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Changes in stubble carbohydrate content during the regrowth of ryegrass (Lolium perenne L.) grown under hydroponic conditions at two nitrogen levels were studied as a function of time by high-performance liquid chromatography. Experimental data showed that regrowth at a non-limiting nitrogen level (1-0 mol m~' NH«N03) involved two different physiological periods. The first occurred during the first 6 d and was characterized by the mobilization of 60 to 90% of the soluble carbohydrates (i.e. glucose, fructose, sucrose, oligofructans and polyfructans). During the second period (6-28 d of regrowth) carbohydrate contents rose to the values observed prior to cutting (20% of dry matter at the 28th d of regrowth).The effect of low nitrogen conditions (0-2 mol m"' NH4NO3) was observed only during the second phase. Plants regrown in a nitrogenstarved medium accumulated 2-3-fold more polyfructans than plants regrown in a non-limiting nitrogen medium. Their fructose and glucose contents remained at 2% of dry matter from the end of the first phase of mobilization.The experimental results are interpreted and discussed in terms of the existence of two distinct fructan synthetic pathways.

J. 1989. Osmoregulation and role of nitrate during regrowth after cutting of ryegrass (Lolium perenne). -Physiol. Plant. 76: 177-182.The osmotic role of nitrate during aftermath growth of Lolium perenne L. cv. Reveille was investigated. Plants were grown from seed in a controlled environment using a liquid medium with 1.0 mM NH4NOJ as nitrogen source. Eight-week-old plants were cut 4.0 cm above the root system and then harvested over a 14-day period of regrowth on the same initial nutrient solution, except that nitrate was ' "^N labelled. Throughout the experimental period, nitrate storage and reduction in roots were low. In stubble and especially in leaves, nitrate accumulated during the first 6 days of regrowth whereas nitrate reduction mainly occurred after this period. Analyses of carbohydrate, chloride and potassium contents in stubble and leaves showed that the accumulation of nitrate osmotically compensated for the decrease in soluble sugars during the first 6 days of regrowth. The cumulative osmotic potential of sugars, chloride and nitrate in differently treated plants was studied in stubble and leaves. Compared with uncut plants, the lower carbohydrate concentrations found in cut plants regrowing on 1.0 mM NH4NO, were compensated for by an accumulation of nitrate. During aftermath growth on low nitrogen nutrition (0.2 mM NH4NO,), chloride replaced nitrate, supporting the proposed osmotic function of nitrate. It is concluded that nitrate is involved in the osmotic adjustment of ryegrass during regrowth after cutting.

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