Evidence of protocarnivory in triggerplants (Stylidium spp.; Stylidiaceae).

Australian triggerplants (Stylidium spp.; Stylidiaceae) trap small insects using mucilage-secreting glandular hairs held at various points on their inflorescence stems and flower parts. Triggerplants are generally found in habitats also containing genera of plants already accepted as carnivorous, two of which (Drosera, Byblis) use the same basic mechanism as Stylidium to trap their prey. In the herbarium, sheets of triggerplants and of accepted groups of carnivorous plants held similar numbers of trapped insects, and in the field, trapping of small prey per unit of glandular surface area was the same at a given site for triggerplants and for nearby carnivorous plants at three sites in northern Australia. Even more important, protease activity was produced by glandular regions of both triggerplants and Drosera after induction with yeast extract. A panel of negative and positive controls, including use 1) of plants grown in tissue culture, which therefore lack surface microorganisms, and 2) of protease inhibitors, shows that this activity 1) is generated by the glandular regions of the triggerplant itself, not by organisms that might reside on the surface of the plants, and 2) is due to proteases. All of this evidence taken together provides strong evidence of protocarnivory in Stylidium, something not previously suggested in the scientific literature, though the insect trapping has been noted informally. Experiments remain to be done to determine nutrient uptake, so triggerplants may well be fully carnivorous.

Processing and localization of bovine beta-casein expressed in transgenic soybean seeds under control of a soybean lectin expression cassette.

We have examined the processing and subcellular localization of a chimeric gene consisting of the bovine milk protein, beta-casein, under the control of a soybean seed lectin promoter and its 32 amino acid signal sequence in the seeds of transgenic soybean plants. The beta-casein expressed in developing soybean seeds is a doublet with apparent molecular weight slightly smaller than the bovine beta-casein and expression of the protein was highest in immature cotyledons. The casein proteins were purified from the immature soybean seeds by immunoaffinity chromatography and were analyzed by two-dimensional gel electrophoresis, blotting, and amino terminal sequencing. The N-terminal sequences of both of the doublet soybean casein polypeptides were identical to the N-terminal sequence of the bovine beta-casein indicating that the 32 amino acid lectin signal sequence was cleaved precisely from the chimeric protein in developing soybean seeds. Analysis of the purified soybean beta-casein polypeptides by mass spectrometry (MALDI-MS) showed that they are not phosphorylated. Absence of added phosphate groups is the cause of the size difference between the soybean beta-casein and native bovine beta-casein protein. Immunolocalization experiments showed that the casein protein was found in the protein storage vacuoles (PSV) in developing and mature soybean seeds. The precise removal of the 32 amino acid lectin amino terminal sequence from the chimeric lectin-casein fusion suggests that the lectin expression cassette can be used for production of pharmaceutical or other recombinant proteins of added value in the developing soybean seed.