The photosynthetic CO2 exchange rate, chlorophyll fluorescence and P700 oxidation (absorption at 830 nm) were recorded in attached leaves of sunflower plants grown in soil by irradiance 460 pmol m'2 s‘i. Ehiring the photosynthesis in 510 cm^ m*3 CO2, 1 % O2, photosystem 1 (PS 1) effíciency was ahnost totally determined by the donor side oxidation under all irradiances. Fluorescence data showed that this control was exercised mostly by ApH-dependent plastoquinol oxidation. At 1.5 pM intracellular [CO2], the PS 1 reduction level on the acceptor side became signifícant and increased as [CO2] -> 0. ApH controlled the electron flow when the rate exceeded the value of 50 pmol(e‘) m'2 s‘i, which was close to the rate supporting photorespiration and CO2 reassimilation at CO2 compensation concentration in 21 % O2. The ApH ability to control the electron transport rate adequately prevented electron carriers reduction at PS 1 acceptor side, with stomata dosed under stress. When the low CO2 oř carbon reduction enzymes inactivation restricted the electron transport downstream of PS 1, open PS 1 centres (oxidised on acceptor sides) percentage declined in proportion to CO2 uptake rate. This makes us doubt the common belief that the rapid electron transport in photosynthesis involves interconnected, mobile electron carrier pools of plastocyanin and ferredoxin (Fd). Rather, the implications are explored in terms of supercomplexes involving cytochrome b(Jf, PC, PS 1, Fd and Fd-NADP reductase.
The nematode Steinernema kraussei (Steiner) was rediscovered in the type locality near Neuenherrsee in Westphalia, Germany. This isolate is morphologically identical with that described in 1923 by Steiner. Steiner's original description is completed by these main characters: the head with two circles of papillae, the labial bearing six and the cephalic four papillae; the excretory pore opening of adults is situated far in front of a nerve ring; the male tail has a fine mucron, spicules are on average 49 pm long in first generation, their manubrium having the ratio length to width 1:1 ; spicule retinaculum is usually well developed, gubcmaculum varies in its shape, but mostly is boat-shaped with hooked proximal part. Infective juveniles are 797 to 1102 pm long and their lateral fields have 8 ridges, but the central pair is less distinct and sometimes tends to merge into one unpaired ridge. Since S. kraussei is the oldest, and now the most completely described nematode species in the genus Steinernema, it has to be considered as the type species of this genus. The living culture is presently maintained in several laboratories and all formerly and future described similar species should be compared with this nematode.