Concentrations of Sucrose and Nitrogenous Compounds in the Apoplast of Developing Soybean Seed Coats and Embryos

Water deficits during seed filling often decrease seed size in soybean (Glycine max L.). The physiological basis for this re-sponse is not known but may result from direct effects of low seed water potential (',) on the seed filling process. To determine whether low l' occurred in reproductive tissues of soybean, we monitored the water status (',I, ls, and I,p) of leaf, pericarp, and seed (embryo and testa) tissue of greenhouse-grown plants subjected to a brief water deficit during the linear period of seed growth. Water deficits were imposed by withholding water and monitored in the reproductive tissues by thermocouple psychrometry. When water was abundant, leaf, pericarp, and seed I, were -0.5 to -0.7 megapascal at midday. When water was withheld, leaf l' decreased to -2.3 megapascals within 6 days. Pericarp 1' also decreased to -1.9 megapascal during this time.Pericarp ls followed the decline in *', but osmotic adjustment was not evident as the pericarp lost turgor completely by day 6.However, seed ',, I,, and 'ip were not significantly different from the controls. These results indicate that the water status of the developing seeds of soybean is not altered by short-term water deficits severe enough to inhibit the metabolic activity of the maternal plant. Maintenance of a favorable water status may be important for the conservation of seed growth rate exhibited by soybean under dry conditions. Water deficits during reproductive development often decrease seed size in soybean (Glycine max L.) (18, 21,26).Recent evidence indicates that the reduction in seed size is due primarily to a shortening of the seed filling period rather than an inhibition of seed growth rate (20,24). Since low TwI2 are known to affect the metabolic activity of the vegetative plant (5,10,12,25), the maintenance of seed growth rate implies either that seed metabolism is relatively insensitive to low TI or that the water status of developing seeds is not affected by water deficits that develop in the maternal tissues.To determine whether low T,, occurred in reproductive

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Effect of Water Deficits on Seed Development in Soybean

Westgate¹,

Dt²

1989

“…The Suc concentration of this fluid has been reported to be 150 to 200 m (Gifford amd Thorne, 1985) and the total amino xids concentration to be 10.5 to 22.5 mM (Hsu et al, 1984), with Gln and Asp being the predominant nitrogenous substances (Rainbird et al, 1984). A Suc concentration of 150 mM was used in this study.…”

Section: Justification Of Growth Medium Compositionmentioning

confidence: 94%

Changes in Soybean Fruit Ca2+ (Sr2+) and K+ (Rb+) Transport Ability during Development

Laszlo

1994

Mineral uptake by soybean (Glycine max [L.] Merrill) seeds during development can significantly affect seed quality and value. Little is known about seed mineral transport mechanisms and control processes, although it is clear that each mineral displays a characteristic accumulation pattern. lon-specific accumulation patterns could result from changes in source availability, in transport kinetics through the seed pod and seed coat, or in the mineral uptake capability of the embryo. CaZ+ and K+ have negligible and high phloem mobilities, respectively. CaZ+ accumulation lags behind dry matter (C and N) and K+ accumulation in soybean embryos. To eliminate source availability influences, the CaZ+ and K+ uptake ability of isolated embryos and of seeds in pod culture was examined during seed development. SrZ+ and Rb+ were used as transport analogs of Ca*+ and K+, respectively. SrZ+ and Rb+ uptake rates by isolated embryos increased with seed fresh weight, indicating that the embryo was not limiting ca*+ accumulation. However, the pod-cultured embryo Sr2+ and Rb+ uptake rate trends differed: Rb+ uptake increased with seed fresh weight, whereas SrZ+ uptake rates remained constant or decreased slightly. Ovule SrZ+ influx data suggest that the pod and seed coat impose a transport barrier that could account for the relative decline in embryo CaZ+ content during development.

“…The concentration of sucrose in the apoplastic volume of seed coats and embryos was estimated using the compartmental efflux kinetics technique reported by Hsu et al (17). These estimates were made between 30 and 35 DAA when seeds were in their linear filling period.…”

Section: Estimation Of Sucrose Concentrations In the Apoplast Of Seedmentioning

confidence: 99%

Relationship of Endogenous Abscisic Acid to Sucrose Level and Seed Growth Rate of Soybeans

Schussler¹,

Brenner²,

Brun³

1991

It has been proposed that abscisic acid (ABA) may stimulate sucrose transport into filling seeds of legumes, potentially regulating seed growth rate. The objective of this study was to determine whether the rate of dry matter accumulation in seeds of soybeans (Glycine max L.) is correlated with the endogenous levels of ABA and sucrose in those sinks. In particular, ABA has been shown to stimulate the movement of sugars in sugar beet (30), grape (7), pea (25), bean (6), and soybean (13). In legumes, exogenous ABA has been shown to stimulate assimilate unloading from seed coats (6, 25) and uptake of assimilates by embryos (15, 26), two processes that potentially limit the movement of assimilates to developing seeds (21, 27). Little information is available, however, to determine whether a relationship exits between endogenous levels ofABA in legume seed tissue and assimilate movement to those sinks.The in vitro uptake of sucrose by soybean embryos is concentration dependent (8,21,27), suggesting that higher concentrations of sucrose in seeds in situ would result in higher seed growth rates (8, 10). We hypothesized that endogenous ABA may control sucrose unloading from seed coats and/or sucrose uptake by embryos, thus regulating the concentration of sucrose available for seed growth. Endogenous concentrations of ABA in seed tissues of legumes have been shown to be positively or negatively correlated with seed growth rate, depending upon stage of development and environmental conditions examined (2,5,18,26). However, relationships between the concentrations of ABA and sucrose in these tissues and between the concentration ofsucrose and seed growth rate were not evaluated in these studies because assimilate levels in seed tissues were not measured.Our objective was to determine whether seed growth rate of soybean is correlated with the concentrations of endogenous ABA and sucrose in reproductive sinks. We evaluated nine PI2 genotypes with seed growth rates ranging from 2.5 to 10 mg seed d-'. We hypothesized that genotypes with high seed growth rates would be characterized by high concentrations of ABA and sucrose in their seed tissues. In addition, endogenous ABA and sucrose levels were compared with sucrose uptake by isolated embryos in vitro to determine their relationship to sucrose flux into developing seeds.