Control of Seed Respiration and Growth in Vicia faba by Oxygen and Temperature: No Evidence for an Oxygen Diffusion Barrier

Abstract

The rate of dry matter accumulation by seeds of Vicia faba L. cv. Minica increases with temperature in the range of 16 to 26°C.The duration of dry matter accumulation decreases with temperature, resulting in a decrease of final seed dry weight. In this study we test the hypothesis that a diffusion barrier for 02, located in the seed coat, inhibits seed respiration and growth. The rate Of 02 uptake of intact seeds and of excised embryos and seed coats (separated seeds) was measured in air and buffer at 16, 20, and/or 260C at various 02 concentrations and developmental stages. Oxygen uptake rates of intact seeds in buffer were only 9 to 15% of those in air. In buffer, the respiration rate of intact seeds decreased at a PO2 below air saturation (21 kilopascals), whereas separated seeds showed a decline of 02 uptake only below 80% of air saturation. In air, embryo excision had no effect on the sensitivity of seed respiration to PO2, at both 20 and 260C. In air at 200C, separated and intact seeds showed similar rates of 02 uptake. Oxygen uptake by intact seeds, both halfway and beyond the linear growth phase, showed a temperature coefficient Q1o of 2.3 and was insensitive to p02 in the range of 80 to 100% of ambient. These results indicate that V. faba seed respiration in air is not limited by the diffusion of 02 into the seed.Both the rate and duration of seed growth are important parameters in yield formation in grain crops (13) and grain legumes (4, 6, 10). Cell division is an important process determining seed growth (5, 7, 10). One of the main environmental factors affecting these processes is temperature (4, 6, 13).The cause and mechanism of the cessation of seed growth in cereals and legumes are not known (5,6,10,13,20,23). With increasing growth temperature (16-26°C), the rate of dry matter accumulation in the seed of Vicia faba increases, but the duration of seed growth decreases. The combined effect is a lower final seed dry weight as temperature increases (4). Similar effects of temperature on seed growth have been reported for soybean (6) and wheat (13). The growth duration of Vicia embryos in vivo is similarly affected by temperature as in vitro (4,5). This has also been found for seed growth rate in soybean by Egli and Wardlaw (6). Thus, the cause of both the cessation of seed growth and the lower final seed dry weight at high temperature may be sought in processes in the seed.The relationship between growth and respiration of devel-668 oping seeds has not received much attention (10,11,20). Ohmura and Howell (15,16) were the first to suggest that 02 uptake by the cotyledons of soybean seeds during maturation may be limited by 02 diffusion through the seed coat. Recently, Sinclair (20, 21) has argued that 02 diffusion into the vascular vessels of soybean seed coats forms a potential limitation to seed respiration and growth. Gale (9) has shown that the CO2 evolution of intact soybean seeds is decreased by 02 partial pressures below ambient (<21 kPa), and suggests that the pod wall and seed coat ...

Seed O2 Uptake and Germination of Cold‐Tolerant and Cold‐Intolerant Cultivars of Muskmelon

“…Clark‐type oxygen electrodes can measure O 2 depletion by intact and decoated seeds through the gas phase in a sealed sample chamber (Bar Nun and Mayer, 1993, de Visser et al, 1990, Walker, 1988, Welbaum, 1993). In our study, the O 2 uptake of intact and decoated NY and P‐202 seeds was measured at 15 and 25°C with an oxygen electrode to determine how seed coats affect O 2 uptake by the embryo.…”

“…An apparatus comprising a Clark‐type oxygen electrode with a Teflon (polytetrafluoroethylene) membrane, a sample chamber (model LD2, Hansatech, Norfolk, England), and a control box (model CB 1, Hansatech) was used to measure O 2 uptake polarographically at a constant temperature of 15 or 25°C through the gas phase (de Visser et al, 1990). The oxygen electrode consisted of a 2‐mm‐diameter Pt cathode and a concentric Ag anode in an epoxy resin disc linked by a KCl electrolyte solution.…”