Effect of Low Temperature on Amino Acid Metabolism in Wintering Poplar

Abstract

Analyses of free amino acids in poplar (Populus geirica) were carried out throughout a year to see the effect of low temperature on a system regulating amino acid metabolism in the tree. The results indicated that during the wintering phase arginine was the major amino acid both in bark and xylem, particularly in xylem, and that at the time of budding and growing glutamine and glutamate became dominant. Changes in the relative levels of glutamine (plus glutamate) and arginine to the total amino acids of the a-ketoglutarate family indicated the presence of a regulatory system annually controlling the synthesis between glutamine (plus glutamate) and arginine. The system appeared to be governed and sensitized by low temperatures. Neither a transition of the synthesis from arginine to glutamine (plus glutamate) nor budding occurred in the poplars which spent the winter months in a greenhouse.Glutamate and glutamine play a major role in amino acid biosynthesis from ammonia as well as from other nitrogenous materials in higher plants (1, 2). Actually, in perennials such as poplar (Populus gelrica) a large amount of glutamine is accumulated both in the living bark and xylem at the time when trees are growing (6).The previous report has shown that prior to the period of accumulation of glutamine, arginine accumulated in the wintering poplar (6). With the arrival of spring, a striking decrease in the arginine level was observed, particularly in the xylem, concomitant with an increase of glutamine and glutamate.In spite of the general acceptance of the importance of exposing dormant perennials to low temperatures to evoke a renewal of active growth (3, 5), little information is available on the transition of amino acid metabolism occurring in the twig of the tree. In an attempt to clarify the biochemical effect of low temperatures on the metabolic activities of wintering plants, the relation between low temperatures and amino acid metabolism in the poplar tree was studied. This paper indicates that the decrease of the accumulated arginine and the increase of glutamine (and glutamate) is coupled with the budding process and that the regulatory system appears to be sensitized by low temperatures.A 5-year-old poplar was grown in the field, and comparable samples of twigs were taken from the tree. For free amino acid analysis, twigs were sampled regularly on the 20th of each month throughout 1 year, and extracts for the analysis were prepared immediately as described previously (6).The results are shown in Tables I and II. Glutamine and glutamate constituted the major fraction of amino acids of the a-ketoglutarate family (glutamine, glutamate, proline, and arginine) (1, 4) during the period of active growth, while arginine was the major amino acid of the family during winter. From the data in Tables I and II, the percentage of arginine (and glutamine plus glutamate) relative to the total of the a-ketoglutarate family of amino acids was obtained (Fig.

Poplar Wood Rays Are Involved in Seasonal Remodeling of Tree Physiology

“…Moreover, a large number of transcripts for nitrate and nitrite reductase, and nitrate transporters, are down-regulated in early spring (Supplemental Table S1). Arg was by far the most abundant amino acid in early-spring samples (Table II), which is consistent with earlier studies showing that this nitrogen-rich amino acid is dominant in the xylem sap (Schneider et al, 1994), phloem exudates, and bark (Sagisaka 1974; of poplar during winter until bud break. Since Arg is considered an important nitrogen storage compound , we conclude that nitrogen metabolism remains adjusted to nitrogen storage in early spring, approximately 2 months before bud break occurs.…”

Phytochrome-Mediated Photoperiod Perception, Shoot Growth, Glutamine, Calcium, and Protein Phosphorylation Influence the Activity of the Poplar Bark Storage Protein Gene Promoter (bspA)

“…Gln is a major transport amino acid in poplar (Sagisaka, 1974;Sauter, 1981;Sauter and van Cleve, 1992). During fall leaf senescence, N is largely transported from leaves to stems as Gln (Sauter and van Cleve, 1992).…”

“…Although NH 4 NO 3 also induced GUS, it is likely that this was through increased levels of Gln since NH 4 and NO 3 are used in the synthesis of Gln through nitrate reductase/nitrite reductase reduction and the GS-GOGAT pathway (Miflin and Lea, 1980). Gln also accumulates in the living bark and xylem of poplars (Populus) and willows (Salix; Sagisaka, 1974;Sauter, 1981;Sauter and van Cleve, 1992) during spring bud break and shoot growth. Accumulated Gln is either stored or mobilized to active sinks such as developing leaves and shoot apices (Dickson et al, 1985;Vogelmann et al, 1985).…”

A Cold Environment Is a Prerequisite for Formation of “Plastid Initials” in Winter Buds of Poplar

“…Previous studies showed that concurrent with the breaking of dormancy, proliferation of mitochondria (8) and fusion of the microvacuoles (7) are initiated in the cortical cells. Furthermore, Arg was found to be a major constituent of the pool of free amino acids in wintering poplar, and when the saplings remained outdoors in winter, changes in the major amino acids from Arg to Gln (Glu) and Asn (Asp) were observed as normal metabolic events in spring (2,4). However, in winter buds of poplars that were housed in a greenhouse during the winter, the changes in the complement of the major amino acids take place in May, with resultant uncoupling of amino acid synthesis and arrested development (2,4).…”

“…Furthermore, Arg was found to be a major constituent of the pool of free amino acids in wintering poplar, and when the saplings remained outdoors in winter, changes in the major amino acids from Arg to Gln (Glu) and Asn (Asp) were observed as normal metabolic events in spring (2,4). However, in winter buds of poplars that were housed in a greenhouse during the winter, the changes in the complement of the major amino acids take place in May, with resultant uncoupling of amino acid synthesis and arrested development (2,4). The sequence of reactions involved in the onset of regrowth may be closely related to the formation of the plastid initials, which may act as the trigger for such processes, and the expression of the genetic information that is responsible for the reactions may well be dependent on the stimulus provided by low temperatures.…”