Citrulline and DRIP-1 Protein (ArgE Homologue) in Drought Tolerance of Wild Watermelon

Drought-affected plants experience more than just desiccationof their organs due to water deficit. Plants transpire 1000times more molecules of water than of CO₂ fixed by photosynthesisin full sunlight. One effect of transpiration is to cool theleaves. Accordingly, drought brings about such multi-stressesas high temperatures, excess photoradiation and other factorsthat affect plant viability. Wild watermelon serves as a suitablemodel system to study drought responses of C₃ plants, sincethis plant survives drought by maintaining its water contentwithout any wilting of leaves or desiccation even under severedrought conditions. Under drought conditions in the presenceof strong light, wild watermelon accumulates high concentrationsof citrulline, glutamate and arginine in its leaves. The accumulationof citrulline and arginine may be related to the induction ofDRIP-1, a homologue of ArgE in Escherichia coli, where it functionsto incorporate the carbon skeleton of glutamate into the ureacycle. Immunogold electron microscopy reveals the enzyme tobe confined exclusively to the cytosol. DRIP-1 is also inducedby treating wild watermelon with 150 mM NaCl, but is not inducedfollowing treatment with 100 µM abscisic acid. The salttreatment causes the accumulation of -aminobutyrate, glutamineand alanine, in addition to a smaller amount of citrulline.Citrulline may function as a potent hydroxyl radical scavenger.     

Penetration of the Mosquito (Aedes aegypti) Midgut Wall by the Ookinetes of Plasmodium gallinaceum

ABSTRACT We observed Plasmodium gallinaceum ookinetes in both intracellular and intercellular positions in the midgut epithelium of the mosquito Aedes aegypti. After epithelial cell invasion intracellular ookinetes lacked a parasitophorous vacuolar membrane and were surrounded solely by their own pellicle. Thus, the ookinete in the midgut epithelium of the mosquito differs from erythrocytic and hepatic stages in that the parasite in the vertebrate host is surrounded by a vacuole. The midgut epithelial cytoplasm around the apical end of invading ookinetes was replaced by fine granular material deprived of normal organelles. Membranous structure was observed within the fine granular area. Most ookinetes were seen intracellularly on the luminal side and intercellularly on the haemocoel side of the midgut epithelial cells. These observations suggest that the ookinete first enters into the midgut epithelial cell, then exits to the space between the epithelial cells and moves to the basal lamina where the ookinete develops to the oocyst.     

The role of auxin in growth of the plumular hook section of etiolated pea seedling

Externally applied GA greatly promoted elongation of the plumularhook section of the etiolated Alaska pea seedling, but IAA hadno such effect when given either alone or with GA. PCIB inhibitedelongation of the plumular hook section both in the presenceand absence of applied GA. The PCIB effect in the absence ofGA was partially overcome by IAA, but not completely. On theother hand, the PCIB effect in the presence of GA was completelyovercome by IAA. No antagonic response was, however, obtainedbetween GA and PCIB. CCC also retarded elongation of the sectionand this inhibition was completely overcome by GA, but not byIAA. There was little difference in the amount of endogenous auxindetectable in GA treated and untreated sections. These resultssuggest that auxin is necessary for the growth of both GA treatedand untreated plumular hook sections and that auxin and gibberellinact differently on the growth of the section. (Received April 24, 1968; )