Metabolism of carbohydrate and lipid reserves in germinated cotton seeds

Abstract

Utilization of reserve lipid and carbohydrates during germination (0-12 h) and postgerminative growth (12-48 h) was studied in cotton (Gossypium hirsutum L.) seedlings. Raffinose and stachyose were utilized during the germination period and early growth; mobilization was associated with α-galactosidase (EC 3.2.1.22) activity. Results from pulse-chase experiments with [(3)H]raffinose supplied exogenously to 4-h soaked seeds indicated that raffinose-derived catabolites contributed to the coincident increase in cotyledon sucrose and starch, and to the small increase in axis dry weight. Starch appears to be an alternative sink for end products of hydrolysis of reserve carbohydrates prior to the onset of rapid axis growth and cotyledon expansion. Mobilization of neutral lipid commenced at about 16 h after soaking, concomitant with development of key glyoxylate-cycle and other gluconeogenesis-related enzyme activities. Axis dry weight increased three-fold between 24 and 48 h. Results from pulse-chase (3 h, 16 h) experiments in which [2-(14)C]acetate was supplied to cotyledons of intact 22-h-old seedlings showed that acetate-derived metabolites were not transported exclusively to the axes, but were partitioned between axes and cotyledons. Only 27% of total incorporated radioactivity was recovered in axes following the chase, 18% was evolved as CO2, and the rest was recovered in water-soluble substances (20%) and polymers (31%) within the cotyledons. Of the polymers, 55% of the activity was in polysaccharides (Starch, pectic substances, hemicellulose, cellulose), 25% in protein, and 20% in unidentified neutral and acidic compounds. Considering these data, the amount of lipid mobilized, and various routes by which supplied [2-(14)C]acetate could be metabolized, it appears that lipidderived compounds contribute only 25-40% of axis dry-weight gain. Lipid-derived substances retained in the cotyledons likely are utilized for expansion and differentiation of the cotyledons into photosynthetic organs.

Germination of CO2‐enriched Pinus taeda L. seeds and subsequent seedling growth responses to CO2 enrichment

“…The germination success of P. taeda declined in proportion to the loss of fatty acid content with seed ageing (Marquez‐Millano 1989). During germination, most lipid reserves are broken down into their constituent fatty acids, converted to sugars, and transported to the cotyledons and axis for dry weight gain and maintenance (Doman et al . 1982; Gori 1979; Shewry & Stobart 1973; Stone & Gifford 1999; Vanni, Vincenzini & Vincieri 1975).…”

“…1982; Gori 1979; Shewry & Stobart 1973; Stone & Gifford 1999; Vanni, Vincenzini & Vincieri 1975). Doman et al . (1982) pointed out that axis dry weight gain in the first 48 h of germination was almost exclusively root growth, which would agree with our findings of earlier radicle emergence and generally longer roots of the CO 2 ‐enriched seed source (Fig.…”

Carbohydrates and carbohydrate enzymes in developing cotton ovules

“…3). At about the time (ca 45 DPA) when ovule carbon import and lipid synthesis cease (Trelease et al 1986), embryo starch is converted to galactosides, which will serve the germinating seed until effective lipid degradation can take place (Doman et al 1982). Raffinose is synthesized by the transfer of galactose to sucrose from galactionol; a second galactose addition produces stachyose.…”

Primary metabolite mobilization during germination in rosewood (Aniba rosaeodora Ducke) seeds

“…Determination of α-amylase activity was performed in seeds after 6, 9, 12, 15, 18 and 21 days of germination according to Doman et al (1982). Plant material was homogenized in 60mM phosphate buffer (pH 6.8), filtered and then centrifuged at 12.000 x g, 4°C, for 15min.…”