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Lipids are important components of living organisms that participate in and regulate a variety of life activities. Lipids in plants also play important physiological functions in response to a variety of abiotic stresses (e.g. salt stress, drought stress, temperature stress). However, most research on lipids focused on animal cells and medical fields, while the functions of lipids in plants were overlooked. With the rapid development of "omics" technologies and biotechnology, the lipidomics has received much attention in recent years because it can reveal the composition and function of lipids in a deep and comprehensive way. This review summarizes the recent advances in the functions and classification of lipids, the development of lipidomics technology, and the responses of plant lipids against drought stress, salt stress and temperature stress. In addition, challenges and prospects were proposed for future lipidomics research and further exploration of the physiological functions of lipids in plant stress resistance.

Context: Photosynthetic electron transport and apparatus are highly susceptible to abiotic stressors during photosynthesis. Hordeum jubatum L. is an ornamental grass with excellent salt tolerance, used for soil improvement and ecological restoration in Northeast China. However, the comparative effects of salt, alkali and drought conditions on the photosynthetic apparatus of H. jubatum under uniform water potential are little known. Aims: We explored the photosynthetic response of H. jubatum to uniform levels of water potential stress induced by three different stressors: salt, alkali and drought. Methods: Seedlings of H. jubatum were irrigated with three concentrations of NaCl, NaHCO3 and PEG-6000 to induce water potentials of −0.21, −0.47 and −0.82 MPa. Transient fluorescence of chlorophyll a in the seedlings was measured, and JIP-test parameters were obtained. Key results: Lower values of J–I phase fluorescence intensity and appearance of a K -band under stress treatments indicated restricted electron transfer from the oxygen-evolving complex in the donor of photosystem II. In addition, the values of Δ I -band and parameters M O and N increased, whereas those of S m, ϕ Eo and ψ O decreased, indicating interruption of electron flow between electron acceptors pheophytin and NADP+. Serious adverse effects of alkali stress on the acceptors were observed; the low water potential induced by NaHCO3 damaged the thylakoid membrane on the chloroplast, resulting in increased degradation of D1 protein. Conclusions: The results suggest that H. jubatum seedlings have greater tolerance to salt and drought stress, but are highly sensitive to alkali stress in the photosynthetic system. Implications: This study provides physiological information for the successful cultivation of H. jubatum under adverse environment conditions. We compared the photosynthetic performance in seedlings of the ornamental grass Hordeum jubatum under salt, alkali and drought conditions by measuring the transient fluorescence of chlorophyll a at uniform levels of low water potential. Results showed that all three stressors inhibited photosynthetic electron transport and apparatus of H. jubatum seedlings, with the most serious effects under alkali stress. These finding will be useful when deciding on cultivation of this grass in adverse environments. [ABSTRACT FROM AUTHOR]

Hordeum jubatum L. is a potential ornamental grass species. Spermidine (Spd) plays a regulatory role in plant stress. This study measured seedling growth, photosynthesis, chlorophyll fluorescence, osmotic regulatory substance contents, and antioxidant enzyme activities in H. jubatum seedlings pretreated with Spd (0–1.5 mM at 0.5 mM intervals) in drought treatments simulating natural water loss. The results indicated that the water content, photosynthetic parameters maximal quantum yield of PSII photochemistry (Fv/Fm), actual quantum yield of photochemical energy conversion in PSII (ϕPSII), and photochemical quenching coefficient (qp) values of H. jubatum shoots decreased significantly with increasing drought intensity. Simultaneously, the contents of malondialdehyde (MDA) and the nonphotochemical quenching coefficient (NPQ) value increased. Spd improved growth and photosynthesis under drought stress. Spd also increased osmotic regulatory substance contents and antioxidant enzyme activities. These results suggest that the drought stress inhibited the growth of H. jubatum and damaged the photosynthetic systems, triggering a range of protective responses. Exogenous Spd mitigated the damage by promoting a variety of responses and adaptive mechanisms, such as adjusting stomatal conductance, promoting photosynthetic capacity, accelerating the synthesis of osmoregulatory molecules, and activating antioxidant enzyme systems. Additionally, 1.5 mM Spd-treated H. jubatum had the best drought tolerance. This study will help to develop an understanding of the effects of exogenous Spd on improving drought resistance and provide a strategy for the H. jubatum landscape effect to be achieved under water-limited conditions. [ABSTRACT FROM AUTHOR]

Hordeum jubatum is a halophyte ornamental plant wildly distributed in the Northeast of China, where the low water potential induced by various abiotic stresses is a major factor limiting plant growth and development. However, little is known about the comparative effects of salt, alkali, and drought stresses at uniform water potential on the plants. In the present study, the growth, gas exchange parameters, photosynthetic pigments, and chlorophyll fluorescence in the seedlings of H. jubatum under three low water potentials were measured. The results showed that the growth and photosynthetic parameters under these stresses were all decreased except for carotenoid (Car) with the increasing of stress concentration, and alkali stress caused the most damaging effects on the seedlings. The decreased net photosynthetic rate (P n), stomatal conductance (G s), and intercellular CO2 concentrations (C i) values under salt stress were mainly attributed to stomatal factors, while non-stomatal factors were dominate under drought and alkali stresses. The reduced chlorophyll and slightly increased Car contents occurred under these stresses, and most significant changed under alkali stress. In addition, the maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPSII), and photochemical quenching coefficient (qP) under the stresses were all decreased, indicating that salt, alkali, and drought stresses all increased susceptibility of PSII to photoinhibition, reduced the photosynthetic activity by the declined absorption of light for photochemistry, and increased PSII active reaction centers. Moreover, the non-photochemical quenching coefficient (NPQ) of alkali stress was different from salt and drought stresses, showing that the high pH of alkali stress caused more damaging effects on the photoprotection mechanism depending on the xanthophyll cycle. The above results suggest that the H. jubatum has stronger tolerance of salt than drought and alkali stresses, and the negative effects of alkali stress on the growth and photosynthetic performance of this species was most serious. [ABSTRACT FROM AUTHOR]

The early seedling stage is highly susceptible to various abiotic stresses. Hordeum jubatum is an ornamental plant with excellent abiotic stress tolerance, and widely distributed in the northeast of China. However, the mechanism of its physiological and transcriptional resistance under different abiotic stresses is still unclear. The results showed that the leaves of H. jubatum adapted to saline-alkali and drought environments by increasing the density of wax and glandular hairs, reducing the stomatal length, width and opening, and the leaf cells completely ruptured and a large number of organelles disintegrated under alkali stress. With the increasing stress concentration, the chlorophyll content and dry weight reduced under the three stresses, which was related to the broken chloroplasts of such conditions. In addition, the balance of Na+ and K+ was disturbed, and the increase of APX and SOD activity was the strategy to maintain the balance of reactive oxygen species and weaken the degree of membrane lipid peroxidation under three stresses. And alkali stress had the most significant effect on above changes. Moreover, Transcriptional sequencing revealed the alkali stress group had the highest number of differential expressed genes (DEGs) compared to the CK among three stresses, and a significant down-regulation of DEGs related to membrane systems under three stresses. In addition, alkali stress resulted in large number of up-regulation of DEGs associated with light repair processes and down-regulation of DEGs in ribosomal pathway with R proteins involving in regulating leaf phenotype and ultrastructure, which also echoed the overall physiological findings. Together, the adaptation mechanisms of three stresses were different in H. jubatum seedlings with higher tolerance of salt stress, and extremely sensibility to alkali stress. • The H. jubatum adapted to salt, alkali and drought environments by increasing wax and glandular hair density, and reducing leaf stomatal size and opening. • Transcriptome sequencing shows the high pH from NaHCO 3 inhibits ribosomal R proteins regulating leaf structure. • The negative effects of alkali stress on leaf ultrastructure, physiological metabolism and transcription process of this species were most serious. [ABSTRACT FROM AUTHOR]