Days Of Illumination Research Articles

Light‐induced glycoalkaloid accumulation of potato tubers (Solanum tuberosum L)

The total glycoalkaloid concentration of non-sprouted potato tubers, cvs Marfona, Fianna, Maris Piper, Kestrel and Golden Wonder, was measured following 15 days of continuous illumination (250 µmol m−2 s−1 photosynthetically active radiation) using high-performance liquid chromatography. Comparisons were made of the influence of four sources of illumination: fluorescent tube-type warm white, high-pressure sodium, high-pressure mercury types MB/U and MBFR/U. Irrespective of cultivar, glycoalkaloid concentrations of tubers placed in the dark remained relatively constant from day 0 to day 15 and did not exceed food safety values of 200 mg kg−1 FW. A highly significant cultivar, light and cultivar × light (P < 0.01) interaction was recorded. Cultivar Kestrel was shown to be light-sensitive with high rates of glycoalkaloid accumulation irrespective of light source, and cv Maris Piper was demonstrated to be light-insensitive. In the majority of cultivars tested, maximal rates of glycoalkaloid accumulation were recorded following exposure of tubers to sodium or fluorescent light, and minimal rates of accumulation were recorded following exposure of tubers to mercury (MB/U and MBFR/U) illumination. In virtually all cases glycoalkaloid concentrations steadily increased with time during light exposure with no indication of cessation. In some instances the α-chaconine/α-solanine ratio decreased over 15 days of illumination (P < 0.05), indicating enhanced α-solanine synthesis over that of α-chaconine. The implications of these results in terms of consumer safety are discussed. © 1999 Society of Chemical Industry

Light-induced glycoalkaloid accumulation of potato tubers (Solanum tuberosum L)

The total glycoalkaloid concentration of non-sprouted potato tubers, cvs Marfona, Fianna, Maris Piper, Kestrel and Golden Wonder, was measured following 15 days of continuous illumination (250 µmol m−2 s−1 photosynthetically active radiation) using high-performance liquid chromatography. Comparisons were made of the influence of four sources of illumination: fluorescent tube-type warm white, high-pressure sodium, high-pressure mercury types MB/U and MBFR/U. Irrespective of cultivar, glycoalkaloid concentrations of tubers placed in the dark remained relatively constant from day 0 to day 15 and did not exceed food safety values of 200 mg kg−1 FW. A highly significant cultivar, light and cultivar × light (P < 0.01) interaction was recorded. Cultivar Kestrel was shown to be light-sensitive with high rates of glycoalkaloid accumulation irrespective of light source, and cv Maris Piper was demonstrated to be light-insensitive. In the majority of cultivars tested, maximal rates of glycoalkaloid accumulation were recorded following exposure of tubers to sodium or fluorescent light, and minimal rates of accumulation were recorded following exposure of tubers to mercury (MB/U and MBFR/U) illumination. In virtually all cases glycoalkaloid concentrations steadily increased with time during light exposure with no indication of cessation. In some instances the α-chaconine/α-solanine ratio decreased over 15 days of illumination (P < 0.05), indicating enhanced α-solanine synthesis over that of α-chaconine. The implications of these results in terms of consumer safety are discussed. © 1999 Society of Chemical Industry

Plastid Transformation in Greening Potato Tuber Tissue

Summary The process of amyloplast-chloroplast transformation in illuminated potato tuber tissue was studied by light and electron microscopy and by analyses of pigment and protein contents. Transformation of amyloplasts into amylochloroplasts begins after 1 day, and the first DAB positive thylakoids appear after 2 days of illumination, indicating the beginning of photosynthetic activity in the thylakoids. At the same time, the appearance of some membrane proteins as well as the increase of chlorophyll and carotenoid contents confirm development of the thylakoid system.

Transition Form of Microbodies. Overlapping of Two Sets of Marker Proteins During the Rearrangement of Glyoxysomes into Leaf Peroxisomes

Several forms of microbodies have been characterized on the basis of their biochemical functions. We have investigated cucumber cotyledons which house two different microbody forms during their development. In these cells, a shift from organelles with the enzymes of beta-oxidation and glyoxylate cycle to peroxisomes with the enzymes of the photosynthetic C2-cycle can be induced by light. The transition state and the time course of changes was studied at different levels of gene expression during the first 2 days of illumination, by quantifying the rate of de novo protein synthesis in cotyledons and by measuring the mRNA activities in vitro. Synthesis and turnover of particular proteins were determined during the transition stage by immunoprecipitation of malate synthase, isocitrate lyase, catalase, multifunctional protein, and thiolase, and quantified by fluorography. From the mRNA activities and the rate of protein synthesis, gene expression for enzymes of the glyoxylate cycle and beta-oxidation started to decrease 24-36 h after onset of continuous light. At that time the rate of synthesis of glycolate oxidase, a leaf peroxisomal marker, is already maximal. By pulse-chase experiments 0-48 h after the onset of light the speed and intensity of protein turnover were measured. Rates of proteolytic degradation of individual enzymes indicated that the different enzymes were not lost simultaneously or all at once. This excludes a destruction of the whole organelle by the lytic compartment.

Chlorophyll‐protein levels and degree of thylakoid stacking in radish chloroplasts from high‐light, low‐light and bentazon‐treated plants

The level of 7 chlorophyll‐carotenoid‐proteins was determined in chloroplasts from radish seedlings (Raphanus sativusL. var. Saxa Treib) grown in high‐light (HL; 90 W m−2and low‐light (LL; 10 W m−2) growth conditions with and without application of the photosystem 2 herbicide bentazon (10−4M) and compared with the degree of thylakoid stacking.The photosynthetic apparatus of HL‐chloroplasts contains higher proportions of the photosystem 1 chlorophylla‐proteins CPI and CPIa than LL‐chloroplasts or chloroplasts from bentazon‐treated plants.In LL‐chloroplasts and in chloroplasts from bentazon‐treated plants a higher proportion of light‐harvesting chlorophylla/b‐proteins (LHCP1, LHCP2, LHCP3, LHCPy) is found. Bentazon treatment changes the proportion of LHCPs to about the same levels under both HL and LL‐growth conditions. The amounts of free chlorophyll found in bentazon chloroplasts (27–29%) is higher than in the HL or LL‐controls (16–18%).The increase in degree of thylakoid stacking (% proportion of appressed membranes per total chloroplasts membranes) of LL‐chloroplasts as compared to HL‐chloroplasts of 7 to 9% (3rd to 5th day of illumination) is paralleled by a similar increase in the LHCPs of 5% and 8% (3rd and 5th day). The importance of light harvesting chlorophylla/b‐proteins as a prerequisite for thylakoid stacking is discussed.

The role of xanthoxin in the inhibition of pea seedling growth by red light

Intermittent periods of red light illumination inhibit the growth of dwarf pea seedlings within 1 day and stop length increase completely in 3 days. Cis,trans-xanthoxin is synthesized within the plant during the 1st day of illumination and reaches a maximum level on the 3rd day. The red light treatment also causes an increase in the levels of violaxanthin, linoleic acid and peroxidase, lipoxygenase and carotene-bleaching activities in the plant. The possible control of xanthoxin production is discussed.

Photophosphorylation during Chloroplast Development in Red Kidney Bean

Cyclic phosphorylation with phenazine methosulfate and noncyclic phosphorylation and reduction with ferricyanide were detected in isolated chloroplasts from greening bean leaves after 3 to 4 hours of illumination. Activity commenced when rapid synthesis of chlorophyll was initiated. Rates of photophosphorylation were comparable to mature levels by 15 to 18 hours of development. Photoreduction of ferricyanide attained a peak value by 12 hours of illumination and subsequently fell to normal levels by 15 to 18 hours. With ferricyanide, the P/e(2) ratios were initially less than 0.1 but were close to 1.0 after 18 hours of illumination. The data suggested that photosystems I and II appeared concomitantly in the chloroplast but were not fully operative until later in development. Proplastids and immature chloroplasts exhibited high capacities to reduce ferricyanide in the dark. The rates of dark reduction rapidly diminished to low levels by 15 hours of illumination when normal rates of photochemical activity were observed. After a 2-to 3-day lag, a rapid increase in leaf fresh weight was noted at the time total chlorophyll content reached steady state values on a fresh weight basis. With fresh weight as an index of growth, primary leaves completed their development after 6 to 7 days of illumination.

Plasma and pituitary luteinizing hormone and peripheral plasma oestradiol concentrations in the normal oestrous cycle of the rat and after experimental manipulation of the cycle.

SUMMARY Plasma and pituitary luteinizing hormone (LH) concentrations were measured by radioimmunoassay at different stages of the normal 4- and 5-day oestrous cycle of rats. Plasma levels were low except between the afternoon of pro-oestrus and the morning of oestrus when levels were high but variable. Pituitary LH content and concentration were less consistent but averaged values showed a steady rise from a low level after ovulation to a peak on the afternoon of pro-oestrus, and a rapid fall that evening when plasma levels rose rapidly. No significant differences were observed in plasma LH between 4- and 5-day cycles; in particular there was no reduction at metoestrus or dioestrus-1 or increase on the evening of dioestrus-2. Plasma oestradiol was already high on the morning of dioestrus-2 in some rats and in all rats by that evening. On the morning of pro-oestrus in the 5-day cycle, plasma oestradiol was still high but somewhat lower than at the corresponding stage in the 4-day cycle. Blocking ovulation by administration of sodium pentobarbitone at prooestrus in a 4-day cycle prevented the rise in plasma LH and the fall in pituitary content. Blocking generally failed in animals whose plasma LH had reached the level of 20 ng/ml or more at the time of injection. Plasma oestradiol levels on the morning of the expected day of oestrus were higher than normal in animals in which ovulation was blocked by pentobarbitone but were below pro-oestrous values. In the anovulatory state induced by exposure to constant light no major increase in plasma LH was detected after 24 days of illumination or after 3 months exposure. Animals rendered anovulatory by injection of testosterone propionate on the 4th day of postnatal life had low plasma LH levels as adults. All three groups had a low pituitary LH content. The animals exposed to long-term light and those treated with androgen generally had plasma oestradiol concentrations below the peak levels seen on the morning of pro-oestrus in the normal cycle.

Gonadotrophin content of pituitaries of rats in constant estrus induced by continuous illumination.

LH and total gonadotrophin of the anterior pituitaries of cycling rats under normal lighting and rats in constant vaginal estrus (CVE) induced by continuous illumination were compared. The ovarian ascorbic acid depletion method and the uterine weight increase in immature mice were employed for LH and total gonadotrophin assays, respectively. Most of the rats placed in constant light developed continuous vaginal cornification within 30 days. There was an increase in pituitary weight and the ovaries were smaller than those of the controls. The pituitary LH content and concentration were markedly decreased in rats in CVE after 50 and 100 days of illumination. Administration of progesterone, SC-13664 (an antiestrogenic compound), or clomiphene or oophorectomy caused an increase in LH. The pituitary total gonadotrophin of rats in CVE was similar to that of normal rats and increased under treatment with SC-13664 or clomiphene and after oophorectomy. Progesterone caused no change.(Endocrinology77: 529,1965)

An estimate of protein turnover in growing tobacco plants

dl-Glutamic acid-1- 14C was injected into growing tobacco plants and the rate of 14CO 2 release was measured. After a period in light to allow isotope to become incorporated into protein, plants were placed in the dark to eliminate by respiration radioactivity from readily accessible pools and metabolically labile proteins. Plants were then placed in the light and growth allowed to resume. There was only negligible incorporation into polysaccharide fractions. The protein fraction contained 71%, of the labelled carbon, and soluble amino acids and other metabolic intermediates accounted for 22%, of the total activity of the plant. From the rate of 14CO 2 release an apparent half-life of 7·0 days was calculated for the protein fraction. This calculation assumes that both the protein fraction and the intermediates contribute isotope to the 14CO 2, but that the intermediate pool is continuously replenished from the protein. It is also assumed that a steady state of growth is re-established on the third day of illumination.

The demonstration of photochemical reducing sites in Chromatium sp

DYAn [I] used blue tetrazolium to demonstrate intracellular particles exhibiting marked reducing activity in illuminated and in non-illuminated plant tissues. The blue-black reduced tetrazolium appeared in granules dispersed throughout the cytoplasm of blue-green algae and within the intracellular chloroplasts of green algae and higher plants. Since the dye was reduced more rapidly and at more numerous sites in illuminated than in non-illuminated cells, she concluded that these stained particles probably represented grana. We have demonstrated similar sites in isolated bean leaf chloroplasts [4]. The present investigation was undertaken to adapt the blue tetrazolium technique to the study of the photosynthetic bacterium, Chromatium sp., and to demonstrate, if possible, the intracellular loci of photochemical reduction. The preliminary results reported here indicate that this technique is more convenient and may prove to be more specific and more reliable than growth or respirometric methods for studying the photoskythetic and dark metabolism of specific substrate by these organisms. Cells were grown in liquid media containing either sodium sulfide or sodium thiosulfate [3], harvested by centrifugation, washed twice with and finally resuspended in 0.01 M phosphate buffer, pH 7.0. The indicator solution was prepared by dissolving 1 mg of tetrazolium blue (Nutritional Biochemicals Corporation) in 30 ml of 0.03 M phosphate buffer, pH 7.0. Solutions of substrate were prepared in tap water and contained either 0.5 per cent Na,S * 9 H,O or 1.0 per cent Na,S,O, * 5 H,O. One ml of the indicator solution was mixed in a Thunberg tube with 1 ml of a IO per cent suspension of cells and 1 ml of either tap water or substrate solution. The tubes were evacuated for three minutes with a water aspirator and sealed. All tubes were prepared in duplicate. One series was placed in a water bath at 27°C and illuminated from below with a loo-watt incandescent bulb in a reflector desk lamp. The second series was completely wrapped with aluminium foil to exclude light and placed in the same bath. The incubation period was varied from I to 24 hours. Although we have not been able to prevent photoreduction of tetrazolium in illuminated cells lacking exogenous subtrate, we have succeeded in delaying for more than an hour any detectable evidence for the reduction by using cells which had been depleted of interfering endogenous materials (starved cells). Usually, intense illumination for two hours was sufficient to starve buffered suspensions of cells which had been harvested from thiosulfate medium. Cells grown in sulfide medium normally contained intracellular sulfur droplets which disappeared only after several days of illumination. Consequently, sulfid-grown cells were not starved for the tetrazolium tests.