Illuminating plant development

Throughout 1994 remarkable progress was made with molecular and genetic studies on signal transduction pathways of photomorphogenesis, the lightdependent development of plants. Analysis of Arabidopsis DET and COP genes suggests that they are involved in suppression of photomorphogenic development in the dark and that this is then reversed by light. Studies with COP1 indicate that this is achieved by redistribution of COP1 from the nucleus, in the dark, to the cytosol in the light⁽¹⁾. Overexpression of COP1 in the light, however, was able to partially suppress photomorphogenic development, confirming its role as a light-inactivatable repressor⁽²⁾. Evidence also suggests that some of the COP gene products may interact directly to form a large complex⁽³⁾.     

ULTRASTRUCTURAL STUDIES OF SPERMATOGENESIS IN THE ANTHOCEROTALES. I. THE BLEPHAROPLAST AND ANTERIOR MITOCHONDRION IN PHAEOCEROS LAEVIS: EARLY DEVELOPMENT

Electron microscopic examination of thin sections showed that the blepharoplast of a young spermatid of Phaeoceros consists of two side-by-side centrioles and an accumulation of osmiophilic, granular matrix at their proximal ends. Lying between these nearly parallel organelles is a dark-staining body that will later disappear at the onset of flagellogenesis. For a brief period the centrioles are oriented perpendicular to the nuclear surface so that the granular matrix at their proximal ends is confluent with the nuclear envelope; furthermore, the nucleoplasm immediately in front of the centrioles becomes densely staining. The multilayered structure (MLS) develops directly under the centrioles. It comprises a band of 12 microtubules (the S₁ stratum) and three lower strata (S_2–4) whose constitutent lamellae are oriented at an oblique angle to the S₁ axis. While the S₁ tubules grow rearward over the nucleus which forms a beak adjacent to the posterior end of the lamellar strata, the centrioles are transformed into basal bodies with the distal growth of the axonemes and the proximal growth of the central cartwheels and lowermost triplets. The proximal ends of the basal bodies and the S₁ tubules overlying the lamellar strata are invested with osmiophilic matrix that extends down to the S₂ layer and may temporarily occlude the lamellar plates. At the onset of nuclear elongation an anterior mitochondrion becomes situated close beneath the lamellar strata which extend laterally beyond the S₁ tubules.