Arundo donax L. (Poaceae) — a C3 Species with Unusually High Photosynthetic Capacity

Gas exchange characteristics, chlorophyll a fluorescence and leaf water potential were investigated in the giant reed, Arundo donax, under natural conditions in an estuarine mangrove swamp in Durban, South Africa. Maximum photosynthetic CO₂ uptake ranged between 19.8 and 36.7 μmol m^?2 s^?1, depending on irradiance, and appeared to be regulated by leaf conductance. There was no saturation of CO₂ uptake or electron transport through PSII (ETR) with increasing irradiance up to 2500 μmol photons m^?2 s^?1. A linear relationship between CO₂ uptake, corrected for respiration (A), and ETR has only been reported for C₄ species and C₃ species when photorespiration is eliminated. From this relationship, it was calculated that 8.5 electrons were transported through PSII for the fixation of one mole of CO₂. Predawn leaf water potential was about ?0.5 MPa and decreased to ?1.5 MPa on a cloudy day and to ?2.1 MPa on a clear day. Diurnal change in leaf water potential had little influence on leaf conductance and hence CO₂ uptake. The molar water use efficiency (WUE) ranged between 4.1 and 9.3 μmol mmol^?1. Percentage photorespiration was between 36 and 39%.     

Induction of Adventitious Buds on Buds of Norway Spruce (Picea abies) Grown in vitro

Resting vegetative buds of Norway spruce, Picea abies (L.) Karst., were induced to form adventitious bud primordia when cultured on medium -containing cytokinin. After transfer of the induced buds to medium lacking cytokinin, adventitious buds developed. The adventitious buds arose from meristems formed de novo in the needle primordia. No differences were found in the ability to form adventitious buds among buds collected from trees ranging from 5–50 years old.     

Induction of Adventitious Buds on Embryos of Norway Spruce Grown in vitro

Adventitious buds were induced when isolated embryos of Norway spruce (Picea abies L.) were cultured on a defined medium containing 2iP. Anatomically different bud primordia were formed at high and low cytoldnin concentrations. The highest percentage of embryos forming bud primordia was obtained after 4–5 weeks on 2iP medium. Buds developed after transfer of the induced embryos to medium without growth regulators. Many of the buds developed into elongated shoots. No root primordia were observed in any of the induced embryos.     

X-RAY MICROANALYSIS IN CELL BIOLOGY AND CELL PATHOLOGY

Electron probe X-ray microanalysis has been used for the last 25 years by biologists to obtain information about the distribution of elements at the cell and tissue level. During this period, progress has mainly been made through the development of more adequate techniques for specimen preparation (mainly low temperature techniques) and quantitative analysis, so that accurate analysis of the physiologically important cellular ions can be carried out. Use ofin vitrosystems and cell cultures may further increase the number of problems to which X-ray microanalysis can be applied. Among the numerous applications of X-ray microanalysis in cell biology and cell pathology, applications in the areas of epithelial ion transport, the role of calcium in secretory and contractile cells, and the role of ions in cell proliferation and cancer are discussed in more detail.