Polyamines and cytokinins in celery embryogenic cell cultures

The effect of inhibitors of polyamine biosynthesis on the development of embryogenic cell cultures of celery (Apium graveolus L.) was studied. Several developmental stages of somatic embryos were compared for differences in the content and biosynthesis of free polyamines and for cytokinin content. Cyclohexylamine and particularly methylglyoxal bis(guanylhydrazone), inhibited both cell division and the organization of polar embryos from globular embryos. Difluoromethylornithine slightly promoted embryo development, especially cell division.The free putrescine content of globular embryos was 6-fold that of fully differentiated plantlets, and that of spermidine 2-fold. Only a slight increase in the spermine content was found with embryo development. These differences were confirmed by data from polyamine biosynthesis. Incorporation of ¹⁴C-arginine into polyamines was slightly higher than that of ¹⁴C-ornithine. Over 96% of this incorporation was detected in the putrescine fraction. Incorporation of ¹⁴C into putrescine in globular embryos was 3 to 4-fold that in fully-differentiated plantlets. Incorporation into spermidine and spermine was, however, higher in plantlets than in globular embryos.Cytokinin analysis revealed considerable differences in the biological activity between the developmental stages of embryogenesis. This could be due to endogenous cytokinins and/or BA taken up from the maintenance medium. Cytokinin levels decreased with increased embryo development. Most of the detected cytokinin-like activity co-chromatographed with BA and its metabolites. Some as yet unidentified peaks of activity were recorded in the globular embryos.The results are considered with respect to the possible participation of polyamines and cytokinins in the development of embryogenic cell cultures of celery. It is suggested that the onset of embryogenesis is characterized by a high content of putrescine and cytokinins, while a decrease in putrescine synthesis and cytokinin content, and an increase in spermidine and spermine content, accompany further embryo development and plantlet formation.Abbreviation ADC arginine decarboxylase - ODC ornithine decarboxylase - 2,4-D dichlorophenoxyacetic acid - DFMA difluoromethylarginine - DFMO difluoromethylornithine - MGBG methylglyoxal bis(guanylhydrazone) - CHA cyclohexylamine - BA benzyladenine - BAR benzyladenine riboside     

Polyamines and carnation flower senescence: Endogenous levels and the effect of applied polyamines on senescence

The polyamines putrescine and spermine were effective in delaying the senescence of carnation buds, but were ineffective when applied to flowers of which the petals had already opened, and were 90° with respect to the stem. Higher levels of endogenous putrescine were detected in the open flowers than in the buds, and this may explain the negative effect obtained when polyamines were applied to open flowers that were picked for commercial distribution.Abbreviations AOA amino-oxyacetic acid - AVG amino-ethoxyvinyl-glycine - SAM S-adenosyl methionine - STS silver thiosulphate     

Growth and decline of a penguin colony and the influence on nesting density and reproductive success

Colonial breeding is characteristic of seabirds but nesting at high density has both advantages and disadvantages and may reduce survival and fecundity. African penguins (Spheniscus demersus) initiated breeding at Robben Island, South Africa in 1983. The breeding population on the island increased in the late 1990s and early 2000s before decreasing rapidly until 2010. Before the number breeding peaked, local nest density in the areas where the colony was initiated plateaued, suggesting that preferred nests sites were mostly occupied, and the area used by breeding birds expanded. However, it did not contract again as the population decreased, so that nesting density varied substantially. Breeding success was related positively to the prey available to the breeding birds and negatively to local nest density, particularly during the chick-rearing period, suggesting a density-dependence operating through social interactions in the colony, possibly exacerbated by poor prey availability when the breeding population was large. Although nest density at Robben Island was not high, nesting burrows, which probably reduce the incidence of aggressive encounters in the colony, are scarce and our results suggest that habitat alteration has modified the strength of density-dependent relationships for African penguins. Gaining a better understanding of how density dependence affects fecundity and population growth rates in colonial breeders is important for informing conservation management of the African penguin and other threatened taxa.     

The conservation status and population decline of the African penguin deconstructed in space and time

Understanding changes in abundance is crucial for conservation, but population growth rates often vary over space and time. We use 40 years of count data (1979–2019) and Bayesian state‐space models to assess the African penguin Spheniscus demersus population under IUCN Red List Criterion A. We deconstruct the overall decline in time and space to identify where urgent conservation action is needed. The global African penguin population met the threshold for Endangered with a high probability (97%), having declined by almost 65% since 1989. An historical low of ~17,700 pairs bred in 2019. Annual changes were faster in the South African population (?4.2%, highest posterior density interval, HPDI: ?7.8 to ?0.6%) than the Namibian one (?0.3%, HPDI: ?3.3 to +2.6%), and since 1999 were almost ?10% at South African colonies north of Cape Town. Over the 40‐year period, the Eastern Cape colonies went from holding ~25% of the total penguin population to ~40% as numbers decreased more rapidly elsewhere. These changes coincided with an altered abundance and availability of the main prey of African penguins. Our results underline the dynamic nature of population declines in space as well as time and highlight which penguin colonies require urgent conservation attention.     

Cytokinins in cut carnation flowers. VII. The effect of zeatin and dihydrozeatin derivatives on flower longevity

Dihydrozeatin, at 4×10^–5 M, delayed the senescence of carnation flowers while tZ, at the same concentration, accelerated it. cis-Zeatin was ineffective. The DHZ derivatives as well as the Z derivatives gave responses very similar to those observed for the parent free bases. While additional experimentation with radiolabelled derivatives is clearly called for, the similarity between the responses observed for the respective derivatives and the free bases, suggests that in the carnation flower there is a great deal of metabolic interconversion.Abbreviations DHZ dihydrozeatin - DHZR ribosyldihydrozeatin - DHZOG glucosyl-O-dihydrozeatin - DHZ9G glucosyl-9-dihydrozeatin - DHZROG glucosyl-O-ribosyldihydrozeatin - cZ cis-zeatin - tZ trans-zeatin - ZR ribosylzeatin - Z9G glucosyl-9-zeatin - ZOG glucosyl-O-zeatin - ZROG glucosyl-O-ribosylzeatin     

Effect of seaweed concentrate on growth and development of the marigoldTagetes patula

The seaweed concentrate Kelpak, made fromEcklonia maxima, and applied as a foliar spray or a root drench at transplanting, improved both the vegetative and reproductive growth of marigolds. Of particular significance is that the overall production of seeds (fruits) was increased by as much as 50% in some instances. Very low concentrations of seaweed concentrate were not always effective, while the higher dosages decreased vegetative growth.     

Metabolism of [8-14]6-(benzylamino)purine by individual carnation flower components

Isolated stem, receptacle, ovary and petal tissues of the carnation flower (Dianthus caryophyllus L. cv. White Sim) all metabolized [8-¹⁴C]6-(benzylamino) purine. Ribosyl 6-(benzylamino)purine was the major metabolite formed in all flower components. The extent of metabolism and the ratios of the various metabolites of 6-(benzylamino)purine detected within each flower component varied. The receptacle, in particular, was distinct from other flower components with respect to the extent of 6-(benzylamino)purine metabolism.     

Metabolism of [14C]trans-zeatin and [14C]benzyladenine by letached yellow, green and variegated leaves of Schefflera

[8-¹⁴C]Benzyladenine (BA) and [8-¹⁴C] trans-zeatin (tZ) were fed through the petiole to mature, detached green, yellow and variegated leaves of Schefflera arboricola. Recovery of radioactivity from the plant material ranged between 4.2 and 22.1%. More radioactivity was recovered when tZ was applied compared to BA. Green leaves or the green parts of variegated leaves yielded more radioactivity than the yellow leaf material. BA was metabolized much faster than the endogenous cytokinin tZ. It would appear that while lower amounts of radioactivity were present in yellow leaves, as well as in yellow parts of variegated leaves, the rate of cytokinin metabolism was nevertheless faster. Metabolites that were formed to a greater extent in these yellow parts were the nucleotides of both cytokinins. Currently it is not known whether or not cytokinins influence chlorophyll and other pigment development in chimeric variegated leaves.     

Cytokinins in cut carnation flowers. IX. Transport and metabolism of iso-pentenyladenine and the effect of its derivatives on flower longevity

Of the four 2iP derivatives applied to cut carnations 2iP, IPA and IPAMP delayed the rate of flower senescence but did not delay longevity. 2iP9G was the least effective. [³H]2iP was rapidly transported to all flower components. The receptacular tissue apparently plays a major role in the distribution of the applied cytokinin to the rest of the flower parts. Over and above possible interconversion between 2iP, IPA and IPAMP the applied [³H]2iP was also converted to 2iP9G, Ade, Ado, tZ and DHZ. The presence of Ade indicates the involvement of cytokinin oxidase-type enzymes while the presence of tZ and DHZ indicates a degree of hydroxylation. These latter steps may contribute to the efficiency of 2iP in the system.     

Seasonal pattern of breeding by Cape and Crowned Cormorants off western South Africa

Crawford, R.J.M., Dyer, B.M. & Upfold, L. 1999. Seasonal pattern of breeding by Cape and Crowned Cormorants off western South Africa. Ostrich 70(3&4): 193–195.

At Bird Island, Lambert's Bay, and Malgas Island, South Africa, small numbers of Cape Cormorants Phalacrocorax capensis may breed at any time of the year, but the main breeding season is from September to February. At Malgas Island, Crowned Cormorants P. coronatus may also breed throughout the year, but mostly from December to March. Counts of the breeding population of Cape Cormorants should be undertaken between October and December, and of Crowned Cormorants in January or February.