Respiratory metabolism in mangrove seedlings

The respiratory gaseous exchanges of detached whole mangrove seedlings (Avicennia, Bruguiera, Rhizophora) in a range of O₂ concentrations from 0 to 21% (air) were markedly reduced by the presence of external CO₂. Aerobic respiration decreased steadily for 16 days but the RQ remained at unity.     

Nitrogen metabolism in tomato seedlings

Tomato seedlings absorbed increasing amounts of nitrate-N. The total uptake was doubled as the concentration of nitrate was quadruplicated. NO₃?N absorption seemed to be accompanied by efflux of OH^? ions which shift the pH of the media to the alkaline side. A minor fraction of the absorbed nitrate accumulated in the tissues while the major part was assimilated into peptides and proteins. The dry matter gain was by the end of experiment relatively higher than the control samples raised on nitrogen-free nutrient solution. Nitrate assimilation seemed to involve its reduction down to ammonia level. Since neither nitrite nor ammonia was recovered in the tissue-medium system, it was postulated that the rate of reduction was slower than the rate of product assimilation. The first step in nitrate reduction (nitrate→nitrate) appeared to be limiting while further reduction steps occurred rapidly and accompanied by simultaneous assimilation of ammonia. The enzyme responsible for the first step of nitrate reduction,i.e., nitrate reductase, was extracted from tomato shoots and roots. The activity in root extract amounted to about 30% of that of the shoot. This may suggest the localization of nitrate reduction in the leaves and realizes the relation between nitrate metabolism and photosynthesis.     

Dihydrozeatin metabolism in radish seedlings

(±)-[8-¹⁴C]Dihydrozeatin was fed to derooted radish seedlings. After three days the plants were harvested and the cytokinin metabolites purified     

Glucose metabolism in anaerobic rice seedlings

More than 80% of the radioactivity from [U-¹⁴C]glucose metabolised by anaerobic rice seedlings or by excised roots or coleoptiles was recovered as ethanol plus CO₂; less than 5% was recovered as water-soluble acidic components. Rates of ¹⁴CO₂ formation from [U-¹⁴C]glucose were similar in roots and coleoptiles in both N₂ and air atmospheres. More ¹⁴CO₂ was formed from [U-¹⁴C]glucose than could be accounted for by ethanolic fermentation, and the specific yields of ¹⁴CO₂ from [6-¹⁴C]glucose and [1-¹⁴C]glucose gave unusually high C-6/C-1 ratios (1.7) in the anaerobic coleoptile. The results may indicate that appreciable pentan synthesis occurs in the anaerobic coleoptile.     

Some effects of oxygen concentration on levels of respiratory intermediates in buckwheat seedlings

Changes in levels of glycolytic and some related respiratory intermediates in young seedlings of buckwheat (Fagopyrum esculentum) following transfer A) from air to anoxia, B) from air to 1.5% O₂, C) from 1.5% O₂ to anoxia and D) from anoxia to air, are recorded and discussed in relation to other measurements made with these seedlings.

On transfer from air to anoxia the changes are similar to those recorded for pea seeds in which it is inferred that glycolysis is faster in anoxia than in air. The results with buckwheat however can be explained in terms of a decreased rate of glycolysis in anoxia. An alternative hypothesis is developed which states that glycolysis is faster in anoxia than in air and that it is the contribution of the pentose phosphate cycle to the total respiratory catabolism which decreases as the oxygen concentration is reduced towards zero.

     

Sorbitol metabolism by apple seedlings

The aims of this work were to compare the roles of sorbitol and sucrose in seedlings of Malus domestica, to discover which tissues synthesize sorbitol and which break it down, and to examine these tissues for enzymes of sorbitol metabolism. The detailed distribution of label was determined after supplying intact seedlings with ¹⁴CO₂, and excised parts of seedlings with [U-¹⁴C]fructose and [U-¹⁴C]sorbitol. The results showed that appreciable synthesis of sorbitol occurred only in the leaves but did not depend directly on photosynthesis. All tissues examined metabolized sorbitol but metabolism was extensive only in root apices, and in leaves which had been kept in the dark. The above experiments suggest that sorbitol supplements but does not replace sucrose. Extracts of apple leaves showed no trace of either a polyol or a polyol phosphate dehydrogenase but did exhibit sorbitol-6-phosphate phosphatase activity. A limited number of experiments with extracts of the blades of Laminaria digitata indicated that they contained mannitol-1-phosphate phosphatase and mannitol dehydrogenase.     

Respiratory activity in rice seedlings germinated under strictly anaerobic conditions

Rice seedlings germinated for up to 96 hr from the imbibition under strictly anaerobic conditions had a certain level of respiratory activity, though less than that of aerobic controls. Nitro-BT positive particles were recognized in coleoptile cells of these seedlings. Respiratory activity in shoots from these seedlings showed a marked rise after exposure to air.     

Sulfur deprivation and nitrogen metabolism in maize seedlings

The objective of this experiment was to elucidate the manner in which N metabolism is influenced by S nutrition. Maize (Zea mays L.) seedlings supplied with Hoagland solution minus SO₄²⁻ exhibited S deficiency symptoms 12 days after emergence. Prior to development of these symptoms, a decline in leaf blade nitrate reductase (NR, EC 1.6.6.1) activity was observed in S-deprived seedlings compared to normal seedlings. Twelve days after emergence, in vitro NR activity was diminished 50% compared to normal seedlings. Glutamine synthetase (EC 6.3.1.2) and NAD-glutamate dehydrogenase (EC 1.4.1.2) activities were less severely affected (19 and 13%, respectively, at day 12). NADP-glutamate dehydrogenase (EC 1.4.1.4) activity and leaf blade fresh weight were not altered by S deprivation. Concentrations of soluble protein and chlorophyll (a and b) in leaf blades were reduced 18 and 25%, respectively, at day 12. A significantly higher concentration of NO₃⁻-N was observed for leaf blade and stem (culms, leaf sheaths, and unfurled leaves) fractions (46 and 31%, respectively) in S-deprived plants. In contrast to the other parameters measured, NR activity in S-deprived seedlings could be readily restored to the normal level by addition of SO₄²⁻. The apparent preferential effect of S deprivation on NR activity could be causally related to the observed changes in NO₃⁻-N and soluble protein concentration.     

Alkaloid metabolism in wounded Catharanthus roseus seedlings.

The effect of mechanical wounding on alkaloid metabolism was analyzed in Catharanthus roseus seedlings. Wounding induced an increase in ajmalicine accumulation, whereas catharanthine remained unaffected. A positive dual effect on vindoline was noticed. Short and mid-term effects were detected between 12 and 24 h after mechanical damage was inflicted, and apparently resulted from the accelerated transformation of the tabersonine intermediaries to vindoline. Long-term effects involved a generalized increase in carbon flux towards alkaloid synthesis. Exposure to ethylene (1 ppm) produced similar results to those observed in wounded seedlings, suggesting that it might be mediating the wound-induced increase in alkaloid synthesis. No synergistic or additive effects were observed when wounded seedlings were exposed to ethylene or jasmonate.     

Rapid metabolism of propylene by pea seedlings

Propylene uptake by intact pea seedlings (Pisum sativum L. cv. Alaska) was easily detected using standard gas chromatographic techniques suggesting rapid metabolism. Comparative studies with highly purified ¹⁴C₃H₆ and ¹⁴C₂H₄ under aseptic conditions verified that propylene was rapidly metabolized and indicated that some aspects of its metabolism were similar to that of ethylene since ¹⁴C₃H₆, like ¹⁴C₂H₄ (Beyer, Nature 1975, 255: 144-147), was oxidized to ¹⁴CO₂ and incorporated into water-soluble tissue metabolites. However, ¹⁴C₂H₆ was metabolized at a substantially faster rate and unlike ¹⁴C₂H₄ the rate of ¹⁴C₃H₆ tissue incorporation exceeded its rate of oxidation to ¹⁴CO₂. In addition the neutral ¹⁴C-metabolites derived from ¹⁴C₃H₆ were chromatographically distinct from those formed from ¹⁴C₂H₄.     

Lipid metabolism in ageing leaves of dark-grown barley seedlings

The rapid senescence of the etiolated leaves of dark-grown barley seedlings in the dark is accompanied by the loss of those lipids associated with the plastids. The linolenate content of the plastid glycerolipids rapidly decreased whereas it tended to increase in the extraplastidic phospholipids. Kinetin treatment slowed down the loss of the plastid lipids and their constituent fatty acids. The hormone treatment brought about increased linolenate, particularly in phosphatidylcholine and monogalactosyldiacylglycerol. The senescing leaf attempts to adapt to ageing by increased membrane synthesis and/or membrane repair. Kinetin appears to control the sequential desaturation of oleate to linolenate.     

Carbohydrate metabolism in growing rice seedlings under arsenic toxicity

We studied in the seedlings of two rice cultivars (Malviya-36 and Pant-12) the effect of increasing levels of arsenic in situ on the content of sugars and the activity of several enzymes of starch and sucrose metabolism: alpha-amylase (EC 3.2.1.1), beta-amylase (EC 3.2.1.2), starch phosphorylase (EC 2.4.1.1), acid invertase (EC 3.2.1.26), sucrose synthase (EC 2.4.1.13) and sucrose phosphate synthase (EC 2.4.1.14). During a growth period of 10-20 d As2O3 at 25 and 50 microM in the growth medium caused an increase in reducing, non-reducing and total soluble sugars. An increased conversion of non-reducing to reducing sugars was observed concomitant with As toxicity. The activities of alpha-amylase, beta-amylase and sucrose phosphate synthase declined, whereas starch phosphorylase, acid invertase and sucrose synthase were found to be elevated. Results indicate that in rice seedlings arsenic toxicity causes perturbations in carbohydrate metabolism leading to the accumulation of soluble sugars by altering enzyme activity. Sucrose synthase possibly plays a positive role in synthesis of sucrose under As-toxicity.     

Effect of chlorsulfuron on phenylpropanoid metabolism in sunflower seedlings

The effect of the herbicide chlorsulfuron on phenylpropanoid titer and metabolism and the role of endogenous ethylene in this response was examined in light-grown sunflower (Helianthus annuus L.) seedlings. Application of chlorsulfuron to the apex resulted in large increases in both total phenolic and hydroxycinnamic acid content in hypocotyls isolated from the treated seedlings. Both of these parameters were increased within 24 h of herbicide treatment, and both reached a maximum level 3–4 days post-treatment. An increase in ethylene evolution was found to proceed in parallel with the alterations of phenolic content. The extractable activities of phenylalanine ammonia lyase,trans-cinnamic-4-hydroxylase, and soluble peroxidase were increased by chlorsulfuron treatment. Chlorsulfuron had little effect on total phenolic content when administered directly to isolated hypocotyl segments. Exogenous ethylene had no effect on the endogenous titer of phenolic compounds. Root-fed cobalt chloride (5 × 10^?4 M) inhibited chlorsulfuron-induced ethylene production by 92% and also inhibited the accumulation of phenolic materials by 56%. Exogenous ethylene was unable to reverse the inhibition caused by cobalt chloride. It was concluded that chlorsulfuron-induced increases in phenolic compounds were not mediated solely by endogenous ethylene.     

Proline-14C metabolism in barley seedlings during vernalization

The metabolism of proline-¹⁴C was examined in vernalized (LT)and unvernalized (HT) barley shoots. The content of prolinein cytoplasmic and cell wall protein fractions was a littlehigher in HT, against the accumulation of free proline in LT.Proline-¹⁴C was more heavily incorporated into HT and the cytoplasmicprotein had a higher radioactivity than the cell wall protein.In LT, the activity in the cytoplasmic protein was lower thanthat in the cell wall. The time course of incorporated proline-¹⁴Cshowed no distinct changes in HT. but decreased remarkably inthe LT cell wall. The distribution of proline-¹⁴C in hydroxyproline and otheramino acids in the two proteins was examined. In the cytoplasmicproteins, the conversion pattern of proline-¹⁴C was very similarin both treatments. The highest hydroxyproline activity wasfound at the beginning of incubation and was maintained at acomparatively high level in the HT cell wall. The LT cell wallshowed a gradual increase in radioactivity due to hydroxyprolineand reached maximum conversion at the last incubation period.Distribution of radioactivity due to incorporated proline-¹⁴Cwas examined by separating barley shoot tissues into three sections. (Received December 5, 1972; )