Hydrogen sulfide (H2S) is an important signaling molecule involved in several stress-resistance processes in plants, such as drought and heavy metal stresses. However, little is known about the roles of H2S in responses to chilling stress. In this paper, we demonstrated that chilling stress enhance the H2S levels, the H2S synthetase (L-/D-cysteine desulfhydrase, L/DCD) activities, and the expression of L/DCD gene in Vitis vinifera L. ‘F-242’. Furthermore, the seedlings were treated with sodium hydrosulfide (NaHS, a H2S donor) and hypotaurine (HT, a H2S scavenger) at 4°C to examine the effects of exogenous H2S on grape. The results revealed that the high activity of superoxide dismutase and enhanced expression of VvICE1 and VvCBF3 genes, but low level of superoxide anion radical, malondialdehyde content and cell membrane permeability were detected after addition of NaHS. In contrast, HT treatment displayed contrary effect under the chilling temperature. Taken together, these data suggested that H2S might be directly involved in the cold signal transduction pathway of grape.
The study was designed to determine the possible relationship between Brassica oleracea var. italica seedlings stored at 2°C in the dark for seven and fourteen days, respectively, and the level of certain antioxidant parameters in particular organs. A parallel objective of the experiment was to determine if the reaction of seedlings to low temperature might be persistent in fully developed plants until harvest time. After 14 days of chilling a significant increase in the glutathione content was observed in the seedling leaves in comparison to the non-chilled plants. During vegetation in field conditions this effect was maintained in leaves up to the stage of formation of flower buds. At harvest the highest content of glutathione was demonstrated in broccoli heads, obtained from plants, which were previously chilled in the seedling phase for two weeks. Peroxidase activity in broccoli seedlings increased each year of the three-year study due to the duration of the cooling time, whereas in the case of catalase the changes were not so distinct. At harvest time the activity of both enzymes in the leaves and flower buds fluctuated according to the particular year of study.
Chilling stress is of major limiting factors influencing the growth and development of warm-season crops like cucumber. In this research, the possibility of chilling tolerance of cucumber seedlings was investigated through employing the drought and low-temperature pretreatments. The factorial experiment consisted of two factors including cucumber cultivars (i.e. ‘Super Dominos’ and ‘Super Star’) and hardening treatments (control, low temperatures at 10°C, and 15°C and drought simulated by 10% and 20% PEG) based on completely randomized design (CRD) in 3 replications. After applying treatments and providing them 48 h opportunity to be recovered, the seedlings were subjected to 3°C for a six-day period and 6 h for each day. All hardening treatments improved seedlings’ growth, chlorophyll content, total phenol (TP) and antioxidant enzyme activities, while reducing chilling injury index and malondialdehyde (MDA) content. Comparing to temperature hardening, the drought pretreatment showed to have a better effect on inducing the chilling tolerance into cultivars. Overall, the results of this experiment showed that employing drought and low-temperature pretreatments enabled cucumber seedlings to mitigate the harmful effects of chilling.
Methyl jasmonate (MJ) is a widely occurring molecule. Since it is synthesized constitutively, its presence is substantial to plant normal growth and development. Moreover, its elevated concentration detected under abiotic and biotic stress conditions seems to be crucial to plant in reacting to adverse events and its ability to survive. Because of the sophisticated biochemical machinery inside the plant body, MJ, among other molecules, helps the plant to adopt to the surrounding environmental changes and is involved in its defense system.
Mung bean CYP90A2 is a putative brassinosteroid (BR) synthetic gene that shares 77% identity with the Arabidopsis CPD gene. It was strongly suppressed by chilling stress. This implies that exogenous treatment with BR could allow the plant to recover from the inhibited growth caused by chilling. In this study, we used proteomics to investigate whether the mung bean epicotyl can be regulated by brassinosteroids under conditions of chilling stress. Mung bean epicotyls whose growth was initially suppressed by chilling partly recovered their ability to elongate after treatment with 24-epibrassinolde; 17 proteins down-regulated by this chilling were re-up-regulated. These up-regulated proteins are involved in methionine assimilation, ATP synthesis, cell wall construction and the stress response. This is consistent with the re-up-regulation of methionine synthase and S-adenosyl-L-methionine synthetase, since chilling-inhibited mung bean epicotyl elongation could be partially recovered by exogenous treatment with DL-methionine. This is the first proteome established for the mung bean species. The regulatory relationship between brassinosteroids and chilling conditions was investigated, and possible mechanisms are discussed herein.
Galactolipase is a lipid acyl hydrolase (EC 3.1.1.26) acting predominantly on galactolipids which constitute up to 80% of total acyl lipids in chloroplast membrane. Evidence is presented on the involvement of this enzyme in plant response to chilling via degradation of membrane lipids and the increase of free, fatty acids, associated with reduced oxygen evolution in the Hill reaction. The occurrence of two pools of fatty acids has been hypothesized. Analysis of numerous plant species showed higher galactolipase activity in the chilling-sensitive than in the chilling-resistant plants. Differences in the pH-dependence curve and in the response to detergents of galactolipases from these two groups of plants suggest heterogeneity of the enzyme. Referring to the hypothesis concerning the role of high melting-point fatty acids of phosphatidylglicerol molecular species in chilling sensitivity the data are presented against generalization of this hypothesis.
Degradation of leaf polar lipids [monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG)] and chlorophyll (Chl) were studied in four Zea mays genotypes differing in chilling susceptibility following dark chilling and post-chilling rewarming at original growth conditions. Assessment of visual chilling injury symptoms during post-chilling rewarming differentiated maize inbred lines into chiling-sensitive (CS) CM7 and Co151 lines and chillingtolerant (CT) S215 and EP1 lines. Severity of chilling injury in CS and CT inbreeds were correlated with the extent of Chl and polar lipids degradation. Chilling for either 4 or 6 days followed by 4 days of rewarming caused more extensive degradation of total polar lipids content in CS than in CT lines. MGDG decreased mostly during chilling whereas DGDG dropped during rewarming only. Chl content was not affected during chilling but its large decrease, greater in CS than in CT lines, was observed upon rewarming. Extent of polar lipids breakdown in CS and CT inbreeds during chilling and post-chilling rewarming is correlated with galactolipase activity in chloroplasts (Kaniuga et al., 1998) and visual assessment of chilling injury. In view of the data it is likely that contribution of galactolipase activity induced during low-temperature stress of CS plants is an important factor responsible for thylakoid lipid degradation and development of chilling injury as postulated previously (Kaniuga 1997). It is suggested that genetically engineered reduction of galactolipase activity or elimination of the factors(s) involved in induction/stimulation of its activity during chilling might increase tolerance of CS species to chilling stress.
Research in our laboratory has focused on the analysis of the functions of a variety of enzymes that are involved in the scavenging of reactive oxygen intermediates (ROI) such as superoxide radicals (·O⁻₂ ) and hydrogen peroxide (H₂O₂). Recent work has been on transgenic plants that over-express glutathione S-transferases (GST) that also have glutathione peroxidase activity. Transgenic tobacco plants that contain gene constructs that encode two different tobacco GST’s had elevated levels of both GST and GPX activity. Analysis of mature vegetative transgenic tobacco plants that over-express GST/GPX failed to show any increase in paraquat tolerance or protection from photooxidative stress. However, seeds of these GST/GPX-expressing tobacco lines are capable of more rapid germination and seedling growth at low temperatures and at elevated salt concentrations. Reduced levels of lipid peroxidation were noted in GST/GPX-expressing seedling compared to control seedlings under both stressful and non-stressful conditions. In addition, GST/GPX-expressing seedlings significantly accumulated more oxidized glutathione (GSSG) than control seedlings during stress. These characteristics clearly indicate that over-expression of GST/GPX in transgenic seedlings can have substantial effects on their stress tolerance. Furthermore, it appears that this effect is due primarily to the elevated levels of GPX activity.
In pot experiments conducted on cucumber cv. Śremski F1, the effect was studied of short-term chilling stress on plants which had grown from seeds germinating in the solution of Asahi SL or treated with this biostimulator during the early growth period. The plants were grown in a phytotron at an air temperature of 27/22ºC (day/night), using fluorescent light with FAR flux density of 220 μmol x m-2 x s-1 and with a photoperiod of 16/8. The biostimulator was applied using the following methods: a) germination of seeds in 0.01% and 0.05% solution, b) watering of plants twice with 0.01% or 0.05% solution, c) spraying leaves with 0.3% or 0.5% solution. Plants sprayed with distilled water were the control. After 24 hours from foliar or root application of Asahi SL, one half of the plants from each experimental series was treated for a period of 3 days at a temperature of 12/6ºC, with all the other growth conditions unchanged. The obtained results show that short-term chilling stress caused a significant increase in electrolyte leakage, free proline content and in the activity of ascorbate peroxidase in leaves, but a decrease in the content of chlorophyll, its maximum fluorescence (Fm) and quantum yield (Fv/Fm), carotenoid content, stomatal conductance, transpiration, photosynthesis, leaf biomass and in the activity of catalase in leaves. Foliar or root application of Asahi SL in the pre-stress period decreased the values of the traits which increased as a result of chilling or increased those which decreased. Higher concentrations of the biostimulator solutions, applied using this method, were more effective. The application of the biostimulator during seed germination did not result in significant changes in the response of plants to chilling stress.
The effectiveness of hydrophobic synthetic polymers in reducing imbibitional chilling stress in germinating bean seeds was evaluated. Two technical polymers and three Polish snap bean cultivars were analysed. Polymers were applied in amounts corresponding to 3.5% of seed weight. In the imbibitional chilling tolerance test, the seeds were rolled up in wet filter paper and left at 5°C for 72 hours, after which they were germinated at 20°C. The seed imbibition rate, germination energy, germination capacity and mean germination time were determined. The poly-mer coatings applied formed a barrier which slowed down seed imbibition, but it also significantly reduced germination energy and led to a decrease in germination capacity. The extent to which imbibitional chilling stress was mitigated was determined by the type of the polymer applied and the bean genotype analysed.
Low-temperature results in various physiological and metabolic disturbances in cells of plants which are sensitive to low-temperatures. Moringa is getting popularity as a field crop because of its multipurpose usage. There is no information available about effects of low-temperature (14-18℃) on moringa seedlings and its mitigation. The present study was conducted to test the performance of moringa seedling grown in wire house under low-temperature conditions in response to foliar application of moringa leaf extract (3% solution), hydrogen peroxide (5 ml L⁻¹), ascorbic acid (50 mg L⁻¹) and salicylic acid (50 mg L⁻¹). Seeds of six moringa accessions [Local landrace grown at Agronomic Research Area, Z.A Hashmi Hall, Firdous Colony; Exotic landrace grown at Lalazaar Colony, Department of Agronomy and Agronomic Research Area] were collected and grown in polythene bags filled with equal ratio of compost, sand, silt and clay. All foliar treatments were applied twice; the first round at the seedling age one month and the second round at the seedling age two months. Foliar application of moringa leaf extract significantly enhanced number of branches (92%) and leaves (39%), leaf total chlorophyll contents (73%), leaf phenolic contents (53%) and membrane stability index (57%) of moringa seedlings compared to control. Healthy and vigorous growth of moringa seedlings with higher concentration of antioxidants ensured the defensive potential of moringa leaf extract against low-temperature condition.
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