Functional Boron Requirement for Leaf Expansion and Its Use as a Critical Value for Diagnosis of Boron Deficiency in Soybean

Abstract

The slow response of shoot dry matter to nutrient stress under many experimental conditions sometimes makes it an unsatisfactory criterion for defining critical concentrations of nutrients for deficiency diagnosis by plant analysis. This study was done to see if the relationship between the B concentration in young leaves and their rate of elongation could be used to define critical values for diagnosis of B deficiency in soybean [Glycine max (L.) Merr.] Soybean was grown in nonrenewed solution culture at two initial B concentrations chosen so that plants at the lower concentration became deficient during the growing period, while those at the higher B concentration remained healthy. Boron deficiency depressed dry matter (DM) of roots and young leaves but increased DM of older, expanded leaves, thus delaying the response of total shoot DM to B deficiency. As B supply became depleted, B concentrations in young leaves declined rapidly from 20 to 3 mg kg−1 DM, giving falsely low values for diagnosis of B deficiency when correlated with shoot DM. The rate of elongation of young expanding leaflet blades was depressed by B deficiency earlier than shoot DM. Correlation of B concentration in young leaves with their elongation rate suggests that they require 12 mg B kg−1 DM to achieve 90% of their maximal rate. It is suggested that this value represents the functional B requirement for leaf expansion and that it provides a more consistent and accurate critical value for diagnosis of B deficiency in soybean than that determined by correlation with shoot DM in the usual way.

Preferential translocation of boron to young leaves inArabidopsis thalianaRegulated by theBOR1Gene

“…In oilseed rape, the critical B concentration was 10-14 mg B kg-1 dry weight in the youngest open leaf (Huang et al 1996). Young leaves of soybean required 12 mg B kg-1 dry weight to achieve 90% of their maximal elongation rate (Kirk and Loneragan 1988). Thus the concentration of 5.9 mg B kg-1 dry weight (Table 1) is considered to be deficient for the growth of young leaves in A. thaliana.…”

Boron Deficiency in Soils and Crops: A Review

“…The alkaline, silt, and sandy loam soils in Northeast Arkansas are also known to suffer from B deficiency (Anonymous, 2007a). Soybean is known to respond positively to B application on deficient sites of the world (Wu, 1986;Kirk & Loneragan, 1988). The increase in oil content and other quality parameters in soybean with combined application of B and sulfur in India have been noticed by Dinesh & Sudkep (2009), and Kumar & Sidhu (2009).…”

The importance of sampling immature leaves for the diagnosis of boron deficiency in oilseed rape (Brassica napus cv. Eureka)

“…They are programmed nutrient addition (Asher and Edwards, 1983) and the functional nutrient requirement for leaf elongation (Kirk and Loneragan, 1988). They are programmed nutrient addition (Asher and Edwards, 1983) and the functional nutrient requirement for leaf elongation (Kirk and Loneragan, 1988).…”

“…They are programmed nutrient addition (Asher and Edwards, 1983) and the functional nutrient requirement for leaf elongation (Kirk and Loneragan, 1988). Consequently, with this conventional approach, correlation of whole shoot dry matter with B concentrations in young leaves leads to a gross underestimation of critical B concentration (Kirk and Loneragan, 1988). In conventional solution culture, nutrient levels in solution fluctuate greatly, due to infreqent solution renewal and plants often experience large changes in nutrient status during the experimental period, possibly ranging from adequacy in the beginning to deficiency at the end in plants of the same treatment.…”