Effect of microwave treatment on the efficacy of expeller pressing of Brassica napus rapeseed and Brassica juncea mustard seeds.

A study was conducted to evaluate the effect of microwave heating on the efficacy of expeller pressing of rapeseed and mustard seed and the composition of expeller meals in two types of Brassica napus rapeseed (intermediate- and low-glucosinolate) and in Brassica juncea mustard (high-glucosinolate). Following microwave treatment, the microstructure of rapeseed using transmission electron microscopy showed a significant disappearance of oil bodies and myrosin cells. After 6 min of microwave heating (400 g, 800 W), the oil content of rapeseed expeller meal decreased from 44.9 to 13.5% for intermediate-glucosinolate B. napus rapeseed, from 42.6 to 11.3% for low-glucosinolate B. napus rapeseed, and from 44.4 to 14.1% for B. juncea mustard. The latter values were much lower than the oil contents of the corresponding expeller meals derived from the unheated seeds (i.e., 26.6, 22.6, and 29.8%, respectively). Neutral detergent fiber (NDF) contents showed no differences except for the expeller meal from the intermediate-glucosinolate B. napus rapeseed, which increased from 22.7 to 29.2% after 6 min of microwave heating. Microwave treatment for 4 and 5 min effectively inactivated myrosinase enzyme of intermediate-glucosinolate B. napus rapeseed and B. juncea mustard seed, respectively. In low-glucosinolate B. napus rapeseed the enzyme appeared to be more heat stable, with some activity being present after 6 min of microwave heating. Myrosinase enzyme inactivation had a profound effect on the glucosinolate content of expeller meals and prevented their hydrolysis to toxic breakdown products during the expelling process. It appeared evident from this study that microwave heating for 6 min was an effective method of producing expeller meal without toxic glucosinolate breakdown products while at the same time facilitating high yield of oil during the expelling process.

Light-dependent regulation of carotenoid biosynthesis occurs at the level of phytoene synthase expression and is mediated by phytochrome in Sinapis alba and Arabidopsis thaliana seedlings.

In chloroplasts, carotenoids are essential pigments involved in photosynthesis. During-photomorphogenesis, a coordinated increase in the amounts of chlorophylls and carotenoids, in conjugation with other components, leads to the formation of a functional photosynthetic apparatus. To investigate the regulation of carotenoid biosynthesis during this process at the molecular level, GGPS, PSY and PDS cDNAs have been cloned from white mustard (Sinapis alba L). GGPS encodes a key enzyme in plastid isoprenoid metabolism, while the products of PSY and PDS catalyse the subsequent steps in carotenoid biosynthesis. Due to the low mRNA levels of the genes involved, the use of a RT-PCR protocol was necessary to measure gene expression during photomorphogenesis. With light, there is an up-regulation of PSY expression, the first gene within the carotenoid biosynthetic pathway, while PDS and GGPS expression levels remain constant. Treatment with different light qualities reveals a phytochrome-mediated regulation of PSY expression in developing white mustard seedlings. To obtain more detailed information on the light-regulation, Arabidopsis thaliana wild-type and phytochrome mutants were utilized. Continuous far-red and red light both increase the expression of PSY in wild-type seedlings, demonstrating that both light-labile and light-stable phytochromes are involved in PSY regulation. The response to far-red light is completely abolished in the phyA mutant, showing that PHYA mediates the increase in PSY transcript levels under these light conditions. In the phyB mutant, the red light response is normal, indicating that PSY expression is not controlled by PHYB but by other light-stable phytochromes. Measurement of chlorophylls and carotenoids under the same light regimes shows that the up-regulation of PSY expression does not necessarily result in an increase of the carotenoid content. Only those light conditions which allow chlorophyll biosynthesis lead to a significant increase of the carotenoid content. Therefore, it is proposed that up-regulation of PSY mRNA levels leads to an increased capacity for the formation of carotenoids. However, this only takes place under light conditions leading to protochlorophyllide photoconversion.

Promoter elements of the mustard CHS1 gene are sufficient for light regulation in transgenic plants.

The expression of chalcone synthase (CHS) genes, which encode the first enzyme of the flavonoid pathway, is under developmental control as well as affected by external stimuli such as light. Varying fragments of the 1 kb upstream region of the CHS1 gene from white mustard (Sinapis alba L.) were fused to the GUS-coding region, and the light-regulated expression of these constructs was analysed in transgenic Arabidopsis and tobacco plants. Studies performed with Arabidopsis seedlings indicate the presence of two elements within the CHS1 promoter mediating light responses via different photoreceptors. One element, located about 150 bp upstream of the transcription start site, is homologous to Unit 1 of the parsley CHS gene, the second, far more upstream element carries sequences similar to Unit 2 of the same gene. Detailed studies on Unit 1-driven expression indicate that this element transfers the expression characteristics of the original gene to both Arabidopsis and tobacco. Although the expression characteristics of Unit 1 are indistinguishable from those of the full-length promoter within the same species, we observed differences in mustard CHS promoter regulation between Arabidopsis and tobacco plants transgenic for the identical construct. The difference in photoreceptor usage by the same promoter element in different transgenic species (Unit 1 from mustard in Arabidopsis vs. tobacco) was also observed for different but homologous promoter elements in the same transgenic species (Unit 1 from mustard and parsley in tobacco). We therefore conclude that the same promoter and even the same promoter element (Unit 1) can mediate different spatial patterns of expression and modes of light regulation in different transgenic species.

[Photomorphogenesis]. / Photomorphogenese

The normal development of the higher plant occurs only in light (photomorphogenesis). The effect of light is due to intracellular development of a morphogenetically active effector molecule (Pfr, a chromoprotein). The point in question is, by which pathways the homeostasis of development (the course of development directed by endogenic factors) and the environmental factor "light" may act together in photomorphogenesis in order to accomplish the normal development of plants. Physiological and molecular analysis of photomorphogenesis is to contribute basically to the problem of surveying the pathways of gens and environmental influences in determining the characteristics of higher organisms, man included. The logical order of the phenomena is shown to have the precedence of an attempt for molecular analysis of photomorphogenesis. A result of the logical order is the insight that all the phenomena induced by Pfr present the spatial and temporal pattern of "primary differentiation". This primary differentiation (= formation of the specific competence) does not depend on light (developmental homeostasis). The photomorphogenesis (= development through the presence of Pfr of the pattern due to the primary differentiation), in accordance with the present knowledge is to be attributed to differential enzymatic induction and repression. This opinion is confirmed by examples. The correlation between the enzymatic activity and the structure (form, shape) still remains an unsolved problem.

The effect of illumination of the malic acid content and anion/cation balance of mustard leaves (Sinapis alba).

1. Mustard plants have been grown under conditions in which the length of artificial day could be controlled. 2. Leaf samples were analysed for malic acid and citric acid, and for a number of inorganic anions and cations. A simple method is described by which sap was obtained from 0.5g. samples of leaves. 3. In days of 16hr. or more, malic acid was accumulated; the chief cation accumulated was calcium. 4. When the day-length was reduced the malic acid content decreased considerably but the calcium content remained the same. There was little change in the pH value of the sap, the balance of anions and cations having been maintained mainly by increases in citrate and nitrate contents. Analyses of the whole leaf still showed some deficiency in anion after sodium, potassium, calcium, magnesium, nitrate, sulphate, inorganic phosphate, chloride, malate and citrate had been accounted for. 5. Analyses at shorter intervals revealed a large diurnal variation in malic acid content, which increased during the first 5-6hr. of the light period, and fell during darkness. 6. The significance of these findings is discussed, and it is suggested that malic acid accumulation is a by-product of photosynthesis, calcium being taken up irreversibly to maintain anion/cation balance, and hence creating a continuing need for anions to balance it.