The very-low-fluence and high-irradiance responses of the phytochromes have antagonistic effects on germination, mannan-degrading activities, and DfGA3ox transcript levels in Datura ferox seeds.

Seed germination can be promoted by the modes of action of two of the phytochromes: the low-fluence response (LFR), which is the classical red (R)-far-red (FR) reversible response and the very-low-fluence response (VLFR) that can be saturated by extremely low levels of Pfr, which can be elicited by a saturating FR pulse. The Datura ferox seed population used in this work had acquired the capacity to germinate through a VLFR after pretreatment in a water-saturated atmosphere (WSA) at constant 25 degrees C. After 12 d in WSA germination after a FR pulse was 82%, while it was less than 10% in darkness. It was found that the VLFR of germination is associated with increments in the embryo growth potential (EGP) and in the activity of two enzymes related to the weakening of the micropylar region of the endosperm (ME); endo-beta-mannanase and beta-mannosidase. The FR pulse also significantly stimulated the expression of DfGA3ox, a GA 3beta-hydroxylase, suggesting that the promotion of germination by the VLFR is associated with an increase in the synthesis of active gibberellins. The promotive action of the VLFR on germination is reduced when the FR pulse is immediately followed by a continuous FR treatment for 24 h (FRc). The effect of FRc cannot be reproduced by hourly FR pulses during the same period, showing that the antagonistic effect of FRc is a high-irradiance response (HIR). The action of the HIR in germination is associated with a decrease of both the mannan-degrading enzyme activity and the expression of DfMan in the ME, whereas no changes in the EGP were observed. The HIR also inhibits the accumulation of DfGA3ox in embryos, indicating that its action on germination is mediated, at least in part, through the modulation of active GA contents in seeds. This is the first report of a gene that participates in the VLFR-HIR antagonism in seeds.

A phytochrome-dependent embryonic factor modulates gibberellin responses in the embryo and micropylar endosperm of Datura ferox seeds.

The promotion of germination by phytochrome is associated with extensive changes both in the embryo and in the micropylar region of the endosperm (ME) of Datura ferox seeds. These changes require de novo gibberellins (GAs) biosynthesis in the embryo, the site where the light stimulus is perceived. GAs stimulate embryo growth potential and move to ME, promoting the expression of genes related with weakening. We report here that, in addition, phytochrome stimulates the sensitivity of the seeds to gibberellic acid (GA). The phytochrome-induced signal is produced in the embryo and enhances the stimulus by GA of embryo growth potential (EGP) and the promotion of the expression of proteins thought to participate in ME weakening: endo-beta-mannanase (EC 3.2.1.78), endo-beta-mannosidase (EC 3.2.1.25) and expansin. Our results suggest that the cytokinins may be a component of the embryonic signal. Phytochrome also modulates DfPHOR and DfMYB transcript levels in ME. These genes show a high identity with components of GAs signaling identified in other species. Expression of DfPHOR in the ME is apparently regulated by phytochrome through the supply of GAs from the embryo to ME, whereas DfMYB expression is regulated by an embryonic factor with some of the characteristics of the one that modulates seed sensitivity to GAs.

Analysis of biologically active compounds in potatoes (Solanum tuberosum), tomatoes (Lycopersicon esculentum), and jimson weed (Datura stramonium) seeds.

Potatoes and tomatoes, members of the Solanaceae plant family, serve as major, inexpensive low-fat food sources providing for energy, high-quality protein, fiber, vitamins, pigments, as well as other nutrients. These crops also produce biologically active secondary metabolites, which may have both adverse and beneficial effects in the diet. This limited overview, based largely on our studies with the aid of HPLC, TLC, ELISA, GC-MS, and UV spectroscopy, covers analytical aspects of two major potato trisaccharide glycoalkaloids, alpha-chaconine and alpha-solanine, and their hydrolysis products (metabolites) with two, one, and zero carbohydrate groups; the potato water-soluble nortropane alkaloids calystegine A3 and B2; the principal potato polyphenolic compound chlorogenic acid; potato inhibitors of digestive enzymes; the tomato tetrasaccharide glycoalkaloids dehydrotomatine and alpha-tomatine and hydrolysis products; the tomato pigments beta-carotene, lycopene, and chlorophyll; and the anticholinergic alkaloids atropine and scopolamine present in Datura stramonium (jimson weed) seeds that contaminate grain and animal feed. Related studies by other investigators are also mentioned. Accurate analytical methods for these food ingredients help assure the consumer of eating a good-quality and safe diet.