Significance of Cyclic Nucleotides in Amaranthin Synthesis by Amaranthus caudatus Seedlings

Explants of 72–76 h old Amaranthus caudatus seedlingssynthesize the betalain pigment amaranthin in response to light.Light can be replaced with a cytokinin or a cyclic nucleotidewith an N⁶-substituent. Cyclic 3'5'-AMP shows only weak activityand that only at high unphysiological concentrations. Even cyclic2'3'-AMP, which docs not act as a ‘second messenger’,induces amaranthin synthesis to a greater degree than cyclic3',5'-AMP. But N⁶-monobutyryl-cyclic 3',5'-AMP and N⁶-2'-O-dibutyryl-cyclicAMPshow high activity, higher even than kinetin at its optimumconcentration of 10^–5 M. 2'-O-Monobutyryl-cyclicAMP, onthe other hand, is considerably less active, suggesting thatN⁶-substitution of the adenine ring is responsible for the enhancedactivity. N⁶-Propionyl, butyryl and valeryladenines are allhighly active, indicating that the cyclic monophosphate moietyis unnecessary for this response. All the compounds tested,including cyclic 3',5'-AMP, show additive effects, but thereis no amplification of the response, typical of second messengeraction. Inhibition of amaranthin synthesis imposed by hadacidin, isrelieved by kinetin, DBc AMP, N⁶-monobutyryl-cAMP and N⁶-butyryladenine. Cyclic 3',5'-AMP is weakly active in this regard. Asnatural cytokinins are N⁶-substituted adenine compounds, andas only N⁶-substituted cyclic nucleotides are able to mimicthe effect of cytokinin, it is concluded that these cyclic nucleotidesfunction as cytokinin analogues and not as ‘second messengers’'. Amaranthus caudatus, amaranthin, cytokinins, cyclic nucleotides     

Diurnal Fluctuations in Relative Water Content, Nitrate Reductase and Proline Content in Water-stressed and Non-stressed Wheat

Diurnal variations in relative water content (RWC), nitrate reductase (NR) and proline content (PC) were studied at 3 h intervals during a 24 h cycle in the flag leaf of wheat (Triticum vulgare, v. Kalyansona) grown under stressed and non-stressed conditions. RWC was lower in stressed plants than in non-stressed ones throughout the 24 h period. Although it was lowest at 12 h, it recovered by 15 h. Non-stressed plants maintained higher NR activity compared to those under stress. The enzyme activity during night was about the same as during day time in both types of plants. Compared to non-stressed plants, stressed ones had lower NO₃^? content. Proline accumulation occurred under stress conditions and had a maximum at 12–15 h. Non-stressed plants exhibited higher PC during night than day time. Changes in temperature and relative humidity were noted during the period and their influence on RWC, NR and proline was discussed.     

Studies on the structural and developmental variation and distribution of stomata in the Rubiaceae

The structure and ontogeny of the stomata has been studied in 26 species of Rubiaceae, in relation to their organographic distribution. The stomata are mostly paracytic on the leaves, but vary on other parts, particularly on the floral disk, where they are exclusively anomocytic. The foliar stomata are mesogenous and paracytic, but may be either dolabrate or trilabrate in origin. The disk stomata are perigenous and are probably derived from the mesogenous paracytic ones by the loss of divisive potential of their meristemoid due to anthogenetic factors. They are regarded to be hydathodal in function. If the dendroid habit is regarded as primitive, in the family, trilabrate stomata were quite possibly derived from dolabrate ones, which are mostly associated with the dendroid habit. Evidence from stomatal ontogeny is shown to be taxonomically important in the Rubiaceae.     

Abnormal Stomatal Opening in Coconut Palms Affected with Root (Wilt) Disease

Studies on the stomatal regulation in the root (wilt) affectedcoconut palms (Cocos nucifera L.) revealed that the diseasedpalms had low stomatal resistance compared to the healthy palms,irrespective of their age. The same trend was observed whetherthe determinations were made at different times of the day (6–18h) or under irrigated and unirrigated conditions or in differentseasons (‘dry’ and ‘wet’). Thus, thestomatal regulation was significantly impaired in the diseasedpalms resulting in excessive water loss compared to the healthypalms. Results are discussed with the available literature onother similar disease caused by fungi, bacteria and mycoplasma-likeorganisms in different plants. Key words: Cocos nucifera L., Stomatal resistance, Root (wilt) disease     

Water stress and root formation in pea cuttings

The stock plants of pea (Pistum sativium L. cv. Alaska) grown for 11 days at 16 W m^?2 38 W m^?2 were subjected to different degrees of moisture stress, simulated with polyethyleneglycol (PEG, 6000) for different periods. The cuttings were made at the end of stress treatments, planted in perlite and allowed to root in a mist propagation chamber. The number of adventitious roots formed on the cuttings from non-stressed plants was significantly higher under low (16 W m^?2) than under high (38 W ^m?2) irradiance. However, under the influence of short duration stress the number of roots increased significantly under high but not under low irradiance. There was significantly poor rooting after prolonged stress under both irradiances. The leaf osmotic potential ψ_π showed a greater reduction with increasing degree and duration of stress at 38 W m^?2 than at 16 W m^?2. The differential rooting behaviour as a result of stress levels and irradiances is discussed in the light of available literature on adventitious root formation.     

The taxonomic value of guard cells seen in surface view

Guard cells, as seen in surface view, are classified into five types; dumb-bell type, rectangular type-A, rectangular type—B, elliptic type and right-angle type. It is proposed that this more detailed classification may have value at higher taxonomic levels, particularly within the Monocotyledones.     

Auxin Balance in the Avena Coleoptile

Coleoptiles of Avena possessed the capacity to degrade infiltrated indole-3-acetic acid (IAA). This activity decreased along the length of the coleoptile from apex to base on the bases of fresh weight, dry weight and protein; the apical 1 cm segment degraded more IAA than segments from other parts of the coleoptile. The naturally occurring inhibitor of the IAA oxidase activity increased in concentration up to 20 mm from the coleoptile apex; beyond, it decreased gradually towards the base. The spatial distribution of this inhibitor does not explain the gradient in IAA oxidase activity. Growth in length of the coleoptile and the IAA inactivating capacity of the apical 1 cm segment, increased 5- and 4,4-fold, respectively, between the ages of 70 and 130 h; but auxin secretion into agar platelets by the apical 2 mm of the coleoptile registered only a 2.7-fold increase. Deseeding and derooting the seedlings reduced the subsequent growth, diffusible auxin content and the IAA oxidase activity of the coleoptiles; derooting proved to be more deleterious than deseeding. A parallel reduction was evident in auxin content and IAA degrading activity following these treatments. Application of the cytokinin 6-benzylaminopurine (BAP) to coleoptiles of derooted seedlings failed to influence their capacity to degrade IAA. Nor was the activity of the aldehyde oxidase, which converts indole-3-acetaldehyde (IAAld) to IAA, affected by such treatment.     

Metabolism of Indole-3-acetaldehyde. III. Some Characteristics of the Aldehyde Oxidase of Avena Coleoptiles

Coleoptiles of Avena contain a soluble enzyme system, capable of oxidizing indoleacetaldehyde (lAAld) to indoleacetic acid (IAA). There is a gradient in the concentration of the enzyme along the length of the coleoptile and the first inter-node. The top 5 mm segment of each organ is relatively richer in this enzyme than the rest of the tissue. The enzyme was purified 17.7-fold by fractional precipitation with ammonium sulphate followed by gel filtration on Sephadex. Optimal pH for lAAld oxidation is ca. 4.4. Activity of the enzyme is normally oxygen obligatory. But, in the absence of oxygen, phenazine methosulphate (PMS) serves as hydrogen acceptor for aldehyde oxidation, but not some other dyes tried. Approximately one mole of oxygen was consumed for each mole of IAA formed. Formation of H₂O₂ could not be detected. Added H₂O₂ inhibited the reaction. Prolonged dialysis progressively inactivated the enzyme. Added NAD, NADP, FMN, FAD, cytochrome c, cyanoco-balamin, folic acid and ascorbic acid did not restore the lost activity. But 10^?3M cysteine restored about 60 % of the lost activity. The enzyme is an acidic protein, isoelectric at pH 4.05. For lAAld, under the conditions of experimentation, a Km of 3.45 × 10^?4M was calculated. Besides lAAld, indole-3-aldehyde and phenylacetaldehyde served as substrates, but not acetaldehyde, propionaldehyde, salicylaldehyde, xanthine, hypoxanthine or catechol. Cyanide, dithionite and mercapto-ethanol totally inactivated the enzyme depending upon the concentration and duration of treatment. X-ray irradiation up to a dosage of 2900 r promoted the lAAld oxidizing activity of cell-free preparations made from irradiated coleoptiles. As yet, no cofactor requirements have been found for the activity. The enzyme is unlikely to be a pyridino- or a flavoprotein.