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Reversible in vivo cellular changes occur during desiccation and recovery: Desiccation tolerance of the resurrection filmy fern Hymenophyllum dentatum Cav.Cambios celulares reversibles observados in vivo durante la desecación y recuperación: Tolerancia a la desecación del helecho película de resurrección Hymenophyllum dentatum Cav. SORAYA ABSTRACTThe present work explores in vivo physiological, morphological and chemical features during full hydration, desiccation and rehydration of the filmy fern Hymenophyllum dentatum with two main objectives: 1) to get further insight about the mechanisms underlying its desiccation tolerance, and 2) to understand how this plant manages mechanical stress induced by water loss and recovery. With these purposes, physiological (relative water content and F v /F m chlorophyll fluorescence parameter), morphological (Confocal Laser Scanning Microscopy and 3D reconstruction) and chemical (FT-IR microspectroscopy) data were obtained and compared between fully hydrated, desiccated and rehydrated tissues of H. dentatum. Remarkable changes in cell architecture and chemical composition were observed in vivo in desiccated leaves. Cells were smaller, showed a collapsed general appearance, and were delimitated by apparently folded cell walls. Marked changes in chloroplasts location and decrease in the number of active chloroplasts were also evidenced. Chemical experiments showed that changes in the secondary structure of proteins and in the polysaccharide composition of the cell wall occur in desiccated cells. All changes were rapidly reversed upon rehydration. This study shows that H. dentatum presents an extreme case of desiccation tolerance, able to withdraw severe, rapid and consecutive dehydration/rehydration induced stress by the function of constitutive systems of protection and reparation, in which cell wall folding plays a relevant role as a protective system against mechanical and oxidative stress. Besides, H. dentatum is proposed as an excellent plant model for the study of dissection tolerance such as one cell layer fern, auto-fluorescence of cellular compartments, and simple long term storage under laboratory conditions, among others. KEYWORDS:Hymenophyllum, desiccation tolerance, confocal 3D microscopy, FT-IR microspectroscopy, rapid dehydration /rehydration. RESUMENEl presente trabajo muestra una exploración in vivo de los rasgos fisiológicos, morfológicos y químicos que caracterizan a los estados de hidratación completa, desecación y rehidratación del helecho película Hymenophyllum dentatum, que persigue 2 objetivos principales: 1) Adquirir conocimientos sobre los mecanismos que subyacen a la tolerancia a la desecación, y 2) entender cómo estas plantas manejan el estrés mecánico inducido por la pérdida y recuperación de agua. Con estos propósitos se obtuvo datos fisiológicos (contenido relativo de agua y parámetro de fluorescencia de clorofila Fv/Fm), ISSN 0016-5301 Gayana Bot. 73(2): [402][403][404][405][406][407][408][409][410][411][412][413] 2016 403In vivo cellular ch...

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. American Geographical Society is collaborating with JSTOR to digitize, preserve and extend access to Geographical Review. http://www.jstor.org This content downloaded from 62.122.77.12 on Fri, 9 May 2014 11:50:14 AM All use subject to JSTOR Terms and Conditions THE GEOGRAPHICAL REVIEW THE GEOGRAPHICAL REVIEW Senegal River in French West Africa. From the spirited preface by M. E. Tisserand to the closing paragraph the report breathes a strong note of optimism, and frequent comparisons are made between the valley of the Senegal and that of the Nile.Irrigation in the region of the Senegal is largely a matter of the future. At present the production of rice and sorghum, the chief food crops, is scarcely sufficient to support the sparse native population of some 200,000.The Senegal, a river nearly 1,000ooo miles long, rises in a range of low mountains southwest of Dakar, flowing thence northwest and west into the ocean at St. Louis. The Niger, which has its source on the southern slope of the same range, flows a long way eastward before turning south and west. The Senegal is a sluggish stream when not in flood, its mean low-water gradient for nearly 600 miles above the mouth being about 2 inches per mile. Thus it is salty during low stage for 100 miles up stream.The irrigable lands are composed of a blanket of silt deposited from the flood waters and of low relief. Like the valley of the Nile this silt blanket is underlain by ground water when not submerged. Much of the soil, particularly in the lower delta, is heavily charged with salt and when dry is often hard and slowly permeable to water.M. Henry has brought together in his report a valuable collection of facts concerning the character of the soil, and the period and height of the flood discharge of the river. It is to be regretted that he has not included data from which the volume of discharge could be computed as well as facts concerning the salt content and the silt load of the stream.The data on rainfall are comprehensive and cover a long period, but temperature data are wanting. For those who seek to support the hypothesis that deforestation causes decreased rainfall this report will be a welcome contribution.The present agriculture of the region is described concisely, and the essentials for future development are boldly outlined. Detailed plans are suggested for control measures by which certain areas of the delta could be utilized more effectively, particularly the basin of the Lac de Guier, a basin tributary to the river about one hundred miles above its mouth.The essential features of the proposed development are to prevent further salting of this basin by sea water and to regulate access of river flood water. The floo...

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