Rhythmic changes in ribonuclease activity in relation to nucleic acid synthesis in cotyledons ofChenopodium rubrum L. and to floral induction of the plants

Ribonuclease (RNAse) activity was investigated in cotyledons ofChenopodium rubrum plants subjected to various conditions of illumination (photoperiodic induction, continuous light, induction cancelled by interrupting the dark period by a light-break). At the end of the dark period of the single inductive cycles RNAse activity of induced plants was inferior to that of plants grown in continuous light. At the end of the first two cycles the activity was lowest after the interruption of the dark period by light. The investigation of the enzyme in 6h intervals showed rhythmic changes in activity to occur in induced plants. Enzyme activity followed a pattern opposed to this of nucleic acid (NA) synthesis in the cotyledons. In plants from continuous light the enzyme activity did not show any rhythm and in plants having obtained a light-break during the inductive period the rhythm was less distinct than in the induced ones. The period length of the endogenous rhythm of NA synthesis in the cotyledons is about half as long as this of flowering and the peaks of flowering coincide with the throughs of NA synthesis.     

Effect of different sugars on flowering ofChenopodium rubrum L. in dependence on the conditions of germination and initial growth

Flowering ofChenopodium rubrum seedlings fed different sugars at a concentration of 0.6 and 0.4 M, reap, during a single inductive cycle was stimulated or inhibited in dependence on the conditions of germination and initial growth. Plants allowed to germinate at alternating temperatures of 28 °C and 5 °C showed a slower initial growth and their development was stimulated by some sugars as compared to controls induced in the absence of sugars. Plants germinated at alternating temperatures of 32 °C and 5 °C exhibited a rapid initial growth and flowering was inhibited after induction in the presence of sugars. On the other hand, development proceeded more rapidly in control plants induced in the absence of sugars after germination at the higher temperature than after germination at the lower one. The differences between the two variants quoted above could be observed also after induction by two 16 h dark cycles. Glucose and sucrose were most effective in stimulating flowering under appropriate conditions of germination. Fructose was less effective and the action of maltose was very weak. Xylose, ribose and galactose were innocuous, while arabinose, glucoso-6-phosphate and mannitol were toxic to the plants. The sugars inhibited root growth in all cases and led to an increase in starch accumulation in the underground and overground plant organs. At a concentration of 0.6 M they mostly inhibited the length of the cotyledons and, especially, of the first leaf; at a concentration of 0.4 M growth of the overground organs was stimulated. The results are discussed with respect to the possible ohanges in photoperiodic sensitivity brought about by the rate of initial growth.     

Effect of rearing conditions on nucleic acid synthesis in the brain of rats of different genotypes

The incorporation of [3H]thymidine into DNA and of [14C]uridine into RNA has been investigated in different areas of brain and in liver of inbred August rats, non-inbred Wistar rats and hybrids between male wild-type and female Wistar rats which were kept either under normal conditions or under intensive sensory stimulation at different age. DNA metabolism has been found to display tissue, regional, age-dependent and interlinear differences. Sensory stimulation influences considerably the synthesis of nucleic acids which is maximal at early ontogenesis stages and in the brain of hybrid animals.     

Localization of starch in shoot apices of vegetative and photoperiodically induced plants ofChenopodium rubrutn

Starch was determined by means of IKI reaction in shoot apices ofChenopodium rubrum plants induced to flowering by two short days and in non-induced plants. Small starch grains were already observed in the meristematic cells at an age of four days after sowing. Larger grains were found in the subapical region of the apex. Heterogeneity increases during further growth of the plants in induced, as well as in non-induced vegetative plants. Starch disappears from the cells potentially giving rise to axillary buds, while the number and size of starch grains increase in cells from which leaf primordia will be formed. This metabolic specifity of leaf and bud primordia is preserved during morphological differentiation and applies to vegetative, as well as to prefloral apices of photoperiodically induced plants. The amount of starch in the different regions of the apex is linked rather with organogenesis than with the quantitative growth in the apex.     

Nucleic acid synthesis and effect of glucose on its kinetics in cotyledons ofChenopodium rubrum l. during photoperiodic induction

In cotyledons ofChenopodium rubrum L. polydisperse RNA is synthesized in the region of the low molecular weight RNAs during photoperiodic induction. After short-time labelling the rate of 4s RNA synthesis was always higher in induced plants than in plants having obtained a light-break in the middle of the dark period. When glucose was added to the nutrient medium during the dark period of a single photoperiodic cycle the rate of nucleic acid (NA) synthesis was higher in non-induced plants than in induced ones at the termination of the dark period. In plants induced by two cycles in the absence of glucose the rate of NA synthesis at the termination of the second dark period was higher in induced than in non-induced plants. This difference is due to the differential kinetics of NA synthesis during darkness. In plants induced in the presence of glucose the peak of the rhythm in NA synthesis was advanced by 4 h relative to that found in plants induced in the absence of sugar. Thus, the termination of the dark period coincided with the negative slope of the oscillation in plants induced in the presence of glucose, while in plants having obtained a light-break NA synthesis decreased only slightly after having attained its peak. In plants induced in the absence of glucose the termination of the dark period coincided with the peak in the rhythm in NA synthesis. The rhythm in NA synthesis of the cotyledons during the dark period of an inductive cycle is out of phase with the rhythm in flower initiation.     

Studies on chemical composition ofChenopodium album L.

Summary Field studies conducted at the Haryana Agricultural University, Hissar, India for two years revealed thatChenopodium album L. contained very high degree of nitrogen, phosphorus, potassium, calcium, magnesium, iron and manganese. Its nutrient content declined with advancement in age of the plant.     

The role of the storage carbon of cotyledons in the establishment of seedlings of Hymenaea courbaril under different light conditions

BACKGROUND AND AIMS: Hymenaea courbaril (Leguminosae-Caesalpinioideae) is a tree species with wide distribution through all of the Neotropics. It has large seeds (approx. 5 g) with non-photosynthetic storage cotyledons rich (40 %) in a cell wall polysaccharide (xyloglucan) as a carbon reserve. Because it is found in the understorey of tropical forests, it has been considered as a shade-tolerant, late-secondary species. However, the physiological mechanisms involved in seedling establishment, especially regarding the interplay between storage and light intensity, are not understood. In this work, the ecophysiological role of this carbon cotyledon reserve (xyloglucan) is characterized, emphasizing its effects on seedling growth and development during the transition from heterotrophy to autotrophy under different light conditions. METHODS: Seedlings of H. courbaril were grown in environments with different light intensities, and with or without cotyledons detached before xyloglucan mobilization. Development, growth, photosynthesis and carbon partitioning (dry mass and [14C]sucrose) were analysed in each treatment. KEY RESULTS: The detachment of cotyledons was not important for seedling survival, but resulted in a strong restriction (50 % less) of shoot growth, which was the main sink for the cotyledon carbon reserves. Carbon restriction promoted an early maturation of the photosynthetic apparatus without changes in the net CO2 fixation per unit area. The reduced surface area of the first leaves in seedlings without cotyledons was evidence of limited growth and development of seedlings in low light conditions (22 micromol m(-2) s(-1) photon flux). CONCLUSIONS: There is an increase in the importance of storage xyloglucan in cotyledons for H. courbaril seedling development as light intensity decreases, confirming that this polymer plays a key role in the adaptation of this species to establish successfully in the shadowed understorey of the forest.     

Effect of light on the development of glyoxysomal functions in the cotyledons of mustard (Sinapis alba L.) seedlings

The degradation of storage fat in the cotyledons of mustard seedlings is unaffected by phytochrome and photosynthesis (irradiation with continuous red or far-red light from sowing of the seeds) although light imposes a strong constraint on the translocation of organic matter from the cotyledons into the seedling axis. Likewise, the development and disappearance of glyoxysomal enzyme activities (isocitrate lyase, malate synthase, citrate synthase) takes place independently of light. It is concluded that the mobilization of storage fat (fatcarbohydrate transformation) is independent of photomorphogenesis. The surplus of carbohydrate produced from fat in the light seems to be converted to starch grains in the plastids, which function as a secondary storage pool in the cotyledons.Abbreviations CS citrate synthase - ICL isocitrate lyase - MS malate synthase     

Effect of light on nucleotide modifications in the transfer RNA of cucumber cotyledons

The effect of light on nucleotide modifications in the tRNA of cucumber (Cucumis sativus L. var. Guntur) cotyledons was studied by chromatographic, electrophoretic and immunological methods. The tRNA from light-grown tissue showed the absence of 2-methylguanosine and a decrease in the relative proportions of ribothymidine and cytokinin-active ribonucleosides when compared to those produced from dark-grown tissue. On the other hand, a significant amount of one species of 2′-O-methyldinucleotide was observed in the tRNA of light-grown tissue which was not detected in the dark-grown tissue. Also, tRNA from light-grown tissue had higher levels of another species of 2′-O-methyldinucleotide. The results showed no difference in the amounts of other modified nucleosides in tRNA between tissues grown under the two conditions. 2′-O-Methyl-l-methyladenosine, a nucleotide modified both in the base and the ribose, apparently specific to plant tRNAs, has been found to be present in the RNA of both light- and dark-grown tissues. These results on the variation in modified nucleotides suggest that light has some role in nucleotide modification and, consequently, in cellular functions.     

Effect of hypoxia on nucleic acid and protein synthesis in different brain regions

The incorporation of [methyl-³H]thymidine into DNA, of [5-³H]uridine into RNA, and of [1-¹⁴C]leucine into proteins of cerebral hemispheres, cerebellum, and brainstem of guinea pigs after 80 hr of hypoxic treatment was measured. Both in vivo (intraventricular administration of labeled precursors) and in vitro (tissue slices incubation) experiments were performed. The labeling of macromolecules extracted from the various subcellular fractions of the above-mentioned brain regions was also determined. After hypoxic treatment the incorporation of the labeled precursors into DNA, RNA, and proteins was impaired to a different extent in the three brain regions and in the various subcellular fractions examined; DNA and RNA labeling in cerebellar mitochondria and protein labeling in microsomes of the three brain regions examined were particularly affected.     

不同光照条件下外源水杨酸对浒苔响应紫外辐射胁迫的影响

为研究不同光照条件下,外源水杨酸(SA)和紫外辐射(UV)对海洋绿藻浒苔的复合效应,在两个光照强度(高光:160 μmol·m^-2·s^-1;低光:70 μmol·m^-2·s^-1)条件下,设置对照(CK)、SA、UV及UV+SA处理(UV=3.2 W·m^-2、SA=10 μg·mL^-1),处理3 d后测定浒苔生长、叶绿素荧光参数、光合放氧速率、超氧化物歧化酶活性、可溶性糖和可溶性蛋白含量等的变化,探讨光照强度、UV及SA的复合效应.结果表明: 低光无UV条件下,SA会促进浒苔生长,降低浒苔叶绿素a(Chl a)和可溶性蛋白含量;高光无UV条件下, SA会抑制其生长,但显著提高了Chl a含量、呼吸速率、光合放氧速率、可溶性糖和可溶性蛋白含量;高光和UV条件下, UV+SA显著促进浒苔生长,提高Chl a和可溶性糖含量;低光和UV条件下,与UV相比,UV+SA提高了浒苔最大光化学效率(F_v/F_m)和可溶性蛋白含量,涨幅分别为139.8%和32.2%.外源SA的加入在一定程度上缓解了UV对浒苔的胁迫作用,且在高光条件下的效果更为显著.     

Effect of (2-chloroethyl) trimethylammonium chloride (CCC) and gibberellic acid (GA3) on the flowering ofChenopodium rubrum L.

U rostliny krátkého dne Chenopodium rubrum L. se dá kvetení indukovat íty?mi 16hodinovými cykly tmy ji? 5 dní po vyklí?ení. Aplikace CCC v koncentraci 2.10^-3mvpr?běhu indukce kvetení zadr?uje a toté? piatí pro GA₃ i tehdy, je-li podáván ve velmi nízkých koncentracích (0,1 a? 0,01 mg/l). Av?ak sou?asná aplikace obou těchto látek v uvedených koncentracích vede k úplné reversi inhibice. Po p?enesení rostlin z média, obsahujícího CCC, na ?istý ?ivný roztok, inhibi?ní ú?inek CCC rychle zmizí a p?echází v slabou stimulaci. Na?e výsledky ukazují, ?e giberelin se zú?astňuje proces? kvetení i u rostliny krátkého dne.     

Effects of light and photoperiodic conditions on abscisic acid in leaves and roots of Acer pseudoplatanus L.

Roots of Acer pseudoplatanus seedlings grown in liquid nutrient medium contained much lower levels of both free and bound abscisic acid than did leaves. The levels of free abscisic acid were similar in young expanding and of mature leaves, but lower in older senscing leaves. Growing plants under long days or short days did not influence the levels of free and bound abscisic acid in leaves. However, under both long days and short days, levels of bound abscisic acid were lower at the end of the dark period than 8 h later during the light period. Phaseic acid was also detected during the light period but never at the end of the dark period.Abbreviations ABA abscisic acid - PA phaseic acid - SD short day - GLC gas-liquid chromatography - LD long day     

Absence of parallelism between polyamine and nucleic acid contents during induced growth of cucumber cotyledons.

The cytokinins (benzyladenine or benzyladenosine) decreased spermidine and spermine contents despite increasing putrescine content, when administered to isolated cotyledons of Cucumis sativus L. var. Guntur in organ culture. KCl decreased putrescine contents, although marginally increasing polyamine contents. The cytokinins and/or KCl augmented nucleic acid biosynthesis and accumulation, resulting in enhanced growth and differentiation of the isolated cotyledons. These observations show that polyamine accumulation and growth are not always coupled.     

Changes in the level of endogenous cytokinins in apical buds ofChenopodium rubrum L.

CCC (2-chloroethyl)trimethylammonium chloride applied to plants ofChenopodium rubrum during floral induction led to an increase in the level of endogenous cytokinins in the apical buds. Application of gibberellic acid or indole-3-acetic acid at concentrations reversing the effect of CCC reduced the level of cytokinins. After simultaneous treatment with both CCC and one of the growth substances this reduction was less pronounced. From the comparison bf the present results, as well as of those published in previous papers it follows that in apical buds ofChenopodium rubrum there exists a mutual interaction between gibberellins and cytokinins. Under certain conditions both these groups of hormones may substitute for each other in flowering. IAA seems to affect flowering by regulating the level of both gibberellins and cytokinins.     

Growth correlations and rna synthesis in different parts of the shoot apical meristem ofChenopodium rubrunt L. induced to flowering

Uridine-³H incorporation and RNA concentration were investigated in different parts of the shoot apical meristem ofChenopodium rubrum using autoradiography and cytophotometry. A single inductive cycle was sufficient to bring about postinductive first events in the shoot apex but not for complete flower differentiation. The initial activation of RNA synthesis manifested itself in all zones of the apex. The first increase was more conspicuous in the peripheral than in the central zone. The indications of the first events in the apices after a single inductive cycle disappear prior to morphological reversal to the vegetative state. Induction by three short days led to rapid flower differentiation. The increase in RNA synthesis and concentration was most conspicuous in the central zone in this case. The ratio of RNA synthesis and content between bud and leaf primordia (B/L) also change in relation to photoperiodic induction. In vegetative plants the B/L ratio was low while after induction it increased. The shifts in activity of RNA synthesis observed in the shoot apical meristem are related to the changes in growth activity of the different parts of the apex. The growth ratios in the apices bear the character of growth correlations. The change in the growth correlations following photoperiodic induction together with the total activation of RNA synthesis are considered to represent one of the first events of the transition to the reproductive state.     

Stability of division-related protein and nucleic acid fractions in synchronized Tetrahymena

The kinetics of RNA synthesis have been studied under various growth conditions using synchronized Tetrahymena pyriformis GL. The curves obtained are approximately linear in growth-supporting media but vary under other circumstances. The presence of amino acids in the medium stimulates RNA synthesis in Tetrahymena as it does in bacteria. Since these induced variations do not influence the essential features of the pre-cytokinetic period it is inferred that fluctuations in the rate of RNA synthesis described by others are probably not essential features of temperature-induced synchrony. In addition, the translational stability of division-related templates at synchronizing temperatures has been investigated. The synthesis of proteins necessary for cytokinesis is shown to be greatly reduced under conditions simulating a heat-shock. Inhibitor studies using cycloheximide indicate that protein synthesis is required longer into the cytokinetic phase than had previously been thought. Collectively the data are all compatible with the hypothesis that synthesis of division-related proteins is drastically reduced in heat-shocked Tetrahymena and that the basis for this reduction is hydrolysis of template RNA without concurrent translation.