Comparative study of the composition of waxes extracted from isolated leaf cuticles and from whole leaves of Citrus: Evidence for selective extraction

The effect of different extraction methods on the composition of samples of soluble cuticular lipids (SCL) of Citrus aurantium L. was investigated. The variation of extraction yields, when whole leaves were immersed in solvent, was studied as a function of solvent type and duration of immersion. Cuticular waxes were also quantitatively extracted from isolated cuticular membranes of C. aurantium and their composition was compared to that of samples obtained by the immersion method. Significant differences were observed. Higher carbon number homologues of the aliphatic constituent classes were discriminated against when whole C. aurantium leaves were extracted by immersion. The alkyl ester fraction was almost entirely lacking in extracts from whole leaves. The dependence on carbon chain length of the saturation concentrations in chloroform of major aliphatic SCL constituents was determined. The results are discussed in terms of the major physico-chemical processes involved in the extraction of SCL.     

Water use efficiency as a function of leaf age and position within the cotton canopy

The gas exchange properties of whole plant canopies are an integral part of crop productivity and have attracted much attention in recent years. However, insufficient information exists on the coordination of transpiration and CO₂ uptake for individual leaves during the growing season. Single-leaf determinations of net photosynthesis (Pn), transpiration (E) and water use efficiency (WUE) for field-grown cotton (Gossypium hirsutum L.) leaves were recorded during a 2-year field study. Measurements were made at 3 to 4 day intervals on the main-stem and first three sympodial leaves at main-stem node 10 from their unfolding through senescence. Results indicated that all gas exchange parameters changed with individual main-stem and sympodial leaf age. Values of Pn, E and WUE followed a rise and fall pattern with maximum rates achieved at a leaf age of 18 to 20 days. While no significant position effects were observed for Pn, main-stem and sympodial leaves did differ in E and WUE particularly as leaves aged beyond 40 days. For a given leaf age, the main-stem leaf had a significantly lower WUE than the three sympodial leaves. WUE's for the main-stem and three sympodial leaves between the ages of 41 to 50 days were 0.85, 1.30, 1.36 and 1.95 μmol CO₂ mmol⁻¹ H₂O, respectively. The mechanisms which mediated leaf positional differences for WUE were not strictly related to changes in stomatal conductance (g_s·H₂O) since decreases in g_s·H₂O with leaf age were similar for the four leaves. However, significantly different radiant environments with distance along the fruiting branch did indicate the possible involvement of mutual leaf shading in determining WUE. The significance of these findings are presented in relation to light competition within the plant canopy during development.     

Citrus replant problem in Iraq II. Possible role of allelopathy

The role of allelopathy in citrus replant problems was investigated in Iraq. The failure of citrus seedlings to grow normally in old citrus orchards was not caused by differences between old and non-citrus soils in electrical conductivity, pH, organic matter, soil texture and those minerals tested. Extracts of soil collected from old citrus orchards significantly reduced the growth of sour orange seedlings. Extracts and decaying sour orange roots reduced the growth of sour orange seedlings as did extracts of non-senescent sour orange leaves and decaying senescent leaves. Thus it appears that allelopathy is at least partly involved in the citrus replant problem.     

Endophage-ectophage ratios and plant defense

Summary Endophagous folivores, which are concealed inside leaf tissue for much of their life cycle, or which live externally but feed internally, should be more successful on heavily defended plants than ectophagous species. This is because endophages are more facile at feeding selectively and can manipulate tissue development to avoid physical and chemical defenses and to enhance nutrition. As a result, endophage-ectophage ratios should increase on more heavily defended hosts. This pattern will likely be strengthened by negative asymmetrical interactions with ectophages and pathogens, which may displace endophages from lightly defended hosts. The hypothesis predicts that endophages should be particularly abundant in resource-poor habitats which seem to support a preponderance of heavily defended hosts. Although data do not yet exist for a rigorous test, several observed cases where endophage distributions seem biased toward heavily defended hosts are at least consistent with the hypothesis. Plant defense levels may have little influence on the total number of herbivores associated with a host, but I suggest that guild structure can be profoundly altered.     

Microsome protein phosphorylation in Acer pseudoplatanus cells as influenced by intracellular alkalinization

Abstract. The authors have previously shown that cell treatments causing intra-cellular alkalinization stimulate the in vivo phosphorylation of a 33-K Dalton polypeptide (33 KP) (Tognoli & Basso, 1987). Here, the authors report that this polypeptide belongs to a protein associated with the microsomal membranes. They show that treatment of cells which induce intracellular alkalinization stimulate 33-KP phosphorylation, whether the phosphorylation is performed in vivo (cells loaded with ³²Pi before treatments) or in vitro (microsomes from control and treated cells, incubated with γ³²P ATP). In both cases, 33 KP is phosphorylated on a serine residue. Microsomes do not show any phosphatase activity towards this phosphorylated protein, indicating involvement of a protein kinase reaction as an effector of changes induced by intracellular alkalinization. The number of phosphorylated sites or molecules of this protein increases as a result of intracellular alkalinization, suggesting that intracellular alkalinization causes topological or conformational modifications to a protein kinase or its substrate protein. The in vitro phosphorylation is not specifically influenced by the pH of the in vitro phosphorylation medium, suggesting that protein phosphorylation is not directly controlled by cytoplasmic pH.     

Single-stranded DNA used as an efficient new vehicle for transformation of plant protoplasts

In relation to the question which DNA form (single- or double-stranded) is transferred by Agrobacterium tumefaciens to plant cells, we studied the behaviour of single-stranded DNA, as compared to double-stranded DNA, when it is introduced into plant protoplasts by electroporation. To this end, we cloned a construct with a plant NPTII gene as well as a CAT gene in the M13 vectors tg130 and tg131. We found that both complementary single-stranded molecules gave rise to substantial CAT activity in plant protoplasts, suggesting that single-stranded DNA is converted into double-stranded DNA by the plant cell replication machinery. Unexpectedly, we found that single-stranded DNA leads to a 3–10 fold higher frequency of stable transformation (selection for kanamycin resistance) than double-stranded DNA. These results indicate that the use of single-stranded DNA might be considered in experiments in which optimal transformation frequencies are needed, e.g. with protoplasts form recalcitrant plant species.Abbreviations ss single-stranded - ds double-stranded - CAT chloramphenicol acetyl transferase - NPTII neomycin phosphotransferase II - RT room temperature     

Plant regeneration from callus of Puccinellia distans (L.) Parl

Callus was induced from seeds of Puccinellia distans (L.) Parl. on MS medium supplemented with 2 mgl^-1 2,4-dichlorophenoxyacetic acid and 0.5 mgl^-1 kinetin. Morphogenesis initiation was achieved during subculture on medium containing 0.1 mgl^-1 2,4-D. From the point of morphogenetic capacity, 3 types of callus were selected. High frequency of plant regeneration was obtained by selection of embryogenic type of callus, and culture on N₆ medium and N₆ medium supplemented with kinetin (5–10 mgl^-1), or kinetin (2 mgl^-1) and IAA (0.5 mgl^-1). A high ratio of albinos among regenerants was observed.     

In vitro development of angiosperm floral buds and organs

In the last twenty-five years, young inflorescences, floral buds and individual floral organs of a number of species have been cultured in vitro. There is considerable variability in the requirement of plant growth regulators and nutritional factors for flower development of different species. This variability is compounded by the fact that the hormonal and nutritional requirements are different at various stages of organ and floral development. Experimental studies on normal and mutant flowers in vitro have provided insights into some of the regulatory processes in floral organogenesis. The potential use of the in vitro technique in elucidating the various mechanisms in flower development is stressed.     

Morphogenic potential of mechanically isolated single cells from Digitalis obscura L. callus

Calli from hypocotyl and root explants of Digitalis obscura L. showed regeneration of adventitious shoots, roots and embryos when transferred to Murashige & Skoog medium supplemented with cytokinins alone or in combination with auxins. Optimum shoot-bud formation was achieved in the presence of IAA and BA, while roots mainly appeared either in absence of growth regulators or with IAA and Kn. Embryo formation took place only in those combinations that included Kn. Embryo development was influenced by the type of auxin, and precocious germination occurred in media with NAA. Mechanically isolated cells from hypocotyl- and root-derived calli were plated in MS medium supplemented with several IAA and BA combinations. Single cells were able to proliferate forming callus within 20–30 days in culture. In order to induce organogenesis, calli were transferred to various regeneration media. Shoot-bud differentiation efficiency depended on both callus origin and medium initially used for cell culture, best results being obtained in calli grown from hypocotyl-derived cells cultured in the presence of casein hydrolysate. A further subculture to medium containing coconut milk and lower concentrations of NH₄NO₃ and sucrose promoted shoot development. Rooting was readily achieved upon transferring shoots onto half-strength MS medium. Plantlets were ultimately established in soil.Abbreviations BA benzyladenine - BM basal medium - CH casein hydrolysate - CM coconut milk - 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indoleacetic acid - Kn kinetin - MS Murashige & Skoog - NAA naphthaleneacetic acid