Anion absorption by etiolated wheat leaves after vacuum infiltration

Energy Supply and Light-enhanced Chloride Uptake in Wheat Laminae

The light-supported component of (36)Cl uptake from 5 mM K(36)Cl by green laminae, either chopped or vacuum-infiltrated, of Triticum aestivum L. seedlings has been determined by subtraction of dark uptake values from light uptake values and the energy sources for the uptake elucidated on the basis of the effects of 3-(3,4-dichlorophenyl)-1,1 dimethylurea (DCMU), carbonyl cyanide p-trifluoromethoxy-phenylhydrazone (FCCP), antimycin A(1) (AA), and N(2) on light and dark uptake. The light-supported Cl(-1) uptake is shown to be partially inhibited by DCMU or AA but unaffected or stimulated by FCCP or N(2). There is no additive effect on inhibition caused by DCMU + N(2) or FCCP + AA but there is an added inhibition caused by DCMU + AA, DCMU + FCCP, and by FCCP or AA in anaerobic conditions. The effect of these inhibitors on photosynthetic gas exchange of chopped tissue has also been determined. On the basis of the results it is concluded that the uptake of Cl(-), supported in the dark by oxidative phosphorylation, is enhanced by light and may be supported by cyclic and non-cyclic electron-flow energy. Uptake is not obligatorily linked to any one energetic pathway and there may be switching from one source to another.

Effect of vacuum infiltration on photosynthetic gas exchange in leaf tissue

Using a manometric method, photosynthetic oxygen evolution and (14)CO(2) fixation have been determined for leaf tissue of Triticum aestivum L., Hordeum vulgare L., Phaseolus vulgaris L., and Lemna minor L. Approximately similar values in the range 0.2 to 0.4 millimoles grams fresh weight(-1) hour(-1) were obtained for both gases. In tissue subjected to vacuum infiltration, O(2) evolution and (14)CO(2) fixation were barely measurable. It is considered that the elimination of photosynthetic gas exchange results from a decreased supply of CO(2) to the chloroplasts. Chopping wheat laminae also leads to a reduction in photosynthetic gas exchange, slices 1 millimeter or less giving only 10 to 20% of the value for whole tissue. Respiration is unaffected by either treatment. Carbonic anhydrase did not improve photosynthetic gas exchange in infiltrated tissue. The use of sliced or vacuum-infiltrated leaf tissue in photosynthetic studies is discussed.

Light-enhanced Chloride Uptake by Wheat Laminae: A Comparison of Chopped and Vacuum-infiltrated Tissue

The time course of (36)Cl(-) uptake from 5 mm KCl by 1.5-mm leaf segments of Triticum aestivum L. seedlings has been determined over 24 hours both in the light and in the dark. A light-enhanced uptake of Cl(-) develops after a few hours. Using whole laminae which have been water-injected by vacuum infiltration, a light-enhanced uptake is apparent from zero time. Uptake values achieved in the light by the two types of tissue are similar but in the dark there is a restricted uptake by the whole infiltrated laminae. It is considered that the slower uptake by whole laminae relative to chopped tissue in the dark is due to cuticular resistance to solute penetration, whereas in the light the impediment is overcome by stomatal opening. A light-enhanced uptake unrelated to stomatal opening is discernible in both tissues. Its energetic basis has not been defined but may be related to substrate exhaustion. The absorption mechanism is not impaired by vacuum infiltration.

Cortical cell fluxes and transport to the stele in excised root segments of Allium cepa L. : I. Potassium, sodium and chloride

From compartmental analysis of radioisotope elution measurements, concentrations and fluxes of K(+), Na(+) and Cl(-) were estimated for cortical cells in root segments of onion, Allium cepa L., relative to a complete nutrient solution. The transported fraction of the total efflux was estimated separately. With the Ussing-Teorell flux ratio equation as the criterion, it was concluded that all three ions were actively accumulated from the outside medium into the cytoplasm and that only Na(+) was actively accumulated into the vacuole. K(+) and Cl(-) moved passively, in both directions across the tonoplast. Failure to account for leakage from the stele via the segment cut ends resulted in an over-estimate of exchange across the tonoplast but did not alter the conclusions qualitatively. The consequences of changing the assumed value of the tonoplast electrical potential (from 0 to+10- mV), and the effects of different experimental procedures, were also assessed, and found not to affect the main conclusions significantly. Separate measurement of ions leaking from the segment ends revealed that Na(+) was transported almost exclusively in an acropetal direction in the stele. Cl(-) appeared at both ends of the segments in similar amounts and K(+) was transported mainly in the basipetal direction. The implications of these findings for the mechanism and site of ion selectivity are discussed.

Metabolic regulation in the senescing tobacco leaf: I. Changes in pattern of p incorporation into leaf disc metabolites

Changes in phosphate metabolism were explored in discs from tobacco (Nicotiana tabacum) leaves of three contrasting types: green leaves which were fully expanded and attached to the plant, leaves which had yellowed following excision and dark starvation, and leaves which had yellowed while attached to the plant. 2,4-Dinitrophenol at 10(-5)m stimulated the respiration rate of discs from green and yellow-detached leaves only slightly, but markedly stimulated that of discs from yellow-attached leaves. Following a 10-minute uptake period the incorporation of (32)P-orthophosphate into phosphate esters and lipids of discs from yellow-detached leaves was resistant to 2,4-dinitrophenol, whereas in discs from green and yellow-attached leaves it was inhibited by 2,4-dinitrophenol. Incorporation into a salt-soluble fraction containing unidentified nucleotide material showed converse behavior in that it was stimulated by 2,4-dinitrophenol in discs from green and yellow-attached leaves; in discs from yellow-detached leaves it was resistant to 2,4-dinitrophenol. In discs from yellow-detached and yellow-attached leaves there was a shift in the labeling pattern of phosphate esters toward increased label in hexose phosphates at the expense of adenine nucleotides, 3-phosphoglycerate, and phosphoenolpyruvate. It is concluded that incorporation into phosphate esters in discs from yellow-detached leaves is by substrate level phosphorylation coupled to enhanced aerobic glycolysis. In discs from yellow-attached leaves, on the other hand, incorporation depends on oxidation phosphorylation, and it is suggested that the shift in labeling pattern is caused by senescence-induced changes in activity of glycolytic enzymes.