Growth and Deposition of Inorganic Nutrient Elements in Developing Leaves of Zea mays L.

Abstract

Spatial distributions of growth and of the concentration of some inorganic nutrient elements were analyzed in developing leaves of maize (Zea mays L.). Growth was analyzed by pinprick experiments with numerical analysis to characterize fields of velocity and relative elemental elongation rate. Inductively coupled plasma and atomic emission spectroscopy were used to measure nutrients extracted from segments of leaf tissue collected by position. Leaves 7 and 8, both elongating 3 millimeters per hour had maximum relative elemental growth rates of 0.06 to 0.08 millimeters per hour with maximum rates 20 to 50 millimeters from the node and cessation of growth by 90 millimeters from the node. Spatial distribution of dry weight density revealed that the rate of biomass deposition was maximum in the most rapidly expanding region and continued beyond the elongation zone. The nutrient elements K, Cl, Ca, Mg, and P showed different distribution patterns of ion density (on a dry weight basis). K and Cl had minimal density in the leaf tips; K density was maximum in the growing region, whereas Cl density was maximum at the region of growth cessation. Ca, Mg, and P had relatively high densities at the base of the elongation zone near the node and also in the tip regions. Near the node, P and Mg densities were higher in the young, growing leaves, whereas Ca density near the node was higher in older leaves that had completed elongation. Deposition rates of all nutrients were greatest in the region of maximum elongation rate.An understanding of the physiology of growth requires knowledge of the spatial distribution of growth within expanding organs and, on the same spatial scale, knowledge of the distribution of growth-associated chemical and physical attributes of the tissue (3,22). In the past decade, growth kinematics (3, 21, 22) have been analyzed to describe quantitatively the effects of environmental variables on development of roots and leaves. In roots, the pattems of growth velocities and REG2 rates have been described for different temperatures (15), levels of water stress (20), and salinity (27). In monocot leaves, growth pattems have been described for different genotypes (24), developmental stages (18), and irradiances (17).The growth rate pattem is also related to the accumulation of plant nutrients in expanding tissue.

Temperature Affects Expansion Rate of Maize Leaves without Change in Spatial Distribution of Cell Length (Analysis of the Coordination between Cell Division and Cell Expansion)

“…Cell flux was therefore considered in a steady state, since, in addition, LER was constant (Fig. 2) and a11 leaves under study were in a developmental stage during which profiles of SER do not vary with time (Schnyder et al, 1990;Meiri et al, 1992). In contrast, cells initiated at the beginning of the incubation period had only crossed 19 and 25 m, respectively, by the end of the experiments at 13 and 21°C.…”

“…Cell division rate (d,) was calculated in each segment (i) by combining the records of SER and of local cell length in the continuity equation (Gandar, 1980;Silk, 1992):…”

“…This implies a change with temperature in cell-wall mechanical properties, such as that observed in roots by Pritchard et al (1990). If, as in the case of maize roots (Silk, 1992), final cell size was not affected by increased temperatures, a change in cell production should match the change in cell expansion rate. We have tested this possibility by examining, with contrasting meristem temperatures, the spatial distributions of LER and of cell production.…”

“…Spatial analysis of elongation and use of the continuity equation (Gandar, 1980;Silk, 1992) provided an adequate framework for analyzing both processes. In monocot leaves, cell division is accompanied by cell expansion, with both processes partly overlapping in time and space.…”

Effects of salinity on xylem structure and water use in growing leaves of sorghum

“…It would be interesting to study hydraulic conductivity in conjunction with xylem fine structure to find the effect of salinity on the putative hydraulic bottlenecks of sorghum. Bernstein et al (1995) used growth data with a continuity equation (Meiri et al, 1992) to calculate local net rates of deposition of water and calcium into the growing tissue of salt-affected and control leaves of sorghum. To explore the functional significance of the salt induced effects on xylem element diameter, we compare the published water deposition rates to the anatomical measurements reported here.…”