The colonization of palynomorphs by chytrids and thraustochytrids during pre–depositional taphonomic processes in tropical mangrove ecosystems

Degrees of colonization of palynomorphs from six mangrove plants by chytrids and thraustochytrids in four mangrove plant communities at each stage of the pre–depositional taphonomic process were investigated using a pollen–baiting method. Chytrids and thraustochytrids were the dominant group colonizing palynomorphs in mangroves, gaining access to the cytoplasm through the wall or aperture. There were no significant differences in the degree of colonization between the different plant communities. Pollen with a larger size and/or extensive apertural region appeared to be the most colonized, while the absence of apertures and the presence of a thick wall seemed to reduce the chance of colonization by these microorganisms. Taphonomic experiments showed that the longer palynomorphs take to settle into the mangrove sediments, the lower the possibility of survival from the destructive colonization by chytrids and thraustochytrids and consequently the less carbon that will be sequestered.     

Late Glacial and Holocene environmental and climatic changes from a limnological transect through Colombia, northern South America

We present a synthesis of the palaeolimnological and palaeoclimatic reconstructions of four sites in Colombia. The record from Lake El Caimito, the westernmost site on the Pacific Coast, dates from the Late Holocene and shows lacustrine sedimentation frequently interrupted by fluvial pulses. These pulses probably reflect periods of increased precipitation related to La Niña phases. East of El Caimito site is the Patía swamp, situated between the Western and Central Andean Cordilleras. The Patía records the dynamics of forest expansion/reduction and changes in water levels. Although the climatic signal of the Patia core is difficult to reconstruct, there is a clear increase in humidity in the Mid-Holocene. The Fúquene Lake record, on the Eastern Andean Cordillera, records dry and cold conditions during the Late Pleistocene, very humid conditions for the early Mid-Holocene, and dry conditions during the mid-Late Holocene. Las Margaritas site, on the eastern savannas, records dry conditions during the Early Holocene and overall humid conditions for the Mid- and Late Holocene. Climate conditions from the Fuquene and Las Margaritas sites seem to reflect the Holocene movements of the Intertropical Convergence Zone (ITCZ); the latter site being more affected by humidity coming from the Amazon region.     

Pollen-based biome reconstruction for southern Europe and Africa 18,000 yr bp

Pollen data from 18,000 ¹⁴C yr bp were compiled in order to reconstruct biome distributions at the last glacial maximum in southern Europe and Africa. Biome reconstructions were made using the objective biomization method applied to pollen counts using a complete list of dryland taxa wherever possible. Consistent and major differences from present‐day biomes are shown. Forest and xerophytic woods/scrub were replaced by steppe, both in the Mediterranean region and in southern Africa, except in south‐western Cape Province where fynbos (xerophytic scrub) persisted. Sites in the tropical highlands, characterized today by evergreen forest, were dominated by steppe and/or xerophytic vegetation (cf. today’s Ericaceous belt and Afroalpine grassland) at the last glacial maximum. Available data from the tropical lowlands are sparse but suggest that the modern tropical rain forest was largely replaced by tropical seasonal forest while the modern seasonal or dry forests were encroached on by savanna or steppe. Montane forest elements descended to lower elevations than today.     

Some characteristics of pollen wall cytochemistry and ultrastructure in Japanese larch (Larix leptolepis Gord.)

Summary The mature pollen of Larix leptolepis Gord. (Conifer) contains five different cell types, and the plasma membrane of the vegetative cell is continuous and organized. The pollen wall is composed of two morphologically and cytochemically distinct domains: the exine and the intine. In the multilayered exine, the ektexine appears granular and the endexine, lamellar. The intine is thick and bilayered with a microfibrillar structure occupying its inner portion. Cytochemical reactions of the exine and the intine are similar to those found in angiosperms. Pollen wall involvement in the male female recognition system is discussed with respecl to the angiosperms.     

Instrumental test to estimate a model of forecast yield: a non-parametric application to the pollen index in South Italy

A statistical test is described to verify the characteristics of the biological information contained in the dynamics of the flowering process. The test focuses on interactions between the pollen index and climatic variables to investigate if the biological indicator can synthesise the information of the pre-flowering phases. The multiple-regression model is built upon two pre-flowering climate macro-indicators extracted by Principal Component Analysis (PCA) and the optimised pollen index is obtained by non-parametric estimation. The empirical analysis is applied to 15 stations located in southern Italy in regions that have a longstanding tradition of olive production. Using the variance explained, we find that an optimised pollen index is fairly well predicted by the pre-flowering climatic data. We conclude that the optimised pollen index makes more parsimonious the modelling for predicting olive production.     

Immuno-gold localization of α-L-arabinofuranosyl residues in pollen tubes of Nicotiana alata Link et otto

Immuno-gold labelling using a monoclonal antibody (PCBC3) with a primary specificity for -L-arabinofuranosyl residues was used to locate these residues in pollen tubes of Nicotiana alata grown in vivo. The antibody bound to the outer fibrillar layer of the pollen-tube wall: the inner, non-fibrillar wall layer was not labelled. Cytoplasmic vesicles (0.2 m diameter) were also labelled. The antibody may bind to an arabinan in the pollen-tube wall.     

Quality of a stress-sensitive Cucurbita pepo L. pollen

The quality of Cucurbita pepo L. pollen was studied using field pollinations and the fluorochromatic-reaction test. The extreme sensitivity of this pollen to dehydration and ageing is demonstrated. Controlled stress applied to mature pollen leads to the development of seedless fruits. Molecular signals seem to be involved in the induction of this parthenocarpy. These results indicate the existence of distinct sequences involved in the completion of the fertilization program of pollen. With pollen altered by stress, the fertilization process may be stopped at different stages of its completion. We bring evidence that Cucurbita pepo plants have developed special adaptations in order to compensate for the poor viability of their pollen.Abbreviation FCR fluorochromatic reaction     

马尾树科及其近缘科花粉形态研究

本文观察了马尾树科(Rhoipteleaceae)、胡桃科(Juglandaceae)以及桦木科(Be-tulaceae)、9属9种植物花粉形态。马尾树科与桦木科桦木属(Betula L.)花粉粒均为扁球形,极面观呈钝三角形,萌发孔类型均为多孔类型,孔之间均有弓形加厚,而且外表面均具细颗粒状雕纹。而胡桃科大多为多边形、散孔类型。根据花粉形态资料,探讨了马尾树科的系统位置。