Effects of combined extreme cold and drought stress on growth, photosynthesis, and physiological characteristics of cool-season grasses.

Abiotic stress is an important factor affecting turf establishment and limiting the sustainability of the turf industry. To alleviate the effects of combined cold and drought stress in cold- and drought-prone regions, it is essential to select and introduce turfgrass germplasms that are suitable for these conditions for successful turf establishment. Thus, we evaluated the effects of combined extreme cold and drought stress on the morphological, plant leaf functional, photosynthetic, and physiological and biochemical traits of 16 wild annual bluegrass (Poa annua) germplasms. We found that there were significant differences (P < 0.05) among different provenances, combined cold and drought stress, and the main interaction factors. Combined cold and drought stress altered the morphological characteristics of the 16 germplasms to varying degrees. Furthermore, combined cold and drought stress significantly reduced the net photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), instantaneous water use efficiency (WUE), chlorophyll content, chlorophyll fluorescence parameters, accumulated intercellular CO2 concentration (Ci), and relative electrical conductivity (REC) and malondialdehyde (MDA), proline (Pro), soluble protein (SP), soluble sugar (SS), superoxide anion (O2.-), hydrogen peroxide (H2O2), and hydroxyl radical (·OH) and other active oxygen, and increased the superoxide dismutase activity (SOD), peroxidase activity (POD), catalase activity (CAT), ascorbate peroxidase activity (APX) and glutathione reductase (GR) activities. Comprehensive evaluation using principal component analysis (PCA), membership function analysis, and clustered heatmaps indicated that the 'HZ' germplasm had stronger combined cold and drought tolerance, whereas the 'ZQ' germplasm was more sensitive to combined cold and drought, which was roughly consistent with the order of morphological damage symptoms. Therefore, it is recommended to use the 'HZ' germplasm for planting projects in cold- and drought-prone areas, while the 'ZQ' germplasm is more suitable for use under warmer and non-water-deficient conditions.

Cytokinin and Metabolites Affect Rhizome Growth and Development in Kentucky Bluegrass (Poa pratensis).

Rhizome growth and development is regulated by phytohormone. However, endogenous phytohormones affect rhizome initiation, and sustained growth in perennial grass species remains elusive. In this study, we investigated the morphological characteristics and the content of indole-3-acetic acid (IAA), zeatin (ZT), gibberellic acid (GA3), and abscisic acid (ABA) in the rhizomes of two different Kentucky bluegrass. Using ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS), we performed metabolite analysis of two different rhizomes. In our study, the multi-rhizome Kentucky bluegrass material 'Yuzhong' had an average of 1113 rhizomes, while the few-rhizome material 'Anding' had an average of 347 rhizomes. The diameter of rhizome and length of rhizome internode in 'Yuzhong' were 1.68-fold and 1.33-fold higher than that of the 'Anding', respectively. The rhizome dry weight of 'Yuzhong' was 75.06 g, while the 'Anding' was 20.79 g. 'Yuzhong' had a higher ZT content (5.50 µg·g-1), which is 2.4-fold that of 'Anding' (2.27 µg·g-1). In contrast, the IAA, ABA, and GA3 content of rhizome were markedly higher in 'Anding' than 'Yuzhong'. Correlation analysis revealed significant correlations between ZT and ZT/ABA with the number of rhizomes, diameter of rhizome, and length of rhizome internode, whereas IAA, ABA, GA3, and IAA/ZT were opposite. In the metabolic profiles, we identified 163 differentially expressed metabolites (DEMs) (60 upregulated and 103 downregulated) in positive ion mode and 75 DEMs (36 upregulated and 39 downregulated) in negative ion mode. Histidine metabolism and ABC transporters pathways were the most significantly enriched in the positive and negative ion mode, respectively, both of which are involved in the synthesis and transport of cytokinin. These results indicate that cytokinin is crucial for rhizome development and promotes rhizome germination and growth of Kentucky bluegrass.

Carbon and nitrogen metabolism affects kentucky bluegrass rhizome expansion.

BACKGROUND: Rhizome is vital for carbon and nitrogen metabolism of the whole plant. However, the effect of carbon and nitrogen in the rhizome on rhizome expansion remains unclear. RESULTS: Three wild Kentucky bluegrass (Poa pratensis L.) germplasms with different rhizome expansion capacity (strong expansion capacity, 'YZ'; medium expansion capacity, 'WY'; and weak expansion capacity, 'AD') were planted in the field and the rhizomes number, tiller number, rhizome dry weight, physiological indicators and enzyme activity associated carbon and nitrogen metabolisms were measured. Liquid chromatography coupled to mass spectrometry (LC-MS) was utilized to analyze the metabolomic of the rhizomes. The results showed that the rhizome and tiller numbers of the YZ were 3.26 and 2.69-fold of that of the AD, respectively. The aboveground dry weight of the YZ was the greatest among all three germplasms. Contents of soluble sugar, starch, sucrose, NO3--N, and free amino acid were significantly higher in rhizomes of the YZ than those of the WY and AD (P < 0.05). The activities of glutamine synthetase (GS), glutamate dehydrogenase (GDH) and sucrose phosphate synthase (SPS) of the YZ were the highest among all three germplasm, with values of 17.73 A·g- 1 h- 1, 5.96 µmol·g- 1 min- 1, and 11.35 mg·g- 1 h- 1, respectively. Metabolomics analyses revealed that a total of 28 differentially expressed metabolites (DEMs) were up-regulated, and 25 DEMs were down-regulated in both comparison groups (AD vs. YZ group and WY vs. YZ group). Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis demonstrated that metabolites related to histidine metabolism, tyrosine metabolism, tryptophan metabolism, and phenylalanine metabolism were associated with rhizomes carbon and nitrogen metabolism. CONCLUSIONS: Overall, the results suggest that soluble sugar, starch, sucrose, NO3--N, and free amino acid in rhizome are important to and promote rhizome expansion in Kentucky bluegrass, while tryptamine, 3-methylhistidine, 3-indoleacetonitrile, indole, and histamine may be key metabolites in promoting carbon and nitrogen metabolism of rhizome.