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

Abstract

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acid and degree of frost resistance during both hardening and dehardening of the hardy winter wheat cultivar Kharkov (unpublished data) casts doubt on this conclusion.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...

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

“…BASF 13 338 treatment did not affect the levels of palmitic, stearic, and oleic acids (Table II). This effect was first observed by St. John (21) and subsequently confirmed by others (3,22,23,26). BASF 13 338 reduced the level of linolenic acid in mono-and digalactosyl diglycerides (21), in the polar lipid fraction (3,22,23) and in the total lipid fraction (3,26).…”

“…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.…”

“…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.…”

“…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 (11). The extracted lipids were purified, and analyzed by GC as previously described (22).…”

Temperature Dependence of Photosynthetic Activities in Wheat Seedlings Grown in the Presence of BASF 13.338 (4-Chloro-5-Dimethylamino-2-Phenyl-3(2H)Pyridazinone)

“…Willemot (31) has shown that inhibition of linolenic acid biosynthesis in winter wheat roots by BASF 13.338 is accompanied by inhibition offrost hardening. St.…”