Vegetative Storage Proteins in Poplar

Abstract

Bark, wood, and root tissues of several Populus species contain a 32-and a 36-kilodalton polypeptide which undergo seasonal fluctuations and are considered to be storage proteins. These two proteins are abundant in winter and not detectable in summer as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunodetection. An antibody raised against the 32-kilodalton storage protein of Populus trichocarpa (T. & G.) cross-reacts with the 36-kilodalton protein of this species. The synthesis of the 32-and 36-kilodalton proteins can be induced in micropropagated plants by short-day conditions in the growth chamber. These proteins are highly abundant in structural roots, bark, and wood and combined represent >25% of the total soluble proteins in these tissues. Nitrate concentration in the leaves and nitrate uptake rate decreased dramatically when LD plants were transferred to short-day conditions; the protein content in leaves was unaffected. A decrease of the 32-and 36-kilodalton polypeptides occurs after transferring induced plants back to LD conditions. Both polypeptides are glycosylated and can be efficiently purified by affinity chromatography using concanavalin A-Sepharose 4B. The 32-and the 36-kilodalton polypeptides have identical basic isoelectric points and both consist of at least three isoforms. The storage proteins show a loss in apparent molecular mass after deglycosylation with trifluoromethanesulfonic acid. It is concluded that the 32-and 36-kilodalton polypeptides are glycoforms differing only in the extent of glycosylation. The relative molecular mass of the native storage protein was estimated to be 58 kilodalton, using gel filtration. From the molecular mass and the elution pattern it is supposed that the storage protein occurs as a heterodimer composed of one 32-and one 36-kilodalton subunit. Preliminary data suggest the involvement of the phytochrome system in the induction process of the 32-and 36-kilodalton polypeptides.Most deciduous, woody perennials exhibit a seasonal variation in the nitrogen levels in many of their tissues. The seasonal fluctuation of nitrogen reserves has been reported in several earlier studies (6,8,22 (17) showed that poplar is extremely efficient at nitrogen conservation. More than 80% of the whole-tree nitrogen content is conserved during dormancy, and the majority of stored nitrogen can be found in the roots. It might be possible to increase biomass production of poplar through clonal selection for a minimal loss of nitrogen during the winter.In this paper, we characterize a 32-and a 36-kD storage protein in vegetative tissues of poplar which show seasonal fluctuations and are supposed to occur as glycoforms. We also demonstrate the induction of these two proteins in micropropagated plants under SDs and their disappearance under LDs using a 32-kD antibody. Involvement of the phytochrome system in the induction process is discussed. MATERIALS AND METHODS Plant MaterialBark and wood from first-order twigs and bark of structural roots were...

Improved growth in a field trial of transgenic hybrid poplar overexpressing glutamine synthetase

“…7). This protein band corresponds in size to VSP previously characterized in poplar bark (Coleman et al, 1991;Langheinrich & Tischner, 1991). The comparison between stained SDS-PAGE gels from control and transgenic plants showed that the 32-kDa polypeptide accumulated in transgenic stems more quickly than in control plants (Fig.…”

Fluctuation of Vegetative Storage Proteins in the Seedlings of Swietenia macrophylla, Analogous to the Seasonal Changes of Those in the Shoot of the Adult Tree

“…Furthermore, the stored nitrogen compounds have been suggested to be mainly used in supporting new shoot growth and development in the following spring while the nitrogen compounds from root absorption in the current year are used for tree growth in later seasons (Stepien et al 1994). Although VSPs have been identified in the vegetative organs of several temperate trees (van Cleve et al 1988;Wetzel et al 1989;Clausen and Apel 1991;Langheinrich and Tischner 1991;Stepien and Martin 1992;Coleman 2001a, 2001b), their seasonal fluctuation was assumed to be similar to that of the other so-called stored nitrogen compounds as above (Wetzel et al 1989). On the basis of this assumption, external factors such as nitrogen application, low temperature and short days play an important role in regulating VSP accumulation (Clausen and Apel 1991;Langheinrich and Tischner 1991;Coleman et al 1991Coleman et al , 1992Coleman and Chen 1993).…”

“…The external factors, such as low temperature and short days, have been emphasized as key signals in inducing VSP accumulation in trees (Causen and Apel 1991;Langheinrich and Tischner 1991;Coleman et al 1991Coleman et al , 1992Coleman and Chen 1993). Recently, we found that the seasonal fluctuation of VSPs was very similar between the tropical tree S. macrophylla and the temperate tree Populus canadensis, suggesting that this seasonal fluctuation pattern in the whole tree might be an important mechanism by which the trees regulated their growth (Tian et al 2003(Tian et al , 2005.…”

“…Vegetative storage proteins in trees, especially in the temperate trees poplar and willow, have been examined at cytological, biochemical and molecular levels (van Cleve et al 1988;Wetzel et al 1989;Clausen and Apel 1991;Langheinrich and Tischner 1991;Stepien and Martin 1992;Coleman 2001a, 2001b). The external factors, such as low temperature and short days, have been emphasized as key signals in inducing VSP accumulation in trees (Causen and Apel 1991;Langheinrich and Tischner 1991;Coleman et al 1991Coleman et al , 1992Coleman and Chen 1993).…”

“…As adult trees are large in size, detached branchlets of trees were often used for studying the mechanism of VSP accumulation (Langheinrich and Tischner 1991). The seedlings of trees are small in size and may be candidates for such study.…”