SUMMARY A microscopic and biochemical comparison was made of the distribution, quantity and composition of lipid in roots of onion, clover and ryegrass infected with the VA mycorrhizal fungus, Glomus mosseae, in uninfected roots and in the external mycelium from infected, aseptically grown onion roots. Abundant oil‐droplets were observed in the internal and external fungal mycelium, in the vesicles and chlamydospores, and adjacent to the appressoria at entry points. Mycorrhizal roots contained significantly more total lipid than uninfected roots. In estimations of separated lipid classes, the mycorrhizal roots consistently showed higher levels of triglyceride than non‐inycorrhizal roots. External mycelium contained high levels of neutral lipids, especially triglyceride, diglyceride and free fatty acids. Compared with uninfected roots, mycorrhizal onion roots contained higher levels of diphosphatidyl glycerol, phosphatidyl serine, phosphatidyl ethanolamine, phosphatidy) choline, phosphatidyl glycerol, phosphatidic acid and phosphatidyl inositol. With the exception of phosphatidyl inositol and phosphatidic acid, these were all prominent components of G. mosseae mycelium.
SUMMARYThe effect of water stress on growth of Triticum durum L, was in\estigated in relation to sugar accumulation and water status ot wheat plants before, during and after a ptriud of water stress. The slight decrease in water potential in the first few days after withholding water had no detectable efTect on growth. Inhibition of growth was only apparent when the water content started to decline. Dry weight continued to increase during water stress, even under severe stress (after day 27) which was associated with a sharp rise in sugar content, accounting for 20 "o of the gain in dry matter between days 27 and 31, The increase in leaf length and leaf area of stressed plants following re-watering, from day 31, was owing to the leaves regaining turgidity after wilting. Growth inhibition coincided with a considerable increase in sugar content. The role of growth inhibition and other factors in sugar accumulation under water stress is discussed. Photosynthesis rather than reserve starch might be the major source of sugar accumulated under water stress in durum wheat.Key words: Water stress, sugars, growth, wheat. INTRODliCTIONSoluble sugars have been shown to increase in the leaves of wheat under water stress (Munns & Weir, 1981; Drossopoulos, Karamanos & Niavis, 1987;Kameli & Losel, 1993). They are also considered to play an importatit role in osmotic adjustment which is widely regarded as an adaptive response to water stress conditions (Turner & Jones, 1980; Morgati, 1984;Kameli & Losel. 1993, 1995. Factors which have been suggested to contribute to this increase under water stress include reduced translocation of sugars out of the leaves, slower utilization because of decreased growth and other changes, such as starch hydrolysis. These might contribute individually or together, under different conditions and in different plant species.The extent to which growth inhibition might be responsible for a rise in sugar concentration under water stress was investigated in this study by comparing the timing of the two responses in the same species. Changes in soluble and insoluble carbohydrates were examined, during and after water stress, in relation to growth. * Prtsent address: Depariement de Btologie, Ecoie Normale Superieure, Vieux-Kouba, Algiers, Algeria, t To whom correspondence shotild be addressed. M.^TERIALS AND METHODSSeeds of durum wheat {Triticum durum L.) \ariety MBB from Algeria were soaked for 24 h and gertninated m vermicuhte for 6 d. The seedlings were planted in pots of mixed compost and vermiculite (2:1 y/y), as described previously (Kameli & Losel, 1993). After 17 d of grow^th with normal water supply, stress was applied by withholding water from half of the pots, selected in a randomized manner. Stressed plants were again watered from day 31. Control plants received full water treatment throughout the period of the experiment. The plants were grown under fluorescent tubes (Osram white, 65/80 W) with irradiance 9()-100 //mol m"' s"', day and night temperatures 22 + 2 and 18 + 2 °C respectively, an...
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