A method for measuring hydraulic conductivity and embolism in xylem

Abstract Hydraulic conductivity of the xylem is computed as the quotient of mass flow rate and pressure gradient. Measurements on excised plant stems can be difficult to interpret because of time-dependent reductions in flow rate, and because of variable degrees of embolism. Using Acer saccharum Marsh. stems, we found that certain perfusing solutions including dilute fixatives (e.g. 0.05% formaldehyde) and acids with pH below 3 (e.g. 10 mol m^?3 oxalic) prevent long-term decline in conductivity. Xylem embolism can be quantified by expressing the initial conductivity as a percentage of the maximum obtained after flow-impeding air emboli have been removed by repeated high-pressure (175 kPa) flushes. Correlation between microbial contamination and declining conductivity suggests that long-term (> 4h) declines are caused by microbial growth within the vessels. Unpredictable trends in short-term (< 4h) measurements may be caused by movements of air emboli in vessels and/or participate matter.     

Wise flies: a pre‐dispersal seed predator prefers hermaphrodites over females in the gynodioecious Polemonium foliosissimum

1. Oviposition choices can profoundly affect offspring performance. Oviposition decisions of the dipteran pre‐dispersal seed predator, Hylemya sp. (Diptera: Anthomyiidae), when choosing among sex morphs of their host‐plant—Polemonium foliosissimum Hook—were evaluated. Polemonium foliosissimum is gynodioecious, with female and hermaphrodite sex morphs that differ in flower size. 2. It was asked: Do female flies preferentially oviposit on hermaphrodite plants and, if so, are oviposition choices correlated with flower size? Is larval survivorship higher on hermaphrodite plants and, if so, is larval success correlated with flower size? Can the differences in oviposition and/or larval success be explained by slight differences in flowering phenology between the sexes? 3. Hermaphrodite flowers received 45% more Hylemya eggs than females. Although hermaphrodites had larger petals and sepals than females, egg loads were not correlated with petal or sepal size. Larval survival was 30% greater on hermaphrodites than females and higher on plants with larger sepals. However, the difference in sepal area between genders did not fully explain larval survival differences. Egg numbers declined over weeks, but differences in egg loads between the sex morphs were not attributable to a slight phenological delay of females. Larval survival declined over the season; however, larval survival differences between sex morphs were consistent. 4. Hylemya preferentially oviposited on hermaphrodites where their larvae had a significantly greater survival rate compared with females. The present results add to the knowledge that intra‐specific choices have consequences for phytophagous insects and that the relationship between antagonists and their gynodioecious host plants is complex.     

Oral deformities in tadpoles (Ranacatesbeiana) associated with coal ash deposition: effects on grazing ability and growth

1. Tadpoles of the bullfrog ( Rana catesbeiana ) collected in a coal ash deposition basin (contaminated with As, Cd, Cr, Cu, Se and other elements) and a downstream drainage swamp had a reduced number of labial teeth and deformations of labial papillae when compared with tadpoles from reference areas. Tadpoles from the coal ash-affected areas had 90% fewer teeth in anterior tooth row number 2 and 40% fewer teeth in posterior row number 1 than reference animals. In the deposition basins, drainage swamp and reference ponds, respectively, 96.2, 85.1 and 2.9% of tadpoles had oral deformities.
2. Tadpoles with deformities were less able to graze periphyton than were normal tadpoles, when tested in the laboratory. When presented with periphyton as a sole food source, tadpoles with deformed teeth had lower (negative) growth rates than those with normal teeth, which had slightly positive growth rates. When particulate food was also available, tadpoles grew well regardless of deformities.
3. It appears that the morphological deformities associated with this coal ash-polluted environment can have ecological ramifications for the affected organisms by limiting the type of food that can be consumed and the ability to grow when multiple food types are unavailable.     

A metabolomic study in oats (Avena sativa) highlights a drought tolerance mechanism based upon salicylate signalling pathways and the modulation of carbon,antioxidant and photo‐oxidative metabolism

Although a wealth of information is available on the induction of one or several drought‐related responses in different species, little is known of how their timing, modulation and crucially integration influence drought tolerance. Based upon metabolomic changes in oat (Avena sativa L.), we have defined key processes involved in drought tolerance. During a time course of increasing water deficit, metabolites from leaf samples were profiled using direct infusion–electrospray mass spectroscopy (DI‐ESI‐MS) and high‐performance liquid chromatography (HPLC) ESI‐MS/MS and analysed using principal component analysis (PCA) and discriminant function analysis (DFA). The involvement of metabolite pathways was confirmed through targeted assays of key metabolites and physiological experiments. We demonstrate an early accumulation of salicylic acid (SA) influencing stomatal opening, photorespiration and antioxidant defences before any change in the relative water content. These changes are likely to maintain plant water status, with any photoinhibitory effect being counteracted by an efficient antioxidant capacity, thereby representing an integrated mechanism of drought tolerance in oats. We also discuss these changes in relation to those engaged at later points, consequence of the different water status in susceptible and resistant genotypes.     

Effect of Shading on the Regrowth of Lolium perenne Swards in the Field

Simulated swards of Lolium perenne cv. S.23 growing in the fieldwere shaded at various stages of regrowth during August andSeptember, when insolation was most likely to be limiting. Reductionof ambient illumination to 50 per cent for periods up to 24days had little effect on the current production of herbage(mainly leaf blade), which progressed at the expense of rootand stubble growth. After defoliation, however, previously shadedswards transferred to full light regrew relatively slowly. Leafarea and leaf extension were increased by shading, but leafappearance rates were only slightly affected. Shading decreasedtiller densi ties, and hence stubble yields, but did not affectmean tiller weights. The dangers of relating herbage yield tocurrent rates of insolation and photosynthesis, and the relevanceof these findings to other grass varieties are discussed.     

Identification and characterization of simple sequence repeat (SSR) markers derived in silico from Brassica oleracea genome shotgun sequences

The availability of sequence data derived from shotgun sequencing programs enables mining for simple sequence repeats (SSRs), providing useful genetic markers for crop improvement. This study presents the development and characterization of 40 SSR markers from Brassica oleracea shotgun sequence and their cross‐amplification across Brassica species. The markers show reliable amplification, genome specificity and considerable polymorphism, demonstrating the utility of SSRs for genetic analysis of commercial Brassica germplasm.     

Can we bring Madagascar's critically endangered palms back from the brink? Genetics,ecology and conservation of the critically endangered palm Beccariophoenix madagascariensis

Madagascar has a highly distinctive flora and is one of the world biodiversity hot spots. There are more than 170 species of palms, the majority of which are vulnerable, endangered or critically endangered endemics. Palms are utilized for many human uses, many of which lead to plant death or seed harvesting. Combined with reduced populations resulting from extensive forest clearing, those species which are harvested from the wild are under additional threat of extinction. Species recovery programmes have the potential to save some of the most iconic species before it is too late. This study documented the current known populations of the critically endangered palm Beccariophoenix madagascariensis, a species utilized for both local and international purposes. The study specifically investigated the genetic diversity and inbreeding within populations and the potential differentiation between populations and with the newly described species B. alfredii . We found that despite critically small population sizes there was considerable genetic diversity within populations. We also found that ecologically and or geographically distinct populations were genetically distinct. Populations within 3 km of each other exhibited considerable gene flow, probably owing to seed dispersal. The populations were inbred but reproductive viability had been maintained. Conservation and recovery options are discussed. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 154 , 589–608.