Higher plants have several strategies to perpetuate themselves under adequate ecophysiological conditions. The production of heterogeneous seeds is one such strategy. That is, to ensure the survival of the next generation, an individual plant might produce seeds that are heterogeneous with respect to the extent of dormancy, dispersion and persistence within the seed bank. Heterogeneity can affect not only certain physiological and molecular properties related to seed germination, but also such characteristics as colour, size and shape, parameters commonly used to differentiate morphs within a heterogeneous seed population. In heterogeneous seeds, the above features determine seed behaviour and alter their mechanism of germination. In this work, emphasis is placed on the existence of seed mutants having major alterations in characteristics of the testa and hormonal response. These mutants constitute a valuable tool for elucidating the mechanism of dormancy, germination and perpetuation of seeds. Finally, ontogeny and heterogeneity are reviewed, providing the first data related to the possible hormonal control of heterogeneity in seeds. These results raise the hypothesis that one of the factors triggering differences in germination among heterogeneous seeds may be an alteration in the signalling and action mechanism of ethylene and abscisic acid (ABA).

Polyamines (PAs) are required for cell growth and cell division in eukaryotic and prokaryotic organisms. The present study is aimed at understanding the developmental regulation of PA biosynthesis and catabolism during flower opening and early fruit development in relation to fruit size and shape. Two full-length cDNA clones coding for S-adenosyl methionine decarboxylase (SAMDC) and spermidine synthase (SPDS) homologs, key steps in the PA biosynthesis pathway, in the stone-fruit of olive (Olea europaea L.) were identified and the spatial and temporal organization of these genes were described. In olive flowers, OeSAMDC gene transcripts were highly expressed in ovary wall, placenta and ovules, while OeSPDS transcript was confined to the ovules of ovary at anthesis stage. A correlation was detected between the SAMDC enzyme activity/accumulation transcript and spermidine (Spd) and spermine (Spm) levels during flower opening, implying that the synthesis of decarboxylated SAM might be a rate-limiting step in Spd and Spm biosynthesis. OeSAMDC and OeSPDS transcripts were co-expressed in fruit mesocarp and exocarp at all developmental stages analyzed as well as in nucellus, integuments and inner epidermis tissues of fertilized ovules. In contrast, the OeSAMDC and OeSPDS genes had different expression patterns during early fruit development. The results provide novel data about localization of PA biosynthesis gene transcripts, indicating that transcript levels of PA biosynthesis genes are all highly regulated in a developmental and tissue-specific manner. The differences between the two olive cultivars in the fruit size in relation to the differences in the accumulation patterns of PAs are discussed.

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The effect of supraoptimal temperatures (300C, 350C) on germination and ethylene production of Cicer arietinum (chick-pea) seeds was measured. Compared with a 250C control, these temperatures inhibited both germination and ethylene production. The effect of supraoptimal temperatures could be alleviated by treating the seeds with ethylene. It was concluded that one effect of high temperature on germination was due to its negative effect on ethylene production. This inhibitory effect of high temperature was due to increased conjugation of 1-aminocyclopropane-1-carboxylic acid to 1-(malonylamino)cyclopropane-1-carboxylic acid and to an inhibition of ethylene-forming enzyme activity.Seeds germinate at a certain optimum temperature, above which germination may be delayed or inhibited, a phenomenon known as thermoinhibition (1). This can be overcome by various phytohormones, one of which is ethylene, and indeed small quantities of this phytohormone are produced in some thermoinhibited seeds (1, 18).The optimum temperature for the germination of Cicer arietinum seeds is 25°C. At 30°C and above the emergence of the radicle is delayed and the capacity for ion exchange in the embryonic axis (1 1), genetic expression (26), and cytokinin levels (25) are all affected. At 25°C ethylene production is related to cell growth (28). In other tissues high temperatures appear to inhibit the conversion of ACC2 into ethylene rather than interfere with the SAM to ACC step (8).In plants ethylene is synthesized from methionine via adenosyl-methionine and ACC (30). The conversion of SAM or adenosyl-methionine into ACC is catalyzed in the cytosol by ACC-synthase and is the principal point ofcontrol for biosynthesis ofethylene (29). The mechanism for the transformation of ACC into ethylene is less well understood. However, EFE activity has been associated with the vacuole membranes (10) and other compartments of the cell (15).ACC is also metabolized into MACC in the cytosol (4 (14), in some tissues the possibility exists that MACC is converted into ACC via MACC-acylase. MATERIALS AND METHODS Vegetable Materials and Seed GerminationSeeds of Cicer arietinum cv Castellana (chick-pea) were bought commercially and stored at 4°C until required.The seeds were washed in sterile, double-distilled water and incubated in batches of 50 at 25°C, 30°C or 35C, for a minimum of 6 h and a maximum of 36 h, in plastic trays containing 175 mL sterile distilled water. The percentage of germination was measured for all the times and temperatures, taking the emergence of the radicle as the definition of germination.The embryonic axes and cotyledons were aseptically removed after incubation to measure ethylene production, levels of free and conjugated ACC, and activity of ACC-synthase and EFE. Ethylene MeasurementsTwenty five (500 mg) isolated embryonic axes and 10 (4.5 g) cotyledons were aseptically transferred to 50 mL flasks containing 0.5 mL distilled water. The flasks were sealed with silicone-rubber stoppers and incubated in darkness at 25°C. After ...

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