Partitioning and mobilization of starch and N reserves in grapevine (Vitis vinifera L.)

Abstract

We followed C and N reserves of grapevines grown in trenches under semi-controlled conditions over a 3-year period after planting. Temporal mobilization of stored C and N and subsequent distribution of reserve materials within the vines were described in parallel with ¹⁵N uptake, particularly during the third growing season. Storage C in the perennial tissues (roots, trunk, canes) was mainly made of starch, which accumulated in the ray parenchyma of the wood. In the permanent tissues, starch and total nitrogen contents were found to decrease early in the development (bleeding sap, budbreak) whereas, on a concentration basis, they decreased only after stage 7 (first leaf fully expanded). Starch started to accumulate again in the perennial tissues during flowering. The same observation was made with total nitrogen, although N levels were much lower than those of starch. The ¹⁵N study showed that N uptake by the roots started at budbreak and increased with vine development, becoming predominant over reserve mobilization only after the onset of flowering. Taken together, these results indicate that the spring growth period can be divided into three main phases: In the first (dormancy to budbreak), significant losses of C and N proceed mainly via root necrosis. In the second period (first leaf to the onset of bloom), a strong mobilization of starch (and, to a lower extent, of N) occurred for supporting vegetative and reproductive growth. At that point, most of the C and N reserves used on the spring flush were those of the roots, rather than those of the old wood (trunk, canes). In the third period (bloom and early berry development), the mobilization process became low and was relieved by N uptake (and CO₂ assimilation) supplying nutrients to the sink structures.

Introduction

Woody plants are particularly reliant on reserves to support rapid seasonal growth phases (Zimmermann, 1971; Loescher et al., 1990; Mooney and Gartner, 1991). Thus, reserve mobilization in perennial crop species is considered to be a major determinant of agricultural yield. In grapevine (Vitis vinifera L.), nitrogen uptake and carbon assimilation remain low for several weeks after bud burst (Hale and Weaver, 1962; Kriedemann et al., 1970; Conradie, 1980; Löhnertz, 1988). Therefore, spring growth flush is mainly sustained by the remobilization process (Scholefield et al., 1978; Conradie (1980), Conradie (1986)).

Carbon reserves in grapevine have long been studied. They consist mainly of starch (Bouard, 1966), but significant amounts of soluble sugars may appear during winter depending on the temperature. Seasonal dynamics of starch and soluble carbohydrates have been described in the canes of some varieties (Eifert et al., 1960; Bouard, 1966). Accordingly, sugars accumulated in the trunk and roots are the first carbohydrates used by emerging shoots in the spring (Scholefield et al., 1978). On that point, it is assumed that sucrose is the major transport form of carbohydrates in grapevine, as in most higher plants (Kuhn et al., 1999). However, while starch fate in the aerial tissues is well documented, the process of starch mobilization in vine roots throughout the growing season has received little attention.

Along with carbohydrates, nitrogen reserves play a crucial role in supporting early season growth of woody plants (Zimmermann, 1971; Conradie, 1980; Tromp, 1983). In grapevine, N reserves are located predominantly in the roots and are made by amino acids (mostly arginine) and proteins (Schaller et al., 1989; Kliewer, 1991). A fraction of these compounds may be lost by the vines through bleeding sap (Glad et al., 1992a) or by mobilization towards the growing upper structures (Conradie, 1991; Glad et al., 1992b). In addition, nitrogen uptake supplements N mobilization during the growing season. Although nitrogen uptake starts early in the development cycle (Conradie, 1980; Löhnertz, 1988), it generally remains low until flowering, even in cases of high nitrogen availability in the soil (Tromp and Ovaa, 1973; Conradie (1980), Conradie (1986)). Accordingly, fine roots are most effective in mineral uptake (Murisier, 1996), but they start to differentiate and develop only several weeks after bud burst (Zapata et al., 2001), root growth flush peaking at or about anthesis (Roubelakis-Angelakis and Kliewer, 1992). Thus, nitrogen remobilization upon spring growth might be the major process accounting for N allocation to the growing tissues of vines, at least until flowering. In that respect, the use of ¹⁵N labelling has proved to be a potent tool to investigate N uptake, storage and mobilization in crop species (Deléens et al., 1994). Thus, it may be used to compare the relative contribution of N reserves accumulated by grapevine during the previous growing seasons to that of the current year N uptake.

Vegetative (including root) growth, dry matter partitioning, and reproductive development of grapevines in trenches under semi-controlled conditions have been described recently (Zapata et al (2001), Zapata et al (2003)). This experimental design has been further used to investigate starch- and total-N partitioning as well as their translocation from the permanent to the annual upper organs. We report here the results of this study conducted on a Pinot noir variety during a 3-year period after planting. Objectives of this study were: (1) to determine at what point and to what extent grapevine relies on stored reserves; (2) to describe further the relative contribution of the root reserves and those reserves located in the trunk or canes; and (3) to elucidate the fate and significance of N reserves accumulated 2 years earlier. The expected results should be of great interest to vine growers with regard to optimizing the timing of nitrogen fertilization.