Respiration of the Roots of Flood-Tolerant and Flood-Intolerant Senecio Species: Affinity for Oxygen and Resistance to Cyanide

The affinity of respiration for oxygen in the roots of six Senecio species studied was low compared with the affinity of cytochrome oxidase for oxygen. Half saturation values of approximately 22 μM oxygen were measured. Root respiration was to a large extent insensitive to cyanide in flood-tolerant as well as in flood-sensitive species. The evidence presented suggests that high activity of salicylhydroxamic acid (SHAM)-sensitive oxidase in Senecio roots was the basis for the low oxygen affinity and for the high cyanide-insensitivity of root respiration in the Senecio species. Methods are described to determine the in vivo activity of the SHAM-sensitive oxidase. It was estimated that it contributed 70% to the total root respiration. The presence of SHAM-sensitive oxidase activity could explain a higher efficiency of root growth respiration under a low oxygen tension if this alternate oxidase was inhibited at a low oxygen concentration in the root medium. However, the SHAM-sensitive oxidase was not specifically involved in either growth respiration or maintenance respiration. Its significance in regulation of the redox state of the cells is discussed.     

Light and Electron Microscopic Observations on the Heterotrich Ciliate Climacostomum virens

SYNOPSIS. Alveolar membranes and an epiplasm exist under the cell membrane of the noncontractile heterotrich ciliate Climacostomum virens. Postciliary microtubular ribbons join at the right of each somatic kinety to form a Km fiber. Two transverse microtubular fibers occur per kinetosomal pair. A myonemal network interconnects the kinetosomal bases intrakinetally and interkinetally. Ultrastructural comparisons are made between the contractile and noncontractile heterotrichs.
The buccal cortex consists of an adoral zone of membranelles, a peristomal field, a buccal tube, the apical membranelles, and a haplokinety. The kineties of the peristomal field and buccal tube are rows of paired kinetosomes, with a postciliary ribbon of microtubules arising from the posterior kinetosome of each pair, and a transverse ribbon and an oblique ribbon from the anterior kinetosome. No Km fibers exist in this region. The haplokinety is a collar of paired kinetosomes surrounding the cytostome; a postciliary microtubular ribbon descends from each kinetosomal pair into the cytostomal region. Ultrastructural details of the buccal cortex of C. virens and other heterotrichs are compared. The nemadesmata which lie under the membranelles are implicated in the body bending of C. virens.
Algae endosymbiotic in the cytoplasm of C. virens are described.     

Relationships between phenology,radiation and precipitation in the Amazon region

In tropical areas, Dynamic Global Vegetation Models (DGVMs) still have deficiencies in simulating the timing of vegetation phenology. To start addressing this problem, standard Fourier‐based methods are applied to aerosol screened monthly remotely sensed phenology time series (Enhanced Vegetation Index, EVI) and two major driving factors of phenology: solar radiation and precipitation (for March 2000 through December 2006 over northern South America). At 1 × 1 km scale using, power (or variance) spectra on good quality aerosol screened time series, annual cycles in EVI are detected across 58.24% of the study area, the strongest (largest amplitude) occurring in the savanna. Terra Firme forest have weak but significant annual cycles in comparison with savannas because of the heterogeneity of vegetation and nonsynchronous phenological events within 1 × 1 km scale pixels. Significant annual cycles for radiation and precipitation account for 86% and 90% of the region, respectively, with different spatial patterns to phenology. Cross‐spectral analysis was used to compare separately radiation with phenology/EVI, precipitation with phenology/EVI and radiation with precipitation. Overall the majority of the Terra Firme forest appears to have radiation as the driver of phenology (either radiation is in phase or leading phenology/EVI at the annual scale). These results are in agreement with previous research, although in Acre, central and eastern Peru and northern Bolivia there is a coexistence of ‘in phase’ precipitation over Terra Firme forest. In contrast in most areas of savanna precipitation appears to be a driver and savanna areas experiencing an inverse (antiphase) relationship between radiation and phenology is consistent with inhibited grassland growth due to soil moisture limitation. The resulting maps provide a better spatial understanding of phenology–driver relationships offering a bench mark to parameterize ecological models.