Abstract
Soybean (Glycine max (L.) Merr) seed coat respiration rates in response to changing O(2) concentration and temperature were examined experimentally and with a mathematical analysis. The experimental observations showed seed coat respiration rates were sensitive to O(2) concentration below 0.25 micromole O(2) cm(-3). There was a steady decline in respiration rates from the saturating O(2) concentration down to about 0 to 0.03 micromole O(2) per cubic centimeter. Seed coat respiration rates were found to change linearly with temperature between 8 and 28 degrees C. The explanation for these results was sought by examining the diffusion of O(2) into the vascular bundles of the soybean seed coat. Differential equations describing O(2) uptake in two distinct zones of the vascular bundle were solved. The outer zone was assumed to be O(2) saturated and respiration proceeded at a constant rate per unit volume. The inner zone was assumed to have respiration rates which were linearly dependent on O(2) concentration. The solution of this mathematical model showed considerable similarity with the experimental results. Respiration rates were predicted to saturate at about 0.31 micromole O(2) per cubic centimeter and to decrease curvilinearly below that concentration. While the mathematical model predicted an exponential response in respiration rate to temperature, it was found that the exponential response is difficult to distinguish from a linear response in the temperature range studied experimentally. Consequently, both the experimental and theoretical studies showed the importance of O(2) diffusion into soybean seed coat vascular bundles as a potential restriction on respiration rates. In particular, it was suggested that increases in the total length of the vascular bundles in the soybean seed coat was the major option for increasing the total respiratory capability.