Institute of Experimental Botany

Exeised roots ofSolanum laciniatum Ait. grown in vitro in a liquid medium will form the typical rich white callus with a high water content. Its formation is made possible by the presence of 2,4-dichlorophenoxyacetic acid and niyo-inositol in the nutrient medium. Choline, ascorbic acid, riboflavin, calcium pantothenate and biotin are inactive. A mixture of thiamine, pyridoxine and nicotinic acid will induce only slight proliferation.

Heat stress severely reduces rice yield and quality; however, differences between the superior, early-flowering and inferior, later-flowering spikelets of indica rice in response to high-temperature stress during grain filling remain unclear. This study investigated the effects of high temperature (HT, 33.6/20.7 °C day/night) on growth, endosperm structure, and hormone and polyamine content of superior and inferior spikelets of heat-sensitive (SG-1) and heat-tolerant (HHZ) indica cultivars. The HT decreased fertilization rate, caused earlier grain filling, and reduced duration of grain filling, thus resulting in decreased grain mass and a poor endosperm structure. In addition, soluble sugar and sucrose content increased, and starch synthesis decreased by HT at the early stage of grain filling. The HT increased polyamine [spermidine (Spd) and spermine (Spm)] and abscisic acid (ABA) content, but reduced zeatin (Z) + zeatin riboside (ZR) and indole-3-acetic acid (IAA) content in the grains. Such effects were more apparent in the inferior than superior spikelets; however, the inferior spikelets of SG-1 were more affected than those of HHZ. At the middle grain filling stage, HT produced little difference between the two cultivars. Our results suggest that the poor development of inferior spikelets of SG-1 under the HT could be attributed, at least in part, to the changed content and ratios of free polyamines [putrescine (Put), Spd, and Spm] and phytohormones (Z+ZR, IAA, and ABA) and the conversion efficiency of sucrose into starch.

Opaque2 is a basic leucine-zipper transcription factor that regulates the expression of several genes involved in the development of maize endosperm. Among the different mutations so far characterized, the o2Italian (o2It) allele has a genomic deletion of 10 bp that interrupts the open reading frame by a premature stop codon. Curiously, the o2It allele still encodes a long o2 isoform (o2It-L) that is recognized by an O2 carboxy-terminal antibody, evidencing that this protein is similar to the wild type isoform. To clarify this phenomenon, we characterized the transcripts generated from the o2It allele and found two transcripts that are produced in a 1:1 ratio. The first transcript carried the 10 bp deletion and matched the genomic sequence of the o2It allele, whereas the second one carried a 15 bp deletion as a result of a 3’ alternative splicing site. The lack of five additional nucleotides restored the correct reading frame and explained the nature of the o2It-L polypeptide. The production of two distinct transcripts from the o2It allele was probably due to the recruitment of different splicing factors as suggested by in silico analysis of the o2It-mutated region. This finding evidences how the recruitment of splicing factors is tightly linked to nucleotide motives that should be present in correct neighboring contexts.

Meristems from 25–90-year-old oak (Quercus robur L. andQ. petraea Matt.) trees and seed embryos were pretreated with polyvinyl pyrrolidone, ascorbic acid, cysteine and citric acid solutions. Tissues were cultured mostly on a WPM medium supplemented with different combinations and concentrations of growth regulators. All the different pretreatments showed a positive effect against the otherwise very rapid and harmful browning of the explants but ascorbic acid (100 mg dm−3) proved to be the most effective. Shooting was induced from seed embryos and meristems originating from adult trees. Rooted plantlets were obtained from explants of seed embryos.

Cultures of isolated mesophyll protoplasts ofBrassica napus L.have shown a positive reaction with the acidic phloroglucinol test for lignin (Wiesner reagent) 30 h after the beginning of the culture period. The reaction was observed in protoplasts and in a very early stage connected with divisions, in which acidic phloroglucinol positive material was primarily deposited like a girdle surrounding the division plane. Brown exudates, which are a serious problem even in young cultures derived from isolated protoplasts, have been secreted into the medium by cells, and also showed a positive reaction. The same staining pattern has been found with toluidine blue 0.

Uptake of magnesium was studied by continuous flow technique for 82 days old rice plants in nutrient solution over a range of 0.2 to 1 ppm or 8.2 to 41 µM magnesium concentration. Uptake of magnesium followed a Michaelis-Menten kinetics with a Michaelis constant, Km of 0.2 × 10-4M and Vm 156 µg g-1 h-1. With increasing flow rate, the rate of magnesium absorption was increased.