Synthesis of poly(A) containing RNA induced by ecdysterone in fat body cells of Calliphora vicina

The insect-hormone ecdysterone causes a de novo synthesis of RNA in the fat body cells of blowfly larvae. Hybridization of the RNA induced by the hormone with ³H-Poly(U) demonstrates that it contains poly(A) sequences and therefore is probably informational. DNA-RNA-hybridization experiments further show that qualitatively new mRNA species are synthesized under the influence of ecdysterone. The inducibility of RNA synthesis is strongly correlated to specific developmental stages.     

Molecular dissection of photosystem I in higher plants: topology, structure and function

Photosystem I catalyses the light driven electron transfer from plastocyanin/cytochrome c ₆ on the lumenal side of the thylakoid membrane to ferredoxin/flavodoxin at the stromal side. Photosystem I of higher plants consists of 18 different protein subunits. Fourteen of these make up the chlorophyll a -containing core, which also contains the cofactors involved in the electron transfer reactions, and four make up the peripheral chlorophyll a / b -containing antenna. Arabidopsis plants devoid of the nuclear-encoded photosystem I subunits have been obtained either by different suppression techniques or by insertional knock-out of the genes. This has allowed a detailed analysis of the role and function of the individual subunits. This review is focused on recent developments in the role of the individual subunit in the structure and function of photosystem I of higher plants.     

Photosystem I Is an Early Target of Photoinhibition in Barley Illuminated at Chilling Temperatures

Light-induced damage to photosystem I (PSI) was studied during low-light illumination of barley (Hordeum vulgare L.) at chilling temperatures. A 4-h illumination period induced a significant inactivation of PSI electron transport activity. Flash-induced P700 absorption decay measurements revealed progressive damage to (a) the iron-sulfur clusters F_A and F_B, (b) the iron-sulfur clusters F_A, F_B, and F_X, and (c) the phylloquinone A₁ and the chlorophyll A₀ or P700 of the PSI electron acceptor chain. Light-induced PSI damage was also evidenced by partial degradation of the PSI-A and PSI-B proteins and was correlated with the appearance of smaller proteins. Aggravated photodamage was observed upon illumination of barley leaves infiltrated with KCN, which inhibits Cu,Zn-superoxide dismutase and ascorbate peroxidase. This indicates that the photodamage of PSI in barley observed during low-light illumination at chilling temperatures arises because the defense against active oxygen species by active oxygen-scavenging enzymes is insufficient at these specific conditions. The data obtained demonstrate that photoinhibition of PSI at chilling temperatures is an important phenomenon in a cold-tolerant plant species.