No abstract

No abstract

ABSTRACIMembranes from homogenates of growing and of dormant storage roots of red beet (Beta vulgaris L.) were centrifuged on linear sucrose gradients. Vanadate-sensitive ATPase activity, a marker for plasma membrane, peaked at 38% to 40% sucrose (1.165-1.175 grams per cubic centimeter) in the case of growing material but moved to as low as 30% sucrose (1.127 grams per cubic centimeter) during dormancy.A band ofnitrate-sensitive ATPase was found at sucrose concentrations of 25% to 28% or less (around 1.10 grams per cubic centimeter) for both growing and dormant material. This band showed proton tramport into membrane vesicles, as measured by the quenching of florescence of acridine orange in the presence of ATP and Mg2@. The vesicles were collected on a 10/23% sucrose step gradient. The phosphate hydrolyzing activity was Mg dependent, relatively substrate specific for ATP (ATP > GTP > UTP > CTP = 0) and increased up to 4-fold by ionophores. The ATPase activity showed a high but variable pH optimum, was stimulated by C1-, but was unaffected by monovalent cations. It was inhibited about 50% by 10 nanomolar mersalyl, 20 micromolar N,N'-dicyclohexylcarbodiimide, 80 micromolar diethylstilbestrol, or 20 millimolar N03-; but was insensitive to molybdate, vanadate, oligomycin, and azide. Proton transport into vesicles from the 10/23% sucrose interface was stimulated by C17, inhibited by NO03, and showed a high pH optimum and a substrate specificity similar to the ATase, incling some proton transport driven by GTP and UTP.The low density of the vesicles (1.10 grams per cubic centimeter) plus the properties of H' transport and ATPase activity are similar to the reported properties of intact vacuoles of red beet and other materials. We conclude that the low density, H+-pumping ATPase of red beets originated from the tonoplast. Tonoplast Ht-ATPases with similar properties appear to be widely distributed in higher plants and fgi.

For Ca2+ to function as a second messenger in signal transduction, it is essential that plant cells maintain low cytoplasmic Ca2 levels relative to internal organelles and the apoplast. At the plasma membrane, Ca2+ is actively transported out of the cytoplasm and current evidence supports the involvement of a primary Ca2 -translocating ATPase in mediating this energy-dependent process. This review examines the preliminary biochemical characterization of this transport enzyme.

A membrane fraction enriced with a mapesium-dependent, monovalent cation-stimulated ATPase was Isolated from red beet (Beta vlgaris L.) storage roots by a combination of differential centrifugation, extraction with KI, and sucrose density gradient centrifugation. This fractio was distinct from eadpamcreticuum, Golgi, mitochondrial, and possibly tonoplast membranes as determined from an analysis of marker enzymes. The ATPase activity associated with tis fraction was further characterized and found to have a pH optimum of 6.5 in the presence of both Mge and K+. The acthiity was substrate specific for ATP and had a temperature optimum near 40°C. Kinetics with MglATP followed a simple MichaelisMenten relationship. However the kinetics of K+-stimulation were complex and suggestive of negative cooperativity. When monovalent cations were present at 2.5 milhmolarity, ATPase was stimulated in the sequence K+ > Rb+ > Na+ > Li+ but when the concentration was raised to 50 nflhlmolarity, the sequence changed to K+ a Na+ a Rb+ > Li. The activity was not synergisticaly stimulated by combinations of Na+ and K+. The enzyme was iosensitive to NaN3, oligomycin, ouabain, and sodium molybdate but sensitive to N,f-icyclobexylcarbodllmlde, diethyistilbestrol, and sodim vanadate. Based on the shiilarity between the properties of this ATPase activity and those from other well characterized plant tissues, it has been concluded that this membrane fraction is enriched with plasma membrane vesicles.Plant storage tissue has provided a convenient system for the study of cellular ion transport. The use of storage tissue in ion flux studies has the advantage that transport can be considered for individual cells unaffected by long distance transport, growth, and photosynthesis (19). Ion transport in storage tissue has been well characterized (19 and references therein) and for red beet, ATP has been shown to be the energy source (18 membrane ATPase of red beet. First, beet storage tissue is available in bulk and thus potentially suitable for enzyme purification and for phosphorylation studies. Secondly, we were interested to know to what extent the unusual transport features of beet (19)-its halophytic nature, propensity for accumulation of sodium, and the large effect of pH on cation accumulation-might be related to the properties of the plasma membrane ATPase. While the ATPase activity in crude membrane fractions from this species (sugar beet) has been analyzed (6), the properties of this activity in purified plasma membrane fractions have not been characterized.In this paper, cell fractionation studies with red beet storage root are presented. A membrane fraction enriched with Mg-dependent, monovalent cation-stimulated ATPase activity distinct from ER, Golgi, and mitochondrial enzyme markers was prepared. The properties of the ATPase activity were similar to those reported for corn (12) and oat (8) root plasma membrane fractions. MATERIALS AND METHODSPlant Material. Red beet (Beta vulgaris L.) storage roots were purchased commercially...

Growth chamber and laboratory experiments were conducted to evaluate foliar absorption and translocation of the isopropylamine (Ipa) or trimethylsulfonium (Tms) salts of glyphosate in Abutilon theophrasti and Setaria faberi. Glyphosate was applied at 250 g ai ha−1. Absorption of 14C-glyphosate in both formulations increased similarly in both species over 72 h. Seventy-two hours after treatment (HAT), A. theophrasti absorbed 26% of applied 14C of both formulations, whereas S. faberi absorbed 43% of both formulations. The addition of 1% ammonium sulfate (AMS) to both formulations increased the amount of herbicide absorbed to 35% in A. theophrasti and 60% in S. faberi 72 HAT. Translocation of absorbed 14C-glyphosate in both formulations (with or without AMS) was greater for S. faberi than A. theophrasti 72 HAT. For A. theophrasti, 17% of 14C absorbed in Ipa and Tms formulations were translocated out of the treated leaf, whereas additions of AMS increased the amount translocated to 25 and 23% for Ipa and Tms, respectively. The largest portion of translocated 14C moved to tissues above the treated leaf. For S. faberi, 37% of absorbed 14C in both Ipa and Tms formulations were translocated out of the treated leaf 72 HAT, whereas 42% translocated when 1% AMS was added to both formulations. In S. faberi, the largest portion of 14C-glyphosate translocated to tissues below the treated leaf. In summary, no differences were found between Ipa and Tms formulations in both weed species.

The GTP-driven component of Ca2+ uptake in red beet (Beta vulgaris L.) plasma membrane vesicles was further characterized to confirm its association with the plasma membrane Ca2+-trans-

No abstract