ABSTRACT
Regulation of Rubisco (D-ribulose-1,5-bisphosphate carboxylase/oxygenase activase (RCA) gene expression and polypeptide content were determined in Brachypodium distachyon leaves, stems and ear elements at different developmental stages under optimal growth conditions as well as under drought and salt stress conditions. B. distachyon leaf contains a much greater amount of Rubisco activase small (RCAS) isoform than the large one (RCAL) under optimal growth conditions. Increased levels of the RCAL isoform compared with the RCAS isoform were found in leaves and in green stems under salt and drought stress, respectively. Transcriptional levels of RCA are almost identical in different leaf positions. Short-term drought and salt stresses did not cause the impairment of RCA gene expression in early seedlings. But gradually increasing drought stress significantly decreased gene expression in early seedling samples. Amounts of the RCAS isoform were found to be more in different leaves of the plant compared with the RCAL isoform and their ratio was constant under normal condition. In green stems gene expression of RCA decreased under salt and drought stresses, although as it was in green leaves protein amounts of RCAL isoform increased compared with the RCAS isoform. All of the above described results clearly indicate that the accumulation of each RCA isoform is differentially regulated by developmental and environmental cues.
Subject(s)
Brachypodium/enzymology , Gene Expression Regulation, Plant , Plant Proteins/genetics , Stress, Physiological , Brachypodium/genetics , Brachypodium/physiology , Droughts , Gene Expression , Photosynthesis , Plant Leaves/enzymology , Plant Leaves/genetics , Plant Leaves/physiology , Plant Proteins/metabolism , Plant Stems/enzymology , Plant Stems/genetics , Plant Stems/physiology , RNA, Plant/genetics , Ribulose-Bisphosphate Carboxylase/genetics , Ribulose-Bisphosphate Carboxylase/metabolism , Ribulosephosphates/metabolism , Salinity , Seedlings/enzymology , Seedlings/genetics , Seedlings/physiologyABSTRACT
Decarboxylating NAD-malate dehydrogenase (NAD-malic enzyme, NAD-ME, EC 1.1.1.39) has been investigated under a long-term drought during pre-anthesis, anthesis and seed-formation phases of ontogenesis of a NAD-ME type C4 plant Amaranthus cruentus L. using cytosol, chloroplast and mitochondrial fractions of mesophyll (M) and bundle sheath (BS) cells. We detected several molecular forms of NAD-ME with different subcellular localization patterns in the studied phases of amaranth ontogenesis. However, no enzyme activity was observed experimentally in chloroplasts of M and BS cells. In the pre-anthesis phase NAD-ME isoform with molecular weight of â¼115 kDa was found in cytosol of M and BS cells of control and drought-exposed plants. One of NAD-ME isoforms with molecular weight of 110 kDa was located in mitochondria of BS cells of control and drought-exposed plants, and a new isoform of â¼121 kDa was formed in mitochondria of BS cells under the influence of drought. After resuming watering this isoform (â¼121 kDa) disappeared again. Approximately 90.6% and 9.4% of the total NAD-ME activity were localized in mitochondrial stroma and cytosol of BS cells, respectively, while in mesophyll cells 100% activity was found in cytosol fractions. The reaction catalyzed by NAD-ME follows Michaelis-Menten equation. NAD(+), l-malate and Mn(2+) activate this enzyme in mitochondria. Appearance of the â¼121 kDa isoform of NAD-ME in the mitochondrial fraction of BS cells under drought and its disappearance after resuming watering could be attributed to one of the protection functions of plants.
