Nitrogen reserves, spring regrowth and winter survival of field-grown alfalfa (Medicago sativa) defoliated in the autumn - PubMed (original) (raw)

Nitrogen reserves, spring regrowth and winter survival of field-grown alfalfa (Medicago sativa) defoliated in the autumn

Catherine Dhont et al. Ann Bot. 2006 Jan.

Abstract

Aims: The objective of the study was to characterize variations in proline, arginine, histidine, vegetative storage proteins, and cold-inducible gene expression in overwintering roots of field-grown alfalfa, in response to autumn defoliation, and in relation to spring regrowth and winter survival.

Methods: Field trials, established in 1996 in eastern Canada, consisted of two alfalfa cultivars ('AC Caribou' and 'WL 225') defoliated in 1997 and 1998 either only twice during the summer or three times with the third defoliation taken 400, 500 or 600 growing degree days (basis 5 degrees C) after the second summer defoliation.

Key results: The root accumulation of proline, arginine, histidine and soluble proteins of 32, 19 and 15 kDa, characterized as alfalfa vegetative storage proteins, was reduced the following spring by an early autumn defoliation at 400 or 500 growing degree days in both cultivars; the 600-growing-degree-days defoliation treatment had less or no effect. Transcript levels of the cold-inducible gene msaCIA, encoding a glycine-rich protein, were markedly reduced by autumn defoliation in 'WL 225', but remained unaffected in the more winter-hardy cultivar 'AC Caribou'. The expression of another cold-inducible gene, the dehydrin homologue msaCIG, was not consistently affected by autumn defoliation. Principal component analyses, including components of root organic reserves at the onset of winter, along with yield and plant density in the following spring, revealed that (a) amino acids and soluble proteins are positively related to the vigour of spring regrowth but poorly related to winter survival and (b) winter survival, as indicated by plant density in the spring, is associated with higher concentrations of cryoprotective sugars in alfalfa roots the previous autumn.

Conclusions: An untimely autumn defoliation of alfalfa reduces root accumulation of specific N reserves such as proline, arginine, histidine and vegetative storage proteins that are positively related to the vigour of spring regrowth but poorly related to winter survival.

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Figures

Fig. 1.

Amounts of proline in roots of two alfalfa cultivars, ‘AC Caribou’ (A and C) and ‘WL 225’ (B and D), defoliated either only twice during the summer (2 Defoliations), or three times with the third defoliation (3 Def.) taken in the autumns of 1997 and 1998 at either 400, 500 or 600 GDD after the second summer defoliation. Samples were taken at the experimental sites of Pintendre (A and B) and Normandin (C and D) in autumn 1997, spring 1998, autumn 1998 and spring 1999. Vertical bars indicate s.e.m. for each sampling date. ND, Not determined since there was no sample in the three-defoliation treatments at Normandin in spring 1999. The s.e.m. was then calculated with results from the two-defoliation treatment.

Fig. 2.

Amounts of arginine in roots of two alfalfa cultivars, ‘AC Caribou’ (A and C) and ‘WL 225’ (B and D), defoliated either only twice during the summer (2 Defoliations), or three times with the third defoliation (3 Def.) taken in the autumns of 1997 and 1998 at either 400, 500 or 600 GDD after the second summer defoliation. Samples were taken at the experimental sites of Pintendre (A and B) and Normandin (C and D) in autumn 1997, spring 1998, autumn 1998 and spring 1999. Vertical bars indicate s.e.m. for each sampling date. ND, Not determined since there was no sample in the three-defoliation treatments at Normandin in spring 1999. The s.e.m. was then calculated with results from the two-defoliation treatment.

Fig. 3.

Amounts of histidine in roots of two alfalfa cultivars, ‘AC Caribou’ (A and C) and ‘WL 225’ (B and D), defoliated either only twice during the summer (2 Defoliations), or three times with the third defoliation (3 Def.) taken in the autumns of 1997 and 1998 at either 400, 500 or 600 GDD after the second summer defoliation. Samples were taken at the experimental sites of Pintendre (A and B) and Normandin (C and D) in autumn 1997, spring 1998, autumn 1998 and spring 1999. Vertical bars indicate s.e.m. for each sampling date. ND, Not determined since there was no sample in the three-defoliation treatments at Normandin in spring 1999. The s.e.m. was then calculated with results from the two-defoliation treatment.

Fig. 4.

SDS–PAGE profiles of soluble proteins and VSP detection (Western blot), during the sampling periods of 1997–98 (A) and 1998–99 (B) at Pintendre, in roots of cultivar ‘AC Caribou’ defoliated either only twice during the summer (2 Defoliations), or three times with the third defoliation (3 Def.) taken in the autumn of 1997 at 400, 500 or 600 GDD after the second summer defoliation. SDS–PAGE profiles were obtained by loading a constant amount of 150 μg of protein per lane and after staining with Coomassie Brillant Blue R-250. Molecular weight standards are listed on the left. Western blots were performed using antisera from the 32-, 19- and 15-kDa VSPs.

Fig. 5.

Relative optical densities of the 32- and 15-kDa VSPs as determined by Western blot analysis. For each sampling period of 1997–98 and 1998–99, relative optical densities were calculated by dividing the optical densities in the autumn and in the spring by the optical density of the two-defoliation treatment measured in the autumn. Relative optical densities are presented for Pintendre and for the two cultivars (‘AC Caribou’ and ‘WL 225’) defoliated either only twice during the summer (2 Defoliations) or three times with the third defoliation (3 Def.) taken in the autumn of 1997 and 1998 at 400, 500 or 600 GDD after the second summer defoliation.

Fig. 6.

Expression of the cold-inducible genes _msa_CIA and _msa_CIG, in November 1998 and April 1999 at Pintendre, in roots of alfalfa cultivars ‘AC Caribou’ and ‘WL 225’ defoliated either only twice during the summer (2 Def.), or three times with the third defoliation taken in the autumns of 1997 and 1998 at either 400, 500, or 600 GDD after the second summer defoliation.

Fig. 7.

Diagrams of the loadings and scores of the first two principal components relating: (A and B) concentrations and pools of organic reserves and root dry weight in autumn 1997, plant density and DM yield in spring 1998; (C and D) concentrations and pools of organic reserves and root dry weight in autumn 1998, plant density and DM yield in spring 1999. Abbreviations used in the observations: starting with C = concentration; P = pool; NoW = Normandin and ‘WL 225’; NoA = Normandin and ‘AC Caribou’; PiW = Pintendre and ‘WL 225’; PiA = Pintendre and ‘AC Caribou’; ending with 0 = two-defoliation treatment; 4, 5 or 6 = a third defoliation in the autumn at 400, 500 or 600 GDD after the second summer defoliation, respectively. Other abbreviations: D98 = plant density in spring 1998; D99 = plant density in spring 1999; Y98 = DM yield in spring 1998; Y99 = DM yield in spring 1999; arg = arginine; his = histidine; pro = proline; rdw = root dry weight; rfo = raffinose oligosaccharide family; st = starch; su = sucrose; ta = total amino acids; tsp = total soluble proteins.

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Nitrogen reserves, spring regrowth and winter survival of field-grown alfalfa (Medicago sativa) defoliated in the autumn - PubMed (original) (raw)