Thermal Inactivation of Plant Growth: Effects on Cotyledon Metabolism

Temperature exposures which normally decrease growth of Pisum sativum seedlings by 50 % were found to be lethal in plants whose cotyledons were removed. Utilization of the two major reserves, starch and protein, decreased at high temperatures. However, the two enzymes responsible for their hydrolysis were thermostable. It appears that the influence of high temperatures on seedling growth is not due to direct effects of temperature on cotyledon metabolism, but rather indirectly through the axis.     

Biochemical Adaptation to the Environment

SYNOPSIS. Biochemical adaptation to environmental parameterssuch as temperature appears to involve two distinct types ofchanges in the organism's chemistry. On the one hand, the quantitiesof certain molecular species present in the cells may change.Alternatively, the actual types of molecules present may vary.Rainbow trout (Salmo gairdneri) acclimated to warm and coldtemperatures exhibit a striking example of this latter typeof adaptation. For all enzymes we have examined in this species,distinct "warm" and "cold" isozymes are present. The isozymesfound in warmacclimated (18°C) trout function well onlyat temperatures above 10–12°C. The isozymes presentin cold-acclimated (4°C) trout function optimally at 2-5°C,temperatures this species normally encounters in winter. Thesedata, plus information on comparable changes in membrane lipids,lead us to propose that adult poikilotherms may undergo a considerabledegree of "biochemical restructuring" on a seasonal basis. Thefactors which control this "restructuring," and the rates atwhich the process occurs at high and low temperatures, are topicsfor future investigation.     

Natural distribution, spread, and variation, in the tobacco mosaic virus infecting Nicotiana glauca in Australia

Nicotiana glauca is a naturalised introduced species widely distributed in Australia. A survey of stands in the central zone of its recorded distribution has shown that a type of tobacco mosaic virus which characteristically induces a bright yellow mosaic symptom (TMV-Y) is commonly associated with N. glauca throughout this zone. Surveys of a natural community of N. glauca less than 5 yr old, and in an experimental block, showed that TMV-Y could spread at a rate, and in a pattern, which could not be explained by contact transmission alone, and which indicated that an airborne vector was probably involved in transmission. These results together have led to the conclusion that the common association of TMV-Y with N. glauca is due to spread of the virus by an unknown vector(s). Seed transmission of TMV-Y in N. glauca has not been detected. Molecular hybridisation analysis has shown that all but one of the TMV-Y isolates studied were related to TMV-U², and that the isolate which was unrelated to U², was partially related to TMV-U¹, TMV-U⁵, and tomato mosaic virus. Selected isolates which showed a close relationship to TMV-U², also showed a close relationship to TMV-U⁵, a distant relationship to TMV-U¹, and tomato mosaic, and very little or no relationship with three other tobamoviruses (sunn-hemp mosaic virus, odontoglossum ringspot virus, and cucumber virus 4). These results show that the Australian TMV-Y isolates are similar to the TMV isolated from N. glauca in California.     

A Comparison of Petiolar Growth of Isolated Hazel Cotyledons in Response to Stratification and Exogenous GA3

Following stratification seeds of Corylus avellana exhibitedtheir characteristic ability to germinate at 20 °C undermoist conditions. Stratification of the intact fruit also stimulatedelongation of the cotyledonary petiole when isolated cotyledonswere transferred to moist conditions at 20 °C. GA₃ inducedboth of these effects in non-stratified material. ABA substantiallydecreased seed germination and the response of cotyledonarypetioles to stratification and GA₃. CCC² applied to stratifiedor GA₃-pretreated cotyledons did not depress the final percentageof growing petioles. Cotyledons can clearly regulate the development of their petiolesin the absence of the embryonic axis. It is concluded that thereis at least one gibberellin-sensitive site in the cotyledonscapable of initiating petiole development independent of axiscontrol.     

Effects of Cycloheximide on Mitosis in Vicia faba Root-meristem Cells

Three different responses of dividing root-meristem cells tocycloheximide have been observed. Cells in anaphase or telophasecan complete these stages and pass into G1; movement of prophaseand metaphase cells into anaphase is reversibly inhibited; entryof G2 cells into mitosis is irreversibly inhibited. While thislast effect is probably a consequence of inhibition of proteinsynthesis by cycloheximide, it is suggested that the reversiblemitotic arrest induced by the drug results from inhibition ofsome other cellular activity, possible related to energy transfer.     

The relation of Late Ordovician glaciation to the Ordovician-Silurian changeover in North American brachiopod faunas

Sheehan, P. M.: The relation of Late Ordovician glaciation to the Ordovician-Silurian changeover in North American brachiopod faunas.
The Ordovician-Silurian changeover of brachiopod faunas in North American epicontinental seas involved the abrupt extinction of endemic Late Ordovician stocks and subsequent repopulation of North American seas by Old World taxa. The Late Ordovician Gondwanaland glaciation may have lowered sea levels sufficiently to place severe stress on the widespread shallow marine faunas in North America, resulting in their eventual extinction. The Late Ordovician depositional history in North America is not well enough known to establish the presence of a latest Ordovician regression, but the earliest Silurian was an interval of off-lap in North America. Therefore, the glacial lowering of sea level is considered to be the most likely cause of the faunal changeover.     

In vivo Chlorophyll Fluorescence Monitoring with Solid State Photosensors

Solid state photosensors with their many advantages have not been utilized for chlorophyll fluorescence research. One reason is their reputed low photosensitivity compared to photomultiplier tubes. A photodarlington sensor has a relatively low photosensitivity and a nonlinear current output versus light intensity. However, when incorporated into an apparatus described in this paper it can respond to fluorescence signals from leaves using light excitation as low as 500 μW/cm². The sensitivity of another solid state device (photovoltaic photodiode) was compared to five photomultipliers using a monochromator-microphotometer testing apparatus. This solid state sensor proved to have equal or greater sensitivity to chlorophyll fluorescence. An apparatus incorporating the photovoltaic photodiode is discussed.     

Divorce among the Yoruba

Divorce rates among the northern Yoruba are not only higher than one might expect in patrilineal societies, but little different from those of the southern Yoruba, with cognatic descent groups. This initial observation challenges the hypothesis that divorce rates are directly correlated with the line of descent. Data on over 300 divorces were collected in four Yoruba towns—two with agnatic and two with cognatic descent groups. The divorces were classed by the length of the terminated marriage and its fertility, and the distribution of the types of divorce were then compared in the four towns. The results suggest that the rate of divorce is primarily correlated with the degree to which a woman is alienated by marriage from her own descent group. But a number of secondary factors seem to be important, and these may cumulatively raise or reduce the divorce rate to a marked degree.     

Carbon Dioxide as the Initial Stimulus for Excystation of Eimeria tenella Oocysts*

SYNOPSIS. The stimulus necessary to initiate in vitro excystation of the chicken coccidium Eimeria tenella was provided by exposure of intact sporulated oocysts to an atmosphere of carbon dioxide. This stimulus produced a thinning and indentation at the micropylar region and oocysts became permeable to trypsin and bile. Sporozoites became active and began to escape from sporocysts into the oocyst cavity and then to the outside thru the altered micropyle after incubation in the enzyme-bile mixture. Activation of sporozoites when CO₂-pretreated oocysts were incubated in trypsin and bile, was used as the criterion to determine the number of oocysts responding to the initial stimulus. Thus, activation of sporozoites within intact oocysts was an indirect measurement of the number of oocysts stimulated during CO₂-pretreatment. Approximately 90% of the oocysts contained active sporozoites after 18 hr of pretreatment with carbon dioxide and 8 hr incubation in trypsin and bile at 38 or 41 C, respectively. Pretreatment of oocysts with air, N₂, O₂, or He resulted in 8% or less activation during incubation in trypsin and bile. Approximately 83% of the oocysts responded to the stimulus during 8 hr CO₂-pretreatment at 41 C, whereas at 38 C, 16 hr of pretreatment were required for a similar response. The stimulus did not elicit a response from oocysts held at 23 C during the pretreatment gasphase. No significant difference occurred in number of oocysts containing active sporozoites after sufficient CO₂-pretreatment for maximum stimulation of oocysts and incubation in trypsin and bile at 38 or 41 C.