A comparison of three methods for determining the stomatal density of pine needles. (1/95)

Alternative methods were compared for determining the stomatal density of needles from two pine species. Densities estimated from air-dried, whole needles using a binocular dissecting scope were compared to densities estimated from vacuum-dried, intact needles using a scanning electron microscope and expanded peels (or macerated cuticles) using a compound light microscope. Differences among methods were expected from two sources: (1) expansion and shrinkage as a function of water content, and (2) differences in geometry of the measured surface. Estimates from the dissecting scope were similar to those from scanning electron microscopy (t=0.509, n=21, P:=0.62), presumably because both used dried, but otherwise intact whole needles. Light microscopy estimates, however, were lower than dissecting scope estimates (t=-2.307, n=13, P:=0.04). After adjusting for expansion due to hydration and changes in needle geometry, differences disappeared (t=-1.205, n=13, P:=0.25). These results are an important consideration for researchers reconstructing palaeo-atmospheric conditions and assessing plant response to environmental change.  (+info)

The Green Revolution: botanical contributions to forensics and drug enforcement. (2/95)

Forensic botany encompasses many sub-disciplines, including plant anatomy, plant ecology, plant systematics, plant molecular biology, palynology, and limnology. Although the field of forensic botany has been recognized since the mid-1900's, the use of trace plant material as physical evidence in criminal casework is still novel. A review of published forensic casework that used plant evidence is presented here. Cases include the analysis of wood evidence in the Charles Lindbergh baby kidnapping, the use of pollen in establishing the location of a sexual assault, and pollen analysis to determine the time of year for burial in a mass grave. Additional cases discuss the use of plant growth rates to determine the time of a body deposit in a field, the use of diatoms to link individuals to a crime scene, and plant DNA typing to match seedpods to a tree under which a body was discovered. New DNA methods in development for plant species identification and individualization for forensic applications are also discussed. These DNA methods may be useful for linking an individual to a crime scene or physical evidence to a geographic location, or tracking marijuana distribution patterns.  (+info)

UV-excited chlorophyll fluorescence as a tool for the assessment of UV-protection by the epidermis of plants. (3/95)

Recently, a new method for estimating epidermal transmission of UV radiation in higher plants has been proposed. The empirical evidence for the usefulness of this method is reviewed here. Direct comparison with spectroscopically determined epidermal transmission yielded equivalent results. A linear correlation to the concentration of epidermal screening compounds has been shown. Relating UV-A and UV-B absorbance allowed some preliminary conclusions about the chemical nature of the screening compounds. A new portable apparatus is presented for the first time, which allows the non-destructive assessment of UV-A screening even under field conditions. Repeated measurements on identical leaves over a time-course of 6 d demonstrated a strong age-dependence in the capacity for the synthesis of UV-A screening compounds upon exposure to UV-B radiation. It is concluded that the new method may provide a valuable tool for the investigation of the acclimation of plants to UV-B radiation and, when accompanied by HPLC analysis, of the reaction of phenolic metabolism to environmental stimuli.  (+info)

Towering tribute to botany. (4/95)

One of the world's greatest plant collections has won a top heritage award at a time when it is highlighting with a tree-top walkway the need to study the forest canopy which is one of the most crucial but least understood habitats.  (+info)

Regulation of potassium transport in leaves: from molecular to tissue level. (5/95)

Over millions of years, plants have evolved a sophisticated network of K+ transport systems. This Botanical Briefing provides an overview of K+ transporters in various leaf tissues (epidermis, mesophyll, guard cells and vascular system) at both the cellular and organelle levels. Despite the tremendous progress in our knowledge of genes encoding K+ transport systems in plants, understanding has not developed of coordinated functioning and operation of these genes or proteins in the context of whole plant physiology and plant-environment interaction. This Botanical Briefing is aimed at filling that gap by analysing electrophysiological and molecular evidence for mechanisms coordinating K+ transport between various leaf cells and tissues in changing environments.  (+info)

Gas exchange measurements, what can they tell us about the underlying limitations to photosynthesis? Procedures and sources of error. (6/95)

The principles, equipment and procedures for measuring leaf and canopy gas exchange have been described previously as has chlorophyll fluorescence. Simultaneous measurement of the responses of leaf gas exchange and modulated chlorophyll fluorescence to light and CO2 concentration now provide a means to determine a wide range of key biochemical and biophysical limitations on photo synthesis in vivo. Here the mathematical frameworks and practical procedures for determining these parameters in vivo are consolidated. Leaf CO2 uptake (A) versus intercellular CO2 concentration (Ci) curves may now be routinely obtained from commercial gas exchange systems. The potential pitfalls, and means to avoid these, are examined. Calculation of in vivo maximum rates of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco) carboxylation (Vc,max), electron transport driving regeneration of RuBP (Jmax), and triose-phosphate utilization (VTPU) are explained; these three parameters are now widely assumed to represent the major limitations to light-saturated photosynthesis. Precision in determining these in intact leaves is improved by the simultaneous measurement of electron transport via modulated chlorophyll fluorescence. The A/Ci response also provides a simple practical method for quantifying the limitation that stomata impose on CO2 assimilation. Determining the rate of photorespiratory release of oxygen (Rl) has previously only been possible by isotopic methods, now, by combining gas exchange and fluorescence measurements, Rl may be determined simply and routinely in the field. The physical diffusion of CO2 from the intercellular air space to the site of Rubisco in C3 leaves has long been suspected of being a limitation on photosynthesis, but it has commonly been ignored because of the lack of a practical method for its determination. Again combining gas exchange and fluorescence provides a means to determine mesophyll conductance. This method is described and provides insights into the magnitude and basis of this limitation.  (+info)

Screening of inbred lines to develop a thermotolerant sunflower hybrid using the temperature induction response (TIR) technique: a novel approach by exploiting residual variability. (7/95)

Plants, when exposed to sub-lethal stress (induction stress), develop the ability to withstand severe temperatures and this phenomenon is often referred to as acquired thermotolerance. Earlier it was reported that induction stress alters gene expression and brings greater adaptation to heat stress and that the genetic variability in thermotolerance is only seen upon induction stress. Based on this concept, the temperature induction response (TIR) technique has been developed to identify thermotolerant lines. By following the TIR technique, sunflower hybrid KBSH-1 parents were screened for high temperature tolerance. Seedlings of parental lines including CMS 234 A, CMS 234 B and 6 D-1 showed considerable genetic variability for thermotolerance and it was attributed to the expression of existing residual variability for stress responses. Thus, the existing variability forms the basis for identifying thermotolerant lines. The identified parental inbred lines were selected and established in the field and crossed to get F1 hybrid seeds. The KBSH-1 hybrid developed from selected variants of parental lines was compared with the original KBSH-1 for thermotolerance. The selected KBSH-1 was more tolerant compared with the original hybrid both at the seedling as well as at the plant level. The physiological and molecular basis of thermotolerance was studied in the KBSH-1 original and the hybrid developed from selected variants of parental lines. The selected hybrid exhibited high tolerance to Menadione (naphthoquinone)-induced oxidative stress. Even the methyl viologen-induced oxidative stress damage was relatively less in the selected hybrid population. The selected hybrid also showed enhanced expression of the heat shock proteins HSP 90 and HSP 104 and also accumulated higher levels of the heat shock transcription factor HSFA.  (+info)

Impetus for sowing and the beginning of agriculture: ground collecting of wild cereals. (8/95)

The Agricultural Revolution in Western Asia, which took place some 11,000 years ago, was a turning point in human history [Childe, V. G. (1952) New Light on the Most Ancient East (Routledge & Kegan Paul, London)]. In investigating the cultural processes that could have led from gathering to intentional cultivation, various authors have discussed and tested wild cereal harvesting techniques. Some argue that Near Eastern foragers gathered grains by means of sickle harvesting, uprooting, plucking (hand stripping), or beating into baskets [Hillman, G. C. & Davies, M. S. (1999) in Prehistory of Agriculture: New Experimental and Ethnographic Approaches, ed. Anderson, P. (The Institute of Archaeology, University of California, Los Angeles), pp. 70-102]. During systematic experiments, we found that archaeobotanical data from regional Neolithic sites support ground collection of grains by early hunter-gatherers. Ground collecting suits the natural shattering of wild species that ripen and drop grains at the beginning of summer. We show that continual collection off the ground from May to October would have provided surplus grains for deliberate sowing in more desirable fields, and facilitate the transition to intentional cultivation. Because ground gathering enabled collectors to observe that fallen seeds are responsible for the growth of new plants in late fall, they became aware of the profitability of sowing their surplus seeds for next year's food. Ground collecting of wild barley and wild wheat may comprise the missing link between seed collecting by hunter-gatherers and cereal harvesting by early farmers.  (+info)