The effects of magnesium deficiency on sugar partitioning do not restrict the root growth in Eucalyptus young plants

Os efeitos da deficiência de magnésio na partição de açúcares não restringem o crescimento de raízes em plantas jovens de eucalipto

Abstract

The symptoms of magnesium (Mg) deficiency have been well documented in crop plants. The relationship between Mg deficiency as an important abiotic stress factor and the sugar partitioning may restrict the root growth and limit the success of planting in the field. Despite of this, the primary physiological effects of low Mg availability remain largely unknown in eucalyptus. This paper aimed to investigate how the Mg deficiency affects biochemical aspects of sugar partitioning associated to dry matter accumulation in roots of Eucalyptus urophylla young plants, clone AEC 144. Experimental work was carried out in a greenhouse, arranged by completely randomized design, consisted by split plot 5x4, using the following Mg levels: 0, 25, 50, 75 and 100% in the Mg concentration of Clark’s nutrient solution. Evaluations were performed at 15, 30, 50 and 120 days after seedlings planting (DAP) in pots. Soluble (SS) and reducing (RS) sugar contents, invertase and sucrose synthase (susy) activity and shoot and root dry matter were measured. Increased sugar concentrations, both SS and RS, were found in leaf tissues from 30 DAP. In root tissues, neither RS nor SS content showed differences between Mg deficiency treatments and control. Significant differences were also not found in both root dry matter accumulation and shoot/root dry matter ratio. The Mg deficiency did not affect sucrose cleaving in roots, which was predominantly catalyzed by acidic invertase, followed by susy and neutral invertase. We concluded that Eucalyptus urophylla is tolerant to Mg deficiency, because the sugar accumulation in the leaf tissues was not enough to constrain the dry matter accumulation in roots.

Keywords:
Woody plants; Mineral nutrition; Assimilate partitioning; Source-sink