Fruit encasing preserves the dispersal potential and viability of stranded Posidonia oceanica seeds.

Posidonia oceanica meadows are the most productive coastal ecosystem in the Mediterranean. Posidonia oceanica seeds are enclosed in buoyant fleshy fruits that allow dispersal. Many fruits eventually strand on beaches, imposing a remarkable energy cost for the plant. This study aims to assess whether stranded seeds retain functional reproductive potential under a variety of environmental conditions. First, we measured the possibility that seeds could be returned to the sea, by tagging fruits and seeds. Second, we quantified the effect of air, sun and heat exposure on the viability and fitness of stranded fruits and naked seeds. The results showed that on average more than half of fruits and seeds are returned to the sea after stranding events and that fruits significantly protect from desiccation and loss of viability. Furthermore, in fruits exposed to the sun and in naked seeds, seedlings development was slower. This study indicates that a significant portion of stranded P. oceanica fruits have a second chance to recruit and develop into young seedlings, relieving the paradox of large energy investment in seed production and apparent low recruitment rate. Additionally, we provide practical indications for seed collection aimed at maximizing seedling production, useful in meadow restoration campaigns.

A physiological mechanism to regulate D-aspartic acid and NMDA levels in mammals revealed by D-aspartate oxidase deficient mice.

Free D-aspartic acid and NMDA are present in the mammalian central nervous system and endocrine glands at significant concentrations, but their physiological role is still matter of debate. The only enzyme known to metabolize in vitro selectively these D-amino acids is D-aspartate oxidase (DDO). To clarify the role in vivo of the enzyme, we generated mice with targeted deletion of Ddo gene by homologous recombination. Mutated animals showed increased amounts of both D-aspartic acid and NMDA in all tissues examined demonstrating a physiological role of DDO in the regulation of their endogenous levels.

D-aspartic acid in the nervous system of Aplysia limacina: possible role in neurotransmission.

In the marine mollusk Aplysia limacina, a substantial amount of endogenous D-aspartic acid (D-Asp) was found following its synthesis from L-aspartate by an aspartate racemase. Concentrations of D-Asp between 3.9 and 4.6 micromol/g tissue were found in the cerebral, abdominal, buccal, pleural, and pedal ganglia. In non nervous tissues, D-Asp occurred at a very low concentration compared to the nervous system. Immunohistochemical studies conducted on cultured Aplysia neurons using an anti-D-aspartate antibody demonstrated that D-Asp occurs in the soma, dendrites, and in synaptic varicosities. Synaptosomes and synaptic vesicles from cerebral ganglia were prepared and characterized by electron microscopy. HPLC analysis revealed high concentrations of D-Asp together with L-aspartate and L-glutamate in isolated synaptosomes In addition, D-Asp was released from synaptosomes by K+ depolarization or by ionomycin. D-Asp was one of the principal amino acids present in synaptic vesicles representing about the 25% of total amino acids present in these cellular organelles. Injection of D-Asp into live animals or addition to the incubation media of cultured neurons, caused an increase in cAMP content. Taken as a whole, these findings suggest a possible role of D-Asp in neurotransmission in the nervous system of Aplysia limacina.

Occurrence of D-aspartic acid in human seminal plasma and spermatozoa: possible role in reproduction.

OBJECTIVE: To determine D-aspartic acid (D-Asp) in human seminal plasma and spermatozoa in fertile and infertile donors. DESIGN: Prospective observation study. SETTING: Department of Pathophysiology for Human Reproduction, Hospital "S. Luca," Salerno, Italy, and Department of Neurobiology and Comparative Physiology, Zoological Station "A. Dohrn," Naples, Italy. PATIENT(S): Ten normospermic, 10 oligoasthenoteratospermic, and 10 azoospermic (nonobstructive) men. INTERVENTION(S): D-aspartic acid was determined by a specific enzymatic high-performance liquid chromatography method on purified seminal plasma and on isolated spermatozoa and by an immunohistochemical method using light and electronic microscopic techniques. MAIN OUTCOME MEASURE(S): Concentration of D-Asp in seminal plasma and in isolated spermatozoa; subcellular localization of D-Asp in the acrosome and nucleus. RESULT(S): The concentration of D-Asp in seminal plasma and in spermatozoa was significantly reduced in oligoasthenoteratospermic donors. In the seminal fluid of normospermic donors, D-Asp occurs at a concentration of 80 +/- 12 nmol/mL semen (10.4 +/- 1.5 microg/mL), whereas 26 +/- 6 nmol/mL semen were found in oligoasthenoteratospermic donors, and 12 +/- 1.5 nmol/mL semen were found in azoospermic donors. In spermatozoa from normospermic donors, D-Asp occurred at a concentration of 130 +/-15 fmol per spermatozoa (17.0 +/- 1.96 ng per spermatozoa), vs. 60.5 +/- 5.0 fmol per spermatozoa from oligoasthenoteratospermic subjects. Other D-amino acids analyzed were not present in seminal plasma or in spermatozoa in a significant concentration compared with D-Asp. CONCLUSION(S): D-aspartic acid occurs in human seminal plasma and spermatozoa and is implicated in male fertility.

Amino acids and transaminases activity in ventricular CSF and in brain of normal and Alzheimer patients.

The present study was conducted to determine the concentration of amino acids in the cerebrospinal spinal fluid (CSF) and the activities of two tramsaminases: glutamic oxaloacetate transaminase (GOT) and glutamic pyruvate transaminase (GPT) in human Alzheimer disease (AD) and normal brain. L-glutamic acid, L-glutamine and L-alanine are the most abundant amino acids in the CSF (50-55% of total amino acids). L-glutamine occurs at much higher levels in Alzheimer CSF compared to the normal CSF (229+/-91.8 nmol/ml in AD versus 107+/-47.2 nmol/ml in normal; P=0.0041). In contrast, L-aspartate occurs at significantly lower concentrations in Alzheimer CSF than normal CSF (46.1+/-25.7 nmol/ml in Alzheimer versus 95.2+/-52.6 nmol/ml in normal; P=0.020). In Alzheimer brain (frontal, parietal and occipital cortices) GOT is present at significantly higher activities than in normal brain cortices (about 1.5 times higher; P<0.01). No significant differences for GPT activity occurred between normal and AD brain. Since CSF receives amino acids from brain tissues, and since GOT catalyzes the conversion of L-aspartate to L-glutamate, the higher concentrations of L-glutamine (which is derived from L-glutamate), and the lower concentrations of L-aspartate found in Alzheimer CSF could be considered as a consequence of the higher activity of GOT that occurs in Alzheimer brain.

Cephalopod vision involves dicarboxylic amino acids: D-aspartate, L-aspartate and L-glutamate.

In the present study, we report the finding of high concentrations of D-Asp (D-aspartate) in the retina of the cephalopods Sepia officinalis, Loligo vulgaris and Octopus vulgaris. D-Asp increases in concentration in the retina and optic lobes as the animal develops. In neonatal S. officinalis, the concentration of D-Asp in the retina is 1.8+/-0.2 micromol/g of tissue, and in the optic lobes it is 5.5+/-0.4 micromol/g of tissue. In adult animals, D-Asp is found at a concentration of 3.5+/-0.4 micromol/g in retina and 16.2+/-1.5 micromol/g in optic lobes (1.9-fold increased in the retina, and 2.9-fold increased in the optic lobes). In the retina and optic lobes of S. officinalis, the concentration of D-Asp, L-Asp (L-aspartate) and L-Glu (L-glutamate) is significantly influenced by the light/dark environment. In adult animals left in the dark, these three amino acids fall significantly in concentration in both retina (approx. 25% less) and optic lobes (approx. 20% less) compared with the control animals (animals left in a diurnal/nocturnal physiological cycle). The reduction in concentration is in all cases statistically significant (P=0.01-0.05). Experiments conducted in S. officinalis by using D-[2,3-3H]Asp have shown that D-Asp is synthesized in the optic lobes and is then transported actively into the retina. D-aspartate racemase, an enzyme which converts L-Asp into D-Asp, is also present in these tissues, and it is significantly decreased in concentration in animals left for 5 days in the dark compared with control animals. Our hypothesis is that the dicarboxylic amino acids, D-Asp, L-Asp and L-Glu, play important roles in vision.

Occurrence and neuroendocrine role of D-aspartic acid and N-methyl-D-aspartic acid in Ciona intestinalis.

Probes for the occurrence of endogenous D-aspartic acid (D-Asp) and N-methyl-D-aspartic acid (NMDA) in the neural complex and gonads of a protochordate, the ascidian Ciona intestinalis, have confirmed the presence of these two excitatory amino acids and their involvement in hormonal activity. A hormonal pathway similar to that which occurs in vertebrates has been discovered. In the cerebral ganglion D-Asp is synthesized from L-Asp by an aspartate racemase. Then, D-Asp is transferred through the blood stream into the neural gland where it gives rise to NMDA by means of an NMDA synthase. NMDA, in turn, passes from the neuronal gland into the gonads where it induces the synthesis and release of a gonadotropin-releasing hormone (GnRH). The GnRH in turn modulates the release and synthesis of testosterone and progesterone in the gonads, which are implicated in reproduction.

A specific enzymatic high-performance liquid chromatography method to determine N-methyl-D-aspartic acid in biological tissues.

Recently we demonstrated that N-methyl-D-aspartic acid (NMDA) is present as an endogenous compound in the nervous tissues and endocrine glands of the rat where it plays a role in the regulation of the luteinizing hormone, growth hormone, and prolactin (FASEB J. 14 (2000) 699; Endocrinology 141 (2000) 3861). Based on the prediction that NMDA could have future importance in neuroendocrinology, we have devised an improved method for the specific and routine determination of NMDA in biological tissue. This method is based on the detection by HPLC of methylamine (CH(3)NH(2)) which comes from the oxidation of NMDA by D-aspartate oxidase, an enzyme which specifically oxidizes NMDA, yielding CH(3)NH(2) as one of the oxidative products of the reaction. The sensitivity of the method permits the accurate determination of NMDA in the supernatant of a tissue homogenate at levels of about 5-10 picomol/assay. However, for those tissues in which the concentration of NMDA is less than 1nmol/g, the sample must be further purified by treatment with o-phthaldialdehyde in order to separate the NMDA from the other amino acids and amino compounds and then concentrated and analyzed by HPLC. Using this method we have conducted a comparative study in order to measure the amount of NMDA in neuroendocrine and other tissues of various animal phyla from mollusks to mammals.