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Erick Amombo, Huiying Li, and Jinmin Fu

Soil salinity is one of the major abiotic stress factors that constrain plant growth and limit crop productivity. About a quarter of the global land area is affected by salinity; therefore, there is increased need to develop salt-tolerant crops. Tall fescue (Festuca arundinacea) is one of the most important cool-season turfgrasses, which has medium tolerance to salinity and has a promising potential to be used as a turfgrass under saline conditions. However, up to now, the maximum use of tall fescue under salinity stress is still limited by inadequate scientific literature. Recent studies have attempted to identify various adaptive responses to salinity stress at molecular, cellular, metabolic, and physiological levels in tall fescue. The successful integration of information concerning signal sensing, molecular tools with recent advances in -omics would certainly provide a clue for creating salt-tolerant tall fescue. Because salinity limits water availability to plants via hindering water absorption, and by inducing physiological drought, here we review and propose a probable mechanism of tall fescue response to salinity stress and to similar effects induced by drought based on published literature.

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Erick Amombo, Longxing Hu, Jibiao Fan, Zhengrong Hu, and Jinmin Fu

Clonal plants can consist of connected individual ramets that enhance resource sharing through physiological integration. This integration enables the whole clone to tolerate environmental stresses. The objective of this research was to investigate the effects of physical ramet connections on the integration of antioxidant enzymes in clonal common bermudagrass (Cynodon dactylon) growing under heterogeneously distributed water; i.e., nonuniform distribution of water due to 20% polyethylene glycol (PEG 6000) treatment on some ramets and not others. The bottom, middle, upper and three fragments of clonal common bermudagrass were subjected to 20% PEG 6000 with water potential of −1.8 MPa to induce heterogeneous and homogeneous drought stress. The control was not treated with 20% PEG 6000. Within the heterogeneous treatment, water stressed clonal fragments generally had higher leaf and root antioxidant enzyme activities with respect to superoxide dismutase, catalase, peroxidase (except for root peroxidase). There was no difference in antioxidant enzyme activity within the connected clonal ramets for homogeneous treatment; i.e., three connected ramets treated with 20% PEG 6000. Osmotically stressed clonal fragments under heterogeneous environments had a lower level of malonaldehyde (MDA) compared with those in homogeneous regimes. The antioxidant enzyme integration was affected by directionality and water availability contrast. This was indicated by significant decline in MDA levels within the heterogeneous treatments as compared with homogeneous treatment, which suggested reduced lipid peroxidation. These results suggested that ramet connections facilitate integration of antioxidant enzymes within clonal plants growing in heterogeneously available water. Enzymes were integrated from clonal fragments growing in water sufficient environment to those in water stressed regimes. This enhanced reactive oxygen species scavenging capacity of the entire clone hence improved drought tolerance.

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Jibiao Fan, Jing Ren, Weixi Zhu, Erick Amombo, Jinmin Fu, and Liang Chen

Cold stress is a key factor limiting resource use in bermudagrass (Cynodon dactylon). Under cold stress, bermudagrass growth is severely inhibited and the leaves undergo chlorosis. Therefore, rigorous investigation on the physiological and molecular mechanisms of cold stress in this turf species is urgent. The objective of this study was to investigate the physiological and molecular alteration in wild bermudagrass under cold stress, particularly the changes of transpiration rate, soluble sugar content, enzyme activities, and expression of antioxidant genes. Wild bermudagrass (C. dactylon) was planted in plastic pots (each 10 cm tall and 8 cm in diameter) filled with matrix (brown coal soil:sand 1:1) and treated with 4 °C in a growth chamber. The results displayed a dramatic decline in the growth and transpiration rates of the wild bermudagrass under 4 °C temperature. Simultaneously, cold severely destabilized the cell membrane as indicated by increased malondialdehyde content and electrolyte leakage value. Superoxide dismutase and peroxidase activities were higher in the cold regime than the control. The expression of antioxidant genes including MnSOD, Cu/ZnSOD, POD, and APX was vividly up-regulated after cold stress. In summary, our results contributed to the understanding of the role of the antioxidant system in bermudagrass’ response to cold.

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Xiaoning Li, Xiaoyan Sun, Guangyang Wang, Erick Amombo, Xiuwen Zhou, Zhaohong Du, Yinkun Zhang, Yan Xie, and Jinmin Fu

Phosphorus (P) is an essential nutrient element that is necessary for plant growth and development. However, most of the P exists in insoluble form. Aspergillus aculeatus has been reported to be able to solubilize insoluble forms of P. Here, to investigate the P-solubilizing effect of A. aculeatus on the performance of perennial ryegrass (Lolium perenne) under P-deficiency stress, we created four treatment groups: control [i.e., no Ca3(PO4)2 or A. aculeatus], A. aculeatus only (F), Ca3(PO4)2 and Ca3(PO4)2 + A. aculeatus [Ca3(PO4)2 + F] treatment, and Ca3(PO4)2 at concentrations of 0 and 3 g per pot (0.5 kg substrate per pot). In our results, the liquid medium inoculated with A. aculeatus exhibited enhanced soluble P and organic acid content (tartaric acid, citric acid, and aminoacetic acid) accompanied with lower pH, compared with the noninoculated regimen. Furthermore, A. aculeatus also played a primary role in increasing the soluble P content of substrate (1 sawdust: 3 sand), the growth rate, turf quality, and photosynthetic capacity of the plant exposed to Ca3(PO4)2 + F treatment, compared with other groups. Finally, in perennial ryegrass leaves, there was a dramatic increase in the valine, serine, tyrosine, and proline contents, and a remarkable decline in the glutamic acid, succinic acid, citric acid, and fumaric acid contents in the Ca3(PO4)2 + F regimen, compared with other groups. Overall, our results suggested that A. aculeatus may play a crucial role in the process of solubilizing Ca3(PO4)2 and modulating perennial ryegrass growth under P-deficiency stress.

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Zhengrong Hu, Erick Amombo, Margaret Mukami Gitau, Aoyue Bi, Huihui Zhu, Liang Zhang, Liang Chen, and Jinmin Fu

Bermudagrass (Cynodon dactylon) is a typical and widely used warm-season turfgrass. Low temperature is one of the key environmental stress limiting its utility. However, little information is available about the differences of cold response between bermudagrass genotypes. Here, we analyzed antioxidant defense system and fatty acid composition in cold-resistant genotype WBD128 and cold-sensitive genotype WBDg17 exposed to chilling stress. Low temperature (4 °C) significantly decreased the relative water content, whereas increased the H2O2 and O2 contents, more profoundly for WBDg17. Under chilling condition, WBD128 had higher anti O2 activity than WBDg17. Besides, the contents of total glutathione, reduced glutathione (GSH) and its oxidized form (GSSG) were markedly increased by low temperature in both genotypes, whereas WBD128 had significantly higher values of GSH, total glutathione, and GSH/GSSG ratio than WBDg17. Moreover, chilling stress increased saturated fatty acids (SFAs) percentage (palmitic acid and stearic acid) in WBDg17. After chilling treatment, the proportion of linoleic acid decreased in both genotypes, particularly in WBDg17. As for unsaturated fatty acids (UFAs), the percentage of linolenic acid was increased in WBD128. In addition, chilling treatment decreased the values of double bond index (DBI), UFA/SFA ratio as well as degree of unsaturation in WBDg17. Finally, chilling stress altered the expression patterns of the genes, which encode one kind of late embryogenesis abundant proteins (LEA), superoxide dismutase (Cu/Zn SOD) C-repeat-binding factor/DRE-binding factor (CBF1), and peroxidase (POD-2). Collectively, our results revealed that natural variation of chilling tolerance in bermudagrass genotypes may be largely associated with the alterations of antioxidant defense system and fatty acid composition.