and LG15. The MADS domain and core motifs of the sweet potato MADS-box genes were identified by motif analysis. We identified 19 MADS-box genes with collinear relationships and analyzed duplication events. Cis-acting elements, such as light-responsive, auxin-responsive, drought-inducible, and MeJA-responsive elements, were found in the promoter region of the MADS-box genes in sweet potato, which further indicates the basis of MADS-box gene regulation in response to environmental changes and hormones. RNA-seq suggested that sweet potato MADS-box genes exhibit tissue-specific expression patterns, with 34 genes highly expressed in sweet potato flowers and fruits, and 19 genes highly expressed in the tuberous root, pencil root, or fibrous root. qRT-PCR again validated the expression levels of the 10 genes and found that IbMADS1, IbMADS18, IbMADS19, IbMADS79, and IbMADS90 were highly expressed in the tuberous root or fibrous root, and IbMADS18, IbMADS31, and IbMADS83 were highly expressed in the fruit. In this study, the molecular basis of MADS-box genes of sweet potato was analyzed from various angles. The effects of MADS-box genes on the growth and development of sweet potato were investigated, which may provide a certain theoretical basis for molecular breeding of sweet potato.

Enriched CO2 and Root-Associated Fungi (Mycorrhizae) Yield Inverse Effects on Plant Mass and Root Morphology in Six Asclepias Species

While milkweeds (Asclepias spp.) are important for sustaining biodiversity in marginal ecosystems, CO2 flux may afflict Asclepias species and cause detriment to native communities. Negative CO2-induced effects may be mitigated through mycorrhizal associations. In this study, we sought to determine how mycorrhizae interacts with CO2 to influence Asclepias biomass and root morphology. A broad range of Asclepias species (n = 6) were chosen for this study, including four tap-root species (A. sullivantii, A. syriaca, A. tuberosa, and A. viridis) and two fibrous root species (A. incarnata and A. verticillata). Collectively, the six Asclepias species were manipulated under a 2 × 2 full-factorial design that featured two mycorrhizal levels (−/+ mycorrhizae) and two CO2 levels (ambient and enriched (i.e., 3.5× ambient)). After a duration of 10 months, Asclepias responses were assessed as whole dry weight (i.e., biomass) and relative transportive root. Relative transportive root is the percent difference in the diameter of highest order root (transportive root) versus that of first-order absorptive roots. Results revealed an asymmetrical response, as mycorrhizae increased Asclepias biomass by ~12-fold, while enriched CO2 decreased biomass by about 25%. CO2 did not impact relative transportive roots, but mycorrhizae increased root organ’s response by more than 20%. Interactions with CO2 and mycorrhizae were observed for both biomass and root morphology (i.e., relative transportive root). A gene associated with CO2 fixation (rbcL) revealed that the two fibrous root species formed a phylogenetic clade that was distant from the four tap-root species. The effect of mycorrhizae was most profound in tap-root systems, as mycorrhizae modified the highest order root into tuber-like structures. A strong positive correlation was observed with biomass and relative transportive root. This study elucidates the interplay with roots, mycorrhizae, and CO2, while providing a potential pathway for mycorrhizae to ameliorate CO2 induced effects.

Impact of salicylic acid and biosilica application on plant growth of shallot under water deficit

Shallot is a horticulture crop with a fibrous root system, which is susceptible to water deficit, particularly in the bulb formation stage. This study was carried out to examine the effects of salicylic acid (SA) and biosilica (Si) exogenous induction on plant growth of shallot grown under water deficit in plastic baskets. A factorial 4×2 experiment was laid out in a randomized complete block design with four blocks. The first factor of treatments was a four-level exogenous induction, i.e., 0.5mM SA, 6mM Si, combination (0.5mM SA and 6mM Si), and control (0 without SA and Si). The second factor was a level of interval irrigations i.e, one-day interval and three-day interval. The results showed that the treatment of combination 0.5mM SA and 6mM Si can maintained a plant height and the number of leaves was better than the control under water deficit. Avoidance was one of the mechanisms of shallot in dealing with water deficit, namely by reducing the stomatal density. Decreased stomatal density was negatively correlated with water use efficiency.

Root Characteristics and Water Erosion-Reducing Ability of Alpine Silver Grass and Yushan Cane for Alpine Grassland Soil Conservation

In Taiwan, intensive forest fires frequently cause serious forest degradation, soil erosion and impacts on alpine vegetation. Post-fire succession often induces the substitution of forest by alpine grassland. Alpine silver grass (Miscanthus transmorrisonensis Hay.) and Yushan cane (Yushania niitakayamensis (Hay.) Keng f.) are two main endemic species emerging on post-fire alpine grassland. These species play a major role in the recovery of alpine vegetation and soil conservation of alpine grassland. However, their root traits, root mechanical properties and water erosion-reducing ability have still not been well studied. In the present study, root characteristics were examined using a complete excavation method. Root mechanical characteristics were estimated by utilizing the uprooting test and root tensile test, and hydraulic flume experiments were performed to investigate the water erosion-reducing ability using 8-month-old plants. The results show that the root architecture system of Alpine silver grass belongs to fibrous root system, while the Yushan cane has sympodial-tufted rhizomes with a fibrous root system. Root characteristics reveal that relative to Alpine silver grass, Yushan cane has remarkably larger root collar diameter, higher root biomass, larger root volume, higher root density, and a higher root tissue density. Furthermore, uprooting resistance of Yushan cane is notably higher than that of Alpine silver grass. However, the root tensile strength of Alpine silver grass is significantly higher than that of Yushan cane. Additionally, hydraulic flume experiments reveal that Yushan cane has significantly lower soil detachment rates than that of Alpine silver grass. Collectively, these findings clearly show that Yushan cane has superior root characteristics and water erosion-reducing ability than Alpine silver grass and is thus more suitable for the conservation of alpine grassland.

Medicago truncatula response to water-deficit stress: whole plant perspectives

Medicago truncatula is a forage legume with agricultural but also scientifical interest, being used as a model plant for the study of legumes’ biology. Within a climate change context, it is of great importance to maintain/increase plant yield in stressful growth conditions to meet the requirements of the increasing world population. In order to achieve this, it is mandatory to further understand the adaptive response of plants to water-deficit stress, for which the use of this model plant results of great utility. In the present study, the simultaneous study of various plant organs with particular focus on the root system allows us a more integrative understanding of water-deficit response mechanisms from a whole-plant perspective. The root tissue was studied in Chapter 1, distinguishing between the thick taproot and the much thinner fibrous root. The different behaviour of both root types under well-watered as well as under water-deficit conditions was studied from a physiological and metabolic perspec-tive. This study highlighted the active role of the taproot rather than being considered a mere nutrient storage organ. The taproot showed a more resilient nature towards water-deficit stress than the fibrous root, while sucrose cleavage modulation, together with proline metabolism sug-gested a crucial role of these pathways in the root adaptation to water-deficit stress. In Chapter 2 we aimed to address different water-deficit conditions that can affect plant water status, using iso-osmotical conditions of salinity (NaCl and KCl), lack of irrigation and an osmoticum (PEG). This approach allows us to identify the similarities and differences in the mechanisms involved in the response to each stress at the whole-plant level. While PEG was dismissed as a reliable drought-stress mimicker, NaCl and KCl led to similar responses, with a slightly higher negative effect of KCl on plant metabolism. On the other hand, an emphasis on the shoot and root protection was observed for NaCl and no-irrigation stress, respectively. The study of the phloem sap allowed us to better understand the responses to the different water-deficit conditions at a whole-plant level. In summary, this study provides further insight into the response at the whole-plant level of M. truncatula to water-deficit conditions from a biochemical, metabolic and physiological point of view.

MYCOLOGICAL ASSESSMENT OF WINTER WHEAT FROM AREAS OF THE RE-PUBLIC OF TATARSTAN

Mycological analysis showed that fungi of the genus Fusarium – 33 %, Penicillium – 17 %, Aspergillus – 10 %, Alternaria – 13 %, Trichoderma – 11 %, Mucor – 12 %, yeast fungi – 6 % were most distinguished. The importance in the symbiotic habitat of filamentous fungi depends on the presence of pH, salts, and mineral fertilizers in the soil. In the Vekhneuslonskiy district, loamy soil predominates, the sprouts of winter wheat growing along the roads were distinguished by a weak root system and single seedlings (soil pH – 7,15±0,7). In the Kaibitskiy Buinskiy districts (in the chernozem soil) – wheat germs were strong, the fibrous root system was strengthened, the pH of the soil in the Kaibitskiy region was 6,35±0,4, in Buinskiy – 6,63±0,8. In mycological analysis, the highest indicator of the total number of fungi (TPG) was recorded in the Verkhneuslonsky region – 19,6х103±0,12 to 25,1х103±0,11, mainly fungi of the genus Fusarium were isolated. In the Kaibitsky district, the HPG was: (12,8х103±0,14 to 20,1х103±0,08) fungi of the genus Aspergillus, Fusarium were isolated. In the Buinsky district, the TPG was: (11,4х103±0,14 to 22,2х103±0,10), the fungi Rhizopus spp, Trichoderma spp. Fusarium. There was a correlation between the indicators of TPG and pH: the more acidic the environment, the less TPG. The growth and development of moldy fungi is not affected by the content of nitrates in the soil, so the content of nitrates in soil samples from the Verkhneuslonsky district was 2,8±0,006, Kaibitsky – 3,2±0,011 to 5,60±0,018, Buinsky 3,10±0,010 to 3,2±0,012.

EMS Derived Wheat Mutant BIG8-1 (Triticum aestivum L.)—A New Drought Tolerant Mutant Wheat Line

Drought response in wheat is considered a highly complex process, since it is a multigenic trait; nevertheless, breeding programs are continuously searching for new wheat varieties with characteristics for drought tolerance. In a previous study, we demonstrated the effectiveness of a mutant known as RYNO3936 that could survive 14 days without water. In this study, we reveal another mutant known as BIG8-1 that can endure severe water deficit stress (21 days without water) with superior drought response characteristics. Phenotypically, the mutant plants had broader leaves, including a densely packed fibrous root architecture that was not visible in the WT parent plants. During mild (day 7) drought stress, the mutant could maintain its relative water content, chlorophyll content, maximum quantum yield of PSII (Fv/Fm) and stomatal conductance, with no phenotypic symptoms such as wilting or senescence despite a decrease in soil moisture content. It was only during moderate (day 14) and severe (day 21) water deficit stress that a decline in those variables was evident. Furthermore, the mutant plants also displayed a unique preservation of metabolic activity, which was confirmed by assessing the accumulation of free amino acids and increase of antioxidative enzymes (peroxidases and glutathione S-transferase). Proteome reshuffling was also observed, allowing slow degradation of essential proteins such as RuBisCO during water deficit stress. The LC-MS/MS data revealed a high abundance of proteins involved in energy and photosynthesis under well-watered conditions, particularly Serpin-Z2A and Z2B, SGT1 and Calnexin-like protein. However, after 21 days of water stress, the mutants expressed ABC transporter permeases and xylanase inhibitor protein, which are involved in the transport of amino acids and protecting cells, respectively. This study characterizes a new mutant BIG8-1 with drought-tolerant characteristics suited for breeding programs.

Medicago sativa and Medicago truncatula Show Contrasting Root Metabolic Responses to Drought

Drought is an environmental stressor that affects crop yield worldwide. Understanding plant physiological responses to stress conditions is needed to secure food in future climate conditions. In this study, we applied a combination of plant physiology and metabolomic techniques to understand plant responses to progressive water deficit focusing on the root system. We chose two legume plants with contrasting tolerance to drought, the widely cultivated alfalfa Medicago sativa (Ms) and the model legume Medicago truncatula (Mt) for comparative analysis. Ms taproot (tapR) and Mt fibrous root (fibR) biomass increased during drought, while a progressive decline in water content was observed in both species. Metabolomic analysis allowed the identification of key metabolites in the different tissues tested. Under drought, carbohydrates, abscisic acid, and proline predominantly accumulated in leaves and tapRs, whereas flavonoids increased in fibRs in both species. Raffinose-family related metabolites accumulated during drought. Along with an accumulation of root sucrose in plants subjected to drought, both species showed a decrease in sucrose synthase (SUS) activity related to a reduction in the transcript level of SUS1, the main SUS gene. This study highlights the relevance of root carbon metabolism during drought conditions and provides evidence on the specific accumulation of metabolites throughout the root system.

Agave sisalana (sisal hemp).

Tropical succulent perennial of 1.5-2 m height, with thick leaves in a basal rosette of elongated sword-shaped leaves from the base. Stems: Two to three years after transplanting, a 20 cm tall stem is formed, which will reach a height of about 1.2 m when flowering. White, fleshy stems develop from underground buds at the base of the plant, first growing sideways and then upwards to form new plants. These new plants are known as suckers (DAFF, 2015). Trunk: The plant base is a short trunk (30-150 cm), from the top of which the spirally arranged leaves grow (DAFF, 2015). The components of the dry weight of sisal fibre are approximately 55-65% α-cellulose, 11-18% hemicelluloses, 7-15% lignin, 1% pectin and 1-8% ash (Elzebroek and Wind, 2008). Leaves: Stiff, heavy, persistent leaves that are 0.6-1.2 m long, 10.2-20.3 cm wide, and 2.5-10.2 cm thick when mature. Leaves are spirally arranged around the trunk, greyish-green in colour and covered by a layer of wax. Leaves contain coarse, cream-coloured or pale-yellow fibres (3%) (DAFF, 2015). Young leaves may have small spines along their margins; they disappear when the plant matures. Leaves have a terminal, dark brown, rigid, very sharp spine, 2-3 cm long. The cross-section at the base of the leaf resembles a flattened triangle (Elzebroek and Wind, 2008). Inflorescences: A large panicle with flowers arranged on the terminal portion in dense clusters, sessile, 4-5 cm long. Perianths with 6 segments, 6 stamens, filaments longer than the perianth segment, 3-4 cm long anthers. Style exserted, stigma 3-lobed (EOL, 2018). It only flowers once at around 2 years. Before flowering, a flower stalk of 4.5-6.0 m develops from the growth point. The flower stalk subdivides to form branches that bear the flowers. The flowers do not produce seed, but form bulbils, which are used for reproduction. Bulbils are borne in the axils of the bracteoles of the inflorescence after flowering. Flowers are yellowish green, with reddish filaments. Roots: A. sisalana has a shallow, fibrous root system up to 60 cm deep. The 2-4 mm thick root arises from leaf scars at the base of the bole beneath the soil surface, and extends up to 5 m horizontally way from the mother plant, forming suckers. These can be used for propagation (DAFF, 2015). Sisal produces subterraneous rhizomes from buds in the axils of the lower leaves. Along the rhizomes there are buds that may grow into new plants, forming colonies. Most of the roots are concentrated in the upper 40 cm of the soil, where they spread horizontally up to 5 m. A number of roots grow deeper than 40 cm, which results in good anchorage (Elzebroek and Wind, 2008). Fruit: This species is monocarpic (i.e., dies after fruiting). Fruits are capsules up to 6 cm long, 2-2.5 cm diameter, stipitate and beaked. Capsules rarely formed, and seeds (if any) are probably not viable. Vegetative bulbils are commonly produced below the flowers in the axils of bracts (Weber, 2003; Acevedo-Rodriguez and Strong, 2005).