Stimulation of Phospholipid Biosynthesis during Frost Hardening of Winter Wheat

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Treatment of 12-day-old winter wheat (Triticum aestivum) plants with BASF 13-338 {4-chloro-5(dimethylamino)-2-phenyl-3(2H)-pyridazinone} 36 hous before frost hardening simultaneousy and completely inhibit accumulation of linolenic acid in the roots during the hardening period and the acquiition of frost resistance. Increased asaturation of fatty acids is therefore probably an important part of the mechanism of cold adaptation in winter wheat.BASF 13-338 also prevents the increase in per cent dry weight in roots and shoots during hardening and causes a decrease in root lipid phosphorus and total fatty adds.The concurrent incea in linoleic acid and decream in linolenic acid in the treated plats, while the level of the otber fatty adds is but ittle affected, suggest that BASF 13-338 specifically inhibits linoleic acid desuae.Although linolenic acid content greatly increases in the roots of winter wheat during frost hardening, it accumulates to the same extent in cultivars showing a large difference in frost resistance (3,7,12). Increased unsaturation of membranes does not seem directly involved in the cold-hardening process in winter wheat. However, the close correlation between percentage of linolenic acid and degree of frost resistance during both hardening and dehardening of the hardy winter wheat cultivar Kharkov (unpublished data) casts doubt on this conclusion. It is possible that linolenic acid accumulation is a prerequisite to hardening, but that all cultivars have acquired this characteristic and that less hardy cultivars have their frost resistance limited by other factors.To test this hypothesis an attempt was made to prevent frost hardening of winter wheat by specifically blocking linolenic acid synthesis during the hardening period by treating the plants with 4-chloro-5(dimethylamino)-2-phenyl-3(2H)-pyridazinone (Sandoz 9785,. St. John and Christiansen (9) showed that treatment of germinating cotton seeds with this compound reduced both the tolerance of the seedlings to chilling and the low temperature-induced increase in linolenic acid content of the polar lipids in the root tips. MATERIALS AND METHODSWinter wheat (Triticum aestivum, cv. Kharkov) was grown and hardened as described previously (11 contained 15 seedlings and 400 g of sand-vermiculite (1:1, v/v). During hardening the humidifier was stopped. Before and during hardening the frost resistance of the plants was tested by controlled freezing. The plants were cut above the crown and the pots were transferred to a programmed freezer (12). The temperature was lowered at a rate of 2 C/hr, equilibrated for 12 hr at -4 C, and kept for 2 hr at each test temperature. At the end of each pause pots were withdrawn and allowed to thaw slowly for 36 hr at 4 C. Survival counts were made after 3 weeks of recovery under initial growth conditions. Frost hardiness was expressed as the temperature at which 50% of the plants died (killing temperature, LT5o).Twelve days after sowing and 36 hr before being moved to the hardening chamber, the plants were tre...

Section: Discussioncontrasting

confidence: 56%

“…Kharkov) was grown and hardened as described previously (11 contained 15 seedlings and 400 g of sand-vermiculite (1:1, v/v). During hardening the humidifier was stopped.…”

Section: Methodsmentioning

confidence: 99%

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Simultaneous Inhibition of Linolenic Acid Synthesis in Winter Wheat Roots and Frost Hardening by BASF 13-338, a Derivative of Pyridazinone

Willemot¹

1977

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“…Many plants capable of cold hardening exhibit an increase in lipid unsaturation (24) and an increased level of phospholipids during hardening (6,16,17,23,26,29). This has led to the speculation that the enhanced fluidity of the membrane by lipid unsaturation is related to cold hardiness.…”

mentioning

confidence: 99%

Chemical and Biophysical Changes in the Plasma Membrane during Cold Acclimation of Mulberry Bark Cells (Morus bombycis Koidz. cv Goroji)

Yoshida¹

1984

ABSTRACTrThe lipid and protein composition of the plasma membrane isolated from mulberry (Morus bombycis Koidz.) bark cells was analyzed throughout the cold acclimation period under natural and controlled environment conditions. There was a significant increase in phospholipids and unsaturation of their fatty acids during cold acclimation. The ratio of sterols to phospholipids decreased with hardiness, primarily due to the large increase in phospholipids. The fluidity of the plasma membrane, as determined by fluorescent polarization technique, increased with hardiness. Electrophoresis of plasma membrane proteins including glycoproteins revealed change in banding pattern during the early fall to winter period. Some of the protein changes could be related to growth cessation and defoliation. However, minor changes in proteins also occurred during the most active period of hardening. Changes in glycoproteins were coincident both with changes in growth stages and with the development of cold hardiness.Following a lethal frost, there is often a loss in the semipermeability properties of the plasma membrane in plants. This had led to the belief that the plasma membrane is the primary site of freezing injury (9,12,18 (24) and an increased level of phospholipids during hardening (6,16,17,23,26, 29). This has led to the speculation that the enhanced fluidity of the membrane by lipid unsaturation is related to cold hardiness. However, no preferential increase in phospholipid unsaturation could be detected in black locust (17) and poplar (29) which are both extreme cold hardy species. These findings have led to the conclusion that membrane unsaturation or fluidity is not related to the development of cold hardiness (6,14,17).In many of the studies relating lipid unsaturation to hardiness, total lipids were investigated rather than the plasma membrane which is considered to be the primary site of injury. This has been primarily due to the lack of methods to isolate sufficient quantities of pure plasma membrane from plant tissues. Recently, we have developed a method of isolating plasma membrane from plant tissues utilizing an aqueous PEG-dextran two- polymer phase system containing NaCI (20, 30). In this report, we followed the changes in lipids, proteins, and fluidity in plasma membranes of mulberry trees during cold acclimation. MATERIALS AND METHODSPlant Materials. Living bark tissues from current twigs of mulberry trees (Morus bombycis Koidz. vc Goroji) were used in the present study. Frost hardiness was evaluated by measuring the electrolyte leakage after freeze thawing of the tissues. Living bark tissues (500 mg) were cut into pieces (1.0 x 0.5 cm) and frozen in test tubes (1.5 x 15 cm) at -3°C for 2 h with small pieces ofice. Thereafter the tissues were cooled by 5°C increments at 1-h intervals. After holding at the desired temperature for 16 h, the frozen tissue pieces were then thawed at 0°C. Upon thawing, the tissues were immersed in 5 ml of distilled H20 and incubated at 25°C for 4 h with a gentle shaking and sub...

“…However, a slight increase in PA and a slight decline in PC during germination at 2 C was observed. Willemot (25) The phospholipid composition of some plant species is reported to be affected by temperature. When rye (Secale cereale L.) seedlings were exposed to cold temperatures (4 C), the relative levels of PC and PI decreased and the proportion of PA increased (24).…”

Section: Resultsmentioning

confidence: 99%

Effect of Temperature and BASF 13 338 on the Lipid Composition and Respiration of Wheat Roots

Ashworth

Christiansen²,

John³

et al. 1981

The fatty acid composition of wheat seedling roots changed in response to temperature. As temperature declined, the level of linolenic acid increased and the level of linoleic acid decreased. The distribution of phospholipid classes was not influenced by temperature. Phosphatidyl choline and phosphatidyl ethanolamine were the predominant phospholipids isolated and comprised 85% of the total lipid phosphorus. Smaller quantities of phosphatidyl glycerol, phosphatidyl inositol, phosphatidic acid, and phosphatidyl serine were isolated. The fatty acid composition of phosphatidyl choline and phosphatidyl ethanolamine were the same and temperature affected the fatty acid composition of both phospholipids in the same manner.Growth in the presence of the substituted pyridazinone, BASF 13 338 (4-chloro-5-dimethylamino-2-phenyl-3(2H)pyridazinone), reduced the level of linolenic acid and increased the level of linoleic acid in the phosphatidyl choline, phosphatidyl ethanolamine, and total polar lipid fractions. BASF 13 338 did not affect the levels of palmitate, stearate, and oleate or the distribution of phospholipid classes.Respiration rates of wheat root tips were measured over a range of temperatures. The respiration rate declined as the temperature decreased. Neither the temperature at which the tissue was grown nor BASF 13 338 treatment influenced the ability of root tips to respire at any temperature from 4 to 30 C. The results indicated that the relative proportion of linolenic acid to linoleic acid did not influence the plants ability to grow and respire over the range of temperatures tested.As the temperature declines in the fall of the year, winter wheat undergoes physiological changes which lead to increased freezing resistance. Considerable research has focused on changes in membrane lipid composition during temperature acclimation. When wheat plants are exposed to cold temperatures, the level of linolenic acid increases and the level of linoleic acid decreases (4,9,27). Fatty acid unsaturation increases to the same extent in cultivars varying widely in resistance to freezing (6,27).Recent studies demonstrated that the substituted pyridazinone BASF 13 338 simultaneously inhibits the accumulation of linolenic acid and the acquisition of winter hardiness (22,23,26 was proposed that an increase in linolenic acid would increase the fluidity of membranes at low temperatures. This should enable wheat to function normally at low temperatures and perform the necessary steps involved in the acquisition of freezing resistance.Our objectives were to characterize the effect of temperature and pyridazinone treatment on the phospholipid and fatty acid composition of wheat roots and to determine the relation between lipid composition and the ability of wheat plants to grow and respire at low temperatures. MATERIALS AND METHODSGrowth of Wheat Seedlings. Winter wheat (Triticum aestivum L. 'Arthur') seeds were germinated in paper seed towels moistened with either distilled H20 or 100 /SM BASF 13 338 (4-chloro-5-dimethyla...