Plant Science Letters最新文献

The sink to source transition of expanding leaves of cucumber was studied by sampling leaves sequentially from the growing stem apex toward the base of the plant. Leaf fresh weight and photosynthetic rate increased in the progression to lower nodes. Sucrose and raffinose concentrations were higher in sink leaves than in source leaves. Galactinol and stachyose concentrations increased during leaf expansion. Both alkaline and acidic α-galactosidase activity declined during leaf expansion, whereas galactinol synthase activity increased abruptly in leaves beginning in the leaf at the fourth node below the apex. This increase in activity corresponded temporally to marked changes in the oligosaccharide composition of the leaves in favor of galactosyl-saccharides, particularly stachyose. Across all leaf positions, galactinol synthase correlated positively with galactosyl-oligosaccharide concentration (r = 0.90) and correlated negatively with sucrose concentration (r = −0.82). The ratio of stachyose to raffinose correlated positively with the ratio of galactinol synthase to α-galactosidase (r = 0.95). The results point to the importance of changes in enzyme levels per se as determinants of changes in soluble carbohydrate levels associated with acquisition of export capability during leaf expansion.

This paper describes a new method for improving both the stability and reproducibility of chloroplast enzyme light-activation systems. Usually, the most labile components of these systems are the thylakoids, the preparation of which must be repeated daily. Freezing the thylakoids in small aliquots in liquid nitrogen and storing them at −90°C in a buffer containing 50% glycerol results in preparations whichare completely stable over an 18-month-period. Enzyme light-activation rates were essentially identical with either frozen or fresh thylakoids. Freezing, however, resulted in a slow decline of NADP-protoreduction rates and also in a gradual uncoupling of non-cyclic photophosphorylation.

Sub-cellular fractions from radiolabelled wheat aleurone cells were isolated using two procedures. Using both procedures, [methyl-¹⁴C]choline, was actively incorporated into phosphatidylcholine in the aleurone grain and oleosome fractions, but [U-¹⁴C]glycerol was poorly incorporated. This was most apparent in quiescent seeds and seeds incubated for 14 h or less. It is proposed that phospholipid-synthesis in the aleurone grain and oleosome fractions takes place from pre-existing storage glycerolipids. In contrast, the microsome fraction incorporated both choline and glycerol. This was more predominant in seeds incubated for 24 h or more and presumably reflects turnover of phospholipids in the endomembrane system. The relevance of these results is discussed in relation to the biogenesis of endoplasmic reticulum in germinating wheat seeds.

The growth hormones 6-benzylaminopurine (BAP), naphthaleneacetic acid (NAA) and 2,4-dichlorophenoxy-acetic acid (2,4-D) were used as a selection tool in some protoplast fusion experiments involving different inbred lines of Petunia. The efficiency of the selection scheme, the possibility of cross-feeding, and the reaction of the tissue to 2,4-D at different development stages are described. The selection scheme was proved highly efficient in experiments carried out by Izhar et al., Mol. Gen. Genet., 190 (1983) 468 and S. Izhar (unpublished), with only a negligible amount of cross-feeding between protoplasts of different lines. Lines sensitive to 2,4-D sprays require 2,4-D for protoplast division and tissue development to callus, while the lines resistant to 2,4-D sprays were not able to use 2,4-D for protoplast division and development.

Cytosine residues were more heavily methylated in rDNA isolated from fruit nuclei of marrow, melon, cucumber and tap root nuclei of turnip, than in total DNA preparations. The rRNA genes showed varying degrees of heterogeneity for both length and methylation as assessed by digestion with restriction endonucleases. Marrow rDNA was not digested by the methylation sensitive restriction endonuclease HpaII and while none of the other rDNAs was extensively digested, cucumber rDNA showed a different pattern of heterogeneity following HpaII digestion to that shown following EcoRI digestion. Cloned (unmethylated) rDNA sequences were extensively digested by HpaII. The relatively high level of methylation of the rRNA genes may be related to the large number of these genes in higher plants.

Cytofluorimetric measurements of the DNA-content in the nuclei during the initiation of callus formation from isolated protoplasts of potato were performed using propidium iodide as fluorochrome. Reproducible measurements were obtained after digestion of the cell walls and after RNase treatment.

Nuclei with high DNA-content were found early in the culture and the frequency of these nuclei increased with time in culture. In addition to highly replicated nuclei, multinucleated cells were found, the frequency of which decreased during prolonged culturing.

Somatic embryogenesis and subsequent plant regeneration was obtained from cultured young inflorescence segments of Sorghum arundinaceum var. sudanense (sudan grass). The inflorescences (10–50 mm in length) were cultured on Murashige and Skoog's medium supplemented with 0.01–5.0 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D). A compact nodular callus and somatic embryos arose predominantly from the rachis. The best response was obtained from inflorescences 10 mm in length. Somatic embryos developed in 72% of the cultures on medium containing 1.0 mg/l 2,4-D. Regenerated plants were normal phenotypically and had 2n=20 chromosome number.