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This work aimed to establish the nutrient fertilization regime for indoor maintenance of Kappaphycus alvarezii seedlings during periods of low sea temperatures using biofloc effluent as a fertilizer. Moreover, we evaluated the development of seaweed seedlings after transplantation into the sea cultivation in Santa Catarina, Brazil. Seedlings were fertilized with biofloc effluent diluted by 25% in three different nutrient fertilization regimes for 4 weeks: single fertilization (SF): seedlings were fertilized for 1 week and remained in seawater for the following 3 weeks; alternating fertilization (AF): alternated 1 week with nutrient fertilization and 1 week without, and continuous fertilization (CF): seedlings were cultivated continuously with biofloc effluent. After this period, samples of each treatment were transferred into the sea cultivation and kept for 5 more weeks. The daily growth rates of plants cultivated in SF and AF were significantly higher than CF in indoor maintenance. However, in sea cultivation, the daily growth rates from AF and CF were significantly higher than SF. In both cases, there were no differences in the carrageenan yield between treatments. Light microscopy and quantification of floridean starch and pigments showed that after the sea cultivation period, floridean starch presence changed from cortical to medullar cells depending on the treatment, but no significant difference in the quantity was observed. Also, seedlings of SF treatment showed a significantly higher phycocyanin content compared to CF treatment. Based on the results, we suggest the continuous fertilization for indoor maintenance in tanks of seaweed seedlings with biofloc effluent.

International audience; AbstractKey messageK fertilization led to a significant increase in fine root biomass, fine root length, and root tip number in the mineral soil layer but does not affect the ecomycorrhizal community structure in the organic horizon.ContextPotassium (K) deficiency is common in Picea abies in the European Alps. Fertilization with other nutrients often influences fine root biomass and ectomycorrhizas, but less is known about the effects of K-fertilization.AimsThe aim of the investigation was to determine the effects of K-fertilization on stem growth and fine root biomass of Picea abies, as well as the influence on ectomycorrhizal community structure of the fine roots.MethodsEight years after a single fertilization of K-deficient Picea abies with 200 kg K ha−1, fine roots were collected from 7 control and 6 K-fertilized plots. Fine root biomass and morphology were determined. The identification of ectomycorrhizal taxa was determined by morphotyping and by amplification of the internal transcribed spacer region of the nuclear ribosomal DNA.ResultsK-fertilization did not affect the amount of fine root biomass and ectomycorrhizal community structure in the Oi + Oe and Oa layers but led to a significant increase in fine root biomass, fine root length, and root tip number in the mineral soil layer.ConclusionAn increase in growth due to K-fertilization leads to great exploration of the mineral soil by fine roots but does not affect the ectomycorrhizal community structure in the organic horizons.

Angiosperms are characterized by the occurrence of double fertilization. However, Podostemaceae is considered an exception with the presence of only single fertilization (syngamy) though two male gametes are formed conventionally. To determine the cause for the failure of double fertilization in Dalzellia zeylanica (Gardn.) Wight, we closely tracked the movement of the male gametes from the time of pollen tube initiation to the time of entry into the megagametophyte to affect fertilization. We report for the first time, the presence of a novel type of three-nucleate/three-celled mature megagametophyte consisting of two synergids and an egg cell in D. zeylanica. Therefore, of the two male gametes formed in this plant, one fuses with the egg cell resulting in syngamy, whereas the other male gamete eventually degenerates due to the absence of its partner i.e. single polar nucleus of the central cell that degenerates prior to the entry of the pollen tube into the synergid. The present work not only highlights the highly reduced nature of megagametophyte but also the occurrence of single fertilization resulting in sperm selection in D. zeylanica.

Since the first description of the double fertilization process in flowering plants (angiosperms) 110 years ago (Nawaschin in Bull Acad Imp Sci St Petersburg 9:377–382, 1898), little progress has been made during the following 100 years to understand the underlying molecular mechanisms. This seems to be in strong contrast to our steadily increasing knowledge of single fertilization in animals, where a large number of key players and the corresponding molecular mechanisms have been unclosed since the mid-1970s. Are the identified fertilization mechanisms ubiquitously dispersed, occurring also in higher plants? The past few years have seen a number of discoveries indicating that general principles of fertilization mechanisms in animals and flowering plants are more conserved than previously thought. Here, we compare the development and morphology of animal and flowering plant gametes, discuss cell–cell communication events between gametes and gametophytes as well as their physical interaction and fusion during single and double fertilization, respectively.

The field experiment of P and K fertilization was conducted in spring of 2004 (a = ordinary fertilization, b = a + P1, c = a + P2, d = a + P3 , e = a + P1, f = a + P2, g = a + P3 , h = a + P2K2. The amounts of added either/or phosphorus (P2O5) and potassium (K2O) were (kg ha-1) 500, 1000 and 1500, for the step 1, 2 and 3, respectively. The triplephoshate enriched with sulphur and zinc (45% P2O5 + 1. 2% S + 0.06% Zn) was used for P fertilization. Potassium salt (KCl containing 60% K2O) was source of K. Nitrogen amount was equilized for all treatments by adequate quatities of CAN (calcium ammonium nitrate: 27% N). The experiment was conducted in four replicates for crop rotation maize (2004) and soybean (2005: residual effects of the fertilization). Applied fertilization considerable influenced on increases of plant available P and K in soil, while differences of pH and humus among tretaments were in range of statistical error. Also, both P and K single fertilization gave tendency to decrease hydrolitical acidity. In general, grain yields of maize were high and ameliorative fertilization had moderate effects on maize yield as well as P and K in grain and leaves increases. Only applications of the highest K rate and PK combination resulted by significant yield increases, for 5% and 12%, respectively. Only application both P and K nutrients resulted by increase of grain quality (protein content). Residual influences of the fertilization were higher because soybean yields were increased up to 21% (influences of P), 17% (influences of K) and 30% (PK influences). However, protein and oil contents in grain were indenpendent on fertilization.

Laboratory rearing and reconstruction of Laodicea undulata (Hydrozoa) life cycle led to the discovery for the first time in Leptomedusae of the potential for ontogeny reversal, i.e. the medusa stage can asexually transform back into the polyp stage. In turn, each rejuvenated polyp stage can newly activate the standard developmental programme towards colony morphogenesis and budding of secondary medusae. These can be considered as clonemates of the initial medusa batch, since they originate by asexual processes. In combination with the ordinary medusa budding process, the potential for reverse development might represent a tool to increase jellyfish population growth rate during the favourable season, but eventually it does not avoid jellyfish to die. Comparably to polyembryony, reverse development leads to offspring multiplication from a single fertilization event, with a wider dispersal of each single genotype; eventually, it favours the enhancement of the overall genetic diversity at small spatial scale. The life cycle of L. undulata from the Mediterranean Sea is re-described, linking previously uncoupled descriptions of either the polyp or the early medusa stages. Taxonomic considerations of the genus Laodicea and a comparison among the known Mediterranean species are also provided.

Bicellular pollen with one vegetative nucleus and one diploid arrested generative cell (”monospermic” pollen) was induced by trifluralin treatment of diploid maize plants at 7–9 days before flowering. The arrested generative cell (seemingly a diploid sperm cell) fused with the central cell of diploid plants and produced shriveled endosperm resembling that of a 2n×4n cross in maize. Dual pollination experiments with a purple embryo marker revealed single fertilization events in which the union of one sperm cell with the egg occurs but there is no union of a second sperm cell with the central cell. Singly fertilized ovules survived at least 4 days. Furthermore, many viable triploid plants were obtained. This technique therefore appears to have the potential for manipulating ploidy level in crops and may become useful in investigating fertilization mechanisms of angiosperms.

The reproduction system inSpiranthes sinensis (Orchidaceae), collected at various localities in Japan, was revealed to be of a peculiar new type which is not to be found in other angiosperms. None of generative cell nuclei has been observed to dividede novo throughout the progamic phase, although they do participate in fertilization. Neither fertilization of the generative cell nucleus with the central nucleus nor formation of endosperm occurred in this plant. Although the chromosome number in the developing proembryonic cells numbered 2n=30, exhibiting diploidy, the number of marker chromosomes was equal to the sum of half the number of marker chromosomes of the parental clones.