The Effect of Grain Number per Ear (Sink Size) on Source Activity and its Water-Relations in Wheat

Blum, A., Mayer, J. and Golan, G. 1988. The effect of grainnumber per ear (sink size) on source activity and its water-relationsin wheat.–J. exp. Bot. 39: 106–114. Work was done to evaluate the nature of sink-source relationshipsin wheat (Triticum aestivum L.), when the strength of the sinkwas modified by the removal of half of the grain from the earat about anthesis. The main hypothesis was that sink-sourcerelationship would be modified by water stress and that a weakersink would improve the drought resistance of the source. Two experiments were performed. The first experiment evaluatedthe effect of de-graining in two wheat varieties grown in thefield. The second experiment (in the greenhouse) evaluated theeffect of de-graining in plants subjected to water stress afteranthesis by immersing the root system in a solution of polyethyleneglycol (6000), as compared with non-stressed controls. In bothexperiments measurements were performed after de-graining toprovide data on leaf gas exchange, leaf water potential, osmoticadjustment of leaves and ears (greenhouse), the percent of stemweight loss as an index of stem reserve mobilization, finalroot weight (greenhouse) and ear weight components. De-graining caused a decrease in flag leaf stomatal conductance,carbon exchange rate (CER) and transpiration and an increasein flag leaf water potential. These effects were stronger withwater stress. De-graining did not affect osmotic adjustmentin the flag leaf but induced better adjustment in glumes andawns. De-graining decreased the percent of stem weight lossand increased final root weight, especially under drought stress. A weaker sink was, therefore, considered to improve plant droughtresistance in terms of the maintenance of higher leaf waterpotential, a larger root, a better osmotic adjustment in theear and, possibly, increased flag leaf longevity. The ‘cost’of this improved drought resistance was in reduced flag leafCER and reduced stem (and root?) reserve mobilization. Key words: Drought resistance, carbon exchange rate, stomata, transpiration, osmotic adjustment, leaf water potential, root, awns, yield     

In Vitro Culture of Orobanche aegyptiaca

Calli derived from seedlings of the parasitic plant Orobancheaegyptiaca were grown on enriched nutrient agar. Growth wasenhanced by the addition of 0.1 mg 1^–1 NAA and 5 % coconutmilk. The calli developed two kinds of elongated protrusions:thin ones which resemble the young root radicle and thick oneswhich resemble the adventitious roots of Orobanche plants. Bothformed pad-like structures when touching the substrate. In liquidculture, some of the calli were observed to surround isolatedcultured tomato roots. Orobanche aegyptiaca Pers., in vitro culture, germination, coconut milk, root parasite     

FACTORS INFLUENCING THE EFFICIENCY OF INCOMPLETE BLOCK DESIGNS IN SENSORY EVALUATION EXPERIMENTS

The efficiencies of incomplete block designs were investigated by comparing two hundred and twenty eight analyses from eleven trials using hedonic scales with corresponding randomized complete block analyses. Of the ten explanatory factors examined, only the panelist, the product type, the number of samples per session and the average score of the data had an effect on the efficiency of incomplete block designs. The effect of product type was attributed to influences of produce consumed outside the trial, and the effect of the data mean reflected decreased conscientiousness with products the panelists disliked. With three and four samples per session, incomplete block designs were 31 % and 2 % more efficient, respectively, than randomized complete block designs. When five or more samples were tested, the incomplete block designs were markedly less efficient. The practical implications of all these effects on experimental design are discussed.     

Changes of the Apoplastic pH and K+ Concentration in the Phaseolus Pulvinus in situ in Relation to Rhythmic Leaf Movements

The apoplastic pH and K⁺ concentration of the extensor of thePhaseolus primary-leaf pulvinus in relation to rhythmic leafmovements have been investigated with double-barrelled ion-sensitivemicro-electrodes. Simultaneous measurements of leaf movementand ion activities in a fine hole of the extensor in situ showedco-existence of ultradian and circadian leaf movements as wellas of ultradian and circadian pH changes in the Water Free Space(WFS) of the extensor apoplast in situ. During circadian leafmovement the H⁺ and K⁺ activities in the WFS of the extensorchange in an antagonistic manner. When extensor cells swell(upward movement of the lamina) the H⁺ activity increases fromapproximately pH 6.7 to 5.9 and the K⁺ concentration decreasesfrom approximately 50 to 10 mol m^–3 and vice versa whenextensor cells shrink. These changes in the ionic activitiesin the WFS must be correlated with large changes in the ioncontent of the DFS and thus support the hypothesis that thecell walls of pulvinar cells serve as reservoirs for K⁺ andH⁺. Key words: Phaseolus pulvinus, apoplastic ionic activities, rhythmic leaf movements, ion-sensitive micro-electrodes (double-barrelled)     

A Stereological Analysis of the Succulent Tissue 5Opuntia ficus-indica (L.) Mill.: I. DEVELOPMENT OF MUCILAGE CELLS

A correlated stereological and developmental analysis of thesucculent tissue of Opuntia ficus-indica was carried out. Thestereological parameters related to mucilage cells were describedas a function of their distance from the apical meristem. Polynomesof the second and third degree were found to describe the developmentalprocess. Three zones of development could be distinguished.The relation of the structure of the tissue to its physiologicalfunction and mucilage secretion is discussed.     

A Stereological Analysis of the Succulent Tissue 5Opuntia ficus-indica (L.) Mill.: II. ULTRASTRUCTURAL DEVELOPMENT OF THE MUCILAGE CELLS

Five stages of the development of the cytoplasm of mucilagecells were followed by stereological analysis and analysed togive numerical (N_v), volumetric (V_v) and surface (S_v) densitiesof organelles and membranes. A quantitative evaluation of membrane areas, membrane sites,and mucilage secretion was obtained based on morphological andhistochemical data. The developmental process from early differentiationto complete degeneration of the cytoplasm is discussed in quantitativeterms.