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Little is known about antiherbivore defenses in non-myrmecophyte Cecropia trees. We compare two non-myrmecophyte Cecropia—Cecropia sciadophylla and Cecropia tacuna—with Cecropia membranacea, a myrmecophyte. High levels of chemical defenses in young leaves and physical toughness of mature leaves compensate for the absence of mutualistic ants in C. sciadophylla. Some C. tacuna trees produce trichilia and Mullerian bodies suggesting it has lost a mutualism with ants. Resumen Poco se sabe sobre las defensas contra a los herbivoros en las especies de Cecropia no-mirmecofitas. Hemos examinado las defensas contra herbivoros en dos especies no-mirmecofitos – Cecropia sciadophylla y Cecropia tacuna. Comparamos estos con Cecropia membranacea, un mirmecofita. Nuestro estudio demuestra que para C. sciadophylla hay niveles altos de defensas quimicas en las hoyas nuevas y la fortaleza fisica de las hojas maduras esto compensa por la ausencia de hormigas mutualistas. Algunos arboles C. tacuna producen trichilia y cuerpos de Muller sugiere la perdida de mutualism con hormigas.

Protein synthesis in dormant embryos of sugar maple (Acer saccharum) was investigated in seeds stratified at 4°C or incubated at 15°C. Seeds stratified at 4°C germinated after 27 days; seeds incubated at 15°C failed to germinate. Stratification increased the embryo's capacity for protein synthesis by day 11 as measured by in vivo incorporation of [35S]-methionine into purified protein. At 4°C protein synthesis in the embryonic axis rose in a linear fashion prior to germination, whereas in cotyledons it increased until day 20 and then declined. Analysis of radiolabelled proteins by two-dimensional gel electrophoresis revealed that the levels of specific proteins were altered by temperature, primarily in the cotyledons. Several proteins were expressed in the cotyledons at 15°C but were absent in unstratified embryos and in embryos stratified at 4°C. That is, the expression of these proteins was repressed during stratification and release from dormancy. Levels of other proteins in the cotyledons declined at 4°C during stratification. We suggest that one or more of these proteins may be associated with the inhibition of growth of the embryonic axis imposed by the cotyledons.

Examen des effets de la lumiere et de la temperature sur la germination des graines de B.p. d'origines geographiques differentes

Seeds of paper birch (Betula papyrifera Marsh.) were induced to germinate by prechilling at 3 C or by red light. The light requirement was mediated by phytochrome and the action of phytochrome during prechilling was investigated. Red irradiation (R) prior to prechilling markedly enhanced the effectiveness of the prechilling treatment in inducing subsequent germination at 18 C. Reversal of this enhancement by far-red irradiation (FR) was more effective when FR was supplied after a 1-week prechill treatment than after a 2-week treatment. The R enhancement effect exhibited a sharp drop as prechilling temperature was increased from 5 to 7 C. This decline is consistent with a membrane phase transition at about 7 C where Pfr action is diminished by a loss in sensitivity of its receptor sites. Although phytochrome action was observed during prechilling treatments, the seeds failed to germinate at prechilling temperatures. Therefore, it was concluded that while potentiation of germination by Pfr occurred during prechilling, some other reaction(s) leading to radicle protrusion requires higher temperatures. In one seed source loss of germination potential was observed with protracted storage at 3 C. This was prevented by R supplied during the prechilling treatment. Taken collectively the data suggest that action of phytochrome during prechilling is accentuated in these seeds by two factors: (a) an increase in the sensitivity (or number) of Pfr receptor sites; and (b) preservation of Pfr by deferment of thermal reversion.