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This study examines how the latitude of cultivation of Ginkgo biloba affects the timing of all phases of its sexual reproductive cycle, from pollination through germination. Seeds produced by trees growing in warm-temperate climates germinate earlier in the year than seeds produced in cold-temperate climates, and they have a longer period of time available for seedling establishment. The embryos of G. biloba seeds possess a temperature-dependent developmental-delay mechanism that allows seeds to survive winter by preventing premature germination in the fall. This and other cold-climate adaptations appear to have evolved within the genus Ginkgo during the early Cretaceous, when the Northern Hemisphere was undergoing dramatic cooling after a long period of stable, warm conditions. Ginkgo biloba seeds possess an odoriferous sarcotesta that attracts mammalian scavengers in Asia—most notably members of the Carnivora—presumably by mimicking the smell of carrion. Seeds cleaned of their sarcotesta germinated faster and at higher percentages than those with their sarcotesta intact, suggesting that animal dispersal plays an important role in promoting seedling establishment. During the Cretaceous, potential dispersal agents included mammals, birds, and carnivorous dinosaurs.
The widespread phenomenon of red and yellow autumn leaves has recently attracted considerable scientific attention. The fact that this phenomenon is so prominent in the cooler, temperate regions and less common in warmer climates is a good indication of a climate-specific effect. In addition to the putative multifarious physiological benefits, such as protection from photoinhibition and photo-oxidation, several plant/animal interaction functions for such coloration have been proposed. These include (1) that the bright leaf colors may signal frugivores about ripe fruits (fruit flags) to enhance seed dispersal; (2) that they signal aphids that the trees are well defended (a case of Zahavi's handicap principle operating in plants); (3) that the coloration undermines herbivore insect camouflage; (4) that they function according to the “defense indication hypothesis,” which states that red leaves are chemically defended because anthocyanins correlate with various defensive compounds; or (5) that because sexual reproduction advances the onset of leaf senescence, the pigments might indicate to sucking herbivores that the leaves have low amounts of resources. Although the authors of hypotheses 3, 4, and 5 did not say that bright autumn leaves are aposematic, since such leaves are chemically defended, unpalatable, or both, we suggest that they are indeed aposematic. We propose that in addition to the above-mentioned hypotheses, autumn colors signal to herbivorous insects about another defensive plant property: the reliable, honest, and critical information that the leaves are about to be shed and may thus cause their mortality. We emphasize that all types of defensive and physiological functions of autumn leaves may operate simultaneously.
Plants have several defense mechanisms against unfavorable environmental conditions. One of these mechanisms is leaf rolling. In this review, leaf rolling as a response to water deficit stress and biochemical changes during leaf rolling in higher plants are reported. For instance, the activities of some enzymes and osmotic substances change during leaf rolling. Leaf rolling increases drought resistance in numerous species in the Gramineae as well as in Ctenanthe setosa, a perennial herbaceous plant that is a suitable model for use in studies of leaf rolling.
The term “cedar glades” has been applied to several different types of plant communities that occur on rocky calcareous soils in eastern North America. A previous paper by the first two authors reviewed in considerable detail the use of this term with regard to type of vegetation on rocky limestone soils in the Nashville (Central) Basin of Tennessee. The present paper reviews use of “cedar glades” as a descriptive term for vegetation in other physiographic regions of eastern North America. In the Nashville Basin, and in some other physiographic regions, the term has been applied to true open cedar glades (“glades”) plus the surrounding redcedar/redcedar-hardwood forest, or (more recently) to the natural rocky treeless openings only. However, outside the Nashville Basin, it has also been used to describe several other disparate vegetation types, such as xeric limestone prairies (limestone glades, prairie barrens), redcedar-little bluestem savanna, dense redcedar forest, redcedar-hardwood forest, and even an open stand of redcedar-pine-sweetgum with warm-season perennial prairie grasses in the understory. In the Great Lakes region of North America and in the Baltic region of Europe, some alvars are similar to cedar glades sensu stricto of southeastern United States. Since many of the rocky calcareous openings in eastern North America can be classified as either cedar glades or xeric limestone prairies, a suite of abiotic, biotic, and anthropogenic-related factors is presented for use in distinguishing between these two vegetation types.
Aluminum being the third most abundant metal in the earth's crust poses a serious threat to crop productivity in acid soils, which comprise almost half of the arable land. This review travels across time and updates research done on aluminum stress in plants. In its phytotoxic forms, aluminum affects root growth by acting in the root apical zone, resulting in growth inhibition in a very short time at micromolar concentrations. The mechanisms of aluminum toxicity in plants may proceed by growth inhibition, callose accumulation, cytoskeletal distortion, disturbance of plasma membrane surface charge, and H-ATPase activity, lipid peroxidation of membranes, production of reactive oxygen species in cytosol and mitochondria, respiratory dysfunction, opening of mitochondrial permeability transition pores, collapsing of inner mitochondrial membrane potential, activation of mitochondrial protease, and induction of nuclear apoptosis, resulting ultimately in programmed cell death. In contrast, the mechanism of tolerance involves the exudation of organic acid anions, complexation of aluminum with organic acids, and subsequent detoxification. Many oxidative stress genes and other metabolically important genes have also been found to be induced under aluminum stress, and overexpression analyses have also shown some plants to develop some degree of tolerance. In the future, researchers in the area of aluminum research should investigate more basic mechanisms of aluminum toxicity and discover and study more aluminum-responsive genes that confer resistance against this toxic metal, to ensure food security for ever-increasing human populations in the future.