Differential Leakage of Intracellular Substances from Imbibing Soybean Seeds

Abstract

Leakage of electrolytes, substances absorbing UV light, and enzymic activities from imbibing soybean (Glycine max IL.I Menf.) seeds were compared to determine the extent that passive diffusion and cellular rupture contribute to each. Imbibing seeds with testae removed had average Arrhenius energies of activation (5 to 25°C) of 3.0 and 15.8 kilocalones per mole, respectively, for the leakage of electrolytes and embryo malate dehydrogenase activity. Leakage of embryo enzymes from imbibing seeds was dependent on loss of testa integrity and subsequent loss of cellular membrane integrity or inability to seal preexisting membrane discontinuities. These data suggest that electrolyte leakage from imbibing seeds is primarily by passive diffusion, whereas the diffusion of intraceDlular macromolecules is primarily dependent on physiological phenomena affecting membrane integrity. Kinetic data and examination of the composition of seed leachates indicated that the leakage of substances absorbing UV light during imbibition is due to both passive diffusion of low molecular weight solutes and macromolecules released from ruptured cells.ferences one would see in the kinetics of leakage of various seed components. If the assays used for seed leakage do not correlate with one another under most experimental conditions they should not be used interchangeably, as they have in the past, to study the leakage processes.In this study, we utilized imbibing soybean seeds to examine commonly used seed leakage assays to gain insight on the contribution of passive diffusion through membranes and cellular rupture (preexisting or induced) to each measurement. Seeds with various degrees of testa integrity were used because testa integrity is a primary factor in controlling legume seed leakage and cellular damage during germination (7,11,12,21,24). Effects of temperature were studied to gain insight into the energetics of the leakage of various seed components during imbibition and effects of 4,2 were studied because of previous studies which indicate a 4iw effect on soybean seed leakage and seedling vigor (28, 29). Our findings indicate that passive diffusion of low mol wt solutes and membrane rupture-dependent diffusion of macromolecules during seed imbibition are quite different kinetically and that the contribution of each process is variable among the methods used for measuring seed leaching.

Positive correlation between the number of root nodule primordia and seed sugar secretion in soybean (Glycine maxL.) seedlings inoculated with a low density ofBradyrhizobium japonicum

“…Because the whole SE and HP of SE displayed an almost equal potential for rhizobium proliferation, the compounds in LP and HW fractions of SE appeared to display a negligible potential. It was reported that imbibing soybean seeds leaked out high molecular materials mainly from the physically damaged cotyledon and diffused out low-molecular substances from the seed coat (Simon 1974;Duke et al 1983). Almost the same amount of secreted sugars and amino acids was observed in a comparative examination of whole seeds and isolated soybean seed coats (data not shown), suggesting that most of the low molecular materials in the SE were derived from seed coats.…”

“…Though the root exudate should be considered as a factor affecting root nodulation, seedreleased compounds may strongly affect rhizobium infection and nodule formation immediately after rooting and germination. Duke et al (1983) suggested that imbibing soybean seeds exuded macromolecules from ruptured embryo cells and low molecules by negative diffusion. Although it has been reported that pathogen growth was enhanced by seed leachates (Schroth and Cook 1964;Nelson and Craft 1989), there are only few studies on the effect of seed exudates on rhizobium proliferation.…”

RhizobiumProliferation-Supporting Substances in Seed Exudates of Common Bean (Phaseolus vulgarisL.)

“…The contents of sugars and amino acids (pmol g-'-seed weight) were calculated by using the average weight of a seed (Hokkaikintoki, 0.65 g; Himetebou, 0.36 g; Kurodanekinugasa, 0.19 g) reported previously , and the respective values of the sugars and amino acids decreased in the order of Kurodanekinugasa (12.47 and 2.24), Himetebou (12.17 and 1.37) and Hokkaikintoki (7.49 and 0.69). It was reported that nutrient leakage from imbibing soybean seeds depended on passive water-diffusion and cellular rupture of the cotyledon (Duke et al 1983), and that water absorption by a small seed was more rapid than that by a large one (Calero et al 1981;Horings et al 1991). Since the seed size of Kurodanekinugasa is the smallest, the contents of sugars and amino acids in the seed exudates of Kurodanekinugasa were considered to have become the highest among the three cultivars.…”

Oxidative Phosphorylation by Mitochondria Extracted from Dry Sunflower Seeds

“…Also, in spite of many attempts in various laboratories, phosphorylating mitochondria ofgerminating seeds have been obtained in only two cases, from peanut cotyledons imbibed for 40 min (27), and from cucumber cotyledons imbibed for 6 h (14). Moreover, the leakage of solutes during seed imbibition suggested some degree of membrane disorganization either in the dry state or following rehydration (5,23,26). It was believed, in particular, that mitochondria were damaged and had to be repaired during the germination period to become functional at the time of radicle emergence (13).…”