Early Cotyledon Research Articles

Abscisic acid or high osmoticum promote accumulation of long-chain fatty acids in developing embryos of Brassica napus

The effects of abscisic acid (ABA) and restricted water uptake on lipid synthesis by early cotyledon stage embryos of Brassica napus L. cv. Nugget were analyzed by comparing fatty acid content and composition of embryos developing in situ with that of embryos cultured on media for up to 3 days with or without ABA (0.1 μM, 1 μM or 10 μM) or sorbitol (0.69 M). Although embryo lipid content increased under all conditions tested, both high exogenous ABA and high osmoticum stimulated preferential accumulation of eicosenoic acid and erucic acids, the predominant fatty acid constituents of storage lipids. In addition, cultured embryos accumulated significantly less oleic acid and had higher levels of linoleic and linolenic acid than embryos which remained on the plant, irrespective of exogenous ABA levels. These observations suggest that ABA or osmotic conditions influence the distribution of fatty acids between the pathways leading to desaturation or elongation, but some other factor(s), not duplicated by the culture treatment, control the availability of substrate for these pathways.

Seed development in Ricinus communis cv. Hale (castor bean). III. Pattern of storage protein and phytin accumulation in the endosperm

The development of the endosperm of castor bean seed from its initial free nuclear state through to the end of maturation is presented. An investigation of the pattern of reserve accumulation in the endosperm at the light microscopy level revealed that the accumulation of soluble and insoluble storage proteins, and of phytin, does not occur simultaneously in all cells of the developing storage organ. Rates of reserve accumulation also vary among regions of the endosperm. Storage protein and phytin accumulation are initiated in a region midway between the periphery and central lumen of the endosperm by the early cotyledon stage of seed development. Afterwards, reserve deposition occurs more intensely in the proximal and more peripheral regions than in the distal and internal regions. A wave of reserve accumulation, or protein body maturation, proceeds from the more peripheral and the proximal regions to the more internal and distal regions as development continues. The last cells to complete reserve deposition are those in regions lying close to the endosperm lumen (into which the cotyledons have expanded) and the outermost two cell layers of the endosperm.

Changes in the content and distribution, in different organs, of the flavour precursors, the S‐alk(en)yl‐L‐cysteine sulphoxides, during seedling development of onions (Allium cepa) grown under light and dark regimes

Flavour precursors accumulated rapidly in onion seedlings (Allium cepa L. cv. Pukekohe Longkeeper, May and Ryan) after emergence of the cotyledon. (±)‐S‐1‐Propyl‐L‐cysteine sulphoxide, found mainly in the shoots, was the predominant flavour precursor. (±) Trans‐S‐1‐propenyl‐L‐cysteine sulphoxide was important during very early seedling growth when very high concentrations were reported in the root and hypocotyl. (±)‐S‐1‐Methyl‐L‐cysteine sulphoxide, a minor component in seedlings grown under a normal light regime, was significant during early cotyledon development in seedlings grown in the dark. It is concluded that onion seedlings would be a suitable tissue in which to investigate the biosynthetic pathways of the S‐alk(en)yl‐L‐cysteine sulphoxides.

Different structure of polytene chromosomes ofPhaseolus coccineus suspensors during early embryogenesis

The pattern of DNA puffs in two pairs of polytene chromosomes (S1 and S2, both involved in nucleolar organization) is described in the suspensor ofPhaseolus coccineus during the heart-like and early cotyledon stages of embryo development. Collected data show that: 1. a structural variability indicating differential DNA replication of bands bearing ribosomal cistrons occurs in the two chromosome pairs and within the same chromosome; 2. within chromosome S1, a positive correlation is found between extra replication (amplification) of band p 13 and under-replication of band p 12; 3. within chromosome S2, bands q 21 and q 22 often evidence a simultaneous DNA amplification; 4. a negative correlation is observed between amplification of band p 13 of chromosome S1 and amplification of bands q 21 and q 22 of chromosome S2; 5. within chromosome S2, no correlation is detectable between amplification of bands p 11 and q 11 and amplification of bands q 21 and q 22.

Embryogeny of Phaseolus coccineus: the ultrastructure and development of the suspensor

Structural specializations occur in the suspensor at the proembryo stage with the formation of wall ingrowths. Soon after the appearance of the ingrowths, mitochondria, plastids, polysomes, and smooth endoplasmic reticulum greatly increase in their abundance within the suspensor cells. By the late globular stage, wall ingrowths are extremely well developed and the cells within the suspensor are packed with cellular organelles. The nucleus of the suspensor cell at the heart stage also takes on an active appearance. The nucleus becomes highly lobed in shape and micronucleoli can also be found. There is little change in the overall ultrastructural pattern of the cell till the cotyledon stage. At this stage, wall thickening occurs in all suspensor cells and the outlines of most of the ingrowths become less obvious. The mitochondria, plastids, and polysomes become less abundant and a change in the configuration of the smooth endospermic reticulum is also observed. The ontogenetic changes of the cellular organelles suggest that the suspensor plays a role during early embryo development, i.e., globular to early cotyledon stage.