Stefan Kappeler

Circadian Oscillations of a Transcript Encoding a Germin-Like Protein That Is Associated with Cell Walls in Young Leaves of the Long-Day Plant Sinapis alba L

As part of an attempt to analyze rhythmic phenomena in the long-day plant Sinapis alba L. at the molecular level, we have searched for mRNAs whose concentration varies as a function of time of day. Differential screening of a cDNA library established from mRNAs expressed at the end of the daily light phase with probes representing transcripts expressed predominantly in the morning or evening has identified one major transcript. The cDNA, Saglp, encodes a predicted 22-kD protein with an N-terminal signal sequence. The protein shows homology to germin, a protein expressed in wheat embryos after onset of germination. The Saglp mRNA level undergoes circadian oscillations in light/dark cycles with maxima between 8 and 12 PM (zeitgeber time [zt] 12-zt16) and minima around 8 AM (zt0). In plants grown from seed in constant light, transcript levels are constitutive. In constant light regular temperature shifts function as an alternative “zeitgeber” to initiate Saglp transcript oscillations. At the cellular level, Saglp transcripts are expressed in the epidermis and spongy parenchyma of young leaves, and in distinct regions of the epidermis and the cortex in stems and petioles. Strong signals are observed in these tissues around zt12, whereas little expression is found around zt20, suggesting that the underlying oscillatory mechanism(s) operate(s) synchronously in different plant organs. The SaGLP steady-state protein concentration remains constant over light/dark cycles. Immunogold labeling shows that the SaGLP protein is associated with primary cell walls.

The proteins encoded by two tapetum-specific transcripts, Satap35 and Satap44, from Sinipis alba L. are localized in the exine cell wall layer of developing microspores

By differential screening of a copy DNA (cDNA) library from flowering Sinapis alba L. apices against cDNAs from vegetative apices, two cDNA clones were isolated representing transcripts that are expressed transiently at an early stage of tapetum development. The Satap35 cDNA encodes a polypeptide with a predicted molecular weight of 12.7 kDa and an isoelectric point of 10.4. The Satap44 cDNA codes for a putative 12.4-kDa polypeptide with an isoelectric point of 7.5. The deduced amino-acid sequences display 76% sequence identity and contain an N-terminal stretch of hydrophobic amino acids which has characteristics of secretory signal sequences. In-vitro transcription of the cDNAs and translation of the resulting RNAs in the presence of canine pancreatic microsomes demonstrates that the two proteins are translocated into the microsomes and that the putative preproteins are proteolytically processed to the mature forms. By immunoelectron microscopy the SaTAP35 and SaTAP44 proteins were detected at the developing peritapetal membrane between the tapetal cytoplasm and the adjacent middle layer of the anther wall. Furthermore, labelling was observed within the locule in association with globules resembling pro-Ubisch bodies which appeared at the tetrad stage. During the early vacuolate stage of microspore development the young exine was strongly labelled. The exine and the peritapetal membrane both are composed of sporopollenin, and the pro-Ubisch bodies are thought to contain sporopollenin precursors. Thus, SaTAP35 and SaTAP44 might be involved in sporopollenin formation and/or deposition.

Functional and technological properties of camel milk proteins: a review

This review summarises current knowledge on camel milk proteins, with focus on significant peculiarities in protein composition and molecular properties. Camel milk is traditionally consumed as a fresh or naturally fermented product. Within the last couple of years, an increasing quantity is being processed in dairy plants, and a number of consumer products have been marketed. A better understanding of the technological and functional properties, as required for product improvement, has been gained in the past years. Absence of the whey protein β-LG and a low proportion of к-casein cause differences in relation to dairy processing. In addition to the technological properties, there are also implications for human nutrition and camel milk proteins are of interest for applications in infant foods, for food preservation and in functional foods. Proposed health benefits include inhibition of the angiotensin converting enzyme, antimicrobial and antioxidant properties as well as an antidiabetogenic effect. Detailed investigations on foaming, gelation and solubility as well as technological consequences of processing should be investigated further for the improvement of camel milk utilisation in the near future.