The Acclimatization of Plants to Chilling Temperatures in Relation to the Fatty‐acid Composition of Leaf Polar Lipids

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acid and degree of frost resistance during both hardening and dehardening of the hardy winter wheat cultivar Kharkov (unpublished data) casts doubt on this conclusion.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

confidence: 81%

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

Willemot¹

1977

“…The effect of 8 h of low temperature on the fatty acids of both PC and PE (Table IV) (Tables II and IV) and before any changes occurred in GA3 sensitivity (preceding paper). This response of aleurone tissue phospholipids to low temperature is quite similar to others reported in the literature, in which exposure to low temperature seems invariably associated with an increase in desaturation of the fatty acid chains of phospholipids of a wide variety of species at all levels of biological organization (4,30). Table V and VI provide information regarding the effect of preincubation treatments on the percentage of fatty acids of component phospholipids ofthe aleurone tissue.…”

Section: Resultssupporting

confidence: 72%

Low Temperature-Induced GA₃ Sensitivity of Wheat

Singh

Paleg²

1984

Exposure of isolated aleurone tissue from the wheat (Triticam aetirum) variety Kite which contains the Rht2 allele, to low temperature (5°C) for 20 h prior to addition of exogenous GA3, resulted in significant changes in the content of lipids, especially phospholipids. Sigificat low temperature-induced changes in both the head group and acyl contents of two phospholipids, phosphatidylcholine and phosphatidylethanolamine, were detected. More importantly, these changes displayed a very close temporal relationship with the low temperature-induced increase in GA3 sensitivity. Further, this relationship was paralleled by a highly significant correlation between the changes in the phospholipids and the changes in a-amylase production. These results underline the possibility that the GA3 receptor sites are membranbased lipids.Aleurone tissue of cereal seeds, when exposed to GA3, synthesizes and secretes hydrolytic enzymes, including a-amylase, into the starchy endosperm (5). Deembryonated seed or isolated aleurone layers thus provide convenient experimental systems for the study of GA3-induced a-amylase production. In the preceding paper, low temperature was shown to increase the GA3 sensitivity of otherwise GA3-insensitive aleurone tissue of several wheat varieties. More cubation of the isolated aleurone layers were as described in the preceding paper. Where dry seeds were involved, the aleurone layers were dissected from deembryonated seeds after boiling them for 5 min.Extraction and Analysis of Phospholipids. At the end of the preincubation period, the aleurone layers were immediately frozen in liquid N2 and freeze-dried and lipids were extracted using hot, water-saturated butan-l-ol (28). The total lipid extract was subjected to partition chromatography on Sephadex G-25 to yield a purified total lipid fraction, which was further fractionated by adsorption chromatography on silicic acid column. This fractionated the total lipids into neutral lipids, glycolipids, and phospholipids. These methods have been described in detail previously (1, 28).Phospholipids were separated into individual classes by TLC as described earlier (13) and quantified by GLC according to Douglas and Paleg (3). All experiments were replicated three times, and data were subjected to analysis of variance as well as multivariate analysis of variance.

“…One of the most obvious ways by which this could be achieved is by alteration of growth temperature. The degree of unsaturation of fatty acids in the membrane systems of many plants and ectothermic organisms is strongly influenced by the environmental temperature (4,14). Exposure to low temperature seems invariably associated with an increase in unsaturation of the fatty acid chains of phospholipids in a wide variety of species at all levels of biological organization.…”

mentioning

confidence: 99%

Correlation between the Lipid Composition and the Responsiveness of Avena sativa Stem Segments to Gibberellic Acid

Jusaitis

Paleg²,

Aspinall³

1982

The lipid compositon of Avena sativa stem segments was malated using BASF 13-338 (formerly Sandoz 9785) and growth temperature, in order to establish whether there were correlations between responsiveness of the tissue to gibberelic acid (GA3) and the presence, before hormone treatment, of specific lipid components. High correlations were obtained between GA3-induced growth and total phospholipid, individual phospholipids, and fatty acids (except for lnolenic acid), total saturated fatty acids, stigmasterol content, and the unsaturated/saturated fatty acid ratio. It was concluded that, although the Upid composition, and particularly the total saturated fatty acid content, seem to be important contributory determinants of the GA,-induced growth response in this system, they may not be obligatory prerequisites, nor the only endogenous factors capable of influencing the response. However, the results are consistent with the hypothesis that membranes are involved in the hormonal mechanism and/or very early stages of the mode of GA3 action in this tissue.Previous studies using Avena sativa stem segments showed that short-term GA3 treatment resulted in no marked changes in lipid components, although significant growth response to the hormone was achieved (6, 7). Moreover, it was suggested (8) that GA3 in this system may be acting in a similar way to GA3 in the liposomal system of Wood and Paleg (16), ie. by interaction with a membrane phospholipid component. Evidence suggests that in model membrane systems lipid composition markedly affects hormonemediated responses (11,15), and hormone-phospholipid interaction was influenced by fatty acid composition (9). This hypothesis could be further tested by examining the GA3-response of Avena stem segments with different lipid compositions before hormone treatment. One of the most obvious ways by which this could be achieved is by alteration of growth temperature. The degree of unsaturation of fatty acids in the membrane systems of many plants and ectothermic organisms is strongly influenced by the environmental temperature (4, 14). Exposure to low temperature seems invariably associated with an increase in unsaturation of the fatty acid chains of phospholipids in a wide variety of species at all levels of biological organization. Similar changes in membrane protein have not been found (5, 12), apart from those occurring as a consequence of changes in the lipid moiety of the membrane in response to the low temperature (17).Another method of altering lipid composition is through the use of compounds which are thought to selectively inhibit synthesis of a membrane component. One such component is BASF 13-338 (4-chloro-5-[dimethylaminoJ-2-phenyl-3[2H]-pyridazinone) (formerly known as Sandoz 9785), a pyridazinone herbicide which reportedly selectively blocks the synthesis of linolenic acid (18:3), thus producing a decrease in 18:3 accompanied by an increase in linoleic acid (18:2), without a shift in the relative proportion of unsaturated/saturated fatty acids of the tissu...