Absorption changes of P-700 reversible in milliseconds at low temperature in Triton-solubilized photosystem I particles.

Triton-solubilized Photosystem I particles from spinach chloroplasts exhibit largely reversible P-700 absorption changes over the temperature range from 4.2 K to room temperature. For anaerobic samples treated with dithionite and neutral red at pH 10 and illuminated during cooling, a brief (1 microseconds) saturating flash produces absorption changes in the long wavelength region that decay in 0.95 +/- 0.2 ms from 4.2 to 50 K. Above 80 K a faster (100 +/- 30 microseconds) component dominates in the decay process, but this disappears again above about 180 K. The major decay at temperatures above 200 K occurs in about 1 ms. The difference spectrum of these absorption changes between 500 and 900 nm closely resembles that of P-700. Using ascorbate and 2.6-dichlorophenolindophenol as the reducing system with a sample of Photosystem I particles cooled in darkness to 4.2 K, a fully reversible signal is seen upon both the first and subsequent flashes. The decay time in this case is 0.9 +/- 0.3 ms.     

Kinetics of reduction of the oxidized primary electron donor of Photosystem II in spinach chloroplasts and in Chlorella cells in the microsecond and nanosecond time ranges following flash excitation

Absorption changes (ΔA) at 820 nm, following laser flash excitation of spinach chloroplasts and Chlorella cells, were studied in order to obtain information on the reduction time of the photooxidized primary donor of Photosystem II at physiological temperatures.In the microsecond time range the difference spectrum of ΔA between 750 and 900 nm represents a peak at 820 nm, attributable to a radical-cation of chlorophyll a. In untreated dark-adapted material the signal can be attributed solely to P⁺?700; it decays in a polyphasic manner with half-times of 17 μs, 210 μs and over 1 ms. The oxidized primary donor of Photosystem II (P⁺_II) is not detected with a time resolution of 3 μs. After treatment with 3–10 mM hydroxylamine, which inhibits the donor side of Photosystem II, P⁺_II is observed and decays biphasically (a major phase with $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 20–40 μ}\text{s}$, and a minor phase with $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{? 200 μ}\text{s}$), probably by reduction by an accessory electron donor.In the nanosecond range, which was made accessible by a new fast-response flash photometer operating at 820 nm, it was found the P⁺_II is reduced with a half-time of 25–45 ns in untreated dark-adapted chloroplasts. It is assumed that the normal secondary electron donor is responsible for this fast reduction.     

Fractionation of cricket testis nuclei on gradients of colloidal silica for study of basic protein changes during spermiogenesis

Nuclei isolated from testes of the house cricket were centrifuged in a gradient of colloidal silica with a density range of about 1.12 to 1.18 g/ml. Fractions were collected from the bottom to the top of the gradient, and the types of nuclei in them were classified by phase microscopy. The distribution of nuclear types in the gradient indicated relatively large increases in nuclear density during spermatogenesis, and that silica-gradient centrifugation can readily yield fractions enriched for nuclei of specific developmental stages needed to study basic protein changes during sperm development. Basic proteins could be extracted from nuclei spun through silica if they were washed with polyvinylpyrrolidone. The histones in different fractions of nuclei were analysed electrophoretically. Fractions of spermatocyte and early spermatid nuclei contained histones of the somatic types as their only basic proteins. Fractions with mixtures of mid-spermatid and earlier nuclei also yielded somatic histones primarily. Essentially pure samples of late spermatid nuclei were obtained. They lacked somatic histones. In one fraction of late nuclei, the spermatid-specific histones TH1 and TH2 were the major proteins present. In another, two additional histone-like components, not detected in previous studies, were also prominent.     

Nitrate reductase activity and growth in Paul's Scarlet rose suspension cultures in relation to nitrogen source and molybdenum

Growth and nitrate reductase activity were measured in Paul's Scarlet rose cell suspensions, cultured in media purified from molybdenum and containing nitrate or urea as sole nitrogen source with or without added Mo. Urea could replace nitrate to yield 80% of the fresh weight in nitrate medium. Nitrate reductase activities were compared by in vivo and in vitro assays. The latter varied due to inactivation during extraction. Compared with activities in cells in complete NO₃ ^- medium, activity in NO₃ ^--Mo cells was reduced to 30% and, in urea-grown cells, to trace amounts. Increases in nitrate reductase activity were found when NO₃ ^- alone was added to NO₃ ^- or urea+Mo cultures. In NO₃ ^--Mo cultures, Mo alone or with NO₃ ^- caused a similar increase in activity, whereas urea-Mo cultures required both NO₃ ^- and Mo for enzyme induction.Abbreviations FAD flavin adenine dinucleotide - Mo molybdenum - NADH reduced nicotinamide adenine dinucleotide - NO₃ ^-+Mo standard MX₁ culture medium - NO₃ ^--Mo MX₁ medium purified of Mo and used for continuous subculture with nitrate - NR nitrate reductase - PSR Paul's Scarlet rose - PVP polyvinylpyrrolidone - U urea - U+Mo MX₁ medium containing urea instead of nitrate - U-Mo MX₁ medium containing urea instead of nitrate and also purified of Mo     

Gas exchanges by Phymatotrichum omnivorum in a closed,axenic system

Gas exchanges byPhymatotrichum omnivorum were studied in a closed, axenic system. The fungus liberated CO₂ and ethylene, and appeared to utilize N₂. Over a 44-day test period, CO₂ increased from 0.1 to 312.8 ml/liter. Oxygen decreased from 211 to 17.8 ml/liter and N₂ decreased from 789 to 669.5 ml/liter during the same period. The combined uptake of N₂ and O₂ was equal to the release of CO₂ in the ambient gas.A rapid increase in ethylene was observed 14 to 28 days after the flasks were inoculated (15 to 160 nliter/liter). Mycelial strands and sclerotial initials formed on the flask sides, but mature sclerotia did not develop.Supported in part by Cooperative Agreement 70-178 from Cotton Incorporated. A contribution of the Texas Agricultural Experiment Station.     

Alkali solubility of hemicelluloses in relation to delignification

The polysaccharide composition of bark from Pinus radiata, Salix fragilis, and Populus euramericana has been determined. All the barks contained lower levels of cellulose and hemicellulose than the corresponding woods; cellulose: hemicellulose ratios were also lower in the barks. Alkali extracted all of the hemicellulose-A but only half of the hemicellulose-B from P. radiata bark without prior delignification. Similar alkaline extraction removed almost all of the hemicellulose (A + B) from ryegrass leaves without delignification. With the other samples tested only a part of the hemicellulose A and B is extracted without delignification. It is suggested that the polysaccharide so extracted represents wall hemicellulose which is not linked to lignin or other wall constituents by alkali-stable links.     

Inhibition of ion accumulation in maize roots by abscisic acid

Summary An inhibition of root growth, a decrease in the amount of potassium (as ⁸⁶Rb) and phosphate (³²P) accumulation by the root, and a partial depolarization of transmembrane electropotential were observed to develop with a similar time course and to a similar extent when intact maize (Zea mays L.) roots were treated with 10^-5 M abscisic acid (ABA). Potassium uptake was inhibited by ABA when excised, low-salt roots were bathed in KCl, KH₂PO₄, or K₂SO₄. ABA did not affect the ATP content of the tissues, the activity of isolated mitochondria, nor the activity of microsomal K⁺-stimulated ATPases.