Planta

Phillips, Donald

doi: 10.1007/BF00387034pmid: 24488191

The effect of exogenous abscisic acid (ABA) on root nodule formation in Pisum sativum cv. Alaska was examined. ABA supplied to the roots at 1.9×10-6M reduced the number of nodules/plant 61% without affecting root or shoot growth. The first noticeable inhibition of nodulation occurred at 3.8×10-7M ABA. ABA at a concentration of 1.9×10-6M inhibited neither root hair formation nor infection of root hairs by Rhizobium leguminosarum. Similar numbers of infection threads penetrated the cortex in both control and treated plants. ABA concentrations of 3.8×10-6M had no effect on the doubling time or maximum density of R. leguminosarum in pure cultures. Normal nodule formation involves a polyploid cortical proliferation. This response to rhizobial infection can be imitated by culturing 1-mm pea-root segments on a medium containing 4.7×10-6M kinetin. Under these conditions a highly significant reduction in the number of polyploid mitoses after 72 h is produced by 3.8×10-8M ABA. A maximum inhibition of 68% was found with 3.8×10-6M ABA. A similar range of ABA concentrations also inhibited the cytokinin-induced cell division in soybean callus. It is concluded that ABA reduces the number of root nodules/plant by inhibiting the cortical cell divisions required for root nodule formation.

Hadley, G.; Johnson, R.; John, D.

doi: 10.1007/BF00387035pmid: 24488192

Electron microscopy of protocorms of Dactylorhiza purpurella infected with a symbiotic Rhizoctonia sp. showed that the intracellular hyphae examined did not penetrate the plasmalemma of the host cell. Walls of hyphae within cells bore many hemispherical protuberances over which the host plasmalemma was closely pressed. we estimate that these protuberances would increase the area of contact between hyphae and host plasmalemma by about 15%. They were not found on hyphae growing on agar. Except for these protuberances, and some vesicles or tubules which invaginated the fungus plasmalemma, no other structures were seen which could be suggested to be adaptations to transport across the living fungus-host interface.

Hall, Shelagh; Baker, D.; Milburn, J.

doi: 10.1007/BF00387036pmid: 24488193

Exudate can be obtained from incisions made in the bark of the stem of actively growing Ricinus plants. 14C-labelled assimilates from a fed leaf are rapidly detected in the exudate. This movement was both acropetal and basipetal from the fed leaf, at rates of over 100 cm h-1. Estimated rates within intact plants were 80–84 cm h-1.

Eschrich, Walter; Evert, Ray; Heyser, Wolfgang

doi: 10.1007/BF00387037pmid: 24488194

Sieve-tube exudate which appears on cut surfaces of stems of Cucurbita maxima as distinct droplets has been depicted in electron micrographs of longitudinal sections of the phloem. The exudate, which was produced from mature sieve tubes only, contained filaments of P-protein, but no mitochondria or vesicles of endoplasmic reticulum. The water-soluble part of the exudate contained at least 12 proteins, as shown by disc-electrophoresis. Enzymic activity was found for peroxidases, acid phosphatases, and aldolases. Color tests and assays for other enzymes, including ATPase, fructokinase, several dehydrogenases, and UDP-glucose: D-fructose-2-glucosyl transferase, gave negative results. With repeated cutting of a stem, the protein content of the exudate increased, while the amount of exudate decreased.

Pahlich, E.

doi: 10.1007/BF00387038pmid: 24488195

Several investigations on the properties of glutamate dehydrogenase from plant sources indicate that the enzymatic activity (reductive amination) follows a Michaelis-Menten-type kinetic when velocity is plotted versus rising concentrations of the substrate α-ketoglutarate. In the course of our investigations on the effect of SO2 on pea plant enzymes we found that SO 4 2- , added as (NH4)2SO4 to the assay system, causes this type of activity response because of its ability to function as an activator. When (NH4)2SO4 is replaced by NH4Cl in the in vitro system however, activity response is sigmoidal. Addition of competitive inhibitor to the latter system again gives rise to a sigmoidal kinetic with reduced initial velocities. Identical kinetic behaviour is observed when either 120 fold enriched enzyme from shoots or highly purified glutamate dehydrogenase from pea roots is used, a fact which justifies the assumption that the enzyme from pea plants belongs to the MIC-type of regulatory proteins (modulator independent cooperativity). The activity response caused by other effectors, especially purine nucleotides, is discussed with regard to the above findings.

Stuart, Tim; Gaffron, Hans

doi: 10.1007/BF00387039pmid: 24488196

In our earlier work we have shown that hydrogen photoproduction by photosystem I of Scenedesmus does not require O2 evolution or cyclic photophosphorylation but must be due to non-cyclic electron flow from organic substrate(s) through photosystem I to hydrogenase, where molecular H2 is released. The kinetics of this reaction are rather complex, in that H2 photoproduction by Scenedesmus evidently occurs in two phases: a rapid initial phase which depends upon the dehydrogenation of a “pool” of H donors, and a later and slower second phase which is limited by the flow of electrons from fermentation. When adapted cells were incubated in the dark with an inhibitor (Cl-CCP or salicylaldoxime), the pool utilized by photosystem I gradually disappeared. However, the pool gave a rapid rate of hydrogen photoproduction when the adapted cells were illuminated immediately after adding the inhibitor. The rate at which the pool was utilized depended upon the light intensity and was not light-saturated at the highest intensity tested (3.4×103 μW cm-2).

Mitchell, John

doi: 10.1007/BF00387040pmid: 24488197

Ultraviolet light-induced, bleached Euglena clones exhibit synchronous steps of cell division in response to daily cycles of light and dark. The cyclic division activity, in the bleached cells, will persist in constant lighting conditions with a period, independent of temperature, of about 24 h. This persisting rhythm of cell division supports the hypothesis that this phase of the cell cycle may be coupled to the fluctuations of the endogenous circadian clock of the cell.

Warren, Richard; Hunt, Gordon

doi: 10.1007/BF00387041pmid: 24488198

Pericarp disks from the fruit of the jackbean (Canavalia ensiformis) when exposed to 14CO2 for 2 days carried out photosynthesis and the canavanine extracted from the tissue was labeled with the radioisotope. When beef liver arginase was allowed to react with this canavanine the products were homoserine, canaline, urea and an unknown compound. The activity ratio of C4:C1 compounds was close to 2:1. No label could be detected in the canavanine from leaves exposed in the same way to 14CO2 and it was concluded that normally canavanine synthesis occurs in the pericarp chlorenchyma.

Evert, Ray; Eschrich, Walter; Eichhorn, Susan

doi: 10.1007/BF00387042pmid: 24488199

The sieve-plate pores of sieve elements in leaf veins of Hordeum vulgare, fixed in glutaraldehyde with postfixation in osmium tetroxide, were lined by the plasmalemma and variable amounts of callose. All pores were filled with endoplasmic reticulum, which was continuous from cell to cell. Mature sieve elements lacked P-protein.

Abbott, A.

doi: 10.1007/BF00387043pmid: 24488200

Analysis of pea root tips taken from attached seedling roots and excised roots cultured in vitro has revealed major differences in cell constituents. The cells of cultured roots have only 40% and 13% of the protein and amino acid content of attached root cells. The nucleic acid content of cultured root cells was shown to be only 20% and 27% of the RNA and DNA respectively found in attached roots. It is suggested that there is excess nucleic acid in whole plant tissues above that required for transfer of genetic information necessary for normal growth and differentiation of root cells.