Plant Science Letters最新文献

Protease activity was determined in oat leaf protoplasts after isolation and washing. Protoplasts were isolated with a cellulase R-10, macerozyme R-10 mixture, which contains high proteolytic activity. Proteases in this cell wall-degrading enzyme mixture were inactivated by heating the enzyme preparation at 50°C for 10 min at pH 6.5. This treatment did not impair the cell wall-degrading activity. Protease activity in protoplasts isolated with heated enzyme was similar after washing to that in protoplasts isolated with untreated enzymes. This provided proof that contaminating proteases were effectively removed during protoplast washing and that the protease activity measured in isolated protoplasts was derived from the protoplasts themselves.

Soybean (Glycine max L. cv. Williams '79) root microsomal suspensions exhibit two proton-pumping activities. The largest proportion of activity, localized at a low density on sucrose gradients and inhibited by nitrate, does not correspond to markers for Golgi, endoplasmic reticulum, plasma membrane, or mitochondria and presumably originates from the tonoplast. There is a small shoulder of proton-pumping activity, which is sensitive to vanadate, localized at a higher density on gradients (37%, w/w). This activity coresponds fairly well with vanadate-sensitive ATPase activity (39%, w/w) and a shoulder of glucan synthetase II activity (39%, w/w). The main peak of glucan synthetase II activity co-equilibriates with the mitochondrial marker cytochrome c oxidase at 43% (w/w). It is likely that this activity originates from the plasma membrane.

Mesophyll (MP) and paraveinal mesophyll protoplasts (PVMP) have been prepared with high yields from primary and trifoliate leaves of soybean, using a Cellulase CEL or CELF and Pectolyase Y-23 enzyme mixture. The PVMP, which are specialized for nitrogen metabolism and storage, are larger than MP and contain very few chloroplasts. This gives rise to considerable difference in the buoyant density of the two protoplast types, which has been exploited to obtain pure preparations of each. The MP and PVMP preparations were free of cellular debri and were stable for several days on ice. The purity of the preparations was further indicated by radial immunodiffusion assay using antibody to a glycoprotein specifically located in the paraveinal mesophyll (PVM) vacuole.

Water loss from fully turgid leaves of Solanum laciniatum Ait. plants cultured in vitro was considerably greater than that from either acclimatized plants or the parent plants from which cultures were established. Microscopic examination of lower epidermal strips from detached leaves (initially fully turgid) of transplanted and parent plants revealed 100% stomatal closure within 30 min. In contrast, half of the stomata from leaves of plants cultured in vitro were still fully open 16 h after detachment. Scanning electron microscopy revealed an absence of visible epicuticular waxes on leaves of plants cultured in vitro. However, since (1) leaf cuticles are mainly effective in controlling water loss after stomatal closure and (2) epicuticular waxes remained considerably reduced on leaves of acclimatized plants, the rapid water loss from leaves of S. laciniatum plants cultured in vitro was attributed primarily to failure of stomatal closure.

Partially purified extracts of Euglena gracilis catalyze synthesis of methionine from methyl-H₄-folate and homocysteine. A reducing system and S-adenosyl-methionine are required for full activity, thus indicating that the enzyme involved is the B₁₂-dependent methyl-H₄-folate homocysteine methyltransferase.

Affinity partitioning in an aqueous two-phase system consisting of dextran, polyethylene glycol and triazine dye-substituted polyethylene glycol was applied to investigate the affinity of NADH-dependent nitrate reductases isolated from tobacco, barley and cucumber to six triazine dyes. The alteration of the partition coefficient of nitrate reductases in the presence and absence of dye-polyethylene glycol conjugates provided qualitative data for the affinity of the enzymes to the triazine dyes. Cibacron Blue F3G-A, widely used as a ligand for purification of nitrate reductase by affinity chromatography had a low affinity for higher plant nitrate reductases compared to other triazine dyes. The strength of interaction between dye and enzyme was not dependent on the enzyme source but on the dye used. The influence of NADH on the binding of triazine dyes to nitrate reductase was also investigated.

Fructose bisphosphatase and the ‘alternate’ phosphatase, when purified to homogeneity from spinach chloroplasts, are only slightly activated upon pre-incubation with Mg²⁺, fructose bisphosphate or sedoheptulose bisphosphate, as well as by a mixture of the divalent cation and either of these sugar phosphates. This activating effect is much smaller than that produced by thioredoxin f_B and becomes null if thioredoxin f_B is present. It is therefore very unlikely that fructose bisphosphate, sedoheptulose bisphosphate or Mg²⁺ may play a significant role in the light activation of the two phosphatases.

Magnesium slowly deactivates the active fructose bisphosphatase but slightly enhances the activity of the already activated ‘alternate’ phosphatase. Owing to their slowness, these processes are likely not to play any significant biological role.