Long distance transport and movement of RNA through the phloem

Cell-to-cell communication is essential for plant development and adaptation to environmental changes. As a strategy for efficient intercellular communication, plants have evolved a plant-specific symplasmic network connected via plasmodesmata that allows a locally restricted information exchange from cell to cell. A rapid information transfer over long distances is enabled via the phloem transport tubes that pervade the complete plant and thus connect even the most distant organs. While communication by small molecules like metabolites and phytohormones is comparably well studied, the intercellular trafficking of proteins and RNAs has only recently emerged as a novel mechanism of cell-to-cell and long-distance signalling in plants. In particular the non-cell-autonomous and systemic transport pathway for specific RNAs seems to play a key role in the co-ordination of important physiological processes, including virus defence, gene silencing, regulation of development, and nutrient allocation. This review is a summary of the current knowledge on RNAs contained in the phloem long-distance transport system, their transport mechanism, and their potential functions.     

Long distance transport of potassium in cereals during grain filling in intact plants

Translocation of labeled potassium (K⁺) from the root to the ear and its distribution within the culm during 4, 8 and 12 h of uptake was studied in intact wheat plants ( Triticum aestivum L. cv. Kolibri) 3 and 5 weeks after anthesis at 0.5 and 5.0 m M K⁺ concentration in the uptake solution. Uptake of labeled K⁺ into the shoot was proportional to the K⁺ concentration applied. After 4 h of uptake about 2% and after 12 h about 7% of labeled K⁺ applied to the roots were taken up into the shoot at both K⁺ concentrations. After 12 h of uptake only 6% of the total label in the culm had reached the ear, while about 40% of the label was found in the upper three internodes. In spite of an increasing concentration of labeled K⁺ during 12 h in the uppermost internode (peduncle), translocation of K⁺ into the rachis was low. The low and uniform K⁺ content found generally in grain dry weight seems therefore to be due to a controlled K⁺ supply to the ear.     

Long distance transport of potassium in cereals during grain filling in detached ears

Ears of wheat plants ( Triticum aestivum L. cv. Kolibri), which were given different and uniform K⁺-nutrition in two experiments, were cut at 2, 4 and 6 weeks after anthesis at 15 cm below the ear. These detached ears were fed 30 m M (experiment 1) or 15, 30, 60 or 90 m M ⁸⁶Rb-K₂ malate (experiment 2) and 146 m M [¹⁴C]-sucrose. After a pulse period of 6 and 4 h, respectively, the ears were transferred to identical non-labeled solutions for additional 0, 4, 8 or 20 h.
About 50% of the K⁺ and sucrose supplied was absorbed by detached ears. This rate declined with plant age and decreasing transpiration. Within the 6 and 4 h uptake period less than 7% of the absorbed K⁺, but 20% of the sucrose taken up were incorporated into the grain. During the chase period labeled K⁺ in the grain increased to 15% and ¹⁴C even to 50% of total tracer uptake. Incorporation of labeled K⁺ into the grain was not affected by the previous K⁺ nutrition of the plant and was proportional to the K⁺ concentration in the uptake solution. Transition of K⁺ from xylem into phloem during its acropetal transport is assumed. No evidence was found that the grain itself could control its uptake of K⁺.     

Long distance dispersal of reef corals by rafting

Settlement of larvae on floating objects and subsequent rafting of colonies provides a mechanism by which corals can bridge immense geographic distances. Reproductively mature colonies, several years in age, have been found attached to material that drifted into Hawaiian waters. During their lifetime, these corals may have traversed a total distance of from 20,000 to 40,000 km and could have completed several circuits of the tropical and subtropical Pacific basin. The ability of coral larvae to drift across vast stretches of open ocean probably does not determine the ultimate range limitation for zoogeographic dispersal of corals.Hawaii Institute of Marine Biology Contribution Number 685     

Long distance pollen transport cause problems for determining the timing of birch pollen season in Fennoscandia by using phenological observations

The male flowering and leaf bud burst of birch take place almost simultaneously, suggesting that the observations of leaf bud burst could be used to determine the timing of birch pollen release. However, long‐distance transport of birch pollen before the onset of local flowering may complicate the utilization of phenological observations in pollen forecasting.

We compared the timing of leaf bud burst of silver birch with the timing of the stages of birch pollen season during an eight year period (1997–2004) at five sites in Finland. The stages of the birch pollen season were defined using four different thresholds: 1) the first date of the earliest three‐day period with airborne birch pollen counts exceeding 10 grains m^?3 air; and the dates when the accumulated pollen sum reaches 2) 5%; 3) 50% and 4) 95% of the annual total. Atmospheric modelling was used to determine the source areas for the observed long‐distance transported pollen, and the exploitability of phenological observations in pollen forecasting was evaluated.

Pair‐wise comparisons of means indicate that the timing of leaf bud burst fell closest to the date when the accumulated pollen sum reached 5% of the annual total, and did not differ significantly from it at any site (p<0.05; Student‐Newman‐Keuls test). It was found that the timing of leaf bud burst of silver birch overlaps with the first half of the main birch pollen season. However, phenological observations alone do not suffice to determine the timing of the main birch pollen season because of long‐distance transport of birch pollen.     

Long distance migration of insects to a subantarctic island

Transoceanic migration of four species of macrolepidoptera to subantarctic Macquarie Island has been detected in 7 out of 33 years during the period 1962–96 and is restricted to spring and autumn. Analyses of synoptic charts during the migration period show that autumn immigrants originated from New Zealand and comprised a single species of noctuid moth,Agrotis ipsilon (Walker). Spring immigrants originated from Australia and comprised two noctuids, Dasypodia selenophora Guenée and Persectania ewingii Westwood and a butterfly, Vanessa kershawi (McCoy). Autumn migrations were associated with depressions in the southern Tasman Sea. Spring migrations were associated with the eastward passage of prefrontal airflows ahead of cold fronts which extended from southern Australia to the west of Macquarie Island. In an analysis of one of these events, winds exceeded 30 ms^?1 at 300 m altitude and could have transported migrants from Tasmania to Macquarie Island overnight in less than 10 h. Flight activity was assisted by the presence of a nocturnal temperature inversion that maintained upper air temperatures above 5 °C. The effect of potential global warming on the migration and colonization of Macquarie Island by insects is discussed.     

Long distance breeding dispersal of a southern elephant seal

Southern elephant seals range extensively during regular foraging excursions. Despite this they are highly philopatric and long range dispersal is rare. At Gough Island, southern Atlantic Ocean, we observed a breeding adult male elephant seal during September 2009, which had been tagged on its natal beach at Marion Island, southern Indian Ocean, in November 1998. The individual was resighted only once on Marion Island, 6 months after tagging. This 3,860 km movement represents dispersal (and likely gene flow) between distinct populations from different elephant seal geographical provinces. Given the polygynous breeding system of this species, the presence of this single male may have a disproportionate genetic effect on the small number of southern elephant seals breeding at Gough Island.     

Long distance movement of Bank voles and Wood mice.

Between November 1963 and October 1965 the long distance movements of Bank voles and Wood mice within an almost isolated 26 ha deciduous woodlot were studied by live trapping at approximately monthly intervals. Dispersal was most marked in juvenile Bank voles where most of the males and about half the females under 13 g, when released and later recaptured, had dispersed.
Dispersal of juvenile Wood mice did not occur after September, before which time the evidence was sparse and inconclusive. It was estimated that about 6% of adult maleand 2% of adult female Bank voles dispersed. Little dispersal of adult Wood mice took place.
The term 'transient' is discussed. True transients in the "once-caught' category are thought to be few. There was no evidence that the trappable population of either species included a significant number of non-resident individuals.     

Long distance nitrogen air pollution effects on lichens in Europe

The epiphytic lichen flora of 25 European ICP-IM monitoring sites, all situated in areas remote from air pollution sources, was statistically related to measured levels of SO₂in air, NH₄⁺, NO₃⁻ and SO₄²⁻ in precipitation, annual bulk precipitation, and annual average temperature. Significant regression models were calculated for eleven acidophytic species. Several species show a strong negative correlation with nitrogen compounds. At concentrations as low as 0·3 mg N l⁻¹in precipitation, a decrease of the probability of occurrence is observed for Bryoria capillaris, B. fuscescens, Cetraria pinastri, Imshaugia aleurites and Usnea hirta. The observed pattern of correlations strongly suggests a key role of NH₄⁺ in determining the species occurrence, but an additional role of NO₃⁻ cannot be ruled out. Some species show a distinct response to current levels of SO₂as well. It may be concluded that long distance nitrogen air pollution has strong influence on the occurrence of acidophytic lichen species.