In five consecutive years lettuce, spinach, spring wheat, endive and maize were grown in pots and the effects of 'native' and soil-applied Zn and Cd on plant Zn and Cd concentrations were studied. The normal interactive pattern was antagonistic, Zn reducing plant Cd uptake, and conversely, but less so. Only in loam soil Zn and Cd were synergistic to some extent, plant Zn uptake increasing with applied Cd.When relating total soil Cd/Zn to plant Cd/Zn separate sets of data could be distinguished for loam and sandy soil, each fitting a straight line. The use of 0.1 M CaCI 2 instead of 'total' extractable soil Cd/Zn makes the two sets of data to coalesce around a single straight line. All crops were found to show a positive linear relationship between 0.1 M CaCl~-extractable soil Cd/Zn and plant Cd/Zn.

In seed plants, the body organization is established during embryogenesis and is uniform across gymnosperms and angiosperms, despite differences during early embryogeny. Evidence from angiosperms implicates the plant hormone auxin and its polar transport, mainly established by the PIN family of auxin efflux transporters, in the patterning of embryos. Here, PaPIN1 from Norway spruce (Picea abies [L.] Karst.), a gene widely expressed in conifer tissues and organs, was characterized and its expression and localization patterns were determined with reverse transcription polymerase chain reaction and in situ hybridization during somatic embryo development and in seedlings. PaPIN1 shares the predicted structure of other PIN proteins, but its central hydrophilic loop is longer than most PINs. In phylogenetic analyses, PaPIN1 clusters with Arabidopsis thaliana (L.) Heynh. PIN3, PIN4 and PIN7, but its expression pattern also suggests similarity to PIN1. The PaPIN1 expression signal was high in the protoderm of pre-cotyledonary embryos, but not if embryos were pre-treated with the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA). This, together with a high auxin immunolocalization signal in this cell layer, suggests a role of PaPIN1 during cotyledon formation. At later stages, high PaPIN1 expression was observed in differentiating procambium, running from the tip of incipient cotyledons down through the embryo axis and to the root apical meristem (RAM), although the mode of RAM specification in conifer embryos differs from that of most angiosperms. Also, the PaPIN1 in situ signal was high in seedling root tips including root cap columella cells. The results thus suggest that PaPIN1 provides an ancient function associated with auxin transport and embryo pattern formation prior to the separation of angiosperms and gymnosperms, in spite of some morphological differences.

No abstract

A simple method of using scanning electron microscopy to observe pollen grains in situ on feral moths (Noctuidae) is described. This method does not require freeze drying, critical point drying, or any chemical fixation procedures to prepare the specimens for scanning. Pollen grains were found mainly on the proboscises of the moths and can be identified directly from the scanning electron micrographs, thus expediting the study of moth–plant relations.

Gluconacetobacter diazotrophicus is an endophytic diazotroph of sugarcane which exhibits nitrogenase activity when growing in colonies on solid media. Nitrogenase activity of G. diazotrophicus colonies can adapt to changes in atmospheric partial pressure of oxygen (pO 2 ). This paper investigates whether colony structure and the position of G. diazotrophicus cells in the colonies are components of the bacterium's ability to maintain nitrogenase activity at a variety of atmospheric pO 2 values. Colonies of G. diazotrophicus were grown on solid medium at atmospheric pO 2 of 2 and 20 kPa. Imaging of live, intact colonies by confocal laser scanning microscopy and of fixed, sectioned colonies by light microscopy revealed that at 2 kPa O 2 the uppermost bacteria in the colony were very near the upper surface of the colony, while the uppermost bacteria of colonies cultured at 20 kPa O 2 were positioned deeper in the mucilaginous matrix of the colony. Disruption of colony structure by physical manipulation or due to ' slumping ' associated with colony development resulted in significant declines in nitrogenase activity. These results support the hypothesis that G. diazotrophicus utilizes the path-length of colony mucilage between the atmosphere and the bacteria to achieve a flux of O 2 that maintains aerobic respiration while not inhibiting nitrogenase activity.