Utilization of lipid and protein storage reserves was examined during germination and early growth of somatic and excised seed embryos in vitro, and seed of interior spruce. High germination frequencies were recorded for somatic and excised seed embryos, and elongation of radicles and hypocotyls observed for both embryo types. Although elongation of the embryo types differed (i.e. somatic ≤ excised seed < seed), fresh weight gain was similar. Utilization of triglycerides in somatic embryos was more rapid than in excised seed and seed embryos, thus it appeared to be under embryo infuence. By contrast, depletion of storage proteins appeared to be influenced by the megagametophyte, with hydrolysis in somatic and excised seed embryos preceding that of the seed embryo by 2 days. Differential utilization of the storage reserves was temporally associated with differences in growth patterns of somatic and seed embryos. The evidence presented indicates that the in vitro germination medium does not entirely supplant the role of the megagametophyte during germination and early growth. The relevance of these results to artificial seed technology is discussed.

Excised axes from cotton (Gossypium hirsutum L. cv. M-8, a double haploid) were imbibed in vitro for 3,6,9,12,18 and 24 h. Data for length, fresh and dry weight and percentage water showed that excised axes undergo a triphasic pattern of growth: an initial burst, a short lag phase and then protracted rapid growth. Analysis of protein content with SDS-PAGE, and of activities of amino-, carboxy- and endopeptidases provided data indicating a direct correlation between major axis elongation growth between 12 and 24 h and enzymatic breakdown of storage proteins (especially those of 48 kDa) by carboxy- and endopeptidase. Data for axes imbibed at 30°C and 0–5°C for 12, 18 and 24 h indicated that a reduction in length and percentage moisture in the cold occurred in parallel with reductions in carboxy- and endopeptidase activities but not in ami-nopeptidase activity. The tentative conclusion is that carboxy- and endopeptidase are probably synthesized de novo in the axis during imbibition and are important in initial breakdown of storage proteins for axial elongation growth.

We have been studying a seed aspartic proteinase, termed AtAP, from Arabidopsis thaliana. In previous work, we purified the proteinase, analysed its activity and isolated the cDNA sequence. In this paper, the expression of the mRNA for the aspartic proteinase was analysed in seed tissues both by Northern blots for overall regulation and by in situ hybridization to follow cell-specific localization of message. We found a 1.9 kb aspartic proteinase message in dry seeds and seed pods. This message was expressed in many different cell types of the mature dry seed. The localization of the protein within these cells was also determined. Antibodies were raised against the AtAP and purified using affinity chromatography on an AtAP–immobilized-pepstatin A–agarose column. This purified antibody recognized several AtAP peptides in seeds. To localize the enzyme in cells, we isolated protein bodies from the dry seeds of Arabidopsis using a non-aqueous isolation method. The AtAP activity and antigenic peptides were found to be highest in the protein body fraction and co-localized with the seed storage protein 2S albumin and the vacuolar marker enzyme α-mannosidase. This protein body localization of the AtAP was confirmed with immunocytochemical localization by electron microscopy and shows that the protein is not secreted by these cells.

Lipoxygenases are widely distributed in the animal and plant kingdoms. These enzymes catalyse the hydroperoxidation of polyunsaturated fatty acids containing cis,cis-1,4-pentadiene moieties. Multiple isoenzymes, with different biochemical properties and tissue distribution, have been described for many plants. Lipoxygenases occur in vegetative tissues, but also accumulate in various seeds, and especially in leguminous seeds. Although several functions have been proposed for vegetative lipoxygenases, the roles of seed lipoxygenases remain enigmatic. In this review we discuss whether physiological functions assigned to vegetative lipoxygenases can be extended to seed isoforms.

The mature seeds of durian (Durio zibethinus L.) are recalcitrant, with the cotyledons storing both starch (amylose, 78% dry weight) and some protein (7%), but having few triglyceride reserves (<1%). Reserve accumulation occurs during the latter third of the 110-d seed developmental period prior to fruit shed. The storage proteins of durian seeds consist of two immunologically related unglycosylated albumins, light and heavy zibethinin (20.2, 21.4 kDa), that account for 37–46% of the total protein during development. Light zibethinin is a single polypeptide, most likely having internal sulphydryl linkages, whereas heavy zibethenin is composed of two sulphydryl-linked subunits. The zibethinins are deposited in swellings of the endoplasmic reticulum (ER) which then either expand or coalesce to form protein storage vacuoles. This mode of protein body formation in durian varies from both the ER–Golgi complex–vesicle–vacuole pathway characteristic of many dicotyledonous seeds and the direct ER to protein storage vacuole pathway involved in deposition of certain prolamins in cereal endosperm cells. Protein storage vacuoles in durian seed storage parenchyma never become fully filled, but contain only diffuse peripheral clumps of zibethinin protein. There is a 15% loss in starch, a precipitous loss of total protein, and a concomitant loss of the zibethinin storage proteins during the 5 d prior to fruit shed, suggesting that both reserve mobilization and germination has begun.