Perception et réaction géotropiques de l'épicotyle d'Asparagus officinalis

Geoperception and georeaction in Asparagus officinalis epicotyls The location and the role of the statenchyma were investigated in Asparagus officinalis epicotyls 1, 2 or 3 cm in length. The statocytes represent a monocellular sheath which comprises the outer layer of the pericycle. Three phases of differentiation (S₁, S₂, S₃) of the statocytes may be distinguished by criteria of cell length, the state of vacuolisation and the sedimentation of amyloplasts and nuclei with respect to gravity. The statenchyma was found to be located only in the first 10 mm of the epicotyl 1, 2 or 3 cm in length; in effect the oldest statocytes (S₃) differentiate into sclerenchyma beneath this level. The geotropic curvature of the epicotyls begins with a positive (downward) curvature and the negative (upward) response is only realized after 15–30 min of geotropic stimulation. The upper limit of the bending is located in the zone containing the mature statocytes (S₃), while the lower limit is located much closer to the base of the epicotyl. Experiments on decapitation of the epicotyls have indicated that the S₁ and S₂ statocytes do not play an important role in the perception of gravity. However, with S₃ statocytes, it has been demonstrated that there is a statistical correlation between the initial rate of curvature of the epicotyls and the length of their sheaths. Thus, the longer the sheath, the more the epicotyls curve. From the results obtained it is proposed that the statocytes are responsible for the geotropic perception of Asparagus officinalis epicotyls.     

Dimension anthropique de l'éruption du Mont Pinatubo, Philippines, entre 800 et 500 ans BP

Before its worldwide famous awakening in 1991, Mt Pinatubo volcano erupted between 800 and 500 year BP. The impacts of this little known eruption are progressively coming to light with the discovery of archaeological sites and the study of oral and geographical records. Recent archaeological excavations have shown that pyroclastic flows and lahar onslaughts have probably led to the abandonment of major settlements on both sides of Mt. Pinatubo. The location of these archaeological sites and the toponyms on the east flanks of the volcano suggest a general redistribution of the population downstream toward lands reclaimed on the sea due to heavy lahar material deposition. These population movements did not occur on the west side of the mountain despite similar land reclamation. Such topographic and socio-demographic changes have deeply disturbed the economic environment since it is hypothesized that extensive trade with China and other foreign “countries” profited from the easy penetration of commercial vessels into the bays that would have been filled up by lahar deposits. Finally oral memory records, such as legends and epics, help define the ethnic groups that have suffered from the eruption (e.g. Aetas, Kapampangans and Sambals). Understanding what happened 500 years ago turns very useful to anticipate the consequences of future events.     

Une nouvelle approche pour évaluer l'état de conservation de l'os et du collagène pour les mesures isotopiques (datation au radiocarbone, isotopes stables du carbone et de l'azote)

Measuring the amounts of nitrogen and carbon in small quantities of ancient bones before radiocarbon dating using elemental analysis is a way to quantify the amount of preserved collagen and the quantity of exogenous contaminating carbon. Such a measurement can be performed on a large number of samples and allows to sort out the specimens with the best preserved collagen, those with the most carbon contamination, and eventually to infer relationships between burial conditions and collagen preservation. This approach is most interesting as a preliminary method to use before attempting radiocarbon dating using accelerator mass spectrometry of bone collagen.