Overwintering and growth regulator treatment effects on celery (Apium graveolens L.) flowering and seed production

Celery (Apium graveolens L.) plants cv. Jason overwintered in a polythene tunnel flowered earlier and grew taller than similar plants given a 10-week cold-treatment at 5°C prior to transplanting in the same tunnel in mid-February. However, there was no significant difference in the yield of seeds obtained from both treatments, plants grown at a density of 4m^-2 yielded less seeds than those at 2m^-2, though the yield per unit area was slightly higher from the high density treatment. Treatment with 100 mgl^-1 GA₃ applied twice just prior to flowering and during anthesis increased flower stalk, flower pedicel and stamen length but delayed flower opening and seed ripening and decreased seed set and seed yield. Treatment with a mixture of 1000 mgl^-1 GA₄ and GA₇ plus 1000 mgl^-1 ethephon on three occasions during seed ripening decreased seed yield and reduced seed germination though those seeds capable of germinating were less dormant than seeds from untreated plants. The size distribution of seeds was unaffected by any treatment other than the preseeding spray with GA₃ which reduced the percentage of medium-size seeds.     

Structural similarities among the high molecular weight protein fractions of oilseeds

Data on the physico-chemical properties of proteins from soybean, groundnut, sesame seed, sunflower seed, safflower seed, mustard seed, rapeseed and cotton seed are fairly extensive. An examination of the available data on high molecular weight proteins suggests that there are similarities in many of their properties. In this report the similarity in amino acid composition, size and shape, molecular weight, secondary structure, subunit composition, association-dissociation at high and low pH, stability towards denaturants, hydrolysis by enzymes and quaternary structure of the high molecular weight proteins is discussed. Based on these similarities a model has been proposed for the associationdissociation, denaturation and reassociation behaviour of the high molecular weight proteins of oilseeds.     

Seed abortion in wind-dispersed pods of Dalbergia sissoo: maternal regulation or sibling rivalry?

Summary Dalbergia sissoo, a wind-dispersed tropical tree, shows a positively skewed distribution of seeds per pod. This is attributed to the enhanced dispersal advantage of few-seeded pods due to their reduced wing loading (ratio of weight to pod surface area) and low settling velocity. The proximate mechanisms causing the positively skewed distribution were investigated. The distribution could not be attributed to the distribution pattern of ovule number per ovary, pollen grain limitation, lack of ovule fertilization, or post-fertilization elimination of many-seeded pods. Rather, it was caused by the post-fertilization abortion of seeds within a pod 2 weeks after fertilization. This intra-pod seed abortion (IPSA) is due to a dominance hierarchy of fertilized ovules from the distal (near stigma) to the basal end, generated by the temporal differences in fertilization. The dominant developing seeds at the distal end cause the abortion of others through the production and diffusion of an aborting agent. When the dominance hierarchy of the siblings is not intense, pods are formed with more than one seed. We argue that the positively skewed distribution of seeds per pod is not due to maternal regulation but is a result of sibling rivalry. We propose that this sibling rivalry is generated by genetic differences in pollen grain fitness and disucss the results in the context of parent-offspring conflict.     

Fiber optic studies of light gradients and spectral regime within Lactuca sativa achenes

Light gradients and spectral regime were measured in Lactuca sativa L. cv. Grand Rapids achenes using fiber optic microsensors. The distribution of scattered light across lettuce achenes was linear for 660 and 730 nm and non-linear for 450 nm light. Spectra for scattered light within intact achenes also showed a non-linear increase with wavelength. The preferential attenuation of blue light by the pericarp and seed explains in part the relative ineffectiveness of blue light with respect to red in triggering germination of lettuce. Calculated action spectra for phytochrome-stimulated germination agree closely in the red with experimentally derived action spectra; however, there is little agreement within the blue.     

Polyamine oxidase activity and polyamine content in maize during seed germination

Polyamine oxidase (PAO, EC 1.5.3.3) activity and polyamine content in the cell wall and soluble fractions obtained from embryos, endosperms and shoots and roots of etiolated or green seedlings of maize ( Zea mays L. cv. WF9) during the first 7 days of germination were investigated. Polyamine content was also determined in the trichloroacetic acid-soluble (free polyamines) and trichloroacetic acid insoluble (bound polyamines) fraction obtained from the same tissues. PAO activity, determined by the radiometric method based on the recovery of the labelled reaction product 1-pyrroline, was mostly localized in the cell wall fraction. The activity was very low in embryos and endosperms and present in traces in roots. In etiolated shoots PAO activity increased sharply, while in green shoots it was low and increased slowly. No polyamines were found in the cell wall fraction and only putrescine was detected in the soluble fraction, with the exception of the embryo, where spermidine and spermine were also present. In the TCA-soluble fraction of embryos, putrescine increased during imbibition, while spermidine and spermine decreased; in the endosperm no relevant changes in polyamines occurred. In the same fraction of green and etiolated seedlings, putrescine increased, giving a peak at days 3–5, while spermidine decreased to very low levels. The amount of bound polyamines was 1–4% of the free ones. The pattern of PAO activity seems to be unrelated to endogenous free polyamine content, which is the same in shoots and roots of etiolated and green seedlings. Enzyme activity, very low in ungerminated seeds, increased continuously during the progression of germination, especially in etiolated shoots, indicating a possible involvement in cell wall formation.     

Seed dimorphism in Salicornia europaea: Nutrient reserves

Median and lateral seeds of Salicornia europaea L. were separately analysed for their sizes and nutrient reserves. The mean air-dry weight of a single median and lateral seed was 0.31 and 0.25 mg, respectively. The composition as well as the concentration of the nutrient reserves were similar in both seed types. The bulk of the cations was derived from K⁺, followed by Mg²⁺, Na⁺ and Ca²⁺. The chloride content was somewhat higher than the sodium content, and phosphate was equalled by acid soluble Ca²⁺ and Mg²⁺. Starchy compounds and sucrose were present in equal amounts, each of them accounted for about 50% of the carbohydrates. Glucose and fructose were less than 1%. Protein-nitrogen (ethanol-insoluble N) was about 34 g (kg dry seeds)⁻¹. About 7 g (kg dry seeds)⁻¹ was ethanol-soluble nitrogen, of which 10% was derived from amino acids. The total lipid content was more than 290 g (kg dry seeds)⁻¹, 65% were calculated to be glycerides. More than 90% of the fatty acids consisted of linoleic and oleic acids, the majority (72%) of which was linoleic acid.     

Respiration and soluble sugar metabolism in sugar pine embryos

Embroys excised from dormant seeds of sugar pine ( Pinus lambertiana Dougl.) incubated at 25°C (non-dormancy-breaking) or stratified at 5°C (dormancy-breaking) were analyzed to determine temperature effects on the relative activities of respiration and fermentative metabolism, the levels of soluble sugers and the activities of the hydrolytic enzymes, invertase and sucrose synthase, as related to the release of dormancy and germinatio. At 25°C, despite a sharp drop in embryo oxygen uptake after 48 h, a simultaneous decline in acetaldehyde and ethanol concentrations indicated that there was not a shift to fermentative metabolism. The concentrations of soluble sugars showed no treatment effects. Embryo invertase (EC 3.2.1.26) activity changed only slightly at either temperature, while stratification was accompanied by a 4-fold increase in sucrose synthase (EC 2.4.1.13) activity (cleavage direction). Upon transfer of stratified seeds to 25°C, embryo sucrose synthase activity rapidly increased almost 10-fold, with the increase beginning prior to germination, while mvertase activity increased 20-fold, concomitant with germination.