Search

Study of the unique leaf anatomy and chloroplast structure in shade-adapted plants will aid our understanding of how plants use light efficiently in low light environments. Unusual chloroplasts in terms of size and thylakoid membrane stacking have been described previously in several deep-shade plants. In this study, a single giant cup-shaped chloroplast, termed a bizonoplast, was found in the abaxial epidermal cells of the dorsal microphylls and the adaxial epidermal cells of the ventral microphylls in the deep-shade spike moss Sehtginella erythropus. Bizonoplasts are dimorphic in ultrastructure: the upper zone is occupied by numerous layers of 24 stacked thylakoid membranes while the lower zone contains both unstacked stromal thylakoids and thylakoid lamellae stacked in normal grana structure oriented in different directions. In contrast, other cell types in the microphylls contain chloroplasts with typical structure. This unique chloroplast has not been reported from any other species. The enlargement of epidermal cells into funnel-shaped, photosynthetic cells coupled with specific localization of a large bizonoplast in the lower part of the cells and differential modification in ultrastructure within the chloroplast may allow the plant to better adapt to low light. Further experiments are required to determine whether this shade-adapted organism derives any evolutionary or ecophysiological fitness from these unique chloroplasts. Key words: bizonoplast; chloroplast; iridescence; iridoplast; Selaginella; shade plant; structure; thylakoid stacking.

Leaves from 12 legume species representing two subtribes were examined by various techniques for the presence of vegetative storage proteins (VSPs) similar to the 27, 29, and 94 kD VSPs of soybean. Polyacrylamide gel electrophoresis (PAGE) of leaf protein followed by western immunoblotting using antibody that recognizes soybean VSP94, a lipoxygenase, demonstrated that this protein is present in six of the nine species tested. Blotting with antibody to soybean VSP27/29, which are glycoproteins, gave labelling in seven species and glycoprotein affino-blots showed that glycosylated proteins ranging around 27 to 29 kD were present in all nine species examined. Immunocytochemical localization studies of eight species demonstrated that proteins antigenically similar to VSP94 and VSP27/29 are specifically accumulated in the vacuole of paraveinal mesophyll (PVM) cells. They were not detectable at significant levels in other mesophyll cells using this technique. Comparisons of protein compositions of isolated PVM and mesophyll protoplasts from seven species further confirmed the specialized nature of the PVM. VSP94 and proteins ranging from 25 to 35 kD molecular mass were the major proteins of PVM of all but one species while Rubisco was quite low in amount compared to mesophyll protoplasts. The results show that VSP synthesis and accumulation is a general feature of legume leaves containing a PVM layer and indicate that the PVM plays a specialized role in nitrogen metabolism and partitioning in these species. Key words: legumes; lipoxygenase; mesophyll, paraveinal; proteins, vegetative storage.

The pyruvate,orthophosphate dikinase (PPDK) gene coding the chloroplast enzyme involved in C4 photosynthesis has a dual promoter system. The first promoter is responsible for the transcription of a larger transcript and its product is targeted to the chloroplast (hence, it is designated as C4Pdk promoter) while the second promoter is responsible for the transcription of a smaller transcript and its product remains in the cytosol. In this study, chimeric maize C4Pdk promoter (0.9 or 1.5 kb)-β-glucuronidase or luciferase fusion genes were introduced into maize plants by Agrobacterium-mediated transformation. The cell- and tissue-specificities of the maize C4Pdk promoter in the transgenic maize plants were examined by histochemical and enzymic activity analyses of the reporters in different photosynthetic cells and tissues. The results showed that the reporter proteins are almost exclusively localized in leaf mesophyll cells. Among the tissues tested, leaf blade had the highest reporter activities with sheath exhibiting about 10% of the activities in blade. Husk, stem, tassel and root had no or very little reporter activities. Taken together, these results suggest that the maize C4Pdk promoter is specifically transcribed in the mesophyll cells of leaf blade and to a much less extent in the mesophyll cells of sheath, but not in leaf bundle sheath cells or other tissues. Furthermore, the 0.9 kb maize C4Pdk promoter sequences appear to contain the necessary cis-acting elements for its cell- and organ-specific expression. [ABSTRACT FROM AUTHOR]

Haloxylon aphyllum and H. persicum of Chenopodiaceae are dominant plants in the continental deserts of the Asian Irano-Turanian region. The photosynthetic organs, assimilating shoots and leaf-like cotyledons of these two species were studied to characterize their photosynthetic types. 13C/12C isotope ratios, the cellular anatomy of as similating organs, primary photosynthetic products, and activities of carbon metabolism enzymes, RUBP carboxylase, PEP carboxylase, malic enzymes, and aspartate aminotransferase, indicate different pathways of CO2 fixation in the photosynthetic organs. Assimilating shoots had attributes of the C4 photosynthesis entirely, while cotyledons lack Kranz-anatomy and incorporated CO2 via C3 photosynthesis. Cotyledons and seeds had lower δ13C values compared to shoots, consistent with the contribution of C3-like CO2 assimilation. Two pathways of carbon donation to the C3 cycle via decarboxylation of C4 acids in bundle sheath cells are suggested to occur in shoots of Haloxylon. The primary photosynthetic product malate can be utilized through NADP+-malic enzyme which occurs in high activity. NADδ-malic enzyme may contribute to C4 photosynthesis (some aspartate is formed as an initial product, the bundle sheath chloroplasts have some grana, and NAD+-malic enzyme is found in bundle sheath cells of shoots, all criteria for NAD+-malic enzyme type photosynthesis). We propose that organ diversity of CO2 fixation pathway in Haloxylon species is an important factor for their growth, survival and reproduction in continental climate deserts. [ABSTRACT FROM AUTHOR]

In situimmunolocalization and Western blot analysis of separated cellular and subcellular fractions, were used to determine the localization of different isoforms of NADP-malic enzyme in both wheat (C3) and maize (C4) plants. In both techniques, an affinity purified anti-(maize 62 kDa NADP-ME) lgG from the maize green leaf isoform also reacted with a 72 kDa protein in tissues of C4 plants as well as C3 plants. The light- inducible 62 kDa isofomi is located in bundle sheath chioroplasts of maize leaves. In etiolated leaves and in roots of maize there is evidence for the occurrence of a 72 kDa isoform which co-migrates on 2-D (SDS and isoelectric focusing) PAGE. The 72 kDa isoform is also present in low levels in green leaves. This form may occur in multiple intracellular compartments; but in situ immunolocalization experiments and Western blot and activity assays on fractionated protoplasts indicate that a significant amount of this isoform occurs in plastids. With regards to C3 plants such as wheat, a 72 kDa isoform in leaves is largely confined to the chloroplasts based on in situ immunolocalization and Western blots and enzyme activity assays with fractionated protoplasts. In maize, it appears that the constitutive expression pattern of a possible C3 ancestral gene for NADP-malic enzyme has been maintained, and a high level expression of a light-inducible isoform located in bundle sheath chloroplasts (62 kDa) has been acquired during its evolution. [ABSTRACT FROM PUBLISHER]