A LIGHT AND ELECTRON MICROSCOPY STUDY ON CARPOSPOROGENESIS OF THE MARINE RED ALGA GRACILARIA VERRUCOSA (HUDSON) PAPENFUSS

THE UTRASTRUCTURE OF CAPOSPOROGENESIS FOR THE RED ALOA GRACILARIA VERRUCOSA (HUDS) PAPENFUSS IS DESCRIBED. CARPOSPORE DIFFERENTIATION PROCEEDS THROUGH FOUR DEVELOPMENTAL STAGES. THE YOUNGEST CARPOSPORES ARE EMBEDDED WITHIN CONFLUENT MUCILAGE AND CONTAIN A LARGE NUCLEUS, FEW STARCH GRAINS, AS WELL AS PROPLASTIDSWITH A PERIPHERAL THYLAKOID. THE SECOND STAGE CARPOSPORES ARE REORGANIZED BYTHE INCREASED NUMBERS OF STARCH GRAINS, THE FORMATION OF SMALL STRAIGHT-PROFILED DICTROSOMES WHICH PRODUCE CARPOSPORE WALL MATERIAL AND THE PRESENCE OF DARK-STAINING BODIES IN THE CYTOPLASM. PLASTIDS FORM THEIR INTERNAL THYLAKOID SYSTEM. DURING THE THIRD STAGE, DICTYOSOMES BECOME CURVED AND CONTINUE TO PRODUCEVESICLES WHICH DEPOSIT MORE WALL MATERIAL OR FUSE WITH EACH OTHER TO FORM LARGE FIBROUS VACUOLES LIVING IN THE PERIPHERAL CYTOPLASM. MATURE CARPOSPORES ARE SURROUNDED BY A TWO-LAYERED CARPOSPORE WALL WITH THE OUTER LAYER REPRESENTING COMPRESSED MUCILAGE FIBRILS. CARPOSPORE MATURITY IS SIGNALLED BY THE MASSIVEPRODUCTION OF CORED VESICLES PRODUCED BY HIGHLY CURVED HYPERTROPHIED DICTYOSOMES.ΠΕΡΙΓΡΑΦΕΤΑΙ Η ΛΕΠΤΗ ΔΟΜΗ ΤΗΣ ΚΑΡΠΟΣΠΟΡΙΟΓΕΝΕΣΗΣ ΣΤΟ ΡΟΔΟΦΥΚΟΣ GRACILARIA VERRUCOSA (HUDS) PAPENFUSS. Η ΔΙΑΦΟΡΟΠΟΙΗΣΗ ΤΩΝ ΚΑΡΠΟΣΠΟΡΙΩΝ ΓΙΝΕΤΑΙ ΔΙΑΜΕΣΟΥ ΤΕΣΣΑΡΩΝ ΑΝΑΠΤΥΞΙΑΚΩΝ ΣΤΑΔΙΩΝ. ΤΑ ΝΕΩΤΕΡΑ ΚΑΡΠΟΣΠΟΡΙΑ ΒΡΙΣΚΟΝΤΑΙ ΜΕΣΑ ΣΕ ΒΛΕΝΝΑ ΚΑΙ ΠΕΡΙΕΧΟΥΝ ΕΝΑ ΜΕΓΑΛΟ ΠΥΡΗΝΑ, ΛΙΓΟΥΣ ΑΜΥΛΟΚΟΚΚΟΥΣ ΚΑΘΩΣ ΕΠΙΣΗΣ ΠΡΟΠΛΑΣΤΙΔΙΑ ΜΕ ΕΝΑ ΠΕΡΙΦΕΡΕΙΑΚΟ ΘΥΛΑΚΟΕΙΔΕΣ. ΤΑ ΚΑΡΠΟΣΠΟΡΙΑ ΤΟΥ ΔΕΥΤΕΡΟΥ ΣΤΑΔΙΟΥ ΑΝΑΓΝΩΡΙΖΟΝΤΑΙ ΑΠΟ ΤΟΝ ΑΥΞΗΜΕΝΟ ΑΡΙΘΜΟ ΑΜΥΛΟΚΟΚΚΩΝ, ΤΟ ΣΧΗΜΑΤΙΣΜΟ ΜΙΚΡΩΝ, ΕΥΘΥΓΡΑΜΜΗΣ ΚΑΤΑΤΟΜΗΣ ΔΙΚΤΥΟΣΩΜΑΤΩΝ ΠΟΥ ΠΑΡΑΓΟΥΝ ΤΟΙΧΩΜΑΤΙΚΟ ΥΛΙΚΟ. ΣΤΗ ΔΙΑΡΚΕΙΑ ΤΟΥ ΤΡΙΤΟΥΣΤΑΔΙΟΥ ΤΑ ΔΙΚΤΥΟΣΩΜΑΤΑ ΓΙΝΟΝΤΑΙ ΚΕΚΑΜΕΝΑ ΚΑΙ ΣΥΝΕΧΙΖΟΥΝ ΝΑ ΠΑΡΑΓΟΥΝ ΚΥΣΤΙΔΙΑΤΑ ΟΠΟΙΑ ΕΝΑΠΟΘΕΤΟΥΝ ΕΠΙΠΛΕΟΝ ΤΟΙΧΩΜΑΤΙΚΟ ΥΛΙΚΟ 'Η ΕΝΩΝΟΝΤΑΙ ΜΕΤΑΞΥ ΤΟΥΣ ΓΙΑ ΝΑ ΣΧΗΜΑΤΙΣΟΥΝ ΜΕΓΑΛΑ ΙΝΩΔΗ ΧΥΜΟΤΟΠΙΑ ΠΟΥ ΒΡΙΣΚΟΝΤΑΙ ΣΤΟ ΠΕΡΙΦΕΡΕΙΑΚΟ ΚΥΤΟΠΛΑΣΜΑ. ΤΑ ΩΡΙΜΑ ΚΑΡΠΟΣΠΟΡΙΑ ΠΕΡΙΒΑΛΛΟΝΤΑΙ ΑΠΟ ΕΝΑ ΔΙΣΤΡΩΜΟ ΤΟΙΧΩΜΑ ΑΠΟ ΤΟ ΟΠΟΙΟ ΤΟ ΕΞΩΤΕΡΙΚΟ ΣΤΡΩΜΑ ΑΝΤΙΠΡΟΣΩΠΕΥΕΙ ΣΥΜΠΙΕΣΜΕΝΑ ΙΝΙΔΙΑ ΒΛΕΝΝΑΣ. Η ΩΡΙΜΟΤΗΤΑ ΤΩΝΚΑΡΠΟΣΠΟΡΙΩΝ ΣΗΜΑΤΟΔΟΤΕΙΤΑΙ ΑΠΟ ΤΗ ΜΑΖΙΚΗ, ΠΑΡΑΓΩΓΗ ΕΜΠΥΡΗΝΩΝ ΚΥΣΤΙΔΙΩΝ ΠΟΥ ΠΑΡΑΓΟΝΤΑΙ ΑΠΟ ΠΟΛΥ ΚΕΚΑΜΕΝΑ, ΥΠΕΡΤΡΟΦΙΚΑ ΔΙΚΤΥΟΣΩΜΑΤΑ

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The anatomy and histochemistry of the adventitious roots of Urginea maritima (L.) Baker and the plant's adaptive strategies to the Mediterranean climate were investigated. The adventitious roots of U. maritima are bounded by a multiple-layered velamen, responsible for rapid water uptake. Both the epidermis and endodermis of the root are uniseriate. The cortex is 741.3 Ìm thick and is composed of numerous large parenchyma cells with storing character. In the cortex, scattered idioblastic cells containing numerous raphides of calcium oxalate exist. The average length of the calcium oxalate needles is 72 ± 22 Ìm. The presence in the cortex of cells containing in their vacuoles soluble polysaccharides is conspicuous after employing the Schiff's staining technique. Also, numerous cortical cells are filled with lipids and become intensely stained brown to black when treated with sudan black B. Morphometric studies have shown that idioblastic cells occupy 19.83% of the cortex relative volume, cells containing lipids 14.38%, and cells containing polysaccharides 11.27%. The cortex storage cells occupy 34.11% of the total root volume. The average volume of the cortical cells is 73143 Ìm 3 . The vascular cylinder is usually 10-arched. The root xylem consists of vessels in short radial rows. The phloem consists of sieve elements located between the vessel rays. Urginea maritima possessing adventitious roots proves to be efficient in storing water during the long summer drought, less susceptible to climatic stress and well synchronized with the climatic fluctuations. Specialized features of U. maritima adventitious roots are, at least in part, responsible for the species' occurrence and frequent dominance in a wide array of semiarid ecosystems of the Mediterranean region