Relationship between boron and calcium in the N₂‐fixing legume–rhizobia symbiosis

Abstract

Because boron (B) and calcium (Ca 2+ + + + ) seem to have a strong effect on legume nodulation and nitrogen fixation, rhizobial symbiosis with leguminous plants, grown under varying concentrations of both nutrients, was investigated. The study of early pre-infection events included the capacity of root exudates to induce nod genes, and the degree of adsorption of bacteria to the root surface. Both phenomena were inhibited by B deficiency, and increased by addition of Ca 2+ , resulting in an increase of the number of nodules. The infection and invasion steps were investigated by fluorescence microscopy in pea nodules harbouring a Rhizobium leguminosarum strain that constitutively expresses green fluorescent protein. High Ca 2+ + + + enhanced cell and tissue invasion by Rhizobium , which was highly inhibited after B deficiency. This was combined with an increased B concentration in nodules of plants grown on B-free medium and supplemented with high Ca 2+ + + + concentrations, and that can be attributed to an increased B import to the nodules. Histological examination of indeterminate (pea) and determinate (bean) nodules showed an altered nodule anatomy at low B content of the tissue. The moderate increase in nodular B due to additional Ca 2+ + + + was not sufficient to prevent the abnormal cell wall structure and the aberrant distribution of pectin polysaccharides in B-deficient treatments. Overall results indicate that the development of the symbiosis depends of the concentration of B and Ca 2+ + + + , and that both nutrients are essential for nodule structure and function.

Factors contributing to in vitro shoot-tip necrosis and their physiological interactions

“…High Ca enhanced tissue invasion by Rhizobium, a phenomenon inhibited by B deficiency. Calcium also increased B redistribution in the nodules of plants grown in B-free media, suggesting that calcium promotes B import to and redistribution from the nodules (Redondo-Nieto et al 2003). These findings suggest that the concentration of both B and Ca in the culture medium influences the uptake of one another.…”

Boron and calcium increasePisum sativum seed germination and seedling development under salt stress

“…Furthermore, Kobayashi et al (1999) demonstrated that Ca 2+ promoted in vitro formation of dimers of borate-rhamnogalacturan II and proposed that Ca 2+ stabilizes pectin polysaccharides of the cell wall through ionic and coordinate bonding in the polygalacturonic acid region. This interaction has recently been shown by imnmunolocalization of pectin polysaccharides in cell walls of pea root nodules (Redondo-Nieto et al, 2003). Regarding legume development, Carpena et al (2000) reported that addition of high Ca during pea growth under B deficiency could mediate mobilisation of B from old to young tissues in pea plants.…”

“…This typical effect of loss of pectin organisation in the absence of B (Matoh and Kobayashi, 2002), could not be reversed by B but only after addition of both B and Ca to salt stressed plants. Although both nutrients can play complementary roles so that Ca could prevent some effects of B deficiency, both nutrients are absolutely required for the maintenance of cell wall structure (Redondo-Nieto et al, 2003). Therefore, although Ca increased germination under salt stress ( Figure 2B), the low availability of B provoked by 75 mM NaCl ( Figure 8A-B), made necessary a continuous supply of extra B for root elongation ( Figure 4B).…”

“…In agreement with this report, measurements of the concentration of B in nodules indicate that it is higher when B-deficient plants grow with a supplement of extra Ca. This is a sign of a BCa interaction in the establishment and maintenance of the symbiosis (Redondo-Nieto et al, 2003).…”

Alleviation of salt-induced ionic, osmotic and oxidative stresses inCajanus cajannodules by AM inoculation

“…The disproportionate presence of Na þ in both cellular and extracellular compartments negatively impacts on the acquisition and homeostasis of essential nutrients such as K þ and Ca 2þ . Potassium is a vital contributor to effective N fixation by legumes (Sanders et al 1999;Høgh-Jensen 2003) and calcium signaling is critical for the establishment of a successful plant-microbe symbiosis (Redondo-Nieto et al 2003;Shaw & Long 2003;Garg & Geetanjali 2007).…”