The intracellular events triggered by the self-incompatibility response inPapaver rhoeas

Summary In recent years self-incompatibility (SI) has come to be recognised as an important model system for studying cell-cell interactions and signalling in flowering plants. In this article we discuss the intracellular events associated with the SI response in the field poppy,Papaver rhoeas. The SI response inP. rhoeas is known to involve a Ca²⁺-based signalling pathway, activated following molecular interactions on the surface of incompatible pollen tubes. Evidence demonstrates that, following a transient increase in the concentration of cytosolic free Ca²⁺ ([Ca²⁺];) initiated by the SI response, phosphorylation of certain cytosolic proteins occurs, followed by activation of pollen gene expression. The magnitude of this transient Ca²⁺ wave and the localisation of cytosolic [Ca²⁺]i following the SI response are discussed. We also describe the character of the proteins specifically phosphorylated in the SI response and the nature of the protein kinases involved in their phosphorylation. Finally, we consider the possibility that the end result of the SI response inP. rhoeas may be analogous to programmed-cell-death mechanisms such as those seen in developmental processes and defence responses in various plant cells.     

POLYGONAL ASPECTS OF CELL FACES. I. PENTAGONS AND HEXAGONS AS PREVAILING TYPES

Wheeler , George E. (Brooklyn Coll., Brooklyn, N. Y.) Polygonal aspects of cell faces. I. Pentagons and hexagons as prevailing types. Amer. Jour. Bot. 49(3): 246–252. Illus. 1962.—Different types of cell faces, classified as to polygon type (i.e., number of sides per face), may predominate in different samples of internal cells and of internal tissues; no single face type is exclusively predominant in all tissues. Pentagons usually are the most numerous type in the cell samples reported in the literature, but hexagons exceed them in some samples. Generally, these 2 “compete” for numerical supremacy. Perpetuation of an already-established, face-type dominance was studied, using data from the literature and from original diagrams. Cell-division orientation, i.e., the location and the relative positioning of new cell-division walls, was found to be the prime factor in maintaining the preponderant type. The polygon nature of the new wall is an additional, but less important, factor. Typical division events tend to favor pentagonal faces; but with an increase in cell division “regularity,” hexagons begin to rise in numbers. During the early stages in tissue differentiation, while mitosis is still occurring, one face type may replace another as the predominating type. Such a shift may be associated with the developmental characteristics of that tissue.     

Effects of pyrophosphate, triphosphate, and potassium chloride on adenylate deaminase from rat muscle

Inorganic pyrophosphate and triphosphate inhibit adenylate deaminase from rat skeletal muscle with K1 values of 10 and 1.5 microM, respectively, in the presence of 150 mM KCl at pH 7. They act by reducing the apparent affinity of the enzyme for AMP, with relatively small effects on Vmax. The inhibitions are diminished by H+, the KI values increasing two- to threefold in going from pH 7.0 to 6.2, and are relieved by ADP. These properties are similar to the inhibitions produced by GTP and ATP, indicating that pyrophosphate and triphosphate act like analogues of the nucleoside triphosphates. Neither of these inhibitors shows relief of inhibition at high concentrations as do ATP and GTP. These results suggest that nucleotides interact with the inhibitor site of the enzyme primarily through their phosphate moieties and with the activator site primarily through their nucleoside moieties. As the concentration of KCl is increased from 25 to 300 mM, the apparent affinities of the enzyme for ATP, GTP, orthophosphate, pyrophosphate, and triphosphate are decreased 8-100-fold. The cooperativity of the inhibitions is increased with the Hill coefficient rising from 1.0 to 1.3-1.8, and the maximum inhibition approaches 100%. Maximum activation by ADP is reduced from 1800% at 25 mM KCl to 80% at 200 mM KCl. Experiments with (CH3)4NCl indicate that activation of the enzyme by KCl involves both specific K+ effects and ionic strength effects.     

Compartmentalized Calcium Signaling in Cilia Regulates Intraflagellar Transport

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Mapping of quantitative trait loci controlling adaptive traits in coastal Douglas-fir. II. Spring and fall cold-hardiness

Quantitative trait loci (QTLs) affecting fall and spring cold-hardiness were identified in a three-generation outbred pedigree of coastal Douglas-fir [Pseudotsuga meniziesii (Mirb.) Franco var. menziesii]. Eleven QTLs controlling fall cold-hardiness were detected on four linkage groups, and 15 QTLs controlling spring cold-hardiness were detected on four linkage groups. Only one linkage group contained QTLs for both spring and fall cold-hardiness, and these QTLs tended to map in close proximity to one another. Several QTLs were associated with hardiness in all three shoot tissues assayed in the spring, supporting previous reports that there is synchronization of plant tissues during de-acclimatization. For fall cold-hardiness, co-location of QTLs was not observed for the different tissues assayed, which is consistent with previous reports of less synchronization of hardening in the fall. In several cases, QTLs for spring or fall cold-hardiness mapped to the same location as QTLs controlling spring bud flush. QTL estimations, relative magnitudes of heritabilities, and genetic correlations based on clonal data in this single full-sib family, supports conclusions about the genetic control and relationships among cold-hardiness traits observed in population samples of Douglas-fir in previous studies. Received: 20 July 2000 / Accepted: 19 October 2000