Carlos Oropeza

Exogenous sucrose can decrease in vitro photosynthesis but improve field survival and growth of coconut (cocos nucifera l.) in vitro plantlets

SummaryCoconut (Cocos nucifera L.) plantlets grown in vitro often grow slowly when transferred to the field possibly, due to a limited photosynthetic capacity of in vitro-cultured plantlets, apparently caused by the sucrose added to growth medium causing negative feedback for photosynthesis. In this paper, we tested the hypothesis that high exogenous sucrose will decrease ribulose 1,5-bisphosphate carboxylase (Rubisco) activity and photosynthesis resulting in limited ex vitro growth. Plantlets grown with high exogenous sucrose (90 gl−1) had reduced photosynthetic activity that resulted in a poor photosynthetic response to high levels of light and CO2. These plantlets also had low amounts of Rubisco protein, low Rubisco activity, and reduced growth despite showing high survival when transferred to the field. Decreasing the medium’s sucrose concentration from 90 to 22.5 gl−1 or 0 gl−1 resulted in increased photosynthetic response to light and CO2 along with increased Rubisco and phosphoenolpyruvate carboxylase (PEPC) activities and proteins. However, plantlets grown in vitro without exogenous sucrose died when transferred ex vitro, whereas those grown with intermediate exogenous sucrose showed intermediate photosynthetic response, high survival, fast growth, and ex vitro photosynthesis. Thus, exogenous sucrose at moderate concentration decreased photosynthesis but increased survival, suggesting that both in vitro photosynthesis and exogenous sucrose reserves contribute to field establisment and growth of coconut plantlets cultured in vitro.

Changes in the Alkaloid Content of Plants of Catharanthus roseus L. (Don). as a Result of Water Stress and Treatment with Abscisic Acid

Summary The alkaloid content of mature leaves in Catharanthus roseus plants increased over two-fold under severe water stress, when the leaf water-potential decreased below -1.9 MPa. The alkaloid content in other plants parts did not change (stem and immature leaves) or decreased (root). An increase in the alkaloid content of mature leaves was also observed when watered plants were treated with 1 mM abscisic acid.

Nitrogen Metabolism in Canavalia ensiformis (L.) DC.: II. Changing Activities of Nitrogen-Assimilating Enzymes during Growth

Summary The ontogeny of glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 1.4.1.14), asparagine synthetase (EC 6.4.5.4) and glutamate dehydrogenase (EC 1.4.1.2) has been followed in cotyledons, roots, stems and leaves of young plants of Canavalia ensiformis . The four enzymes were found in all regions. Glutamine synthetase activity increased in the leaves with time and remained low in the cotyledons. Initially glutamate synthase activity in the cotyledons was NADH-dependent but later became Fd-dependent. Asparagine synthetase specific activity was highest in the roots until day 5 after which activity was similar in all regions. While glutamate dehydrogenase specific activity decreased with time in the leaves it increased in the cotyledons and roots. We suggest that in the early stages of seedling growth asparagine synthetase and glutamate dehydrogenase both play a fundamental role in the reassimilation of ammonium released from canavanine. When the plant acquires full photosynthetic capacity the glutamine synthetase/glutamate synthase pathway becomes the principal pathway of reassimilation in the aerial parts of the plant.

Occurrence of phosphorylated proteins and kinase activity in coconut tissues cultured in vitro in a mediumthat induces somatic embryogenesis

Abstract The presence of tyrosine kinase and tyrosine-phosphorylated proteins was investigated in coconut tissues cultured in vitro. In order to study this phenomenon, plumular explants were taken from mature zygotic embryos and cultured in a medium that induces somatic embryogenesis. Immunoblot analyses of soluble proteins of coconut cultured tissues with a recombinant monoclonal antibody against phosphotyrosine detected protein bands with molecular masses ranging from 170 to 27xa0kDa. The highest response was exhibited by plumule-forming callus, which decreased both in number and intensity of bands with a longer time of in vitro culture. The specific immunodetection was corroborated by incubating the membranes with anti-phosphotyrosine antibody in the presence of 1xa0mM phosphotyrosine. Tyrosine phosphorylated proteins was also suggested by the presence of phosphoproteins resistant to alkaline treatment. In plumule, plumular callus and callus with globular embryos and shoots, a 41-kDa protein remained phosphorylated after alkaline treatment. In plumule, most [ 32 P]-proteins remained phosphorylated after alkaline treatment. Phosphoaminoacid analysis in protein hydrolysates from [ 32 P]-labelled 41-kDa protein showed the presence of [ 32 P]-tyrosine and [ 32 P]-threonine. Evaluation of tyrosine kinase activity in these tissues by the use of RR-SRC, a synthetic peptide substrate (derived from the amino acid sequence surrounding the phosphorylation site), showed that the activity was highest in plumule forming callus and initial explant, whereas in other tissues, tyrosine kinase activity decreased to values close to zero. Genistein, a specific tyrosine kinase inhibitor, diminished the ability of soluble extracts from coconut tissues cultured in vitro to incorporate 32 P into RR-SRC. These results suggest the presence of tyrosine phosphorylated proteins and tyrosine kinase activity in coconut tissues that have been cultured in vitro.

Formation of L-canavanine in in vitro cultures of Canavalia ensiformis (L.) DC.

In vitro tissue cultures of Canavalia ensiformis (L.) D.C. derived from hypocotyl have been obtained. They were found to accumulate L-canavanine depending on the medium where they were grown. Addition of polyethylenglycol (4%) to the culture medium led to a reduced accumulation of l-canavanine and an increase in the amino acids and the quaternary ammonium compounds contents.

Is abscisic acid responsible for abnormal stomatal closure in coconut palms showing lethal yellowing

Summary Lethal yellowing induced permanent stomatal closure in coconut palms ( Cocos nucifera L.) is central to the development of the diseases symptoms such as decreased photosynthesis, leaf yellowing and palm death, but the cause of this abnormal permanent stomatal closure is unknown. Since abscisic acid (ABA) can cause stomatal closure, ABA concentrations were measured in the roots, leaves, and leaf xylem sap to test for a correlation with the degree of stomatal closure as disease severity advanced. Concentrations of ABA in leaf and xylem sap extracts increased with disease progression but not until the later stages of the disease, well after abnormal stomatal closure. ABA concentrations in the roots were also not correlated with stomatal closure. Transpiration declined proportionally in response to increasing ABA concentrations (10 −8 , 10 −6 , 10 −4 mol L −1 ) in a detached coconut leaf bioassay but all extracts from healthy and diseased coconut palms reduced transpiration to similar levels. Likewise, all coconut palm leaf extracts reduced stomatal aperture 60–70 % in Commelina communis leaf epidermal strips with no notable differences between healthy and diseased palms. Thus, the results indicate that bulk ABA concentrations in leaf xylem sap or leaf tissue are not responsible for the abnormal stomatal closure in lethal yellowing disease.

Determination of l-canavanine and l-canaline in plant tissues by high-performance liquid chromatography

Dosage simultane de ces deux acides amines en presence dautres acides amines. Applications au haricot de Madagascar

Biochemical Changes in Roots of Coconut Palms (Cocos nucifera L.) Affected by Lethal Yellowing

Summary Respiration rates and protein concentrations of lateral and subtending roots of coconut palms were studied at various stages of development of lethal yellowing (LY) disease, including LYpositive symptom-less palms, and compared to respiration rates and protein concentrations of healthy palms. No visual symptoms were apparent in the roots of LYpositive symptomless palms. However, respiration rates and protein concentrations were already lower in LYpositive symptomless palms and they continued to decrease as the disease developed. The appearance of root necrosis coincided with the onset of leaf yellowing in above ground parts. Implications of these findings are discussed in the context of root damage, as a central process in the mode of pathogenicity of the disease.

Amine oxidase activity in Canavalia ensiformis during early growth: a histochemical study

Summary The distribution of amine oxidase has been studied in light-grown Canavalia ensiformis (L.) DC. plants during germination and early growth, using a histochemical staining technique. Different regions of the plant showed characteristic staining profiles which varied according to the age of the plant and the substrate used. Putrescine- and cadaverine-induced staining occurred more frequently than spermidine-induced staining. Spermine-induced staining was rarely seen. Except for roots and the embryo, amine oxidase activity was detected in all regions of the plant although in some parts, such as the cotyledons, its presence was limited and transient. However, high activity was found in young internodes and petioles. In the internodes and petioles of 13-d-old plants staining was inhibited by the carbonyl-group reagents aminoguanidine and hydroxyethylhydrazine and the metal chelators 8-hydroxyquinoline and diethyl-dithiocarbamate, while p-chloromercuribenzoic acid inhibited spermine-induced staining only. Staining profiles in the roots, cotyledons and embryos were not affected by the presence of 2,4-dichlorophenol. The results suggest that staining is a reliable indicator of amine oxidase activity, and indicate the presence of a diamine oxidase similar to that found in other legumes.

Nitrogen Metabolism in Canavalia ensiformis L. DC.: I. Arginase and Urease Ontogeny

Summary The ontogeny of arginase and urease has been followed in cotyledons, roots, stems and leaves of young Canavalia ensiformis plants. Both enzymes were found in all organs. Arginase activities were highest in stems and roots, whereas urease activity was highest in the cotyledons. Urea and ammonia pools were measured in all organs studied and, in general, decreased with time, except in leaves where a marked increase in ammonia was observed. The data are discussed in relation to the mobilization and distribution of canavanine from cotyledons to other regions during germination and subsequent seedling growth.