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An emerging family of bcl-2-like genes has been identified from nematode to humans. These genes play a role in the maintenance of homeostasis. Its members have highly conserved domains that are important for their dimerization. Since nothing is known about the importance of these genes in plant cells, we have investigated their presence in an alga as well as in three higher plants both by Western analysis and by immunocytochemistry. Immunoblots revealed the presence of a protein immunoreacting with the anti-bcl-2 polyclonal antibody in leaves of tobacco plants. Furthermore, immunocytochemical localization has shown that this protein is mainly associated with mitochondria, plastids, and nuclei of plant cells. Taken together, our results suggest that bcl-2 is a protein highly conserved throughout evolution.

We have isolated a full length cDNA clone (designated PTGRP) encoding a proline-rich protein from leaves of Lycopersicon chilense. Sequence analysis of the 552-bp insert revealed that the open reading frame encodes a 12.6-kDa protein. The deduced amino acid sequence of PTGRP consists of a C-terminal proline-rich domain with two identical repeat motifs Phe-Pro-Met-Pro-Thr-Thr-Pro-Ser-Thr-Gly-Gly-Gly-Phe-Pro-Ser. The N terminus lacks proline and is hydrophobic. Unlike other proline-rich proteins this protein contains five glycine-rich repeat motifs (Gly-X)n representative of glycine-rich proteins. Southern blot analysis showed that PTGRP is a member of a small gene family within the L. chilense genome. Northern blot experiments revealed that the PTGRP gene is significantly down regulated by water stress. PTGRP mRNA transcription decreased 5- to 10-fold in leaves and stems after 4-8 days of water stress. The mRNA reaccumulated when the drought-stressed plants were rewatered. The in situ hybridization experiments also revealed that PTGRP mRNAs were more abundant in leaf sections of plants watered regularly compared with those of plants submitted to water stress. Down regulation of the PTGRP gene was also observed in desiccated cell suspensions of L. chilense and in those treated with abscisic acid, mannitol, and NaCl. Based on the common features of proline-rich proteins (high proline content, repeated motifs, and a putative signal peptide) and their involvement in the cell wall, it is likely that the PTGRP protein is targeted to the cell wall. Its down regulation by drought could be correlated with the remodeling of the plant cell wall in response to water stress.

Some of the events during the growth and asexual differentiation of Physarum polycephalum amoebae are described. Encysted amoebae contain low levels of protein and RNA. When these cells are mixed with bacteria and inoculated onto agar plates, there is an increase in cellular RNA content followed by an increase in protein content. The cellular RNA and protein contents of all strains tested decrease during the subsequent cell divisions. In nondifferentiating cells (strain Cl at 30 degrees C and strain LU648), RNA and protein contents continue to decrease, and the cell eventually encyst. In the asexually differentiating strain Cl grown at 26 degrees C, the cellular RNA and protein contents stop decreasing and begin to increase when the first amoebae become committed to form plasmodia. At early stages of differentiation a new 36,000 molecular weight polypeptide appears. In fully formed plasmodia another polypeptide of 38,000 molecular is observed. These two plasmodial-specific polypeptides are among the most abundant plasmodial proteins.