Distribution of Boron in Cells of Dicotyledonous Plants in Relation to Growth.

Abstract

Relatively little is known about the locus of boron in the plant cell or its availability for movement from one site to another. It appears that little or no reutilization of boron occurs in dicotyledonous plants, and an external available supply is needed throughout the period of growth. As the borate ion complexes readily with various polyhydroxy compounds (13), localization of boron in certain cellular fractions might not necessarily imply an important physiological role at these sites; nevertheless, information on its distribution or localization within the plant cell could contribute to a better understanding of its function.Boron determinations on various intracellular fractions separated by differential centrifugation indicated certain consistent trends regarding the distribution of boron within the cell, particularly in relation to growth, boron utilization and boron availability. These results have been briefly summarized (12) and will be reported fully here. MATERIALS AND METHODSSunflower (Helianthus annuus L., var. Mammoth Russian) and mung bean (Phaseolus aureus Roxb.) were grown in nutrient solutions in a controlledenvironment room under conditions previously described (10). The seeds were sown in quartz sand, watered with tap water, and one week later the seedlings were transferred to nutrient solutions contained in wide-mouth, low-boron soft glass quart fruit jars wrapped in black cloth. The sunflower plants were grown in solutions of the macronutrient composition previously described (10); the solutions for the mung beans consisted of a one-eighth concentration of Hoagland and Arnon's no. 1 solution (3). Iron, manganese, zinc and copper were added to both solutions at concentrations of 5.0, 0.5, 0.05 and 0.02 ppm respectively.As Plants were harvested at several periods for various determinations. Twenty-five g fresh tissue samples were used; this included the terminal bud regions and the blades of the two youngest, fully expanded leaves of about 11 plants for sunflower and the terminal bud regions and the leaflets from the youngest, fully expanded leaf of about 45 plants for mung bean. The samples were prepared and separated into various intracellular fractions by the procedure used bv Gordon (2). The tissue was ground in a chilled mortar with the aid of acid-washed sand in 50 ml phosphate buffer, 0.2 M, of pH 7.0, made 0.3 M with sucrose. The homogenate was strained through 200-mesh nylon cloth; the material that passed through is designated homogenate filtrate and that remaining in the cloth as homogenate residue (

Distribution and Partitioning of Newly Taken-up Boron in Sunflower

“…Furthermore, our results indicate that the leaf-to-leaf B gradient is produced mainly by water-soluble B and that cell-wall-bound B is distributed rather evenly among the leaves. These results were consistent with our previous report on sugar beet plants (Matoh et al, 2001), and the data in sunflower plants by Skok and McIlrath (1958). 10 Boron uptake experiments revealed that newly taken-up B is delivered preferentially to the younger leaves (Figures 2a and 3).…”

Selection and partial characterization of a boron-tolerant tobacco cell line

“…1991) and/or glycoproteins (Blevins and Lukaszewski 1998). Isolation of these complexes (Kobayashi et al 1996) supported the early hypothesis of Skok and Mcilrath (1958) that B is involved in the formation of structural units or building blocks of the cell wall. Therefore in developing B-deficient conditions, wall B content remained constant while soluble B content declined near zero.…”

“…Accordingly, in the present study it was assurped that soluble B is mainly represented by cytoplasmic and vacuolar B and insoluble B is represented by B bound to the cell wall. Skok and Mcilrath (1958) showed that when plants began to develop deficiency symptoms, the amount of insoluble B remained constant while that of soluble B declined to near zero. These findings suggest that although the volume of the symplasmic B pool is much larger than that of the apoplasmic one and subsequently variations in the symplasmic pool following the changes in the B supply, are more pronounced, the level of B uptake is controlled by both cell wall and cytoplasm, as suggested by Brown and Hu (1994) and Dannel et al (1999).…”

Two Chains of Rhamnogalacturonan II Are Cross-Linked by Borate-Diol Ester Bonds in Higher Plant Cell Walls

“…A number of metabolic disorders that are consequences of B deficiency have been discussed in recent reviews (Dugger, 1983;Parr and Loughman, 1983; Loomis and Durst, 1992). Skok and McIlrath (1958) pointed out that the locus of B in the plant cell was little known, and the issue has never been resolved. We have shown that in cultured tobacco cells more than 98% of the B is present in the cell wall (Matoh et al, 1992), and that a BPC can be isolated from radish (Xapkanus sativus) cell walls (Matoh et al, 1993a).…”