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

Self Cite

193

102

The lipid composition of plasma membranes and tonoplasts from etiolated mung bean hypocotyls was examined in detail. Phospholipids, sterols, and ceramide monohexoside(s) were the major lipid classes in both membranes. The content of phospholipids on a protein basis was higher in the tonoplast, but the content of total sterols was similar in both membranes. Accordingly, the sterol to phospholipid molar ratio in the plasma membrane was higher than that of the tonoplast. Phosphatidylethanolamine and phosphatidylcholine comprised the major phospholipids in both membranes. Phosphatidylinositol, phosphatidylserine, and phosphatidylglycerol were identified as minor phospholipid components. The content of phosphatidylinositol and phosphatidylglycerol was relatively high in the tonoplast, comprising 11 and 5% of the total phospholipids, respectively. Although special care was taken against the degradative action of phospholipase D and phosphatidic acid phosphatase during the isolation of these membranes, by adding EDTA, EGTA, KF, choline, and ethanolamine to the homogenizing medium, significant amounts of phosphatidic acid, about 15% of the total phospholipids, were detected in the plasma membrane. On the other hand, the content of phosphatidic acid in tonoplasts and other membrane fractions was very low. This fact may indicate that high levels of phosphatidic acid occur naturally in plasma membranes. Phosphatidylglycerol in both membranes and phosphatidylinositol in the tonoplast contained high levels of palmitic acid, which comprised more than 50% of the total fatty acids. Significant differences were observed in the sterol compositions of plasma membranes and tonoplasts. More than 90% of the sterols in the plasma membrane were unesterified, while the tonoplast was enriched in glycosylated sterols, especially acylated sterylglycosides. Ceramide monohexoside was found to be specifically located in these membranes, in particular, in the tonoplast, in which it comprised nearly 17% of the total lipids. is quite limited regarding the lipid composition of plasma membranes and tonoplasts, which also possess very important physiological functions including in the former, transport (22), cell wall biosynthesis (14), hormone action (24), phytochrome responses (18), and disease resistance (27), and in the latter, cellular compartmentation of lytic enzymes, acids, ions, and secondary products (I 1, 13). In addition, these membranes have been shown to play an important role in cold acclimation (29,31,33), freezing injury (26), and chilling stress (32).Recently we have established isolation methods for plasma membranes and tonoplasts from etiolated mung bean hypocotyls (34,35). In the present study, we have analyzed the lipid composition of both membranes and compared them. Plasma membranes are characterized by their high content of phosphatidic acid and tonoplasts by their high content of ceramide monohexoside. MATERIALS AND METHODSPlant Materials. Seeds of mung bean (Vigna radiata [L] Wilczek) were imbibed and germinate...

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Lipid Composition of Plasma Membranes and Tonoplasts Isolated from Etiolated Seedlings of Mung Bean (Vigna radiata L.)

Yoshida¹,

Uemura²

1986

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193

102

“…Many plant tissues including potato tubers have been shown to increase the degree of unsaturation of their membrane fatty acids in response to low temperatures (14,15,26,27,30). Increased membrane lipid unsaturation during low temperature exposure has been interpreted as a beneficial acclimation response.…”

Section: Discussionmentioning

confidence: 99%

“…Several chemical or physical changes can occur to a membrane's component fatty acids which can lead to increased membrane permeability: (a) peroxidation of unsaturated fatty acyl-lipids (12,15,18,23,27,28), (b) deesterification and accumulation of FFA in the bilayer (6,9,15,20,21), (c) loss of diacylglycero-lipids (15,20,21,23,27), or (d) transition of membranes and their component acyl-lipids from a normal flexible liquid-crystalline structure to a solid gel structure at a critical low temperature (15,18,20,21,23,27,28,30). Our objectives were to determine if tuber membrane fatty acyllipid composition could account for alterations in membrane permeability, and if membrane permeability could influence potato tuber sugar content and subsequent processing quality.…”

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confidence: 99%

Fatty Acids, Membrane Permeability, and Sugars of Stored Potato Tubers

Spychalla¹,

Desborough²

1990

The relationships of potato (Solanum tuberosum L.) tuber membrane permeability and membrane lipid composition to sugar accumulation were examined. Tubers from four potato cultivars were stored for 40 weeks at 30C and 90C. Rates of tuber membrane electrolyte leakage, total fatty acid composition, free fatty acid composition, and sugar content were measured throughout the storage period. Storage of tubers at 30C caused dramatic increases in total fatty acid unsaturation, membrane permeability, and sugar content compared to tubers stored at 90C. Cultivars with higher levels of fatty acid unsaturation had lower rates of membrane electrolyte leakage and lower sugar contents. We propose that high initial levels or high induced levels of membrane lipid unsaturation mitigate increases in tuber membrane permeability during storage, thus positively influencing the processing quality of stored potato tubers.Sucrose, glucose, and fructose are the major sugars which accumulate in potato (Solanum tuberosum L.) tubers. High levels of reducing sugars (glucose and fructose) lower the suitability of tubers for processing. Reducing sugars react with free amino groups during frying leading to the formation of a brown pigment, which can make chips and french fries (crisps and chips in the United Kingdom) unacceptable for consumers. Excess sugars in stored tubers commonly arise from two situations. Storage of tubers longer than 7 months can lead to 'senescent sweetening,' and storage below approximately 7°C can lead to 'cold-induced sweetening' (1). However, low temperature storage of potato tubers can also have the beneficial results of lowered respiration rates, slowed physiological aging, inhibition of sprouting, reduced evaporative water loss, and minimized microbial pathogenesis (1).Sugars accumulate in tubers when there is an imbalance between starch degradation, starch synthesis, and respiration of carbohydrate. One potential source of metabolic imbalance ' From a disseration submitted to the graduate school of the

“…A similar response in the pattern of protein synthesis has been observed for excision shock (32). For other environmental stresses the response is not as dramatic; however, water stress (2,7,18,31), osmotic shock (13), wounding (8,29,30), cold acclimation (5,17,33,34), and salt stress (12, 31) result in an increase in the net synthesis of some proteins and a decrease in the synthesis of others, with or without a concomitant induction of unique stress proteins.We have initiated studies to analyze the influence of salt stress on the pattern of protein synthesis in barley roots. Barley is the most salt tolerant grain of major agricultural importance and has been grown in fields salted-out by previous irrigation practices (1 1, 25).…”

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confidence: 99%

The Effects of Salt on the Pattern of Protein Synthesis in Barley Roots

Hurkman¹,

Tanaka²

1987

116

ABSTRACIThe effect of salt stress on the incorporation of r5Sjmethionine into protein was examined in roots of barley (Hordeum vulgare L. cv California Mariout 72). Plants were grown in nutrient solution with or without 200 millimolar NaCl. Roots of intact plants were labeled in vivo and proteins were extracted and analyzed by fluorography of two-dimensional gels. Although the protein patterns for control and salt-stressed plants were qualitatively similar, the net synthesis of a number of proteins was quantitatively changed. The most striking change was a significant increase of label in two protein pairs that had pIs of approximately 63 ad 6.5. Each pair consisted of proteins of approximately 26 and 27 kilodaltons (kD). In roots of control plants, the 27-kD proteins were more heavily labeled in the microsomal fraction relative to the 26-kD proteins, whereas the 26-kD proteins were enriched in the post 178,000g supernatant fraction; in roots of salt treated plants, the 26-and 27-kD proteins were more intensely labeled in both fractions. Labeling of the 26-and 27-kD proteins returned to control levels when salt-stressed plants were transferred to nutrient solution without NaCl. No cross-reaction was detected between the antibody to the 26-kD protein from salt-adapted tobacco cells and the 26-and 27-kD proteins of barley.Plants are often subjected to a wide variety of environmental stresses throughout their life cycles. One approach to understanding the ability of plants to tolerate environmental stresses is to identify stress-induced changes in the levels of individual proteins, with the assumption that adaptation to stress is the result of altered gene expression. Protein synthesis responds dramatically to environmental stresses such as heat shock (6, 21) and anaerobiosis (27) where the synthesis of most proteins ceases and the synthesis of a new set of proteins is induced. A similar response in the pattern of protein synthesis has been observed for excision shock (32). For other environmental stresses the response is not as dramatic; however, water stress (2,7,18,31), osmotic shock (13), wounding (8,29,30), cold acclimation (5,17,33,34), and salt stress (12, 31) result in an increase in the net synthesis of some proteins and a decrease in the synthesis of others, with or without a concomitant induction of unique stress proteins.We have initiated studies to analyze the influence of salt stress on the pattern of protein synthesis in barley roots. Barley is the most salt tolerant grain of major agricultural importance and has been grown in fields salted-out by previous irrigation practices (1 1, 25). Barley genetics and physiology have been extensively studied (4), as has the relationship between salt tolerance and ion transport both on a cellular and whole plant level (reviewed: 16, 20, 26). However, little work has been done on the effect of salt stress on protein synthesis in barley. Barley was included in studies of the effects of ions and organic solutes on the in vitro stability of polysomes (3) and the in ...